RESEARCH ARTICLE | JANUARY 05 2024
Thermal performance comparison of closed loop pulsating
heat pipe with DI water and Al2O3/DI nanofluid 
Kamlesh Parmar  ; Ibrahim Nagme; Sachin Thakur; Abhishek Singh; Ajit Kumar Parwani; Sumit Tripathi;
Nirmal Parmar
AIP Conf. Proc. 2960, 040005 (2024)
https://doi.org/10.1063/5.0183494
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06 January 2024 17:54:16
Thermal Performance Comparison of Closed Loop Pulsating
Heat Pipe with DI Water and Al2O3/DI Nanofluid
Kamlesh Parmar1, a), Ibrahim Nagme1, b), Sachin Thakur1, c), Abhishek Singh1, d),
Ajit Kumar Parwani1, e) Sumit Tripathi1, f) and Nirmal Parmar2, g)
1
Institute of Infrastructure, Technology, Research and Management, Ahmedabad, India - 380026
2
Institute of Chemical Process Fundamentals (ICPF), Prague, CZ, Europe
a)
Abstract. Pulsating heat pipe (PHP) has been a research interest in the areas of thermal management in various
engineering applications such as electronics cooling. The present work focuses on thermal performance
improvement of a PHP by experimentally studying the effects of thermal parameters such as type of working fluids
(nanofluid and deionised water), temperature range, and filling ratios on thermal resistance of the PHP.
Experimental studies are conducted to measure thermal resistance of a closed loop pulsating heat pipe (CLPHP)
having five turns, and the preparation method of Al2O3 (Aluminium Oxide) nanoparticles are also presented. The
working fluids in the present work are DI (deionised) water and Al2O3/DI nanofluid with a surfactant, and
experiments are performed for different filling ratios of the working fluid in the CLPHP. The variation of thermal
resistance of CLPHP with pressure and time are presented and discussed. It is observed that the thermal resistance
was minimum with 60% of filling ratio of Al2O3/DI water nanofluid.
Keywords: Pulsating heat pipe (PHP), Thermal performance, DI water, Al2O3 Nanoparticles, Nanofluid and
thermal resistance
INTRODUCTION
An operative thermal management system is essential for cooling of electronic devices. Hence, electronic thermal
management methods have undertaken a drastic evolutionary change over the last few decades [1]. Typically, heat
pipes are used for cooling applications for such electronic devices. A heat pipe is a simple heat transmission device
that uses an evaporation-condensation cycle to move heat from one place to another. A heat pipe heat exchanger
(HPHX) is a group or bundle of heat pipes housed in a single housing or casement that is used to transmit heat from
one medium to another. Typically, heat pipes are often referred to as superconductors of heat because of their capacity
for quick heat transmission with little heat loss. The container (the pipe), the working fluid within the pipe, and the
thermosyphon effect are the only main parts required for a complete operation. Heat pipes are very efficient thermal
conductors because boiling and condensation have very high heat transfer coefficients. Considering copper, which has
an effective thermal conductivity of around 0.4 kW/(m⋅K), long heat pipes may reach 100 kW/(m⋅K) in terms of
effective thermal conductivity [2]. To address the thermal management demands of electronic devices, new types of
Recent Advances in Mechanical Infrastructure
AIP Conf. Proc. 2960, 040005-1–040005-8; https://doi.org/10.1063/5.0183494
Published by AIP Publishing. 978-0-7354-4780-6/$30.00
040005-1
06 January 2024 17:54:16
Corresponding author: kamlesh.parmar.20pm@iitram.ac.in
b)
ibrahim.nagme.19m@iitram.ac.in
c)
sachin.thakur.21mm@iitram.ac.in
d)
abhishek.singh.19m@iitram.ac.in
e)
ajitkumar.parwani@iitram.ac.in
f)
sumittripathi@iitram.ac.in
g)
nirmalparmarphd@gmail.com
heat pipes were invented by Akachi in 1990 which is called the Pulsating heat pipes (PHPs) or Oscillating heat pipes
(OHPs) [3].
PHPs being the newest member of heat pipe have high heat transport capacity and are a kind of heat exchanger
that work on an oscillation-driven flow of vapor and liquid slug in a long tube which is bent into many turns. The
characteristic that separates PHPs from other conventional heat pipes is that it does not have wicked structures. It can
be a powerful tool for waste heat recovery and heat dissipation, which is a step towards sustainable development. PHP
has numerous applications such as electric vehicle battery cooling [4-5], avionic and space [6], renewable energy
applications and electronics device cooling [6-7], heat exchangers, cryogenics, PV cooling, and fuel cell cooling [7].
A sketch of pulsating heat pipe with filling valve, number of turns along with condenser, evaporator, and adiabatic
sections is shown in Figure 1.
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FIGURE 1. A sketch of a closed loop pulsating heat pipe
In the literature, many experimental studies have been performed related to PHPs in terms of their working and
improving the performance efficiency. It is noted that there are various parameters that can be varied to influence the
working of the pulsating heat pipes. Zhang and Faghri presented that the heat transfer in PHP occurred in such a way
that the effective thermal resistances were very low with specific charge ratios [2]. They concluded that detailed design
tools were required to evaluate the performance of PHPs [2]. Nazari et al. discussed that in cryogenic applications
PHPs are great heat exchangers [7]. The thermal conductivities at cryogenic temperatures can reach 12000 W/m⋅K,
which is a much bigger value when the best of the metallic heat conductor is brought down to those temperatures [7].
Kim et al. studied the behaviour of flow in PHPs and performed a comparison between closed-loop pulsating heat
pipes (CLPHPs) and closed-end pulsating heat pipes (CEPHPs) [8]. They used ethanol and R314 as working fluids in
their study and found that CEPHPs had 33% lower thermal resistance and also the maximum allowable heat flux was
20% higher when ethanol was used as a working fluid. In case of CLPHPs when R–134a was used, thermal efficiency
reduced by 72% and maximum allowable heat flux increased by 117% [8]. In CLPHPs circulation mode was observed
while in CEPHPs fluid oscillations were observed, and it was found that the thermal performance of PHPs was
improved with an increase in volumetric fraction of working fluid in condenser section [8]. Wang et al. studied
oscillating heat pipes under different conditions to analyse cooling of batteries within electric vehicles [9]. They used
battery surrogate systems for their experiment purpose and verified that battery surrogate systems had to be away from
an adiabatic system of a pulsating heat pipe. In their work, an ingenious dual-serpentine-channel flat-plate oscillating
heat pipe (FPOHP) was created and manufactured for electronic cooling with several heat sources and sinks [9].
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Liu et al. noted that the FPOHP had good gravity adaptation with a relative variation in the total thermal resistances
ranging from 7.1% to 25.2% for all inclination angles [10]. Considering this, the FPOHP showed strong promise for
electronic cooling applications with high-heat-flux using a variety of heat sources and sinks. Mathematical models for
studying effect of thermal stabilities at various operating conditions in CLPHPs were also presented by them [10].
Chen et al. explained that the improvement and comprehension of the heat transfer performance of thermal instability
in various designs of CLPHP sinks would benefit from the development of a nonlinear identification approach, overall,
they concluded that PHPs could be a good reliable system for cooling various devices [11]. Due to the instabilities of
nano-fluids in thermal analysis of experimental findings, researchers have also performed simulation studies using 3D
models from thermal performance comparison. Further, various studies on performance evaluations of heat pipes using
nanofluids are also available in the literature. One essential element in consideration for enhancing the heat transfer
procedure is settling of nanoparticles in the evaporator. Al2O3 nanofluids have higher heat transfer characteristics and
have been explored over the last decade [12]. A successful experimental study was carried out by Soni and Parwani
on a closed-loop OHP with FR of 30%, 50%, 70%, 90%, and 100%, and thermal performance was gauged by
measuring thermal resistance [13]. For each heat input, the values of thermal resistances decreased at 70% filling ratio
(FR) and the thermal performance was at its peak [13]. Zhou et al. estimated a hybrid PHP with carbon nanotube
Nanofluid for cooling the battery of an EV [14]. They used working fuel as ethanol and selected carbon nanotubes
(CNTs) Nanofluid solution by considering a filling ratio of 35% [14]. In the present work, we perform experimental
studies on a CLPHP and compare the performance in terms of thermal resistance using working fluid with and without
nanoparticles.
EXPERIMENTAL METHODOLOGY OF PHP SETUP
The experimental setup for PHP is shown in Figure 2, which has vertical orientation of 5 turns, overall width of 183.5
mm, and height of 282.3 mm. To construct the PHP, long capillary copper tubes having inside diameter of 2.15 mm
and outside diameter of 4.15 mm are used, and the bending radius of PHP is 9 mm. The PHP has three sectionsevaporator, adiabatic, and condenser sections, and the length of these sections can be changed when required. Level
screws are used to level the complete setup.
FIGURE 2. Pulsating heat pipe experimental setup
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Experimental Setup Description
Two mica heaters (each 400 W at 230 V; Max: 400˚C, 200 mm x 60 mm) are used to apply the thermal load on the
evaporator section. In addition, a variable transformer (variac) is utilized to maintain a constant heat supply at 110 V.
Thick glass wool was used as insulating material to minimise the heat losses.
The PHP was cooled using natural convection as the condenser section was open to air. A thick glass wool wrapped
in aluminium foil that insulates the tube well against heat below the condenser portion forms the adiabatic section.
This PHP is a closed-loop device with only one pressure gauge and one charging valve. A vacuum was created with
the aid of the provided syringe and valve, and the working fluid was charged in the required filling ratio.
With a multi-channel digital temperature indicator that has very high accuracy (±1% error), K-type thermocouples
were used to measure temperature. The condenser section of the PHP was equipped with two thermocouples (T 1, T2),
and the evaporator section loops with three thermocouples (T 3, T4 & T5), as shown in Figure 2. Each thermocouple
was attached to a multi-channel digital temperature indicator (MS-1208). A variac was utilized to control the voltage
supply. The entire experimental setup was constructed at the Heat and Mass Transfer Laboratory, Institute of
Infrastructure, Technology, Research and Management (IITRAM), Ahmedabad.
Preparation of Al2O3 (Aluminium Oxide) Nano Particles
Firstly, 3.75gm of Al(NO3)3 and 1.25gm of NaOH were taken along with two different beakers. In the next step,
Al(NO3)3 was collected with 10 ml DI water in beaker-A, and NaOH with 7.5 ml DI water in beaker-B. The beakerA was put on magnetic rotation and then the content of beaker-B was added dropwise to achieve a proper solution,
afterwards, the solution was kept on magnetic rotation for 1 hour for proper mixing.
XRD (X-ray diffraction) analysis and Infrared Spectroscopy confirmed that the nanoparticles formed were up to the
standards. XRD analysis of Al2O3 was conducted at Institute of Plasma Research (IPR), Ahmedabad, India.
DI Water (20 ml), Al2O3 (20 mg) and surfactant SDS (Sodium Dodecyl Sulphate) (40 mg) were mixed together in
Ultrasonic Cleaner. The use of surfactant helped to prepare suspension of nanoparticles in the DI water. The
preparation of Al2O3 nanoparticles and Al2O3/DI water nanofluid were prepared at the Physics laboratory of IITRAM,
Ahmedabad.
Experimental Procedure
Initially, the evaporator was heated to remove unwanted previously used fluid or gases. Further, with the help of an
injection vacuum was created and working fluid was filled through the charging valve. The experiments were
conducted with two different filling ratios (40% and 60%) and two different charging fluids (DI water, and Al2O3/DI
water nanofluid). A series of experiments were performed to measure temperature in the evaporator and condenser
sections of the CLPHP setup and data were collected at 2 minutes of interval throughout the experiment.
The numerical equations used are as follows:
R=
𝑇e −𝑇 c
Qi/p
, °C /W
040005-4
(1)
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After the magnetic rotation, the solution was centrifuged at 7000 rpm for 10 minutes. This centrifuge process was
repeated by draining out the water and adding fresh DI water again, in this way the impurities were removed. However,
while draining out the water proper care was taken so that the nanoparticles were not removed along with water. In
the final step, the nanoparticles were collected and kept in the furnace at 60 oC for 24 hours to remove any moisture
content [15].
Where, R = Thermal resistance of PHP, °C /W
Qi/p = Heat input by the mica heater, W
𝑇e = Average evaporator temperature, °C
𝑇 c = Average condenser temperature, °C
Here, 𝑇e and 𝑇c were calculated by,
𝑇c =
𝑇e =
T1+T2
2
, °C
T3+T4+T5
3
, °C
(2)
(3)
Where, T1 and T2 are temperatures of K-type thermocouples attached with the condenser, while T3, T4 and
T5 are temperatures of K-type thermocouples attached to each loop on the evaporator, respectively.
RESULTS AND DISCUSSION
The thermal performance of a closed-loop PHP has been measured with DI water as well as with Al2O3/DI-water
nanofluid (with surfactant) as working fluids using selected thermal parameters such as thermal resistance, different
filling ratios, and constant heat input.
FIGURE 3. Variation of thermal resistance with temperature differences at a heat input of 350 W
Figure 4 shows the variation of thermal resistance as a function of pressure at a constant heat input of 350 W.
From the plotted results, it is observed that the thermal resistance of PHP is comparatively higher for DI water
with 40% FR compared to DI water with 60% FR. When the Al 2O3/DI water nanofluid with surfactant is used as
a working fluid in the PHP, the thermal resistance is reduced compared to DI water. In addition, the thermal
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Figure 3 shows a variation in thermal resistance as a function of the temperature differences at a constant heat input
of 350 W. The comparison between DI water and Al 2O3/DI water nanofluid are plotted at filling ratios of 40% and
60%. The thermal performance of PHP was observed better between temperature differences between 20oC to 30oC
for both the working fluids and filling ratios. The thermal resistance of PHP is linearly dependent to temperature
difference for both working fluids and filling ratios at given constant heat input.
resistance of PHP presented a lower value for Al2O3/DI water nanofluid at 60% FR compared to DI water at both
mentioned filling ratios.
FIGURE 4. Variation of thermal resistance with pressure within PHP at a heat input of 350 W
06 January 2024 17:54:16
FIGURE 5. Variation of evaporators and condensers temperature with time
Figure 5 shows the plot of individual temperature measurements at the evaporator and condenser sections with
respect to time at a constant heat input of 350 W. The individual temperatures of the condenser section behave in
linear trend approximately initially up to 20 minutes. However, the artefact is noted when the time increases from
20 to 30 minutes at the temperatures of the condenser section. Moreover, when the time increased from 30 to 50
minutes, the individual temperatures of the condenser section come in proper trends as earlier.
040005-6
FIGURE 6. Variation of average temperature with time at evaporators and condensers
CONCLUSIONS
Thermal performance of a closed-loop pulsating heat pipe (CLPHP) was measured with DI water as well as Al2O3/DI
water nanofluid with surfactant as working fluids using various thermal parameters such as thermal resistance,
pertinent filling ratios and constant heat input. The thermal resistance is observed to be linearly dependent on the
temperature difference of the evaporator and condenser irrespective of the type of working fluid and filling ratio at a
given constant heat input. In addition, the temperature difference increased gradually over a time for both working
fluid and filling ratios. Most importantly, the thermal resistance was found to be minimum while using Al2O3/DI water
nanofluid as a working fluid with 60% of filling ratio. Thus, the CLPHP setup showed more consistent results with
thermal performance improvement by using Al2O3/DI water nanofluid with 60% filling ratio.
ACKNOWLEDGMENTS
The authors would like to thank Dr. Paritosh Chaudhuri for the tests conducted at the Institute of Plasma Research,
Ahmedabad. The authors would like to express gratitude to Dr. Dheeraj Kumar Singh, Assistant Professor, IITRAM
Ahmedabad, for the laboratory equipment in the Physics Lab. The authors would like to thank Dr. Sanil Shah, Mr.
Deepak Kumar, and Mr. Amit Bhojani, IITRAM Ahmedabad for help and support during the experimental studies.
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In continuation of the previous result, Figure 6 shows the variation of average temperature with respect to time at the
evaporator and condenser sections for DI water and Al 2O3/DI water nanofluid with surfactants using various filling
ratios for 40% and 60%. The plotted graph shows that the average temperature at the evaporator for both working
fluids and filling ratios is less scattered than condensers with DI water as working fluid with both filling ratios.
However, the use of working fluid as nanofluid that was prepared from Al2O3 showed low temperature values for
condensers as well as a consistent trend; these lower temperature values of condenser temperature with consistent
trends show the improvement of CLPHP thermal performance by using Al2O3/DI water nanofluid as a working fluid.
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