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					Selection Criteria
    Reliability
  Ease Of Use
       Cost
     Safety
  Maintenance
 Warm-Up Delay
Description
Ability of the concept to reliably pasteurize enough safe drinking water.
How easy is the device concept to setup and operate.
How much does the device concept cost to initially produce.
Does the concept pose any physical safety risks to the operator or owners (potential for sh
How expensive will it be to maintain the concept device, both parts and labor.
How long from setup does it take the concept device to start producing pasteurized water.
s (potential for sharp edges, broken glass, hot surfaces, etc.)?

asteurized water.
A




                                                                    B                                                                                 D




                                                                                                                                                       E


                                         A                              B                           C                            D                         E                         F
                                                        Serpentine Flow, Convective
                                                                                         Parabolic Reflector, Evac     Serpentine Flat Plate,
                                                      loop Circulation, Coiled Tube in                                                          Coiled Tube, Braided HX,
                              SPIHX (Previous Design)                                  tube collector, Tube in Tube      Tube in Tube HX,                                     Batched Bottles
                                                         Tube HX, Upstream Temp                                                                  Automotive Thermostat
                                                                                        HX, Automotive Thermostat     Automotive Thermostat
                                                                Regulation
     Selection Criteria Weight Rating Notes     Wtd      Rating     Notes      Wtd      Rating    Notes     Wtd       Rating Notes      Wtd     Rating Notes      Wtd      Rating Notes    Wtd
    Thermal Efficiency     40%   3              1.20       4                   1.60       5                 2.00        3               1.20      2               0.80       1             0.40
    Cost                   30%   4              1.20       4                   1.20       1                 0.30        4               1.20      5               1.50       5             1.50
    Ease of Use            10%   4              0.40       4                   0.40       4                 0.40        4               0.40      4               0.40       1             0.10
    Safety                 15%   4              0.60       4                   0.60       2                 0.30        4               0.60      4               0.60       5             0.75
    Maintenance             5%   2              0.10       3                   0.15       2                 0.10        4               0.20      2               0.10       1             0.05
                     Total Score      3.50                           3.95                          3.10                      3.60                      3.40                       2.80
                           Rank         3                             1                              5                         2                         4                          6
                       Continue?       No                            Yes                            No                        No                        No                         No
Final Concept Selection:

The Subsystem Scoring Matrix computed a system consisting of the:

Serpentine Flat Plate Collector
Coiled Tube in Tube HX
Automotive Thermostat

However, it was noted in subsystem concept generation that certain aspects of some concepts could be combined into the final design, these were:

Convective Loop Circulation System for circulating flow through the collector until pasteurization
Upstream Temp Regulation to prevent water contamination and provide more verifiable factor of safety for pasteurization

Because of the complexity of the two concepts listed above, they will need to be mathematically modeled and/or tested to veri fy their effectiveness.

NOTE: In addition to the results of the Subsystem Scoring Matrix, it was decided to create a final Pugh diagram of entire s ystems incorporating different permutations of the generated subsystems. This was done because it was noted
that some subsystems may work better with others or be rated better when in conjunction with certain others. For example, an extremely low cost option may dominate a more thermally efficient one, as a result of the high cost
consideration for this project. The results of this generation are as follows:

Thermal Efficiency:
The SPIHX design was chosen as the reference. It's thermal efficiency was set in the middle, to provide a benchmark for desi gns that could be more efficient, because the purpose of the project is to improve on this design. The Batched
Bottles were least efficient because they do not use a heat exchanger or utilize any sort of flow system. Most efficient is the parabolic reflector with evacuated tube collector because it concentrates solar energy far more than a flat plate
collector can, yielding higher temperatures. Concept E has a low thermal efficiency (at the expense of low cost) because th e black plastic tubing does not conduct heat as well as the aluminum or copper used in the other collectors, and
the heat exchanger used is the lest efficient as obtained in the subsystem scoring matrix. Concept D is expected to perfor m similarly to the previous concept, but with less leaks and greater reliability (reflected in the Maintenance
criterion).

Cost:
With thermal efficiency set where it was, cost was set at four for the SPIHX for being less expensive than the parabolic coll ector design, more than the batched bottle and coiled tube concepts for their use of cheap materials and
inexpensive subsystems, and about equal with the other flat plate concepts. The cost was chosen as about equal with concepts B and D because the serpentine flow path and divorced heat exchanger concepts use more tubing but save
on the use of multiple large area flat plates.

Safety:
Safety was chosen at 4 for the SPIHX because the device is self contained, as opposed to the parabolic collector that utilize s a large fragile reflector and hot glass tubing which can easily injure operators. The batched bottles were safest
because they only use bottles, no hot collectors or sharp reflectors. The other designs use a similar self contained package to the SPIHX so the safety was set equal.

Maintenance:
Maintenance refers to the amount of work an operator must put into the system for it to function, as well as the ease of clea ning or replacing worn or damaged components. All systems use the same reservoir and water acceptance
concept, so total system capacity was left out of this criterion, except in the case of batched bottles where the constant ne ed to replace bottles yields a completely unreasonable level of maintenance. The SPIHX concept is rated low for
maintenece because of the inability to access the flow channels for cleaning. The best maintence score was given to concept D because the modular construction of setting apart the valving and the heat exchanger lends itself easier for
individual component replacement, and this design directs flow through tubing in the collector, which is easy to clean. The parabolic collector requires high maintenence to prevent corrosion of the collector, and also requires tracking of
the sun. Coiled tube also ranks low on maintence because air buildup in the top loops of the tubing will restrict flow and would have to be bled off manually somehow. Concept B was rated at three because it is easier to maintain than
the SPIHX design because of the separate compononents and tube driven collector, but uses more total tubing and has a more co mplicated valve design than Concept D because of the convective loop and upstream temp regulation valve.

Ease of Use:
Ease of use deals with how simple it is to connect, empty, and operate the system. All the systems listed with the exception of the batched bottles, use the same bucket and tubing water delivery and acceptance method as the first
concept. The ease of use of this concept was rated at 4, and the batched bottles was rated as a 1 as a result of the constan t changing of bottles that would be required by the user.

Result:
Attempts to permutate different concepts using the previously conceived subsystems still pointed towards using the design tha t combined all the best rated subsystems with the best ideas generated in the brainstorming of unused
concepts.

FINAL CONCEPT:
Serpentine Flow, Convective loop Circulation, Coiled Tube in Tube HX, Upstream Temp Regulation
As conceived from Subsystem Scoring Matrix, and verified by Full System Scoring Matrix.
              Concept Selection Matrix             Concept selection was into subsystems. These results would contribute to a final concept, incorporating all or most of
                                                   the best concepts listed here




                                                                                                            Collector Concepts
                                                                   A                                  B                                 C                                D
                                                              (reference)
                                      Segment                  First Gen                   Serpentine Flat Plate                   Black Coil                       Evac Tube

              Selection Criteria       Weight       Rating       Notes         Wtd    Rating        Notes        Wtd Rating          Notes         Wtd Rating          Notes          Wtd

             Thermal Efficiency           35%          3            -          1.05      4             -         1.40      2            -         0.70      5            -            1.75

             Material Cost                25%          4            -          1.00      3             -         0.75      5            -         1.25      1            -            0.25

             Reliability                  30%          3                       0.90      4                       1.20      2                      0.60      2                         0.60

             Maintenance                  10%          3            -          0.30      4             -         0.40      3            -         0.30      2            -            0.20
                                     Total Score                  3.25                               3.75                             2.85                             2.80
                                            Rank                    2                                 1                                 3                                4
                                       Continue?                   No                                Yes                               No                               No

              Collector Considerations:

              The first generation design used parallel flat thin plates of aluminum coated with a selective surface to collect solar energy and distribute it to the water. Plates
              were located under a glass glazing. According to the previous team's documentation, this method lent itself easily to leaks, bulging of the collector from water
              pressure, and difficult fabrication. These problems are reflected in reliability and maintenance.

              Concept B, listed as Serpentine Flat Plate, retains the flat plate collection concept and the use of glazing of the previous design, but directs the flow through a
              serpentine path of tubing to prevent leaks and contribute to easier manufacturing. The tubes would be aluminum and soldered to the collection plate, as well as
              coated with a selective surface. This design will add reliability to the system, and add to the efficiency by routing the flow through a longer path in the collector.
              This will increase cost.

              The Black Coil collector design was conceived as an extremely low cost system. This design would integrate the flow pattern and the collection into one flat spiral of
              black plastic tubing. The coil would serve as a flat plate collector, contained underneath a glazing, and the water would be routed through the coils, heating up as it
              reached the center. The main problem with this concept is that air will build up in the tops of the arcs of tubing as the water heats up, reducing efficiency and
              impinging on the flow. This problem is reflected in the reliability as well as maintenance criteria.

              Evacuated tubes were also considered. These use nested glass tubing, with a vacuum drawn between them. the inner tube would be coated with a selective
              surface, and the water would be routed through the inner tube. These are highly efficient and reliable. However, they are the highest cost option and can break
              easily. The fabrication would also be difficult, from sealing and pulling a vacuum within the tubes. This design would also need to track the sun, or be employed in
              banks of several collectors. The difficulty of tracking the sun is reflected in the reliability and maintenance criteria.




Revision A
01/11/08
                                                                                                      Heat Exchanger Concepts
                                                                   A                                  B                       C                                          D
                                                              (reference)
                                      Segment                  First Gen                   Coiled tube in tube          Braided Tube         Straight tube in tube
             Selection Criteria        Weight       Rating       Notes         Wtd    Rating      Notes      Wtd Rating     Notes    Wtd Rating     Notes       Wtd

             Thermal Efficiency          50%           4            -          2.00      5            -         2.50      2             -         1.00      1            -         0.50

             Material Cost               40%           3            -          1.20      3            -         1.20      5             -         2.00      4            -         1.60

             Maintenance                10%            2            -          0.20      3            -         0.30      3             -         0.30      3            -         0.30
                                     Total Score                  3.20                               3.70                             3.00                             2.10
                                           Rank                     2                                  1                                3                                4
                                      Continue?                    No                                Yes                               No                               No

               Heat Exchanger Considerations:

               The first generation design used a second and third parallel plate of aluminum underneath the collector plate, creating a channel for flow to return heat to the
               collector water after pasteurization. This is cost effective and gets good heat transfer for the slow flow rates involved. This design was subject to the same faults as
               the previous collector, with high potential for leaks and bulging, reducing efficiency. The additional flat plates also add cost, and the unit would have to be
               completely disassembled for maintenance or cleaning, with the potential for further jeopardizing the seals.

               The coiled tube in tube uses a coiled conductive tube containing the hot pasteurized water that runs through a larger tube th at accepts incoming water. This gives
               good thermal efficiency because of the high surface area of exposure, but is more expensive than other methods. The fact tha t this heat exchanger is not integrated
               into the collector makes it easier to maintain or replace.

               Braided tube was conceived as the lowest cost option. Two tubes would be braided and soldered together. Flow of pasteurized water would run against the
               incoming cold water flow to facilitate better heat transfer. The braided tubes would be insulated. Because of the reduced s urface area of exposure, and the
               necessity to conduct through two wall thicknesses of pipe, this design has a lower thermal efficiency. However, it could be easily maintained with pipe cleaners if
               necessary, and is the lowest cost option.

               Straight tube in tube heat exchanger consists of a smaller diameter tube containing hot pasteurized water running inside of a larger diameter tube with cold input
               water, running in opposite directions. Although inexpensive, some simple mathematical modeling was done on this design and r evealed a very low thermal
               efficiency for the low laminar flow rates involved in this project.




Revision A
01/11/08
                                                                                                                        Multiple
                                                                                                                        Thermostats




                                                                                                                                                                                 Density Driven




                                          Thermostat Valve in
                                          custom enclosure


                                                                                                                             Flow Control Concepts
                                                                        A                                   B                                   C                                     D                                E
                                                                (Previous Design)
                                                            Automotive Thermostat                Multiple Thermostats                 Manual valve                           Electronic on/off                 Density Driven
              Selection Criteria       Weight        Rating         Notes           Wtd    Rating       Notes         Wtd Rating            Notes               Wtd Rating        Notes           Wtd Rating       Notes         Wtd

             Reliability                 35%            2               -           0.70     3              -         1.05     1      (If operated correctly)   0.35   1              -           0.35   1             -         0.35

             Ease Of Use                 15%            5          No Interface     0.75     5         No Interface   0.75     1       Constant Attention       0.15   5         No Interface     0.75   5        No Interface   0.75

             Cost                        25%            5               -           1.25     3              -         0.75     5                 -              1.25   1       Must be Overcom    0.25   3             -         0.75

             Maintenance                 15%            4               -           0.60     4              -         0.60     1                 -              0.15   5              -           0.75   4             -         0.60

             Warm-Up Delay               10%            2               -
                                                                                    0.20     2              -
                                                                                                                      0.20     3                 -
                                                                                                                                                                0.30   4              -
                                                                                                                                                                                                  0.40   2             -
                                                                                                                                                                                                                                 0.20
                                      Total Score                    3.50                                3.35                                2.20                                  2.50                             2.65
                                            Rank                       1                                   2                                   5                                     4                                3
                                       Continue?                     Yes                                 Yes                                  No                                    No                              Yes

             Flow Control Considerations:

             Previous design used an automotive thermostat valve contained in a custom designed aluminum housing. This was relatively inexpensive, but cycling and warm-up
             delay reduced the reliability. These problems were party due to the need for the heat in the collector to conduct through th e water in the plumbing leading to the
             valve for it to open. This increased time to open and then shocked the valve with the hotter collector water.

             Multiple thermostats is an attempt to increase reliability of the thermostat valve system by adding a second valve. This wou ld decrease the chance of unpasteurized
             water passing through the valve and contaminating the output. One idea that came out of this concept is detecting the temper ature at a different point in the stream
             of water than where the valve actually opened. This could reduce the cycling of the valve by providing a buffer of hot, past eurized water between the valve and the
             valve sensing.

             Manual valve would rely on someone with a thermometer opening the valve when the water was pasteurizing. This method is unsa fe and can easily lead to the
             consumption of contaminated water due to human error.

             Electronic on/off system would use a solenoid and temperature sensor to regulate flow. This design would require battery cha nges and is prohibitively expensive for
             this project.

             Density driven flow works on the phenomena of convection loops. As water heats up, a pressure differential develops and driv es flow through a loop. This would
             circulate the flow past the collector until the density changes sufficiently to reach a spillover at a point higher than the inlet. This ensures water leaving the system is
             pasteurized without the use of a valve. This relies on the unit being perfectly oriented for this height difference to be ef fective, and is therefore highly unreliable, and
             would require constant watching to avoid contamination. The concept of the convection loop circulating flow through the coll ector was considered a viable method
             for fixing the conduction problem and increasing the output of the thermostat valve.

             The automotive thermostat option was chosen, but it was acknowledged that components of the multiple thermostat idea (sensing in a different area than where the
             flow is released, coined as "Upstream Temperature Regulation System") and the density driven concept (convection loop cycling flow, coined "Convection Loop
             Circulation System") can increase the reliability and output.


Revision A
01/11/08
             flow is released, coined as "Upstream Temperature Regulation System") and the density driven concept (convection loop cycling flow, coined "Convection Loop
             Circulation System") can increase the reliability and output.




Revision A
01/11/08

				
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posted:11/14/2011
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