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Experimental Research of a Thermoelectric Cooling System Integrated with Gravity Assistant Heat Pipe for Cooling Electronic Devices

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Abstract

As the computer systems process data more rapidly, large amounts of heat are generated in very small areas. Thermal management of the central processing unit has become crucial to avoid malfunction and failure of critical hardware. A thermoelectric cooling (TEC) system is proposed to remove the heat that is generated by electronic device in this paper. To improve the performance of this system, a gravity assistant heat pipe (GAHP) is attached on the hot side of the thermoelectric cooling module, serving as a heat sink. A mathematical model of heat transfer, based on the energy conservation, is established for the integrated system. A prototype is designed, built and tested in a climatic chamber under various conditions, comparing with a TEC system with air cooling heat sink. It is found that the cooling capacity is improved by approximately 73.54% and the electricity consumption was reduced by 42.20% to produce the same amount of cold energy.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer-review under responsibility of the scientific committee of the 8th International Conference on Applied Energy.
doi: 10.1016/j.egypro.2017.03.975
Energy Procedia 105 ( 2017 ) 4909 4914
ScienceDirect
The 8th International Conference on Applied Energy ICAE2016
Experimental research of a thermoelectric cooling system
integrated with gravity assistant heat pipe for cooling
electronic devices
Xiaoqin Suna,*, Yanjia Yanga,Hongliang Zhanga,Huiwei Sia,Liang Huanga,
Shuguang Liaob,Xiaosong Gua
aSchool of Energy and Power Engineering, Changsha University of Science and Technology, Changsha 410114, China
bChangsha Maxxom High-tech Co., Ltd., Changsha 410015, China
Abstract
As the computer systems process data more rapidly, large amounts of heat are generated in very small areas. Thermal
management of the central processing unit has become crucial to avoid malfunction and failure of critical hardware.
A thermoelectric cooling (TEC) system is proposed to remove the heat that is generated by electronic device in this
paper. To improve the performance of this system, a gravity assistant heat pipe (GAHP) is attached on the hot side of
the thermoelectric cooling module, serving as a heat sink. A mathematical model of heat transfer, based on the energy
conservation, is established for the integrated system. A prototype is designed, built and tested in a climatic chamber
under various conditions, comparing with a TEC system with air cooling heat sink. It is found that the cooling
capacity is improved by approximately 73.54% and the electricity consumption was reduced by 42.20% to produce
the same amount of cold energy.
1. Introduction
Keywords: Thermoelectric cooling (TEC); Gravity assistant heat pipe (GAHP);Cooling capacity; Energy consumption
The server computers work continuously and provide services to many clients simultaneously, which
results in greater heat production and high temperature that must be managed in order to avoid
malfunction and failure of critical hardware [1].In various applications, however, the traditional passive
cooling systems, including air cooling, water cooling, liquid cooling and so on,are reaching the limits in
terms of cooling capacity for high power electronic devices [2].Under this condition, thermoelectric
cooling (TEC) system, known as an active cooling method, is considered to be one of the alternative
* Corresponding author. Tel.:+86-150-849-91523; fax:+86-731-852-58407.
E-mail address: xiaoqinsun@csust.edu.cn.
Available online at www.sciencedirect.com
© 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer-review under responsibility of the scientific committee of the 8th International Conference on Applied Energy.
4910 Xiaoqin Sun et al. / Energy Procedia 105 ( 2017 ) 4909 – 4914
technologies with light and compact size, quiet and vibration-free operation, free from long-term
maintenance, and operation with DC voltage [3].
It is important that the hot side of the thermoelectric module be cooled to prevent damage to the
hardware and itself [4]. For this reason, the thermoelectric module must be combined with a cooler such
as heat sink or water cooling to dissipate the heat of the hot side for effective operation. To improve the
energy conversion efficiency of TEC system, kinds of methods were proposed to enhance the heat
dissipation of the heat side[5]. Liu et al. [6] presented a thermoelectric mini cooler coupling with a micro
thermosiphon cooling system for cooling CPU. A looped heat pipe heat exchanger was attached to the hot
side of the thermoelectric cooler as a heat sink. It was found that the thermoelectric operating voltage of
12V could achieve the lowest thermal source surface temperature, maximum cooling capacity and higher
COP. Tan and Zhao [7] utilized phase change material (PCM) as a heat sink to reduce hot side
temperature of thermoelectric modules during daytime cooling period for space cooling purpose. The
average system cooling COP was increased by 56% because of the PCM integration. Wang et al. [8] used
a heat sink and a fan to enhance the heat dissipation of the hot side and maintain the temperature of optical
chips of the laser. The results showed that the performance of TEC was improved by increasing the heat
sinks size and fans flow rate [9].
Among all the proposed techniques, TEC system integrated with heat pipe is more attractive because of
the great amount of phase change heat transfer (condensation and evaporation).This paper proposed a
thermoelectric cooling system integrated with a gravity assistant heat pipe for cooling electronic devices.
Agravity assistant heat pipe (GAHP) is attached on the hot side of the thermoelectric cooling module,
serving as a heat sink. A mathematical model of heat transfer, based on the energy conservation, is
established for this integrated system. Afull-scale prototype is designed, built and tested in a climatic
chamber under various conditions, comparing with a TEC system with air cooling heat sink to illustrate
the performance of this proposed new TEC system.The cooling capacity was used to evaluate the
viability of the proposed system.
2. Description of the proposed thermoelectric cooling system integrated with heat pipe
The thermoelectric cooling (TEC) system integrated with gravity assistant heat pipe (GAHP) was
designed and developed for cooling the electronic devices. Heat pipe, which can transport amount of heat
with small temperature differences within short time because of the phase change heat transfer inside the
pipes or tubes, is introduced to enhance the heat dissipation of the hot side of thermoelectric module, as
shown in Fig. 1. To improve the heat absorption, a heat sink was installed on the cold side of
thermoelectric module. The GAHP with a flat and smooth evaporation surface to reduce the contact
thermal resistance, was attached on the hot side of thermoelectric module. An axial fan was installed
above the heat sink on the cold side of thermoelectric module to cool down the temperature of electronic
devices and on the condensation zone of the GAHP to blow the heated air into the surrounding ambient,
respectively. When DC current was applied to the thermoelectric cooling system, the Peltier cells
absorbed heat from the heat source and dissipated heat to the hot side of thermoelectric module. The heat
was then passed through the evaporate zone of the gravity assistant heat pipe to further transport heat to
the condensation zone, which could result in two-stage heat transfer process.
The cooling capacity of thermoelectric module was
2
1
2
cc
QITIRkT
D
'
(1)
where Tcwas the cold side temperature,oC; Thwas the hot side temperature, oC; ǻTwas the temperature
difference between cold and hot sides,oC; Iwas the input current, A; Rwas the electric resistance of
Xiaoqin Sun et al. / Energy Procedia 105 ( 2017 ) 4909 – 4914 4911
thermoelectric module, ȍ; kwas the heat conductivity of TEC, W/(m·oC);and
D
was the Seebeck
coefficient, ȝ9oC.
The heat dissipation through the hot side equals to the heat absorption from evaporation zone and the
heat dissipation from condensation zone.
  
2
1
11
==
2
hc ecbcfbairh
QITIRkT ATTQUATTQ
R
D
cc c
'
(2)
where R1was the thermal resistance of evaporation zone, (m2·oC)/W;Aewas the heat transfer area of
evaporation zone, m2; cwas the surface temperature of evaporation zone, oC; and Tbwas the boiling
temperature of working fluid, oC; Uwas the total heat transfer coefficient, W/(m2·oC); Afwas the heat
transfer area of condensation area, m2; and Tair was the ambient air temperature, oC.
Cold side
Heat
absorption
Hot side
Electron
flow
N-type
semiconductor
P-type
semiconductor Hole
flow
Evaporation zone of heat pipe
Condensation zone of heat pipe
Heat
dissipation
Fig.1 Schematic diagram of a TEC system integrated with GAHP
3. Experimental test under various ambient environments
The efficiency and heat transfer characteristics of thermoelectric cooling system integrated with
gravity assistant heat pipe was investigated for comparison with the performance of thermoelectric
module with heat sink using a fabricated laboratory model to measure the amount of heat that could be
removed from a given heat source (two 100W heater) under various operating conditions.A box
consisting of two identical parts was developed, one part with TEC system integrated with GAHP and one
part with TEC system with heat sink, as shown in Fig. 2. For the TEC system with heat sink, both the hot
and cold sides were connected with a heat sink and a fan to enhance the heat transfer. For the TEC system
with GAHP, the condensation zone was higher than the evaporation zone to utilize the gravity. The
evaporation zone of heat pipe was made of four tubes with diameter of 8 mm, and the condensation zone
was made of a microchannel heat exchanger. Together, these two zones operated on the closed
evaporation condensation cycle using of gravity forces for the working fluid circulation. The geometrical
parameter of the microchannel heat exchanger was shown in Table 1.
A heat sink was attached on the cold side of thermoelectric module to improve the heat absorption.
The heat sink is made from two aluminum finned heat exchangers with 200 mmh69 mm base plate (4.6
4912 Xiaoqin Sun et al. / Energy Procedia 105 ( 2017 ) 4909 – 4914
mm thick), 2.59 mm fin pitch, 200 mmh31.4 mm fin size (0.6 mm thick), and 54 fins. The box was
located into a climatic chamber, which was used to produce an air temperature and relative humidity that
replicated the outdoor environment. The thermoelectric module used during the experiments was shown
in Table 2.
Table 1. Geometrical parameter of condensation zone (mm)
Total size Flat tube Fin
Height Width Thickness Height Width Height Pitch thickness
275 142 26 2.5 25.4 10 1.5 0.1
Table 2 Technical specifications of TEC-12708 at reference temperature of 50 oC at hot side
Type Dimensions
(L×W×H, mm)
Couples
N
Qmax (W) Imax (A) Umax (V) '
7
max
(oC)
ZT factor
12708 40h40h5.4 127 81 8.5 16.4 75 0.6
Fan
Humidifier
Heater
Evaporator
Pre-heater
T
1,
v
1
T
2,
v
2
T
5
T
3
T
4
T
6,
v
3
T
7
T
8
T
9
T
10
T
11,
v
4
T
1,
v
1
T
2,
v
2
T
3
~T
5
T
6,
v
3
T
11,
v
4
T
7
~T
10
37
Heater Fan Condensation zone Heat sink
Fig. 2 The experimental apparatus for TEC system integrated with GAHP
4. Results and discussion
Fig. 3 depicts the temperature variation during the tests for all cases. To be clear, there was a
protection of the heaters, which will shut down the power when the heater surface temperature was higher.
Therefore, the temperature fluctuation was caused by the intermittent operation of heaters. The mean air
temperature for different cases are shown in Table 4. The air temperature was reduced by either TEC
system with heat sink or TEC system with GAHP. The air temperatures that was induced by the TEC
system with GAHP were the lowest ones for all cases under various conditions. For the conditions when
ambient air temperature was 30 oC, 35 oC and 40 oC, the temperature caused by two TEC systems did not
vary a lot. That was, the gravity assistant heat pipe did not improve the performance of TEC system
significantly when the ambient air temperature was lower. This was the heat sink helped remove the heat
from hot side of thermoelectric module enough. There was no heat accumulation for both TEC systems.
However, for the conditions when ambient air temperature was 45 oC and 50oC, the air temperature was
remarkably lower for the TEC system with GAHP than it for the TEC system with heat sink. The heat
Xiaoqin Sun et al. / Energy Procedia 105 ( 2017 ) 4909 – 4914 4913
sink was not able to remove the same amount heat as the gravity assistant heat pipe did. Consequently,
the air temperature was higher.
0510 15 20 25 30 35 40 45
30
31
32
33
34
35
36
Temperature (
o
C)
Time (min)
Heater
TEC+heat sink
TEC+GAHP
0510 15 20 25 30 35 40 45
33
34
35
36
37
38
39
40
Heater
TEC+heat sink
TEC+GAHP
Temperature (
o
C)
Time (min)
0510 15 20 25 30 35 40 45 50
38
39
40
41
42
43
44
45
Temperature (
o
C)
Time (min)
Heater
TEC+heat sink
TEC+GAHP
(a) Tair =30 oC (b) Tair =35 oC (c)Tair =40 oC
0510 15 20 25 30 35 40
40
41
42
43
44
45
46
47
48
49
50
Temperature (
o
C)
Time (min)
Heater
TEC+heat sink
TEC+GAHP
0510 15 20 25 30 35 40 45 50
42
44
46
48
50
52
54
56
Temperature (oC)
Time (min)
Heater
TEC+heat sink
TEC+GAHP
(d) Tair =45 oC (e) Tair =50 oC
Fig.3 Mean air temperature in the box under various conditions
Fig. 4shows the variation of cooling capacity of two TEC systems. The cooling capacity of TEC
system with heat sink increased and reached the peak when the ambient air temperature was 40 oC. With
the increase of ambient air temperature, the cold side temperature increased; while the hot side
temperature did not increase a lot because of the heat sink. According to Eq. 1, the cooling capacity
increased. After that, the cooling capacity decreased because the Fourier heat and Joule heat increased the
hot side temperature along with the increase of ambient air temperature.
The cooling capacity decreased a little for the TEC system with GAHP with the increasing ambient air
temperature. The heat dissipation from the condensation zone of GAHP reduced because of the higher air
temperature. Therefore, the temperature difference between hot and cold sides increased, resulting in the
reduction of cooling capacity. The utilization of GAHP increased the cooling capacity by approximately
73.54%, comparing with the TEC system with heat sink. That was for the same amount of cold energy,
the electricity consumption was reduced by 42.20%.
30 32 34 36 38 40 42 44 46 48 50
80
100
120
140
160
180
200
220
240
Cooling capacity (W)
Ambient air temperature (
o
C)
TEC+GAHP
TEC+Heat sink
Fig.4 Cooling capacity of TEC systems
4914 Xiaoqin Sun et al. / Energy Procedia 105 ( 2017 ) 4909 – 4914
5. Conclusion
A thermoelectric cooling system coupled with a gravity assistant heat pipe was designed and
developed based on a theoretical model to enhance the heat dissipation from hot side of thermoelectric
module. To figure out the performance of this proposed TEC system, an experimental apparatus was built
in a climatic chamber. The cooling capacity, inlet and outlet air temperature through the thermoelectric
module, and the temperature within the test box were measured, compared with a TEC system with heat
sink. The cooling capacity was improved by 73.54% using GAHP and the electricity consumption was
reduced by 42.20% to produce the same amount of cold energy. The cooling capacity for the TEC system
with heat sink increased and then decreased with increasing ambient air temperature, which would
influence the performance of electric device. In contrast, it did not varied a lot because of the self-adjust
of heat pipe.
Acknowledgements
This work was supported by the International Cooperation Project (2015DFA61170), the National
Natural Science Fund (51608051), the Education Department of Hunan Province (15B014, 14B011) and
the Science and Technology Department of Hunan Province (2016JJ3006, 2015JJ2003).
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Biography
Sun Xiaoqin, PhD, lecturer at Changsha University of Science and Technology, focusing
on the research of energy saving technologies for buildings and physical energy storage
technology.
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The miniature thermoelectric cooler (TEC) is a promising device for microelectronics applications with high cooling performance and short response time. In this paper, a comprehensive numerical analysis focusing on the cooling performance and response time of the TEC is performed by finite element methods (FEMs). The effects of load current, geometric size, ratio of length to cross-sectional area and substrate's thermal resistance on the performance of the TEC are studied. The results show that the performance of TECs has been improved by reducing the TEC's size and ratio of length to cross-sectional area, resulting in a maximum cooling temperature difference of 88^oC, a cooling power density of 1000Wcm^-^2 and a short response time on the order of milliseconds. Furthermore, the substrate, which hinders the circulation of heat between the TEC and the atmosphere, also has a significant influence on the performance of the TEC.
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