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ECE 480 Final Report

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					             Spring 2011
     ECE 480 / ME481 Final Report


           Design Group ECE 8 / ME 12
            The “Cool” Sparty Project

Student Alumni Foundation / MSU Alumni Association


             Design Group Members:
              Maitham Aleid (ECE)
             Ashley Kulczycki (ME)
              Brian Rockwell (ME)
              Nicholas Stuart (ME)
                Diana Toan (ME)
              Ahmad Zahid (ECE)


                Industrial Advisors:
                  Dan DiMaggio
                    Ben Hatala


                Faculty Advisors:
                 Dr. Neil Wright
                Dr. Hassan Khalil
Executive Summary
        Sparty is the Michigan State University mascot and is the focus of a project sponsored by
the MSU Student Alumni Foundation. He makes regular appearances at a wide variety of events
ranging from football games to weddings. The suit he wears consists of thick foam over the
extremities, a solid chest plate covering the torso, and a helmet that covers the entire head. This
design causes the suit to be highly insulated and prevents the body from rejecting waste heat to
the environment. The result is a high risk of overheating and dehydration for the occupant as
well as severe discomfort that limit the amount of time that someone can remain in the suit. The
goal of this project is to design a cooling system for the suit in order to improve wearer safety
and comfort as well as the increase amount of time that an individual can wear the suit. Although
prior research has been conducted to identify cooling systems currently available, no suitable
solution has been found.

        This project was undertaken by an interdisciplinary team of engineering students
consisting of four mechanical engineers and two electrical engineers. The group collaborated in
identifying significant design considerations and then generated design concepts. The
considerations identified include cooling performance, durability, weight, and cost. Other goals
include maximizing the duration that the system would remain effective and ensuring that the
mascot suit and components placed in the suit could be washed between uses. Additionally, as
Sparty is a widely recognized figure, his appearance must remain unaltered.

        Several concepts were proposed including the use of Peltier junctions, fans, and a chilled
water circulation system to remove heat from the body. In the end, three concepts were deemed
most capable of meeting these targets. The first of these was the use of a phase change material
to absorb heat in the suit. Another design specified the use of a high pressure air tank to
periodically inject fresh air into the suit to remove heat through convection and the evaporation
of sweat. The third design was a combination of both of these cooling methods which has the
advantage of combining continuous cooling through the phase change material as well as
transient, on-demand cooling through the high pressure air system.

         As none of the three most promising designs contained electrical systems, the continued
development of the mascot cooling system was performed by the mechanical engineers. At this
point the electrical engineers in the group began work designing and constructing a cooling chest
to chill the phase change packs before use.

        Work on the mascot cooling system continued with modeling to predict the performance
of each of the designs selected for development. Modeling of heat generation in the human body
indicated that for the anticipated activity level for Sparty at an athletic event, he generates
approximately 329 W of heat and rejects 55 W of heat through respiration. Modeling of the heat
removed by the cooling systems was conducted for a variety of possible implementations and
suggested a high potential for heat removal. Under the final specification of the system, it was
predicted that heat could be removed from the suit at an average rate of 49 W over two hours
with phase change material and an additional 157 W could be removed with the high pressure air
system.

       Based on the results of the modeling, it was decided that prototyping and testing and
would be conducted with a combined phase change material and the high pressure air system.
Component level testing was then conducted in order to optimize the design of the air delivery
system and selection of phase change material before final prototype assembly. It was
determined that the high pressure air system was best implemented using a single tube running
through the suit and scuba tank providing the high pressure air. Phase change materials from
multiple manufacturers were ordered and evaluated and it was determined that Glacier Tek
RPCM® offered a superior product for the desired application.

        After constructing the prototype, testing was conducted by observing temperatures within
the chest plate and at the underarm during a highly-controlled one-hour exercise regimen. This
test was performed once with no cooling systems implemented, once with each system
individually, and then again with both systems together. The results demonstrated that the phase
change material reduced temperatures within the chest plate by an average of over 5 °C and
reduced core body temperatures as measured at the underarm by an average of 2 °C as compared
to the control case. The high pressure air system was also shown to be effective at reducing
temperatures within the suit and lowering the body temperature. However, the testing conducted
did not indicate that the combined system was more effective than the either system alone. This
result was unexpected and it is suggested that additional testing be conducted to verify this result.

        While this work was being conducted, the electrical engineers worked to develop a phase
change material cooling chest to keep the phase change packs at low temperature until use. This
would be especially valuable for long events such as football and basketball games where it
would be desirable to have a second set of phase change packs that could be substituted into the
suit. This cooling chest was designed to be portable and optimized for the refrigeration of the
phase change packs. The design chosen consisted of Peltier junctions built into the side of a
cooler with a heat sink and fan on either side.

        In order to maintain a specified temperature within the cooling chest, a control system
must be implemented. Several design concepts were generated, including a temperature control
system with one set point, a temperature control system with two set points, and a time delay
system. Additionally, a combination of a one set point temperature control system and time
delay system was considered. After evaluating the different design alternatives, the combined
control system design was selected.
         Analysis of the cost of the system showed that the cost of constructing the cooling system
independent of the phase change material cooling chest would be approximately $860.
Maintenance and operating costs were also estimated over a 10 year program life. The cost of
refilling the air tank is the primary operating expenditure and therefore the cost of the cooling
system program depends heavily on the number of refills annually and the price paid for those
refills. Assuming that the unused portion of donated funds could be invested at a 1% annual
return, the total donation required to fund the program for 10 years would be approximately
$8,300 if the tank is refilled 100 times per year at the standard rate. However, if the tank were to
be refilled 50 times per year or if the cost of refills could be reduced by 50%, then the total cost
of the program would be $5,700. The cost of constructing the refrigeration system is
approximately $160 with a 10 year cost of $730 including projected maintenance.

        Based on the work conducted, it is recommended that the Student Alumni Foundation
implement both the phase change material and the high pressure air cooling systems. Both
systems have been shown to be effective and they complement each other in that one system
provides continuous cooling while the other can be available for supplemental additional relief.
However, it is likely that the high pressure air system will only be used at more demanding
events such as football and basketball games and would not be desirable at events such as
appearances at weddings or in the dorm. Additionally, the portable air tank will allow the high
pressure air system to be used during parades when the tank may be concealed in the automobile
carrying Sparty. Real-world testing is recommended to determine the optimal uses of the
systems. Although the phase change material cooling chest has been shown to be a successful
proof of concept, its relatively high cost and requirement of an external power source inhibits its
usefulness at this point in its development. A more effective solution would be to use a generic
cooler and either ice or ice packs to keep the phase change material frozen.
Table of Contents
     I.        Introduction ................................................................................................................ 1

     II.       Mascot Cooling System ............................................................................................. 1

           Design Review ................................................................................................................ 1

              Problem Definition ...................................................................................................... 1
              Design Constraints and Considerations ...................................................................... 2
              Concept Generation ..................................................................................................... 3
              Concept Evaluation ..................................................................................................... 5
           Modeling ......................................................................................................................... 9

              Overview ...................................................................................................................... 9
              Modeling of Heat Generation ...................................................................................... 9
              Modeling of Cooling Systems .................................................................................... 10
           Prototype Manufacture.................................................................................................. 14

           Testing........................................................................................................................... 18

              Peliminary Testing ..................................................................................................... 18
              Component Level Testing .......................................................................................... 21
              System Level Prototype Testing ................................................................................. 24
           Economic Analysis ....................................................................................................... 28

           Conclusions and Future Work ...................................................................................... 31

     III.      Phase Change Material Cooling Chest .................................................................... 33

           Design Review .............................................................................................................. 33

           Modeling ....................................................................................................................... 35

           Manufacturing ............................................................................................................... 36

           Testing........................................................................................................................... 39

           Economic Analysis ....................................................................................................... 41

           Conclusions & Future Work ......................................................................................... 44
IV. Final Recommendation ............................................................................................ 44

References ......................................................................................................................... 45
I.     Introduction
        Sparty is Michigan State University’s active mascot for sporting events and various other
events. His suit is primarily composed of thick foam arms and legs, a solid chest plate, and a
helmet that covers the entire head, all of which result in a highly insulated system that inhibits
rejection of waste body heat. The goal of the project is to design a cooling system for this suit in
order to improve wearer comfort and safety. This task was undertaken by an interdisciplinary
team of four mechanical engineering students and two electrical engineering students. The group
collaborated in defining design requirements and parameters in then generating design concepts.
However, none of the design concepts selected for continued development involved electrical
componentry and therefore at this point the electrical engineers began work developing a cooling
chest to refrigerate the phase change packs that are part of the proposed cooling system. The first
section of this report will describe the efforts to design the mascot cooling system for Sparty
while the second section of this report will describe work done to create this phase change
material (PCM) cooling chest.


II.    Mascot Cooling System
Design Review

Problem Definition

        Currently no cooling system is used inside Sparty, which can lead to serious problems for
the students portraying Sparty such as overheating and dehydration. Temperature readings taken
at various locations within the suit after the first half the MSU home basketball game against
Indiana on January 30, 2011 revealed skin temperatures approaching the normal core body
temperatures (37 °C). These data are presented in Table 1. Such small temperature differences
between the core and skin temperatures prevent sufficient heat transfer to cool the body.
Furthermore, the interior of the suit was drenched in sweat, leading to further wearer discomfort
and indicating the potential for severe dehydration. The MSU Student Alumni Foundation (SAF)
has investigated currently available cooling systems, but has not found anything suitable. The
most common systems currently available consist of vests with ice packs, however, this system is
not ideal because they are uncomfortably cold and melt quickly due to the large temperature
differences relative to ambient conditions and the human body.




                                                                                                   1
                  Table 1. In-suit temperatures at halftime of a basketball game

                                       Chest          33.4 °C
                                       Abs            33.3 °C
                                       Underarm       36.2 °C
                                       Bicep          36.8 °C
                                       Back           26.2 °C
                                       Under Chin     24.4 °C
                                       Ambient        14.4 °C


        The goal of the project is to design a cooling system for the mascot suit in order to
improve wearer comfort and safety. The design should be safe for the wearer and cause no added
discomfort. The system must not alter the appearance of Sparty or limit his mobility and should
be lightweight, preferably not more than 15 pounds. Additionally, this weight should be evenly
distributed and contact pressures should be minimized. The design should allow the person to
stay in the Sparty suit for two hours as compared with the current one hour duration. There
should be little or no weight added to the head and no continuous loud noises. The system should
also be easily separated from the suit or be able to be washed in a standard washing machine.


Design Constraints and Considerations

       Safety is the top priority. The main purpose of the project is to increase comfort and
decrease the health risks of heat exhaustion or dehydration, therefore creating additional risks
runs counter to the objective.

       Cooling performance is the second most important consideration as transferring heat
away from the wearer is the goal of the project.

        The mobility of Sparty is important to allow MSU’s beloved mascot to continue with his
antics. These include running, jumping, sitting, and push-ups. Furthermore, since Sparty is
forbidden from talking, he communicates through his upper body motions. Losing mobility
would decrease his appeal.

        The current duration that Sparty can be in action is about one hour. This is limited by
safety concerns related to overheating and dehydration. The baseline goal is to provide Sparty
with a safe and comfortable environment for one hour, but the target solution would expand this
time to two hours.

        The device should be durable to allow for multiple uses and minimize upkeep cost. The
cooling system should be able to last as long as the suit, or better, it should outlive the suit and be
transferable to subsequent suits.
                                                                                                      2
        Noise is both a safety and aesthetic consideration. Sparty should be able to hear
instructions and interact with his surroundings. Additionally, those around Sparty should not hear
any noises emanating from the suit.

       The weight of the device should be evenly distributed and contact pressure should be
kept low in order to prevent negative impacts on comfort and mobility.

        Since the project has a fixed budget, cost is an important consideration. Although, the
SAF has indicated that cost is not of absolute importance to them, production and maintenance
costs should be reduced when possible.

      Due sanitary and long term comfort considerations, the added design should be easily
removed or washable.

        Based on the discussion of the design parameters presented above, a relative weighting
for each parameter was developed. Table 2 presents these weightings.

                          Table 2. Weighting of design considerations

                                Selection Parameters Weight
                                Safety                   20%
                                Cooling Performance      15%
                                Mobility                 13%
                                Duration                 13%
                                Durability               13%
                                Noise                    13%
                                Weight                   8%
                                Cost                     4%
                                Washable                 4%
                                 Total                   100%


Concept Generation

       A number of design alternatives were proposed to meet the design specifications and
constraints. These include:

   1. Peltier Junction
      This design utilizes a Peltier junction to generate a temperature gradient and thus transfer
      heat away from the body. This would require a power source.



                                                                                                  3
2. Fans
   This design uses fans within the suit to continuously introduce and circulate ambient air
   within the suit thus removing heat and evaporating perspiration produced by the body.
   This would also require a power source.

3. Phase Change Material (PCM) Vest
   This design incorporates a phase change material to absorb heat produced by the body.
   The amount of heat absorbed depends on the material properties of the PCM including
   melting temperature, latent heat of fusion, and the amount of PCM. In most existing
   systems, the PCM is contained in small held in a vest and can be removed. An example
   of a PCM vest is shown in Figure 1.




                   Figure 1. Sample vest for wearing PCM packs [1]

4. External High Pressure Air (HPA) Tank with Vest
   This design utilizes a tube system built into a vest and an external HPA tank. The tank
   will be used to force air through the tubing system into the suit in order to affect
   convective and evaporative cooling. Figure 2 illustrates a possible tubing layout, although
   that shown is from a system that uses chilled water to cool the body. For the HPA, a
   series of holes in the tubing would introduce air into the suit, whereas the water system
   pictured in Figure 2 is closed and maintains separation between the cooling fluid and the
   rest of the system. As the tank will be separate from the suit, this will be a transient
   cooling solution in which Sparty will connect to the air tank briefly at regular intervals.
   This system would implement a quick connection device to allow time efficient
   connection and disconnection from the system.




                                                                                               4
   5. Water Vest
      This design uses a pump to transport chilled water through a tubing system for cooling.
      An example of such a tubing system is illustrated in Figure 2. This system will require
      either an electrically or a manually driven pump, as well as a cold water reservoir, such as
      a cooler full of ice and water.




               Figure 2. Vest fitted with tubing for chilled water circulation [2]

   6. Internal HPA Tank with Vest
      The difference between the internal HPA tank design and the external HPA tank design is
      the source of air. The internal HPA tank design uses the same vest tube system pictured
      in as the external tank system, but with a smaller HPA, such as one that would be used in
      paintball. This tank will be embedded within the suit and would have the potential to
      provide continuous air flow to the user rather than intermittent bursts of air during breaks.

   7. External HPA + PCM Vest
      This design combines the PCM vest with the external tank HPA system. The vest will be
      similar to the one pictured in Figure 2, with added internal pockets for PCM packs. The
      PCM packs will provide continuous cooling while the tubing on the vest will allow the
      user to connect to the external air tank for a short burst of air.



Concept Evaluation

       The aforementioned concepts were evaluated based on predicted advantages and
disadvantages and the most promising designs were selected for continued development. This
                                                                                                 5
evaluation is presented in Table 3. The design using fans and the design with chilled water
circulation were abandoned after this analysis. The use of fans determined to be unfeasible due to
the lack of space within the suit for packaging, the potential to create noise, and the need for a
power source. It was also decided that the water vest design would not be pursued due to the
required pump and cold reservoir which would make packaging with in the suit impractical. It
was decided that the remaining five concepts (Peltier junction, PCM vest, HPA (external), HPA
(internal), external HPA/PCM) would continue to be evaluated.

           Table 3. Advantages and disadvantages for the various design alternatives




                                                                                                6
                     Advantages                                     Disadvantages
Peltier Junction     • Can include a control system to maintain     • Hot side reaches high
                     temperature                                    temperatures
                     • Available in different sizes                 • Requires a heat sink
                     • Junctions flat and easy to package           • Requires a power source
Fans                 • Continuous cooling                           • Noise
                                                                    • Difficult to package in suit
                                                                    • Requires a power source
PCM Vest             • Allows engineering the temperature for phase • Difficult to manufacture sealed
                     change                                         packaging for PCM
                     • Can distribute material (i.e. weight)        • Limited heat capacity
                     • Easily worn in the form of a vest            • Potential for heat absorbtion from
                     • Must have close contact with the skin for    environment
                     cooling
HPA (External)       • Removes heat via evaporation of sweat        • Does not offer continuous cooling
                     • Quick relief                                 • Noise
                     • Air pressure can be set to user preference   • Must be connected to an external
                     • Lightweight                                  source of air
                     • Air cooled due to isenthalpic expansion

Water Vest           • Cooling can be modulated by flow rate and    • Requires a pump
                     temperature of fluid                           • Requires a power source
                                                                    • Requires a cold reservoir/chilling
                                                                    device
HPA (Internal)    • Remove heat via evaporation of sweat            • Limited capacity of air tank
                  • Continuous cooling                              • Air tank must be embedded in suit
                  • Air pressure and timing can be set to user      • Noise
                  preference
External HPA/ PCM • Provide continuous cooling and on demand • Noise
                  relief                                       • Complexities of packaging systems
                  • Remove heat and improve comfort via        together
                  evaporation of sweat


       These five concepts were then evaluated based on predicted performance on the nine
design parameters previously developed. These results are presented in the concept scoring
matrix shown in Table 4.

              Table 4. Concept scoring matrix for objective comparison of designs




                                                                                                          7
                                                           HPA                HPA        External
                        Peltier Junction   PCM Vest
                                                        (External)         (Internal)   HPA/PCM
 Selection
               Weight Score Weighted Score Weighted Score Weighted Score Weighted Score Weighted
 Parameters
 Safety           17%    2       0.34      5    0.85   4      0.68     3         0.51   4     0.68
 Cooling
                  15%    1       0.15      3    0.45   3      0.45     2         0.30   5     0.75
 Performance
 Mobility         13%    4       0.52      4    0.52   4      0.52     3         0.39   4     0.52
 Duration         13%    2       0.26      3    0.39   2      0.26     2         0.26   4     0.52
 Durability       13%    3       0.39      4    0.52   4      0.52     4         0.52   4     0.52
 Noise            13%    5       0.65      5    0.65   2      0.26     2         0.26   3     0.39
 Weight            8%    3       0.24      3    0.24   5      0.40     4         0.32   3     0.24
 Cost              4%    2       0.08      4    0.16   3      0.12     4         0.16   3     0.12
 Washable          4%    2       0.08      5    0.20   4      0.16     4         0.16   4     0.16
                 100%            2.71          3.98           3.37               2.88         3.9



        The Peltier junction scored lowest in cooling performance because it consumes power
and unless heat is effectively removed from the hot side of the junction, they will result in a net
addition of heat to the system. Effectively removing heat from the Peltier junctions requires large
heat sinks which cannot be packaged within the suit.

        The PCM vest scored highest in safety because this system uses nontoxic PCM packs and
is therefore relatively inert compared to the other electrical and compressed air systems.
However, anticipated cooling performance and duration were only moderate, although scoring in
other areas was very good.

        Since the external HPA vest consists of a system of tubes and a mesh vest, it scored best
in the weight category. The HPA tank will be connected to the vest intermittently when cooling
is needed. Thus, its score in the duration category is the worst. It also scored poorly in the noise
category due to the noise produced by rapid airflow through the system. The internal HPA vest
has a small air tank embedded within the suit. Because of the limited air capacity of the tank, it
scored poorly in cooling performance and duration.

      The external HPA/PCM scored the highest in cooling performance and duration by
combining the cooling methods of the two design alternatives.

        The three best scoring solutions were the PCM vest, external HPA vest, and the external
HPA/PCM vest. The Peltier junction and internal HPA Vest scored the worst. Based on the
scores and evaluations presented in Table 4, the three highest scoring solutions were chosen for
further analysis.


                                                                                                       8
Modeling

Overview

       Analysis of the heat generated by and removed from the mascot suit is based on the
energy balance relating the change of energy in the suit (  ) to the heat generated by the
human body (        ), the heat lost through respiration ( ), the heat lost to the PCM (           ),
and the heat extracted by the HPA system (        ). This relation is presented in Equation 1.

                                                                                             (1)

Modeling of Heat Generation

         Models were created to describe the heat transfer in the Sparty suit system. It was
assumed that heat is generated through metabolism and removed through heat loss due to
respiration and the cooling systems implemented. Further assumptions were made that the entire
suit is perfectly insulated and that no heat loss occurs except through the mechanisms described.
This assumption represents a worst case scenario for removing heat from the suit. Therefore,
models were implemented for heat generation of the human body, heat loss through respiration,
heat removed by an HPA system with an external tank and heat absorbed by a PCM vest. The
cooling effects of the HPA system were further broken down and into convective and
evaporative cooling.

          Human metabolic rate is presented in [3] as being proportional to body surface area and
is listed for several common activities. The activity selected to represent an activity level similar
to that performed by Sparty was that of someone walking about doing moderate lifting or
pushing. This task has a metabolic rate of 140 kcal/m2·hr. A relation for body surface area is also
presented in [3] and is shown in Equation 3. Weight (m) and height (h) are in kg and cm,
respectively, and the area (A) calculated is in m2.

                                                                                             (3)

Using this equation, surface area for the assumed suit wearer is 2.02 m2 and thus metabolic rate
due to activity is 283 kcal/hr or 329 W.

       Metabolic rate can also be can also be presented in terms of metabolic equivalent per task
(MET) which is the metabolic rate per unit of body mass. One MET is equivalent to 1 kcal/kg·hr.
Thus as calculated, Sparty’s metabolic rate is 3.53 MET. This is consistent with the published
value of 3.5 MET for light or moderate conditioning exercise and calisthenics as presented in [4].


                                                                                                        9
        Heat lost through respiration was modeled using the following equations from [3].
Respiratory heat loss is separated into two components, that due to latent heat loss of evaporation
in the lungs (Qel) and that due to the sensible heat loss (Qsl) as the air changes temperature. Both
of these are a function of the mass flow rate of dry air ( ) in kg/hr, which is a function of the
metabolic rate (M) in kcal/hr. The latent heat loss is also a function of the ratio of the mass of
water to the mass of dry air inspired (yi) and expired (yo) and depends on the heat of vaporization
of water, λ. The sensible heat loss depends upon the heat capacity of air (cp), temperature of the
air inspired (Ti), and that of the air expired (To). These may be written as

                                                    ,                                       (4)

                                                        ,                                   (5)

where

                                              ,                                             (6)

and

                                                     ,                                      (7)

        The evaporative and sensible heat losses through respiration were estimated to be 25.6 W
and 29.1 W, respectively. Thus, the total heat loss through respiration is 54.6 W. Therefore the
net heat added to the system by the human body is approximately 274 W.



Modeling of Cooling Systems

         The convective cooling effect of forcing air through the suit was calculated using
correlations adapted from [5] assuming for internal flow. The dimensions of the cavity in the
chest plate were assumed to be defined by a 1 meter chest circumference, a 0.45 m flow length
from approximately the hips to the top of the torso, and a cavity thickness of 2 cm. For Reynolds
numbers below 2300, the flow will be laminar. Reynolds numbers for internal flow are a
function of the mean fluid velocity (um), the hydraulic diameter (Dh), and the kinematic viscosity
(υ) as is illustrated in Equation 8.

                                                                                            (8)

where

                                                                                            (9)

and Ac is the cross-sectional area and P is the perimeter.
                                                                                                  10
       For laminar flow the Nusselt number is constant at 4.36.

       For Reynolds numbers above 2300, the flow will be turbulent and the Nusselt number is
estimated using the correlation

                                                                                             (10)

where Pr is the Prandtl number and ReD is the Reynolds number based on the hydraulic diameter
of 3.9 cm. f is the friction factor determined by

                                                                                             (11)

for laminar flow,

                                                                                             (12)

for turbulent flow below a Reynolds number of 20,000, and

                                                                                             (13)

for turbulent flow above a Reynolds number of 20,000.

       Using the Nusselt number, the heat transfer coefficient (h) was calculated as

                                                                                             (14)

where k is the thermal conductivity of air. The convective heat transfer may then be calculated

                                                                                             (16)


       The resultant convective heat transfer for a variety of flow velocities is presented in the
Table 5.




                                                                                                     11
               Table 5. Convective heat transfer for corresponding glow velocities

                               V (m/s)    Q (W)      Flow Condition
                                 0.5       18.4         Laminar
                                   1       30.6         Turbulent
                                   2       67.6         Turbulent
                                   5        151         Turbulent
                                  10        252         Turbulent


        The model for evaporative cooling of sweat was also taken from [3]. The heat loss due to
evaporative cooling (Qe) is a function of an evaporative transfer coefficient (ke), the wetted area
(Aw) and the water partial pressure at the surface (Ps) and of the air (Pa). The evaporative transfer
coefficient is a function of the air velocity and has been determined experimentally. Also, the air
in a HPA tank is essentially dry and thus Pa is zero. Based on observations, the inside of the suit
becomes saturated with water and therefore the surface partial pressure of water is assumed to be
at the saturation pressure at 34 °C, an approximation of the temperature measured within the suit.
The evaporative heat transfer is then calculated as

                                                                                             (17)

where

                                                                                             (18)

for air velocity (v) above 0.58 m/s and

                                                                                             (19)

for velocity below 0.58 m/s.

        The heat loss due to evaporation is presented in Table 6 for a variety of flow velocities.

                               Table 6. Heat loss due to evaporation

                                         V (m/s) Q (W)
                                           0.5         170
                                             1         265
                                             2         412
                                             5         736
                                            10        1142
       The total heat loss due to the HPA is the sum of the losses due to convection and
evaporation. This total is presented in Table 7 for several flow conditions.

                                                                                                     12
                           Table 7. Total heat removed by HPA system

                                      V (m/s)    Qtotal (W)
                                        0.5         188
                                         1          296
                                         2          479
                                         5          887
                                        10         1394


        Several PCM’s were investigated. The selected PCM for the final design has a melting
point of 15 °C, a heat of fusion of 195kJ/kg. Based on the heat of fusion, the vest which contains
4 packs each containing 50 g of PCM would be able to absorb 48.8 W of energy. This is over a
two-hour period.

        Based on this analysis, it was decided that a combination PCM and HPA system would
be pursued through prototype construction and testing. Additionally, it was decided that a
refrigeration system would be designed and constructed in order to maintain PCM packs in a
frozen state so that they could be readily available for use. With this system a second set of PCM
packs can be employed such that while one set is being used the other can be refrigerated and
then when necessary the packs can be switched out and the fresh packs can be used while the
warm packs can be refrozen. The details of the design process for this auxiliary system are
presented in Section 2 of this report.

        In actual performance of the system, the velocity of the air flow in the suit was
determined to be 0.21 m/s, based on the discharge of 2.27 m3 (80 ft3) over 7 minutes and forty
seconds through the chest plate cavity previously described. This result predicts laminar flow and
thus a constant Nusselt number. Under these conditions, the heat loss due to convection would be
18.4 W and the heat loss due to evaporation would be 137 W, as illustrated in Figure 3. Thus in
addition to the 48.8 W of continuous cooling contributed by the PCM, an additional 155 W of
transient cooling can be generated through the HPA system. Though this is less than the total
heat introduced by the human body, testing has shown that this is sufficient to significantly
increase the comfort level and safety of the suit occupant.




                                                                                                13
               Figure 3. Sparty and the heat losses experienced. Picture from [10]



Prototype Manufacture

        After evaluating the design alternatives, a prototype was manufactured based on the
combined HPA system and PCM design. To control the pressure of the air released from the
tank, a regulator and welding hose were connected to the tank. In developing a model for the
high pressure air system of the design, clear vinyl tubing of 6.1 m (20 feet) length with outer and
inner diameters of 6.35 mm (0.25 inch) by 4.32 mm (0.170 inch), respectively was obtained at
Home Depot®, used and taped down to a cotton T-shirt in the configuration shown in Figure 4.
Holes were drilled through the tubing 7.62 cm (3 inches) apart at a diameter of 1.59 mm (1/16
inch, 1/16 inch drill bit). The free end of the tubing was closed with hot glue to help maintain air
pressure within the tubing system. The air hose was then attached to a quick connect that would
connect the air tube system to the welding hose of the air tank. A compression coupling, outer
diameter 6.35 mm (¼ inch) by 6.35 mm (¼ inch) Female Iron Pipe (FIP) and a pipe reducing
coupling, 6.35 mm (¼ inch) FIP by 3.18 mm (1/8 inch) FIP, were obtained from Home Depot®
and used to attach the vinyl tubing to the quick connect coupler.




                                                                                                  14
          Figure 4. First tube configuration design (front and back have same design)

      To achieve better air distribution a second prototype as shown in Figure 5, was
manufactured and tested. The front and back of the shirt have the same tube configuration.




          Figure 5. Second tube configuration design (back has mirror design of front)

         After testing with the initial prototype, modifications were made and a final prototype
was manufactured. For purposes of easy transport of the system to follow Sparty to its various
activities, a smaller scuba air tank of 2.27 m3 (80 ft3) capacity was selected and obtained from
ZZ Underwater World. This tank was transported by securing it to a dolly with a bungee cord
obtained from Home Depot®. A paintball tank adapter was used to connect the air tank to a
regulator and the regulator connected to a welding hose with a quick connect end. The final
prototype used identical vinyl tubing and connections as the initial prototype with 19 holes
drilled 12.7 cm (5 inches) apart in a 3.05 m (10 foot) tube with hole diameters increasing in size
from 0.99 mm (0.039 inch, gauge 60) to 2.31 mm (0.091 inch, gauge 42) starting from the quick
connection. In addition to the high pressure air system, use of a PCM was also incorporated into


                                                                                                15
the final design. The Concealable Cool Vest purchased from [6] allows for storage of 4 PCM
packs, shown in Figure 6.




                               Figure 6. Cool vest PCM pack [6]

        Velcro straps obtained at Jo-Ann Fabric and Craft Stores® were hand sewn into the inner
side of the vest by a member of the design group. The configuration of the hand sewn straps
matches the configuration shown in Figure 5, allowing the vinyl tubing to be secured to the vest,
while still being able to be removed to wash the vest.

       The complete system consisting of the PCM vest, tubing, quick connect coupler, and the
scuba tank are shown in Figure 7.




  Figure 7. Complete system consisting of the cooling vest with attached tubing connected to a
              quick connect coupler hooked up to a scuba tank, the HPA source

       The PCM vest with cold packs and the tubing are shown on the test subject in Figure 8.

                                                                                                16
                  Figure 8. Test subject wearing cooling system

The inside of the vest and the air tank are displayed in Figure 9.




     Figure 9. (a) Inside of the vest and (b) air tank with regulator attached


                                                                                 17
Testing

Overview

        This section is divided into three parts, Preliminary Testing, Component Level Testing
and System Level Prototype Testing. Preliminary Testing contains the testing procedure, testing
data, and data evaluation of the two main components of the final design, prior to their selection
for use in the final design. Component Level Testing contains the testing procedure, testing data,
and data evaluation. Finally, System Level Prototype Testing contains the testing and final
validation of the design concept. All human testing was performed on a male member of the
design group that is 23 years old, 182 cm tall, and has a mass of 76 kg.



Peliminary Testing

       Before committing to the final prototype design, its two main components, the PCM and
High Pressure Air System (HPA), must first be evaluated for feasibility.

        The first test involved measuring the temperature of the air released from a 6.23 m3 (220
cubic feet) HPA Tank regulated at various output pressures. Using thermocouple probes, the
output air temperature of the HPA tank was measured at five different pressures from a 6.35 mm
(0.25 inch) diameter hose. The thermocouple probe was held parallel to the air flow,
approximately 1 cm (0.41 inch) from the hose opening as illustrated in Figure 10.




                        Figure 10. HPA temperature measurement setup

       Shown in Table 8 are the ambient temperature was 20 °C and the HPA tank air
temperature data.




                                                                                                18
                  Table 8. HPA tank air temperature data at various pressures

                                Output Pressure      Temperature
                                  (kPa (psi))           (°C)
                                   140 (20)             18.4
                                   210 (30)             14.0
                                   280 (40)             17.0
                                   340 (50)              8.4
                                   410 (60)              7.0


        Using these temperature data, the optimum output pressure was determined to be
approximately 280 kPa (40 psi). At this pressure, the air temperature is cool enough to provide
comfortable evaporative and convective cooling while also conserving the amount of
compressed air stored in the tank. In addition, the temperature of the air will decrease further the
longer the duration of the air flow.

               Phase Change Materials from four different manufacturers were evaluated. The
material properties and size varied with each brand.




Figure 11. PCM packs pictured with 15 cm (6 inch) ruler for scale (left to right, top down): First
 Line Technology PhaseCore 28 [7], Glacier Tek Renewable PCM® [6], Texas Cool Vest PCM
                             [8], and Steele Thermo-strips [9]

                                                                                                  19
        As shown in Figure 11, the PCM packs vary in size. They pictured next to a six inch ruler
for scaling purposes. The material properties of each PCM are compared in Table 9.

                  Table 9. Material properties for the PCM shown in Figure 11

                                   First Line    Glacier Tek     Texas Cool Vest       Steele
   Melting Temperature [°C]            28            15               18.3               0
   Latent Heat of Fusion
                                       126            195              192.5            N/A
   [kJ/kg]
                                   Proprietary    Proprietary
   Material                                                        Hexadecane        Proprietary
                                   Salt Blend      RPCM®


        Due to the limited number and small size of the sample PCM packs, a proper objective
evaluation based on a complete vest fitted with multiple PCM packs was difficult to conduct. In
addition, comparing the melting times of the PCM packs cannot be completed because of their
varying masses. Instead, the best PCM was selected based on its melting temperature, latent heat
of fusion, and relative feel against the skin.

        The First Line [7] PCM had the highest melting temperature of 28 °C and the lowest
latent heat of fusion of 126 kJ/kg. The advantage of this PCM is that its freezing temperature is
well above room temperature, allowing it to be refrozen without additional equipment. Its high
melting temperature also made it difficult to feel against the skin compared to the other brands.
This, combined with its low latent heat of fusion eliminated it from the final design.

       The Steele Thermo-Strip [9] PCM had a melting temperature of approximately 0 °C,
much too cold to wear comfortably against the skin. Its latent heat of fusion was also unknown.
Thus, this PCM was eliminated from the final design.

        The last two materials considered, Glacier Tek’s RPCM [6] and Texas Cool Vest’s
Hexadecane [8], are very similar. Their melting temperatures differ by only 3.3 °C and the latent
heat of fusion for each is nearly identical. Both feel comfortable on the skin and can be felt
through a cotton shirt or similar material. The significant difference between the two PCMs is
their material composition. Texas Cool Vest uses hexadecane, which is harmful or fatal if
swallowed, harmful if inhaled, and causes severe skin, eye, and respiratory tract irritation. On the
other hand, Glacier Tek’s proprietary PCM is made from “high-technology processed fats and
oils” [6] and is “classified as food grade by the U.S. Food and Drug Administration (FDA)” [6].
It is non-toxic and safe for contact with skin. Because of this, Glacier Tek’s PCM was chosen for
the final design.




                                                                                                   20
Component Level Testing

       In this section, the components of the final design and the prototypes leading to the final
design are tested and evaluated. These include:

   1.   Vinyl Air Tubing Hole Size and Spacing
   2.   Preliminary Prototype
   3.   Scuba Tank
   4.   PCM Melt Time

    The three factors that affect the air velocity leaving the tubing and flowing into the vest are
tank output pressure, hole spacing, and hole size. To determine the optimal hole size and
spacing, the tank output pressure was held constant at 280 kPa (40 psi) and the hole size and
spacing was varied.

       For the first test, 1.6 mm (1/16 inch, 1/16 inch drill bit) diameter holes were drilled 7.6
cm (3 inches) apart in a 3 m (10 foot) long vinyl air tube segment.




                        Figure 12. HPA tubing initial hole spacing and size

         The free end of the vinyl air tube was sealed with glue using a hot glue gun. This forced
the air to escape via the drilled holes. The air tube was then connected to a 6.23 m3 (220 cubic
feet) HPA tank with the output pressure regulated to 280 kPa (40 psi). Using this configuration,
it was observed that the majority of the air escaped in the first 0.9 m (3 feet) of tubing. There was
little or no air reaching the last 1.5 m (5 feet) of holes in the air tube.

         Next, the hole spacing was increased to 12.7 cm (5 inches) and the hole diameter was
decreased to 1.25 mm (0.05 inch, 1.25 mm drill bit). Tests with the air pressure set to 280 kPa
(40 psi) yielded slightly better results than the initial setup. The majority of air now escaped
through the first 1.5 m (5 feet) of air holes while leaving the last 1.5 m (5 feet) with very little air
flow. The next configuration used hole diameters that increased along the length of the tube. A
total of 19 holes were drilled 7.6 cm (3 inches) apart, with the first hole diameter drilled to 1.01
mm (0.040 inch, gauge 60 drill bit). The next hole was drilled to 1.04 mm (0.041 inch, gauge 59
                                                                                                      21
drill bit) and each hole following was drilled one gauge size larger all the way to the last hole at
2.37 mm (0.0935 inch, gauge 42 drill bit). Testing this setup at a tank output pressure of 280 kPa
(40 psi) yielded a more uniform air flow along the entire length of the tubing.

        Next a preliminary prototype was built by fastening the air tubing to a t-shirt using duct
tape. The Sparty chest plate was then placed over the shirt and the air tubing connected to the air
tank at 280 kPa (40 psi). Two different tubing configurations were tested. The front is illustrated
in Figure 13; with the tubing pattern the same on the back of the shirt.




           Figure 13. First HPA tubing configuration (same design on front and back)

         Using this configuration, air flow reached the front and back of the shirt, however,
insignificant air flow reached the front midsection or back midsection. The second configuration
is illustrated in Figure 14.




              Figure 14. Second HPA tubing configuration (mirror design on back)

        The second configuration was tested using the same tank output pressure and yielded
better results. The resulting airflow was spread more uniformly across the entire front and back
of the shirt.

                                                                                                  22
        In order to test the tubing configuration accurately, the t-shirt was cut in the same pattern
as the PCM vest as illustrated in Figure 15.




  Figure 15. T-shirt preliminary prototype cut down to the same size as the PCM vest for more
                                        accurate testing

        The t-shirt in Figure 15 (a) is worn underneath the PCM vest shown in Figure 15 (b). The
dotted lines indicate the location of the PCM packs. Two PCM packs are placed in the front and
two are placed in the back. Wearing the tube-fitted t-shirt and PCM vest with PCM packs
inserted was comfortable. The placement of the tubing did not cause discomfort or pressure
points on the front or back. Now that the tubing configuration was finalized, Velcro straps were
hand stitched permanently into the PCM vest to hold the tubing and to create the final prototype.

        Before beginning the testing of the final prototype, a 2.27 m3 (80 cubic feet) scuba tank
was obtained for use as a portable air source. The scuba tank holds 2.27 m3 (80 cubic feet) of
compressed air at a maximum internal pressure of 20.7 MPa (3000 psi). To determine the total
usage time of the scuba tank, the output regulator was set to five different pressures, and the
length of time to deplete the scuba tank from 20.7 MPa (3000 psi) to 1.4 MPa (200 psi), which is
the minimum tank internal pressure, while attached to the hose was measured.




                 Figure 16. HPA tank depletion time for various output pressures
                                                                                                   23
       As illustrated in Figure 16, the scuba tank usage time varies significantly depending on
the output pressure. An average break time for Sparty is five minutes. An output pressure of 70
kPa (10 psi) to 140 kPa (20 psi) would allow Sparty enough continuous air flow for three to six
five-minute breaks. Depending on the preference of the user, a greater output pressure could be
used for a shorter time for the same number of breaks. Keep in mind that scuba tanks are also
available at 3.4 m3 (120 cubic feet) capacities for longer usage times.

       To determine the total melting time of the phase change material, the PCM vest was worn
underneath the Sparty suit until the PCM packs were melted completely. The suit-wearer
attempted to recreate activities similar to that of the real Sparty to simulate realistic energy
expenditure. The suit-wearer alternated walking up and down stairs, performing jumping jacks,
pushups, and lunges with standing still. After 2 hours the cooling effect of the PCM packs had
been significantly reduced and the packs were approximately 90 percent melted.


System Level Prototype Testing

         Using the final prototype, four tests were conducted to measure its effectiveness on the
core body temperature of the wearer. For each test, the test subject performed a set of exercises
designed to simulate the typical energy expenditure of Sparty over the course of one hour. Table
10 lists the exercises and time intervals at which they were performed.

               Table 10. Ten minute cycle of exercises performed in prototype test

                            Start Time
                                            Exercise
                            (minutes)
                                    0:00    Rest/Take Temperatures
                                    1:00
                                            Climb Stairs
                                    2:00
                                            (up and down 4 flights)
                                    3:00
                                    4:00    Jumping Jacks (1 minute)
                                    5:00
                                            Rest
                                    6:00
                                    7:00    Pushups (10)
                                    8:00    Lunges (10)
                                    9:00    Rest


         One exercise cycle is ten minutes long. There are six cycles in each test for a total run
time of one hour. After each cycle, the temperature of the subject is measured at three locations
as illustrated in Figure 17: the center of the chest, the middle of the upper back, and the right
underarm.
                                                                                                   24
           Figure 17. Thermocouple probe locations taped to the test subject’s t-shirt

        In order to measure the temperatures, three thermocouple probes were taped to the
subject’s body at these locations. A voltmeter with electronic cold junction compensation was
used to read the temperature of each probe. In addition, the subject was asked to subjectively rate
his comfort on a scale from one to ten after each cycle.

         The first test was conducted without the use of a cooling system. The subject wore only
the Sparty costume consisting of foam legs, arms, and a composite chest plate. To simulate the
Sparty head, the subject wore a knit winter hat. For the second test, the subject wore the PCM
vest fitted only with PCM packs underneath the chest plate. The third test removed the PCM
packs, and used the HPA system in the vest. The subject would connect to the HPA tank and
receive a burst of 280 kPa (40 psi) air during the 5:00 – 6:00 minute time interval every other
exercise cycle for a total of 6 minutes throughout the test hour. For the fourth test, the subject
used both the PCM packs and HPA system. The results of the four tests are shown in Figure 18.




                                                                                                 25
Figure 18. Final prototype testing results comparing (a) underarm temperature values, (b) back
temperature values, (c) chest temperature values, and (d) subjective comfort values for each of
                                       the hour test runs


                                                                                             26
Test 1: No Device

        With no cooling device, the subject’s body temperature at 60 minutes measured higher
than the starting temperature for all three thermocouple locations. There is some fluctuation in
the underarm temperatures, but they remain within a 1 °C range with the exception of the high
temperature reading at the 30-minute mark. The fluctuation in the underarm temperature
measurements for this test and for the other three tests may also be attributed to movement of the
thermocouple probe during the jumping jacks exercise. As the test subject’s arms move up and
down, the thermocouple probe may move back and forth as well. The chest and back
temperatures steadily increase for the duration of the test. The plot of the comfort values shows
the subjective comfort level of the test subject on a scale from one to ten. The comfort of the
subject decreased steadily for the duration of the test as perspiration accumulated.

Test 2: PCM Packs

         This test involved using only the PCM packs in the vest worn underneath the costume
chest plate. The subject’s body temperature at 60 minutes measured lower than the starting
temperature for the underarm and back locations. The chest location showed a steady increase in
temperature and then a sharp spike at the 60-minute mark. The fluctuations in the back and chest
temperature data are most likely due to shifting of the PCM packs over the thermocouple probes
during the test. It can be seen from Figure 7 and Figure 17 that the thermocouple probes in the
chest and back locations are situated in-between the PCM packs in the front and back. Any slight
shift in the PCM pack or thermocouple probe could affect the temperature measurement and can
explain the spikes in the chest and back temperatures. The underarm temperature increased at the
10-minute mark, decreased steadily until 30 minutes, and then increased again until the end of
the test. From 0 to 10 minutes, the subject is mostly dry. The accumulation of perspiration
around the 15-minute mark may have increased the effectiveness of conduction between the
PCM and the test subject, thus reducing his temperature until the 30-minute mark. At about 30
minutes, the PCM is at its maximum effectiveness. After this point, its effectiveness decreases
due to melting. Thus, the underarm temperature increases until the end of the test. The relative
comfort of the subject still decreases steadily for the duration of the test, but is slightly above the
comfort values of the case where no device was present.

Test 3: High Pressure Air System

        For this test, the PCM vest was worn without the PCM packs inserted into the pockets.
Only the HPA system was used to cool the subject using the fitted air tubes in the PCM vest. The
subject received a 2-minute burst of 280 kPa (40 psi) HPA during the 10-20, 30-40, and 50-60
minute intervals. For all the thermocouple locations, the temperature at 60 minutes measured
lower than the starting temperature. Each cycle that the subject received a 2-minute burst of 280
kPa (40 psi) air had a lower measured temperature than the cycle prior. This pattern is present in

                                                                                                    27
each of the thermocouple locations but is more prevalent in the back and chest locations. This
test shows that the flow of cool air through the suit is very effective at cooling the subject for
short periods of time. The comfort rating of the subject was approximately the same as the PCM
pack test.

Test 4: PCM Packs + HPA System

         The fourth test utilized both components of the final prototype, the PCM vest with PCM
packs inserted and the burst of HPA for 2-minutes every other exercise cycle. The temperature
plots exhibited the same pattern as Test 3, where the temperature measured after the HPA burst
exercise cycle was lower than the cycle prior. Only the back temperature showed a lower final
temperature relative to the starting temperature, while the underarm and chest locations showed
greater final temperatures. Similar to Test 2, the PCM packs may have affected the temperature
measurements of the chest and back locations due to shifting. Even though the final underarm
temperature is greater than the initial temperature, the difference between them is very small. For
this test, the comfort of the subject is relatively higher than the previous four tests.

Testing Summary

      HPA decreased the measured temperature for the exercise cycle in which it was used.
      On average, the PCM reduced the core temperature of the subject.
      Variation in data can be attributed to the shifting of thermocouple probes/PCM,
       differences in clothing material, and differences in attachment methods.
      Testing can be improved by using a data logger for continuous temperature measurement
       over time.



Economic Analysis

        A summary of the expected costs of manufacturing this system are presented in Table 11
along with the expected longevity of components. The primary component costs are the cold
packs and vest, the air tank, and the tank regulator. The labor required to assemble the system
and sew the Velcro into the vest also constitute significant portions of the construction cost. It is
expected that two hours of shop labor would be required to assemble the system components and
that this labor would cost $50 per hour. Additionally it is expected that four hours of seamstress
labor would be required to sew in the Velcro tubing attachments and that this labor would cost
$25 per hour. All other costs are those actually incurred in constructing the prototype or are
actually prices of the components and include applicable taxes. It is anticipated that annual
maintenance will include replacing the tubing and repairing the Velcro used to secure the tubing
to the vest. Additionally it is expected that a new vest and a new set of cold packs will be

                                                                                                  28
required every year other year. Other components of the system are expected to last more than
ten years.

                             Table 11. Construction costs of the system

                                                                 Expected
                     Item                           Price
                                                                 Life (years)
                     Tubing                         $2.27        1
                     Velcro and Supplies            $7.40        1
                     Cold Pack and Vest             $191.95      2
                     Welding Hose                   $18.42       >10
                     Dolly                          $28.56       >10
                     Hardware                       $9.20        >10
                     Air Tank                       $148.40      >10
                     Tank Connector                 $63.60       >10
                     Regulator                      $102.87      >10
                     Extra Cold Packs               $88.15
                     Shop Labor (2 hours)           $100.00
                     Seamstress Labor (4 hours)     $100.00
                     Total                          $860.82


        Operating costs will include refills of the air tank as well as maintenance of the system.
These costs are summarized in Table 12. As this table shows, refilling the air tank is anticipated
to be the dominant operating cost. It is expected that the tank will be refilled approximately 100
times per year and that each refill will cost $5.30. However, it is likely that due to the large
number of refills and the nonprofit and high profile nature of the Sparty program, a lower rate
could be negotiated. A conservative estimate of $5.30 per refill will be used. Hydro testing of the
air tank is required every five years in order to ensure that the tank is proper sealed and does not
pose a safety hazard. All other maintenance costs are related to replacement of components
based on their expected longevity as described above. One hour of shop labor is expected
annually to prepare replacement tubing and four hours of seamstress labor are expected to
replace worn Velcro.




                                                                                                 29
                             Table 12. Operating costs of the system

                Recurrence               Item                           Price
                Annual Operating         Tank Fill-ups (100 per year)   $530.00
                Annual Maintenance       Tubing                         $2.27
                Annual Maintenance       Velcro and Supplies            $7.40
                Annual Maintenance       Shop Labor (1 hours)           $50.00
                Annual Maintenance       Seamstress Labor (4 hours)     $100.00
                Total Annual
                                                                        $639.67
                Maintenance
                2 Year Maintenance       Cold Pack and Vest             $191.95
                5 Year Maintenance       Hydrotesting Air Tank          $40.00


        Total costs of the system over ten years are shown in Table 13 both in today’s prices and
assuming an inflation rate of 2% annually. In this table, construction occurs in year zero with
maintenance occurring at the end of the first year. No maintenance costs have been added to the
operating costs in the tenth year because this analysis only deals with the costs of the program
over ten years and any maintenance costs incurred in the tenth year would be to prepare the
system for use in the eleventh year.

                        Table 13. Stream of expenditures over ten years

                                 Expenditures        Expenditures
                            Year  in Today's         After Inflation
                                     Prices              (i=2%)
                              0     $860.82             $860.82
                              1     $639.67             $652.46
                              2     $831.62             $865.21
                              3     $639.67             $678.82
                              4     $831.62             $900.17
                              5     $679.67             $750.41
                              6     $831.62             $936.54
                              7     $639.67             $734.78
                              8     $831.62             $974.37
                              9     $639.67             $764.46
                             10     $530.00             $646.07
                            Total    $7,955.62          $8,764.10



                                                                                               30
        An analysis of the current investment that would be required to fund the program for ten
years is presented in Table 14. For example, if a donation were to be requested to sponsor the
program for a ten year period, this analysis shows the amount that would be required assuming
several interests rates that could be made on funds up until the point at which they were required.
Interest rates of 1%, 3%, and 5% were examined. Although current market returns are near 1%,
rates up to 5% were investigated as this is more consistent with long-term market returns.

        Table 14 also shows an analysis of funding required if the program were to only consume
50 tanks of air annually. Note that this analysis would also be valid if the program were to
negotiate a 50% reduction in the cost per fill-up. It is likely that use of the air tank will likely
only be desired at events that are of long duration, in a warm environment, or require a large
amount of activity from Sparty, such as athletic events or parades. The air cooling system would
likely not be necessary at events such as weddings, parties, and other short indoor appearances.
Therefore while Sparty may attend a few hundred events per year, it is likely that only the air
cooling system would only be implemented at a fraction of those. Assuming a 50% reduction in
air tank fill-up expenditures, the cost of the program drops by over 30%. Based on current
market conditions of approximately 1% interest, the program would require a onetime donation
$8,340 to fund for ten years assuming 100 tank fill-ups per year at the standard price or $5,670
assuming a 50% reduction in expenditures on compressed air.



                     Table 14. Money required to fund program for ten years

                                 Necessary Current          Necessary Current
                  Interest
                                Funds at 100 Fill-ups       Funds at 50 Fill-ups
                   Rate
                                     per year                    per year
                     1%              $8,344.14                  $5,666.48
                     3%              $7,595.72                  $5,182.65
                     5%              $6,369.35                  $4,390.42


Conclusions and Future Work

        After evaluating the design alternatives and the prototype test results, the solution for the
most effective cooling of Sparty is the external HPA/PCM vest combination. Subjectively, the
design is an attractive solution due to its compact size and ability to be comfortably worn under
the Sparty chest plate without hindrance to the mobility of the user. Based on analysis and
testing, the PCM vest alone will provide significant cooling, however the added HPA system will
further increase the cooling performance and increase comfort by removing sweat from the suit.


                                                                                                  31
        The analyses of the cooling systems demonstrate that the combined system will
effectively cool the user. Analysis shows that the PCM vest could absorb enough of the heat
energy generated to provide continuous comfort. Testing of the performance of the PCM vest
with the Sparty suit further shows that the net body temperature change is zero to minimal after 1
hour of physical activity, hence providing a sustainable environment for the user. Additionally,
the external HPA system will provide cooling effect through rapid transient cooling. The analysis
shows that the system can provide high cooling rates through modes of convection and
evaporation. Test results of the system further demonstrates that the body temperature decreases
after each period that HPA is pumped through the suit. Also, in having a hole configuration of
increasing hole diameter, the air pressure is maintained throughout the system as to provide
uniform comfort throughout the suit.

        Based on the economic analysis, the expected initial construction cost of the system was
determined to be $860 with annual operating costs including air tank fill-ups and maintenance of
the system to be $640. Assuming that Sparty will only require the air tank at events of long
duration or high physical activity, the cost to fund the program for 10 years at the current market
interest rate of 1% would be $5,670 at 50 air tank fill-ups per year.

        Future studies to improving the system include further investigation of various hole
configurations, including hole spacing, size, and pattern to target specific areas of interest
beneath the chest plate. Additional to this objective is to examine a pattern that will maintain the
greatest air pressure throughout the tube system to provide uniform comfort in the suit. Other
work includes investigating alternative materials for the vest that may be more breathable and
lightweight, further increasing the comfort to the wearer. In the final prototype, an 80 cubic feet
air tank was utilized, which has the potential to provide a total of 8 minutes of use. Depending on
the desired needs of the user for various events, air tanks of a larger capacity may be considered.
A further study that may be pursued is additional testing of cooling performance for longer
duration, warmer environments, and larger amounts of physical activity.




                                                                                                 32
III.    Phase Change Material Cooling Chest
Design Review

        The objective of the PCM cooling chest is to maintain the temperature of frozen PCM
packs. The cooling chest should also be portable and inexpensive. To maximize the performance
of the cooling system, a control system should be implemented.

         After researching cooling systems currently available on the market, it was found that
most products were expensive, large in size, and immobile. The thermoelectric effect of the
Peltier junction was determined to be the most suitable for the objective and is illustrated in
Figure 19. When a voltage is applied to a Peltier junction, a temperature gradient is rapidly
produced across the junction, resulting in a hot and a cold side. The cold side of the junction is
used to reduce the interior temperature of the chest. However, heat must be removed from the hot
side at a high rate in order to maintain its cooling effect.




                                 Figure 19. Peltier junction [11]

        The cooling chest should be able to hold four PCM packs, the number of packs used in a
PCM vest. In order to maximize the heat transfer on both sides of the Peltier junction, a heat sink
and fan was attached on each side. The interior fan and heat sink was used to circulate cool air
within the chest while the exterior fan and heat sink was used remove heat from the hot side. A
temperature sensor was required to regulate the temperature within the chest. Using this, the
product would have a controlled interface between the power source and the cooling system to
reach the required temperature.

       The control system controls the fan on the cold side of the heat sink by turning it on and
off. Fan activation must be controlled on the cold side to allow sufficient time for the Peltier
                                                                                                33
junction to reduce the temperature of the heat sink. Upon reaching the desired temperature, the
fan turns on to circulate the cooled air. Multiple design concepts were generated for the control
system.

   1. Temperature Control System - One Set Point
       A one set point temperature control system uses an op amp and potentiometer. The
       temperature set point can be fixed by adjusting the potentiometer value.
   -   Pros: Small circuit and easy to change its set point.
   -   Cons: Having one set point would turn the fan on and off constantly.

   2. Time Delay System
       This system will delay the operation of the fan, allowing time for the Peltier junction to
       cool the heat sink.
   -   Pros: The delay system connects to a relay allowing the fan to connect directly to the
       power supply
   -   Cons: The room temperature varies continuously, thus changing the time needed to chill
       the heat sink.

   3. Temperature Control System (Two Set Points)
       The system would send a signal depending on the range of the two set points. Using a
       latching relay, the system can be manipulated to set the on and off temperature points.
   -   Pros: It is adaptable to any temperature environment and would not result in the fan
       turning on and off at high frequency.
   -   Cons: It is not readily available.

   4. Combining “Temperature Control System (One Set Point)” & “Time Delay System”
       The time delay system would maintain the same function but the temperature control
       system would initiate the timer once a predetermined temperature had been reached.
   -   Pros: Starting the timer at a specific temperature would reduce the effects of unknown
       starting temperature
   -   Cons: This system is not as efficient as the two set point control system.
        The most suitable design was determined to be the two set point temperature control
system. This control system can be built using a 12 V DC latching relay to connect it to a
temperature system. A normal SPDT relay needs 12 Volts to switch the circuit and reset when
the signal is gone. The latching relay works the same as a normal relay but rather than resetting
when no signal is received, the latching relay will reset when a different signal is received. This
will allow a range to be set that will let the fan turn on after reaching the lower temperature set

                                                                                                    34
point and turning off after reaching the higher temperature set point. However, due to time
constraints, it was not feasible to obtain a 12 V DC latching relay.

       Thus, it was decided that the prototype system would consist of a one set point
temperature control system and a time delay system.


Modeling

       The Peltier junction cooling system consists of a cooling system and a control system.
The goal is to capture heat in the cooling chest using a heat sink and fan and then transfer it to
the ambient environment using a Peltier junction. The device is pictured in Figure 20.




              Figure 20. Peltier junction, heat sink and fan assembled together [12]

        The control system is designed to maintain the air temperature within the cooling chest at
a temperature below 15 °C, which is the melting temperature of the PCM. When the temperature
of the heat sink decreases, the temperature of the air that the fan circulates also decreases. Thus,
the control system was designed to send a signal to the fan when the heat sink reached a set
temperature. The recommended current required for the fan is 0.30 A. Knowing the resistance of
the fan to be 31.28 Ω, an 18 Ω resistor was placed in series with the fan to create a total current
of 0.30 A.

         Two circuits were designed for the control system, a temperature control and a time delay
circuit. Both systems were designed to work together once connected to the power source. A
diode will act as a temperature sensor connected with a potentiometer using an operational
                                                                                                35
amplifier. By doing so, the set point was manipulated using the potentiometer. The temperature
sensor was placed inside the interior heat sink of the cooling box. Once the heat sink reached 15
°C, the diode signaled the time delay circuit.

         When the time delay system receives the signal from the temperature system, the timer
will start. The time delay system will work based on a NE555 timer sending 12 V to the relay.
The relay will work as a switch with the coil connected to the chip. Once 12 V flows into the
coil, the relay will switch to the on position until the 12 V signal stops. When the relay switches,
it will connect the fan to the voltage source. The following equation is used to calculate the time
delay in the system and is a function of the resistance and capacitance.

                                                                                             (12)

        The time delay used in the circuit is 6 minutes. This was chosen because after 6 minutes
the temperature of the heat sink inside the cooling chest will reach from 4 °C from a starting
temperature of 15 °C. At this temperature, the conditions are suitable for starting the fan in order
to cool the air inside the chest. Based on this specified time delay, and using equation (12), the
resistance and capacitance used are 3.3 MΩ and 100 µF, respectively. In Figure 21, a flow
diagram of the control system is pictured.




                Figure 21. Cooling chest flow of command for the control system



Manufacturing

       The materials used for the cooling system include one power supply, two Peltier
junctions, two heat sinks, and two fans. The power supply was used to convert a 110 V AC to
14.7 V DC and provide a maximum current of 5.8 A. The Peltier junctions used could reach a
temperature of -10 °C within 4 to 6 seconds each. The cooling effect of the Peltier junction
would be larger by using two junctions and placing them on the heat sink. Heat sinks can be
made of aluminum or copper. Even though copper is a more conductive material, it is higher in
cost and weight. Hence, aluminum heat sink with dimensions 60 x 80 x 20 mm was selected in
developing the prototype. The fans were 60 x 60 mm and each required at least 12V and
200mA. The fans will be placed toward the heat sink to circulate the air.


                                                                                                    36
        The Peltier junctions were attached between the two heat sinks using thermo compound.
The thermo compound is a type of material that would help conduct heat from the Peltier
junctions to the heat sink. Tape was used to secure both heat sinks and fans together. A hole was
cut out of the side of the cooling chest and the heat sink was fitted in. Two fans were connected
to the system, one on the “hot side” of the heat sink and another one on the “cold side” of the
heat sink.

       Then the control system that contains temperature control and time delay systems was
assembled. The temperature control system primary components are a 1N4007GP diode and a 50
Ω potentiometer. The diode is used to read different voltages with the changing of the
temperature. The potentiometer examines its voltage against the diodes using an op-amp.

                        Table 15. Temperature control system parts [13]

                           Part               Type
                           Chip               LM358N
                           Socket             8-pin
                           Resistors          18 Ω, 820 Ω, 1 kΩ, 10 kΩ
                           Transistor         2N3904
                           Diode              1N4007GP
                           Zener Diode        3.3 V
                           Potentiometer      50 kΩ


        The output of the signal is connected to the time delay system. After receiving the signal,
a timer would start counting for 6 minutes. Then this system is sending a 12V signal to a relay to
switch to the circuit that will let the fan connect to the power supply.

                             Table 16. Time delay system parts [14]

                                 Part             Type
                                 Chip             NE555
                                 Socket           8-pin
                                 Resistors        18 Ω, 3.3 MΩ
                                 Capasitors       0.01 µF, 100 µF
                                 Diode            1N4148
                                 Relay            SPDT


        Both temperature controlling system and time delay system were soldered carefully on
the PC board based on Figure 22. Figure 22 displays the connection of the fans to the power
source.
                                                                                                 37
     Figure 22. Temperature and time delay control system schematic for the cooling chest

       The power supply, the Peltier junctions, and the fans were soldered on the PC board and
the PC board was attached to the cooling box.




                     Figure 23.Cooling system with control system circuit




                                                                                             38
                       Figure 24. Prototype of the cooling chest plugged in



Testing

       Preliminary test results showed that the system will cool air inside the chest to below 15
°C by forcing air over the chilled heat sink. However, it takes a long period of time to reach that
temperature. For this reason, further tests were conducted to find the fastest and more efficient
method to reach the desired result by lowering the power consumption. In addition, other
methods of building the control system were explored.

   A) Tests of the fan starting at different times

        These tests compared the air temperature and heat sink temperatures over time using
different set point temperatures.
Test 1:
        This test involves using two Peltier junctions instead of one. The junctions will be placed
side-by-side between the two aluminum heat sinks. The Peltier junctions will start the same time
as the fans and will run for one hour. Using two Peltier junctions, the heat transfer between the
heat sinks will be accelerated. This test is does not use a control system and just connects to a
DC battery.




                                                                                                 39
          Table 17. Temperatures for the hot side of the heat sink with no control system

                        Time          Inside Air             Heat Sink
                      (minutes)    Temperature (°C)       Temperature (°C)
                           0              23.00                  23.30
                          10              19.80                  27.00
                          20              17.50                  30.00
                          30              17.00                  30.20
                          40              16.50                  30.20
                          50              16.00                  30.10
                          60              15.50                  30.20


Test 2:
        This test uses a starting temperature of -1 °C. The time for the cold side of the Peltier
junction to chill the heat sink to -1 °C is 15 minutes. However, the time for the heat sink to reach
5 °C is only 6 minutes. After reaching 5°C, the temperature decreases at a much slower rate.
Table 18. Temperatures for the cold side of the heat sink after starting the fan when the heat sink
                                         reaches -1 °C

                        Time          Inside Air             Heat Sink
                      (minutes)    Temperature (°C)       Temperature (°C)
                           0               23.8                   23.8
                          15               23.7                    4.0
                          25               15.3                   12.8
                          35               13.5                   11.2
                          45               13.0                   10.8
                          55               12.8                   10.8
                          65               12.8                   10.7


Test 3:
         This test is to activate the fan when the temperature decrease of the heat sink begins slow
down as it reaches the low temperature set point. As a result from the test, it took 7 minutes to
reach 4 °C from 23 °C, then another 7 minutes to reach to -1 °C. The cooling performance in
this test was improved from the second test when the fan was not activated until the heat sink
reached -1 °C. The air temperature within the cooling chest reaches 15 °C in this test faster than
in the second test.

                                                                                                  40
Table 19. Temperatures for the cold side of the heat sink after starting the fan when the heat sink
                                          reaches 4 °C

                      Time          Inside Air              Heat Sink
                    (minutes)    Temperature (°C)        Temperatures (°C)
                        0              23.7                    23.8
                        7              21.0                     8.0
                       17              16.5                    13.7
                       18              15.0                    12.4
                       28              14.0                    11.7
                       38              13.5                    11.1
                       48              13.2                    11.0
                       58              13.0                    10.8
                        68               12.8                    10.7


   B) Tests of the control system to let the heat sink reaches 4 °C


    The test results show that by applying one set point on the control system for the fan to start
below the temperature, would allow it to turn on and off after reaching the set point. The fan will
raise the temperature of the heat sink immediately allowing no time for the fan to remain on
when the temperature is above the set point. Also, by employing a time delay for the fan to start
working after several minutes, the results will differ depending on the starting temperature of the
air. When the heat sink was at 23 °C it took 7 minutes to reach 4 °C, were when it was 27 °C it
took 10 minutes.

    However, combining the two systems, the one set point temperature control system and the
time delay system, would allow a more consistent final result. It would be designed so that a
temperature system that would send a signal when the temperature of the heat sink reaches 15
°C. The time it would take the heat sink to reach 4 °C from a 15 °C is 5 minutes. The delay
system would be placed to start after receiving a signal from the temperature system.



Economic Analysis

        A summary of the expected costs for manufacturing the PCM cooling chest along with
the components and all are presented in The primary components for the cooling system are the
insulated container, Peltier Junctions, Heat Sinks, Thermo Compound, and Fans. The labor
required to assemble the system and solder the circuit is anticipated to require three hours of
labor and can be performed at the MSU Electrical Engineering Shop at a rate of $20 per hour.
                                                                                                 41
Required maintenance will include replacing the Peltier junctions and fans every two years.
Also, the thermo compound between the Peltier junctions and heat sinks will need to be replaced
annually to prevent reductions in efficiency. The price of some circuit components could be
reduced if obtained through the Electrical Engineering Shop.

        Table 20. The primary components for the cooling system are the insulated container,
Peltier Junctions, Heat Sinks, Thermo Compound, and Fans. The labor required to assemble the
system and solder the circuit is anticipated to require three hours of labor and can be performed
at the MSU Electrical Engineering Shop at a rate of $20 per hour. Required maintenance will
include replacing the Peltier junctions and fans every two years. Also, the thermo compound
between the Peltier junctions and heat sinks will need to be replaced annually to prevent
reductions in efficiency. The price of some circuit components could be reduced if obtained
through the Electrical Engineering Shop.

                             Table 20. Costs for constructing the system

                                                              Expected Life
                     Item                           Price
                                                              (years)
                     Peltiers Junctions (2)        $27.00     2
                     Fans (2)                      $10.50     2
                     Thermo Compound                $9.99     1
                     Insulated Container           $29.99     >10
                     Heat Sinks (2)                $20.00     >10
                     Potentiometer                  $1.00     >10
                     Chip NE555                     $0.45     >10
                     Chip                           $0.98     >10
                     Potentiometer                  $1.00     >10
                     Diodes (2)                     $1.96     >10
                     Transistor                     $1.00     >10
                     Shop Labor (3 hours)          $60.00
                     Total                         $163.87


       A schedule of maintenance costs is presented in Table 21. As previously mentioned, the
thermo compound needs to be replaced every year and the Peltier junctions and fans should be
replaced every two years. Performing this maintenance in the Electrical Engineering Shop would
be the most economical option.




                                                                                                42
                          Table 21. Maintenance costs for the system

                Recurrence             Item                               Price
                1 Year Maintenance     Applying Thermo Compound           $9.99
                2 Year Maintenance     Replacing Peltiers                 $27.00
                2 Year Maintenance     Replacing Fans (1 hours)           $19.50
                2 Year Maintenance     Shop Labor (2 Hours)               $40.00
                Total 2 Year
                                                                          $96.49
                Maintenance


       The total cost of the system over 10 years is shown in Table 22, which shows the cost in
today’s prices and if there was inflation of 2% each year. The construction of the product is
shown in the first row and subsequent rows show the maintenance cost in each year.

                        Table 22. Stream of expenditures over ten years

                               Expenditures in     Expenditures After
                       Year
                               Today's Prices       Inflation (i=2%)
                         0        $163.87                $163.87
                         1          $9.99                 $10.19
                         2         $96.49                $100.39
                         3          $9.99                 $10.60
                         4         $96.49                $104.44
                         5          $9.99                 $11.03
                         6         $96.49                $108.66
                         7          $9.99                 $11.48
                         8         $96.49                $113.05
                         9          $9.99                 $11.94
                        10         $96.49                $117.62
                       Total       $696.27                $763.28


       An analysis of the current investment that would be required to fund the cooling box for
ten years is presented in Table 23. This is the same as the analysis that was conducted for the
mascot cooling system. At current interest rates of approximately 1%, a onetime donation of
$730 would be sufficient to cover all costs associated with the cooling box for ten years.




                                                                                              43
                   Table 23. Money required to fund the program for ten years

                          Interest Rate    Necessary Current Funds
                               1%                    $728.39
                               3%                    $666.65
                               5%                    $566.83


Conclusions & Future Work

         The cooling chest could be used to insulate the PCM without turning on the system. To
increase the longevity of the cooling chest and conserve energy, it is recommended to only use
the cooling chest in room temperatures exceeding 15 °C. Since the room temperature can change,
creating a control system using hysteresis is more effective. When rebuilding the control system,
it is better to build the system using the concept of latching relay for the on/reset switch.


IV.    Final Recommendation
        Based on the work conducted, it is the recommendation of this group that the SAF
implement both the PCM and HPA cooling systems. Each system has been shown to be effective
at transferring heat away from the body and reducing temperatures measured within the suit.
Furthermore, the two systems complement each other well in that one provides continuous
cooling while the other can be used when needed to provide additional relief. Furthermore, it is
likely that the use of the HPA system will not be desired for every event that Sparty attends since
many of his events are short, in relatively cool environments, and require less activity. For
example, a brief appearance at a wedding or in the dorm would necessitate less cooling than a
football or basketball game appearance. Additionally, it is recommended that at least two sets of
PCM packs be maintained so that fresh packs can inserted into the suit when desired, as they
almost certainly will be at the half time of football and basketball games or during other multi-
hour events.

        Although the cooling box designed for this project has been shown to be a successful
proof of concept, its relatively high cost, requirement for annual maintenance, and requirement
for an external power input inhibit its usefulness at this stage in development. It is therefore
recommended that a generic cooler be used to keep the extra PCM packs cool until use. A
generic cooler with ice or ice packs would be nearly as effective at keeping the PCM packs
frozen, but at a fraction of the cost and complexity and allow for greater portability.




                                                                                                   44
References
1. Drägerwerk AG & Co. Dräger CVP 5220. N.p.: Drägerwerk AG &, n.d. Web. 17 Feb. 2011.
      <http://www.draeger.com/media/10/02/44/10024408/cvp5220_br_9046018_en.pdf>.

2. "Gear Guide: Cooling Vests & Apparel." ActiveMSers: Staying Active With Multiple
      Sclerosis. N.p., 03 Sept. 2010. Web. 17 Feb. 2011.
      <http://www.activemsers.org/tipstricks/choosingacoolingvest.html>.

3. Cooney, David O. Biomedical Engineering Principles: an Introduction to Fluid, Heat, and
      Mass Transport Processes. Vol. 2. New York: M. Dekker, 1976. Print.

4. Ainsworth BE, Haskell WL, Whitt MC, Irwin ML, Swartz AM, Strath SJ, O'Brien WL,
      Bassett DR Jr, Schmitz KH, Emplaincourt PO, Jacobs DR Jr, Leon AS. Compendium of
      Physical Activities: An update of activity codes and MET intensities. Medicine and
      Science in Sports and Exercise, 2000;32 (Suppl):S498-S516.
      <http://prevention.sph.sc.edu/tools/docs/documents_compendium.pdf>

5. Incropera, Frank P. Introduction to Heat Transfer. 5th ed. Hobokenm NJ: Wiley, 2007. Print.

6. RPCM® Cooling Vest Web Store. Web. 17 Feb. 2011. <http://store.coolvest.com/>.

7. "Cooling Vests." First Line Technology. Web. 17 Feb. 2011.
      <http://www.firstlinetech.com/products/phasecore/cooling-vests/>.

8. Texas Cool Vest. Web. 17 Feb. 2011. <http://www.texascoolvest.com/>.

9. Steele Body Cooling Vest - Relief from Heat Stress via Vest Cooling Technology. Web. 17
       Feb. 2011. <http://www.steelevest.com>.

10. "Inspiration Information." Fall Extension Conference. Web. 15 Apr. 2011.
        <http://fec.msue.msu.edu/fec/inspiration_information>.

11. "Picking a Peltier." Dan's Data - PC Hardware and Gadget Reviews! Web. 21 Feb. 2011.
        <http://www.dansdata.com/pelt.htm>.

12. RazorConcepts. Web. 21 Feb. 2011. <http://www.razorconcepts.net/thermoelectrics.html>.

13. "LM158/LM258/LM358/LM2904 Low Power Dual Operational Amplifiers." National
       Semiconductor, Oct. 2005. Web. <http://www.national.com/ds/LM/LM158.pdf>.
14. "LM555 Timer." National Semiconductor, July 2006. Web.
       <http://www.national.com/ds/LM/LM555.pdf>.



                                                                                             45

				
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