EFFECT OF DESIGN PARAMETERS ON THE PERFORMANCE OF A CLOSED LOOP PULSATING

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EFFECT OF DESIGN PARAMETERS ON THE PERFORMANCE OF A CLOSED LOOP PULSATING Powered By Docstoc
					INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING
  International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
  6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME
                         AND TECHNOLOGY (IJMET)

ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)                                                     IJMET
Volume 4, Issue 3, May - June (2013), pp. 306-317
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   EFFECT OF DESIGN PARAMETERS ON THE PERFORMANCE OF A
              CLOSED LOOP PULSATING HEAT PIPE

                   Ch. Sreenivasa Rao1, Avssks Gupta2, K. Rama Narasimha3
   1
       Department of Mechanical Engineering, Madanapalle Institute of Technology and Science,
                                    Madanapalle , India.-517325
   2
       Department of Mechanical Engineering, JNTU college of Engineering, Hyderabad-500085,
                                                India
           3
             Centre for Emerging Technologies, Jain University, Bangalore-562112, India.


   ABSTRACT

            Pulsating heat pipes (PHP) have emerged as very promising passive devices for heat
   transfer applications especially suited for thermal management of electronics. A closed loop
   PHP made of brass with 1.5 mm ID and 2.5 mm OD with a single loop is tested in the present
   work at atmospheric conditions. This paper attempts to describe the effect of working fluid,
   heat input, orientation and fill ratio as primary design parameters on the performance of PHP.
   The transient and steady state experiments are conducted for various heat loads, fill ratio and
   working fluids. Acetone and Propanol are used as working fluids during the experimentation.
   The performance quantities of PHP like thermal resistance and heat transfer coefficients are
   evaluated. The results showed that Acetone exhibits better heat transfer characteristics of
   PHP compared to Propanol. The PHP is tested for horizontal, 300 and 600 orientations. The
   results indicate that the performance of PHP changes with different fill ratio, orientation and
   heat load. Better heat transfer performance is obtained for zero and 300 orientations and at a
   fill ratio of 80%.

   Keywords: electronic cooling, closed loop pulsating heat pipe, pressure pulsations, design
   parameters and thermal performance.

   1. INTRODUCTION

         Thermal management of modern electronics is the challenge of the day in the wake of
   component miniaturization and attracted the attention of researchers to develop efficient
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6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME

cooling systems. Several cooling methods are employed to cool the electronic devices. The
oscillating or pulsating heat pipe (OHP/PHP) is a promising two-phase heat transfer device
for applications like electronic cabinet cooling. It is simple in structure with a coil of capillary
dimensions filled with certain working fluid in it and extended from the heat source to sink.
PHP does not contain wick structure to return the condensate back to the evaporator section
unlike a conventional heat pipe. Instead, PHP works on the principle of fluid pressure
oscillations that are created by means of differential pressure across vapor plugs from
evaporator to condenser and back. The vapor formed at the evaporator is pushed towards the
condenser in the form of discrete vapor bubbles amidst packets of fluid. The vapor gets
condensed at the condenser releasing the latent heat of vaporization and returns to the
evaporator to complete the cycle. The thermal performance of an actual PHP depends upon
the temperature gradient exists between the evaporator and the condenser section.
        PHP was first proposed and patented by Akachi[1] as a passive cooling device and
gains the attention of many investigators.
        Although a plethora of heat pipe technology is established, the open literature
available on PHPs is limited. The numerical studies on PHPs reported in the literature are
limited to estimate the complex behavior of thermo-fluidic transport phenomena. More over
the mathematical models proposed in the literature on PHPs needs experimental verification
[2, 3, and 11]. Characterization of thermal performance in multi-loop PHPs has been reported
in few experimental investigations.[4,5,6,7,8]. Results on thermal performance of single loop
PHP are also reported in some literatures [9, 10]. Experimental results mainly focused on
flow visualization studies and the measurement of temperature variation pattern. The effect of
working fluid, heat input, tube material, orientation and fill ratio are identified as primary
design parameters affecting the performance of PHP which requires detailed investigation
[12].
        Lee et al. (1999) conducted few performance tests on a multi loop PHP made of brass
using Ethanol as working fluid. The PHP was tested for different orientations (30°-90°). Most
active oscillations caused by the formation or estimation of bubbles are observed in bottom
heating with fill ratio of 40-60%.
        Khandekar (2003) demonstrated the existence of multiple quasi-steady state in a PHP
by developing an experimental set up of PHP made of copper tubes of inner diameter 2mm
and outer diameter 3mm.Experiments were conducted for the heat input range of 10-20 W
with Ethanol as the working fluid at 60% fill ratio. The data was recorded for 12 hrs
continuously. The multiple quasi steady states observed were named as steady state 1, 2&3.
The flow in steady state 1 was unidirectional with alternate fluid movement and stop over due
to which intermittent heat transfer was happened. In steady state-2, a tendency of liquid hold-
up was observed in the condenser section which made the evaporator zone becomes drier.
Poor thermal performance was reported in the steady state-2. In steady state-3, unidirectional
continuous flow pattern with no stop-over was observed leading to least thermal resistance. It
was showed that churn flow takes place in the evaporator and slug flow in the condenser
zone.
        Rama Narasimha et.al (2010) presented the experimental results for a single loop PHP
made of copper. Lower thermal resistance was found at atmospheric pressure when compared
to Vacuum pressure levels maintained inside the PHP [19]. The performance characteristics
such as thermal resistance and heat transfer coefficient are estimated and analyzed for
different heat inputs, working fluids and evacuation levels.


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       Y.Zhang et al (2011) explained that the thermal performance of many PHPs degraded
                 on
 as the Inclination angle is varied and some may not operate at all. If the inner diameter of
 PHP is sufficiently smaller that aids the PHP to perform at low inclination angles. (The
 orientation is considered to be 0° for horizontal heat mode, +90° bottom heat mode and -
 90° top heat mode operation).
       Thus from the literature study, it is understood that not many experimental
 investigations were reported on single loop PHP and needs further research progress in this
 area. More over the scope of the suitability of Propanol as a promising thermal dissipation
 fluid is not verified. The experimental results available so far are only related to copper or
 aluminium PHP. There are no experimental results available related to PHP when it is made
                                   present
 of other materials. Hence in the present work, a single loop brass PHP is considered for the
 experimental study. Acetone and Propanol are considered as the working fluids for PHP
 operation. The transient experiments are conducted for various heat inputs. The thermal
                             r
 resistance and heat transfer coefficient are evaluated.

 2. EXPERIMENTATION

   2.1 Instrumentation Made With the Experimental Setup




                      Fig. 1 Photograph of PHP Experimental setup

        Fig. 1 shows the pictorial view of the experimental setup. In this setup, the basic
components used in PHP are brass tube, borosilicate glass tube, silicon rubber tube, a non
return valve, a tape heater and thermocouples.
                                             from
        Brass is an alloy and would be free from fouling effects unlike the pure copper under
the action of continuous interaction with working fluid flowing through it. More over the
fouled surfaces make the fluid gets clogged and affects the thermal performance of PHP
                                 ances
severely. Under these circumstances Brass can be used as a good conductor of heat. The ID
of the brass tube selected is 1.5mm and the OD is 2.5mm.
                                                U-turn
        The glass tube attached between the U turn Brass tube is considered as adiabatic
                                                      et.al,2004)
section which was specified earlier (by khandekar et.al,2004) in the literature. Having the
transparent surface, it permits to capture the flow visual effects. The glass tube is made of
borosilicate, which can resist temperature up to 1200° C.
                                                                               ar
        Silicon rubber tubes of 2mm inner diameter and 4mm outer diameter are used as the
connectors between glass and copper tubes. They are thermal insulators and can resist
temperatures up to 400°C. They are leak proof and expand at higher temperatures.

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                                                                              used.
        In order to maintain unidirectional fluid flow; a non return valve is used The valve is
made of stainless steel and has inner diameter of 5mm. The ball and seating arrangement is
used with a ball diameter of 4mm.
                                          0 50
        A tape heater of heating capacity 0-50 W is attached to the evaporator section and acts
as the source of heat input.
               type
        Six K-type thermocouples are connected for temperature measurements, four in the
evaporator section and two in the condenser section. The wire diameter of thermocouples is
1mm and can measure temperature up to 1000° c with a maximum error of ± 0.1° C. T          The
temperature values are recorded at a frequency of 1Hz.
        The experiment is performed with three working fluids viz. Propanol, distilled water
and acetone. The working fluid is injected into the heat pipe using a syringe.

2.2 Experimental Procedure
     The experimental test facility as shown in figure 1 is setup to characterize the pulsating
  heat pipe thermal performance and the following procedure is adopted during the
  experiment:
  1. Before filling the fluid in the PHP it is ensured that no traces of working fluid used in
     previous cycle of experimentation is available.
  2. The required amount of working fluid is then filled through the filling valve using a
                                             non return
     syringe by opening the one end of the non-return valve such that the fluid directly enters
                        ction.
     the evaporator section. It is reported in the literature (Khandekar, 2004) that the PHP
     develops true pulsating motion when the fill ratio is between 20% - 80% and it is also
     stated that 50% is the optimum fill ratio. Hence, in the present work, experiments are
                 or
     conducted for fill ratios ranging from 50% to 80%,
  3. Now the air is filled through the filling valve provided on the brass tube using another
     syringe. This is done to ensure simultaneous formation of liquid slug and vapor bubbles.
                                             wattage
  4. The display unit is ON and required wattage is set using the power supply unit. In the
     present experimentation, heat input is varied from 7w to 12w in steps of 1w.
  5. The cooling water is allowed to the condenser section of PHP from the constant head
     water bath.
                                      transfer
  6. .In the present work, the heat transfer behavior of PHP is analyzed for the inclination
     angles of 0°, 30° and 60°.
  7. The transient experiments are conducted and the temperatures at various locations of
     the PHP are recorded from the temperature data logger. The experiments are continued
     till steady state is reached. The measurement has inherent uncertainties. The thermo
              temperature
     couple-temperature display system has uncertainty of ±2% of full scale.

3. RESULTS AND DISCUSSION

                                                                     heat
        The performance effectiveness and understanding of the heat transfer characteristics
of closed loop pulsating heat pipe is evaluated by measuring wall temperature at different
points of the CLPHP. The uncertainty in condenser and evaporator temperature Uc and Ue
are evaluated respectively using the relations of Kline et al. (1953). Accordingly


            % Ue =

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            % Uc =
 The maximum temperature uncertainty found from the equations is about 6%.

 3.1. Effect of Heat Input


                                                    70
                      Evaparator Temperature Te C




                                                    65
                      0




                                                    60                                                                                 12 W
                                                                                                                                       11 W
                                                                                                                                       10 W
                                                                                                                                       9W
                                                                                                                                       8W
                                                    55




                                                    50
                                                         0   100   200   300      400       500       600     700   800   900   1000

                                                                                         Time t (s)

                                                                         Effect of heat input on evaparator
    Fig.2 Variation of Evaporator Temperature with time at different heat load for
                            Propanol at a fill ratio of 60%

         Fig.2 shows the variation of evaporator wall temperature with time for Propanol at a
                  .                                                            tor
fill ratio of 60%. It can be seen from the fig.2 that the variation of evaporator temperature
with respect to time is periodic in nature at steady state. As there is a continuous pressure
pulsation during the flow in a PHP, the evaporator temperature versus time curve is periodic
                                              pulsating
in nature. It is also clear that the pressure pulsating effect is less at lower heat load and
                                                                           .
consequently the evaporator temperature rises at lower heat load of 8 W. It is also clear that
the system takes more time to reach the steady state at lower heat input of 8 W.

                                                    33



                                                    32



                                                    31
                       Condenser Temperature Tc C
                      0




                                                    30



                                                    29
                                                                                                                                       12 W
                                                                                                                                       11 W
                                                    28                                                                                 10 W
                                                                                                                                       9W
                                                                                                                                       8W
                                                    27



                                                    26



                                                    25
                                                         0   100   200   300      400      500        600     700   800   900   1000

                                                                                         Time t (s)

                                                                         Effect of heat input on Condensor
                             Temperature
Fig.3 Variation of Condenser Temperature with time at different heat load for Propanol
                                at a fill ratio of 60%

                                                     wa                     espect
         Fig.3 shows the variation of condenser wall temperature with respect to time at
                            Propano              io
different heat inputs for Propanol at a fill ratio of 60%. It is clear from figure 3 that the
    denser
condenser wall temperature is less at lower heat load of 8 W compared to higher heat inputs.
This is because of very slow and intermittent motion of the working fluid at lower heat load.
As the movements of the working fluid is slow at lower heat input due to lower energy
                                                                             section.
levels, the hot fluid takes more time to reach the condenser from evaporator sectio

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3.2. Effect of Fill ratio

                                                            68


                                                            66


                                                            64




                       Evaporator Temperature Te C
                       0
                                                            62


                                                            60


                                                            58                                                                                               80%

                                                                                                                                                             70%

                                                            56                                                                                               60%

                                                                                                                                                             50%

                                                            54


                                                            52


                                                            50
                                                                  0   100       200     300       400      500         600        700   800   900    1000

                                                                                                         Time t (s)

                                                                                       Effect of heat input on evaporator
Fig.4 Variation of Evaporator Temperature with time at different fill ratio for Acetone
                               at a heat load of 10 W

  Fig. 4 shows the variation of evaporator wall temperature with time at different fill ratios
  for Acetone at a heat load of 10 W. It is understood from the figure that the minimum
  evaporator temperature is recorded at 80% fill ratio. At higher fill ratio less vapor bubbles
  exists in the tube with consequent decrease in the evaporator temperature.
  The thermal performance of PHP can be studied by its thermal resistance and heat transfer
  coefficient. The thermal resistance of PHP is given by

       Te − Tc
  R=           (K/W)                                                                  (3.1)
          Q

                                                            4.5




                                                             4
                             Thermmal Resistance, R (K/W)




                                                            3.5



                                                                                                                                                            50%

                                                                                                                                                            60%
                                                             3
                                                                                                                                                            70%

                                                                                                                                                            80%



                                                            2.5




                                                             2
                                                                  7         8                 9            10                11          12         13
                                                                                                        Heat Input, Q (W)




   Fig. 5 Effect of Thermal Resistance on heat load at different Fill ratio for Acetone

         Fig. 5 shows the variation of thermal resistance with heat load for Acetone at different
fill ratios. From the figure it is clear that the thermal resistance decreases with increase in
heat load at all fill ratios considered. The fill ratio of 80% exhibits the lower values of
thermal resistance compared to lower fill ratios considered. As the temperature difference
between evaporator and condenser is less at higher fill ratio of 80%, the magnitude of thermal
resistance is also less. On the other hand at lower fill ratio, the pressure pulse oscillation is
decreased in overcoming the flow friction between the fluid and the valve and hence the rate
of heat transferred also decreases. Consequently the overall thermal resistance is increased as
a result of increase in temperature difference.

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The convective heat transfer coefficient of PHP is given by

            Q
    h=               (W/m2K)                                                                                                        (3.2)
         A(Te − Tc )


                                                                                1800




                                                                                1600
                          Heat Transfer Co-efficient, h (W/m2 K)



                                                                                1400




                                                                                1200                                                                                                                  50%

                                                                                                                                                                                                      60%

                                                                                                                                                                                                      70%
                                                                                1000                                                                                                                  80%




                                                                                             800




                                                                                             600
                                                                                                       7         8                  9            10                11             12           13
                                                                                                                                               Heat Input, Q (W)

                                                                                                                       Effect of heat input on Thermal Resistance for Accetone



Fig. 6 Effect of Heat Transfer coefficient on heat load at different Fill ratio for Acetone

        Fig 6 shows the variation of Heat transfer coefficient with varying heat loads for
Acetone at different fill ratios. From the figure, it is seen that the Heat transfer coefficient
increases with increase in heat load at all fill ratios considered. Higher values of heat transfer
coefficient can be seen at higher fill ratio of 80% which indicates better performance of brass
PHP.

3.3. Effect of Working Fluid

                                                                                                  65




                                                                                                  60
                                                                   Evaporator Temperature Te 0C




                                                                                                  55




                                                                                                  50                                                                                           ACCETONE
                                                                                                                                                                                               2-PROPANOL



                                                                                                  45




                                                                                                  40
                                                                                                       0   100       200      300       400      500       600      700     800        900   1000
                                                                                                                                              Time t (s)




Fig. 7 Variation of Evaporator Temperature with time for different working Fluids at a
                        heat load of 12 W and a fill ratio of 60%

        The variation of evaporator wall temperature with respect to time for different
working fluids at a fill ratio of 60% and at a heat input of 12 W is shown in Fig 7. From the
figure it is clear that the evaporator wall temperature is higher in case of Propanol and lower
in the case of Acetone. It is also observed that the system takes more time to reach the steady
state in case of Propanol when compared to Acetone. More random motion of the fluid is
observed in case of Propanol due to higher perturbations during the flow.


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                                                                         40


                                                                         38


                                                                         36




                                       Temperature Difference Te-Tc 0C
                                                                         34


                                                                         32


                                                                         30


                                                                         28                                                                                              ACCETONE
                                                                                                                                                                         2-PROPANOL
                                                                         26


                                                                         24


                                                                         22


                                                                         20
                                                                              0   100       200         300       400      500         600      700   800        900   1000
                                                                                                                        Time t (s)

                                                                                                      Effect of working fluid on temperature
 Fig. 8 Variation of Temperature difference with time for different working Fluids at a
                        heat load of 12 W and a fill ratio of 60%

        Fig. 8 shows the variation of temperature difference between evaporator and
condenser with time for different working fluids at a fill ratio of 60% and at a heat input of 12
W. It is seen that the temperature difference between the evaporator and condenser is less for
Acetone and more for Propanol. This shows that Acetone can transfer heat with less
temperature difference compared to Propanol. The temperature difference between
evaporator and condenser for Acetone is found to be around 210C and for Propanol it is
around 310C.

                                                                4.25




                                                                3.75
                       Thermmal Resistance, R (K/W)




                                                                3.25




                                                                2.75


                                                                                                                                                                          ACCETONE
                                                                2.25                                                                                                      2-PROPANOL




                                                                1.75




                                                                1.25
                                                                              7         8                     9              10                11           12            13
                                                                                                                          Time t (s)

                                                                                                  Effect of working fluid on Thermal Resistance
  Fig. 9 Effect of Thermal Resistance on heat load for different working fluids at a fill
                                      ratio of 60%

       Fig.9 shows the variation of thermal resistance with heat input for different working
fluids at 60% fill ratio. The figure indicates that the thermal resistance decreases with
increase in heat input in case of both the working fluids considered .Further it is seen that
Acetone exhibits lower values of thermal resistance compared to Propanol. This is due to
lower value of temperature difference between evaporator and condenser in case of Acetone.
The lower values of thermal resistance of Acetone indicate that Acetone has better heat
transport capability compared to Propanol.




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                                                                                          2800


                                                                                          2600


                                                                                          2400




                                                 Heat Transfer Co-efficient, h (W/m2 K)
                                                                                          2200


                                                                                          2000


                                                                                          1800


                                                                                          1600                                                                                               ACCETONE
                                                                                                                                                                                             2-PROPANOL
                                                                                          1400


                                                                                          1200


                                                                                          1000


                                                                                              800
                                                                                                    7               8              9               10                11          12          13
                                                                                                                                                Time t (s)

                                                                                                                    Effect of working fluid on Heat Transfer Co-Effiecient



Fig. 10 Effect of Heat Transfer coefficient on heat load for different working fluids at a
                                    fill ratio of 60%

        The variation of Heat transfer coefficient with respect to heat input for different
working fluids at a fill ratio of 60% is shown in Fig.10. It is seen that the Heat transfer
coefficient increases with increase in heat input for the working fluids considered. Acetone
shows higher heat transfer coefficient values compared to Propanol. This is due to the lower
values of temperature difference between evaporator and condenser for Acetone.

3.4 Effect of Orientation

                                                 75



                                                 70




                                                 65
                                perature Te 0C




                                                 60
                  Evaparator Tem




                                                                                                                                                                                              zero degrees
                                                 55                                                                                                                                           30 Degrees
                                                                                                                                                                                              60 Degrees



                                                 50



                                                 45



                                                 40
                                                                                          0             100   200        300      400       500        600     700        800   900   1000
                                                                                                                                              Time t (s)




  Fig.11 Variation of Evaporator Temperature with time for different orientation at a
                        heat load of 10W and a fill ratio of 60%

        The orientation of PHP plays a very important role in its thermal performance. In the
present work, experiments are conducted at zero, 30 and 60 degree orientations of PHP with
respect to horizontal. Fig. 11 shows the variation of evaporator temperature with time for
different orientations considered. From the figure, it is seen that the evaporator wall
temperature is less at an orientation of zero and 30 degree compared to 60 degree.




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                                                                                45




                                                                                40



                                                                                35




                      Temperature Difference Te-Tc C
                      0
                                                                                30


                                                                                                                                                                                 zero degrees
                                                                                25                                                                                               30 Degrees
                                                                                                                                                                                 60 Degrees


                                                                                20



                                                                                15



                                                                                10
                                                                                       0        100   200   300       400   500        600        700   800        900   1000
                                                                                                                              Time t (s)




Fig.12 Variation of Temperature Difference with time for different orientation at a heat
                         load of 10W and a fill ratio of 60%

       Fig. 12 shows the variation of temperature difference between evaporator and
condenser with time for different orientations considered. From the figure, it is seen that the
temperature difference between evaporator and condenser is less at an orientation of zero and
30 degree compared to 60 degree. This shows that the PHP is desired to be operated at zero
or 30 degree compared to 60 degree orientation.

                                                                                      3.5




                                                                                       3




                                                                                      2.5
                                                       Thermmal Resistance, R (K/W)




                                                                                       2


                                                                                                                                                                                zero degrees
                                                                                      1.5                                                                                       30 Degrees
                                                                                                                                                                                60 Degrees


                                                                                       1




                                                                                      0.5




                                                                                       0
                                                                                            7         8           9          10              11               12         13
                                                                                                                               Time t (s)




Fig. 13 Variation of Thermal Resistance with heat load for different orientation at a fill
                              ratio of 60% for Acetone


        Fig. 13 shows the variation of thermal resistance with Heat input at various
orientations considered for Acetone at a fill ratio of 60%. It is observed from the figure that
the thermal resistance decreases with increase in heat load at all orientations considered. It is
also observed that the thermal resistance is less at zero and 30 degree orientations compared
to 60 degree. As the fluid should overcome the effects of gravity more at 60 degree
orientation, there is more resistance for heat transfer and flow at this orientation. Hence, it is
desirable to operate the PHP at zero or 30 degree orientations to achieve better heat transfer
characteristics.




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                                                                 3500



                                                                 3000




                        Heat Transfer Co-efficient, h (W/m2 K)
                                                                 2500




                                                                 2000


                                                                                                                                            zero degrees
                                                                 1500                                                                       30 Degrees
                                                                                                                                            60 Degrees



                                                                 1000




                                                                 500



                                                                   0
                                                                        7   8    9             10             11            12         13
                                                                                                Time t (s)

                                                                                Effect of orientarion on Heat Transfer Co-Effiecient




Fig. 14 Variation of Heat Transfer coefficient with heat load for different orientation at
                            a fill ratio of 60% for Acetone

         Fig. 14 shows the variation of heat transfer coefficient with Heat input at various
orientations considered for Acetone at a fill ratio of 60%. It is observed from the figure that
the heat transfer coefficient increases with increase in heat load at all orientations considered.
It is also observed that the heat transfer coefficient is more at zero and 30 degree orientations
compared to 60 degree showing better heat transfer capability of PHP operation at zero and
30 degree orientations.

4. CONCLUSIONS

       Experimental studies are conducted on a single closed loop brass PHP in the present
work and the thermal performances of the PHP are studied. The following conclusions can be
drawn from the present work:
1. Brass PHP showed intermittent flow of the working fluid with perturbations at lower heat
   loads.
2. The PHP showed better heat transfer performance at a fill ratio of 80%.
3. Acetone is found to be the better working fluid compared to Propanol in terms of its
   lower thermal resistance and higher heat transfer coefficient.
4. PHP should be operated at zero and 30 degree orientations for its better thermal
   performance.

REFERENCES

 [1]   Akachi, H. “Structure Of Heat Pipe”, US patent, 4921041, 1990
 [2]   Shafii, B. M., Faghri, A., Zhang, Y., “Thermal modeling of unlooped pulsating heat
       pipes, Journal of Heat Transfer” Vol. 123, No. 6, 2001, pp. 1159-1172.
 [3]   Zhang, Y., Faghri, A., “Heat Transfer in a pulsating heat pipe with open end,
       International Journal of Heat Mass Transfer”, Vol. 45, No. 4, 2002, pp. 755-764.
 [4]   Cai, Q., Chung-lung Chen, Julie F. Asfia, “Operating Characteristic Investigations in
       Pulsating Heat Pipe”, journal of heat transfer, vol. 128, 2006, pp.1329-1334.



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6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME

 [5]    Charoensawan, P., Khandekar, S., Groll, M. and Terdtoon, P. “Closed loop pulsating
        heat pipes”, part-A; Parametric experimental investigations”, Applied Thermal
        engineering, Vol.23 No.6, 2001, pp.2009-2020.
 [6]    Khandekar, S., “Multiple Quasi- Steady States in a Closed Loop Pulsating Heat Pipe”,
        NTUS-IITK 2nd joint workshop in mechanical, Aerospace and Industrial
        Engineering, April 5-6, 2008, IIT, Kanpur, India.
 [7]    Khandekar, S., “Thermo Hydrodynamics of Pulsating Heat Pipes”, Ph.D Dissertation,
        University of Stuttgart, Germany, 2004.
 [8]    Meena, P., Rittidech, S., Tammasaeng, P, “Effect of inner Diameter and inclination
        angles on operation limit of closed-loop Oscillating heat pipes with check valves”,
        American journal of Applied Sciences, vol. 1, No.2,2008,pp.100-103.
 [9]    Rama Narasimha, K., “Studies on Pulsating Heat pipes” Ph.D. Dissertation,
        Visveswaraya Technological University, India, 2009
 [10]   Rama Narasimha, K., Rajagopal, M.S., Sridhara, S.N., “Influence of Heat Input,
        Working Fluid and Evacuation Level on the Performance of a Pulsating Heat Pipe”
        Journal of Applied Fluid Mechanics, Vol. 5, No. 2, Issue 10, 2012, Accepted for
        Publication.
 [11]   Rama Narasimha, K., Rajagopal, M.S., Sridhara, S.N., Seetharamu, K. N.,
        “Parametric studies on Pulsating Heat Pipes”, International Journal for Numerical
        Methods for Heat and Fluid Flow, Vol. 20, Issue 4, 2010.pp. 392-415.
 [12]   Nagvase S.Y., Pachghare P.R., “Parameters affecting the function of closed loop
        pulsating heat pipe: A Review”, Research Journal of Engineering Sciences, Vol 2(1),
        2013, pp. 35-39.
 [13]   M.M. Shete and Prof.Dr.A.D.Desai, “Design and Development of Test-Rig to
        Evaluate Performance of Heat Pipes in Different Orientations for Mould Cooling
        Application”, International Journal of Mechanical Engineering & Technology
        (IJMET), Volume 3, Issue 2, 2012, pp. 360 - 365, ISSN Print: 0976 – 6340,
        ISSN Online: 0976 – 6359.
 [14]   M.N.Khan, Utkarsh Gupta, Shubhansh Sinha, Shubhendu Prakash Singh and Sandeep
        Pathak, “Parametric Study of the Performance of Heat Pipe – A Review”,
        International Journal of Mechanical Engineering & Technology (IJMET), Volume 4,
        Issue 1, 2013, pp. 173 - 184, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359.




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