Effect of design parameters on the performance of a closed loop pulsating

International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –

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

306

EFFECT OF DESIGN PARAMETERS ON THE PERFORMANCE OF A

CLOSED LOOP PULSATING HEAT PIPE

Ch. Sreenivasa Rao1, Avssks Gupta

2, K. Rama Narasimha

3

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 60

0 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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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.

International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976

6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May

Y.Zhang et al (2011) explained that the thermal performance of many PHPs degraded

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

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

of other materials. Hence in the prese

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

resistance and heat transfer coefficient are evaluated.

2. EXPERIMENTATION

2.1 Instrumentation Made With

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.

Brass is an alloy and would be free f

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

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.

The glass tube attached between the U

section which was specified earlier (by khandekar et.al,2

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.

Silicon rubber tubes of 2mm inner diameter and 4mm outer diameter ar

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.

ional Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976

6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME

308


on angle is varied and some may not operate at all. If the inner diameter of


orientation is considered to be 0° for horizontal heat mode, +90° bottom heat mode and



area. More over the scope of the suitability of Propanol as a promising thermal dissipation



of other materials. Hence in the present work, a single loop brass PHP is considered for the



r coefficient are evaluated.

Instrumentation Made With the Experimental Setup

Photograph of PHP Experimental setup

1 shows the pictorial view of the experimental setup. In this setup, the basic


return valve, a tape heater and thermocouples.

Brass is an alloy and would be free from fouling effects unlike the pure copper under



ances 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.

The glass tube attached between the U-turn Brass tube is considered as adiabatic

section which was specified earlier (by khandekar et.al,2004) in the literature. Having the


borosilicate, which can resist temperature up to 1200° C.

Silicon rubber tubes of 2mm inner diameter and 4mm outer diameter ar



ional Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –

June (2013) © IAEME


on angle is varied and some may not operate at all. If the inner diameter of


orientation is considered to be 0° for horizontal heat mode, +90° bottom heat mode and -



a promising thermal dissipation



nt work, a single loop brass PHP is considered for the



1 shows the pictorial view of the experimental setup. In this setup, the basic


rom fouling effects unlike the pure copper under



ances Brass can be used as a good conductor of heat. The ID

turn Brass tube is considered as adiabatic

004) in the literature. Having the


Silicon rubber tubes of 2mm inner diameter and 4mm outer diameter are used as the





In order to maintain unidirectional fluid flow; a non return valve is used

made of stainless steel and has inner diameter of 5mm. The ball and seating arrangement is

used with a ball diameter of 4mm.

A tape heater of heating capacity 0

as the source of heat input.

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

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

previous cycle of experimentation is available.

2. The required amount of working fluid is then filled through the filling valve using a

syringe by opening the one end of the non

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%

stated that 50% is the optimum fill ratio. Hence, in the present work, experiments are

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.

4. The display unit is ON and required w

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.

6. .In the present work, the heat tr

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

couple-temperature display system has uncertainty of ±2% of full scale.

3. RESULTS AND DISCUSSION

The performance effectiveness and understanding of the he

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

% Ue =



309

In order to maintain unidirectional fluid flow; a non return valve is used


used with a ball diameter of 4mm.

A tape heater of heating capacity 0-50 W is attached to the evaporator section and acts

type thermocouples are connected for temperature measurements, four in the


1mm and can measure temperature up to 1000° c with a maximum error of ± 0.1° C. T

temperature values are recorded at a frequency of 1Hz.


and acetone. The working fluid is injected into the heat pipe using a syringe.

experimental test facility as shown in figure 1 is setup to characterize the pulsating


Before filling the fluid in the PHP it is ensured that no traces of working

previous cycle of experimentation is available.

The required amount of working fluid is then filled through the filling valve using a

syringe by opening the one end of the non-return valve such that the fluid directly enters

ction. 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


or fill ratios ranging from 50% to 80%,

Now the air is filled through the filling valve provided on the brass tube using another


The display unit is ON and required wattage is set using the power supply unit. In the


The cooling water is allowed to the condenser section of PHP from the constant head

.In the present work, the heat transfer behavior of PHP is analyzed for the inclination

The transient experiments are conducted and the temperatures at various locations of


steady state is reached. The measurement has inherent uncertainties. The thermo

temperature display system has uncertainty of ±2% of full scale.

3. RESULTS AND DISCUSSION

The performance effectiveness and understanding of the heat transfer characteristics



are evaluated respectively using the relations of Kline et al. (1953). Accordingly



In order to maintain unidirectional fluid flow; a non return valve is used. The valve is


50 W is attached to the evaporator section and acts

type thermocouples are connected for temperature measurements, four in the


1mm and can measure temperature up to 1000° c with a maximum error of ± 0.1° C. The


experimental test facility as shown in figure 1 is setup to characterize the pulsating


Before filling the fluid in the PHP it is ensured that no traces of working fluid used in

The required amount of working fluid is then filled through the filling valve using a

return valve such that the fluid directly enters

ction. It is reported in the literature (Khandekar, 2004) that the PHP

80% and it is also


Now the air is filled through the filling valve provided on the brass tube using another


attage is set using the power supply unit. In the


The cooling water is allowed to the condenser section of PHP from the constant head

ansfer behavior of PHP is analyzed for the inclination

The transient experiments are conducted and the temperatures at various locations of


steady state is reached. The measurement has inherent uncertainties. The thermo

at transfer characteristics



Kline et al. (1953). Accordingly



% Uc =

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

3.1. Effect of Heat Input

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

fill ratio of 60%. It can be seen from the fig.2

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

in nature. It is also clear that the pressure pulsati

consequently the evaporator temperature rises at lower heat load of 8

the system takes more time to reach the steady state at lower heat input of 8

Fig.3 Variation of Condenser Te

Fig.3 shows the variation of condenser wa

different heat inputs for Propano

condenser wall temperature is less at lower heat load of 8

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

levels, the hot fluid takes more time to reach the condenser from evaporator sectio

50

55

60

65

70

0 100

Evap

ara

tor

Tem

pera

ture

Te

0C

25

26

27

28

29

30

31

32

33

0 100

Co

nd

en

ser

Tem

pera

ture

Tc

0C



310

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

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

. It can be seen from the fig.2 that the variation of evaporator temperature



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.

Fig.3 Variation of Condenser Temperature with time at different heat load for Propanol

at a fill ratio of 60%

Fig.3 shows the variation of condenser wall temperature with respect

different heat inputs for Propanol at a fill ratio of 60%. It is clear from figure

denser wall temperature is less at lower heat load of 8 W compared to higher heat inputs.


As the movements of the working fluid is slow at lower heat input due to

levels, the hot fluid takes more time to reach the condenser from evaporator sectio

Effect of heat input on evaparator

200 300 400 500 600 700 800 900 1000

Time t (s)

12 W

11 W

10 W

9 W

8 W

Effect of heat input on Condensor

200 300 400 500 600 700 800 900 1000

Time t (s)

12 W

11 W

10 W

9 W

8 W



Evaporator Temperature with time at different heat load for

Fig.2 shows the variation of evaporator wall temperature with time for Propanol at a

tor temperature



ng effect is less at lower heat load and

. It is also clear that

mperature with time at different heat load for Propanol

espect to time at

io of 60%. It is clear from figure 3 that the

compared to higher heat inputs.


lower energy

levels, the hot fluid takes more time to reach the condenser from evaporator section.



311

3.2. Effect of Fill ratio

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

Q

TTR ce −

= (K/W) (3.1)

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.

Effect of heat input on evaporator

50

52

54

56

58

60

62

64

66

68

0 100 200 300 400 500 600 700 800 900 1000

Time t (s)

Evap

ora

tor

Tem

pera

ture

Te

0C

80%

70%

60%

50%

2

2.5

3

3.5

4

4.5

7 8 9 10 11 12 13

Heat Input, Q (W)

Therm

mal R

esis

tance, R

(K

/W)

50%

60%

70%

80%



312

The convective heat transfer coefficient of PHP is given by

)( ce TTA

Qh

−

= (W/m2K) (3.2)

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

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.

Effect of heat input on Thermal Resistance for Accetone

600

800

1000

1200

1400

1600

1800

7 8 9 10 11 12 13

Heat Input, Q (W)

Heat

Tra

nsfe

r C

o-e

ffic

ien

t, h

(W

/m2

K)

50%

60%

70%

80%

40

45

50

55

60

65

0 100 200 300 400 500 600 700 800 900 1000

Time t (s)

Evap

ora

tor

Te

mp

era

ture

Te

0C

ACCETONE

2-PROPANOL



313

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.

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.

Effect of working fluid on temperature

20

22

24

26

28

30

32

34

36

38

40

0 100 200 300 400 500 600 700 800 900 1000

Time t (s)

Tem

pera

ture

Dif

fere

nce T

e-T

c 0C

ACCETONE

2-PROPANOL

Effect of working fluid on Thermal Resistance

1.25

1.75

2.25

2.75

3.25

3.75

4.25

7 8 9 10 11 12 13

Time t (s)

Th

erm

ma

l R

es

ista

nce

, R

(K

/W)

ACCETONE

2-PROPANOL



314

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

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.

Effect of working fluid on Heat Transfer Co-Effiecient

800

1000

1200

1400

1600

1800

2000

2200

2400

2600

2800

7 8 9 10 11 12 13

Time t (s)

Heat

Tra

nsfe

r C

o-e

ffic

ien

t, h

(W

/m2 K

)

ACCETONE

2-PROPANOL

40

45

50

55

60

65

70

75

0 100 200 300 400 500 600 700 800 900 1000

Time t (s)

Evapara

tor Tem

pera

ture

Te 0

C

zero degrees

30 Degrees

60 Degrees



315

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.

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.

10

15

20

25

30

35

40

45

0 100 200 300 400 500 600 700 800 900 1000

Time t (s)

Tem

pera

ture

Diffe

rence T

e-T

c 0

C

zero degrees

30 Degrees

60 Degrees

0

0.5

1

1.5

2

2.5

3

3.5

7 8 9 10 11 12 13

Time t (s)

Th

erm

mal

Res

ista

nce,

R (

K/W

)

zero degrees

30 Degrees

60 Degrees



316

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.

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[4] Cai, Q., Chung-lung Chen, Julie F. Asfia, “Operating Characteristic Investigations in

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Effect of orientarion on Heat Transfer Co-Effiecient

0

500

1000

1500

2000

2500

3000

3500

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

He

at

Tra

nsfe

r C

o-e

ffic

ien

t, h

(W

/m2

K)

zero degrees

30 Degrees

60 Degrees



317

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[8] Meena, P., Rittidech, S., Tammasaeng, P, “Effect of inner Diameter and inclination

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Effect of design parameters on the performance of a closed loop pulsating

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