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 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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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
EvaparatorTemperatureTe
0
C
25
26
27
28
29
30
31
32
33
0 100
CondenserTemperatureTc
0
C
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
TT
R 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)
EvaporatorTemperatureTe
0
C
80%
70%
60%
50%
2
2.5
3
3.5
4
4.5
7 8 9 10 11 12 13
Heat Input, Q (W)
ThermmalResistance,R(K/W)
50%
60%
70%
80%

312
The convective heat transfer coefficient of PHP is given by
)( ce TTA
Q
h
−
= (W/m2
K) (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)
HeatTransferCo-efficient,h(W/m2K)
50%
60%
70%
80%
40
45
50
55
60
65
0 100 200 300 400 500 600 700 800 900 1000
Time t (s)
EvaporatorTemperatureTe0
C
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 210
C and for Propanol it is
around 310
C.
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)
TemperatureDifferenceTe-Tc0
C
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)
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)
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)
EvaparatorTemperatureTe0C
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)
TemperatureDifferenceTe-Tc
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)
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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