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Research Papers

# Application of Thermoelectric-Adsorption Cooler for Harsh Environment Electronics Under Varying Heat Load

[+] Author and Article Information
Ashish Sinha1

G. W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332ashish.sinha@gatech.edu

Yogendra Joshi

G. W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332

1

Corresponding author.

J. Thermal Sci. Eng. Appl 2(2), 021004 (Oct 21, 2010) (9 pages) doi:10.1115/1.4002590 History: Received February 17, 2010; Revised September 08, 2010; Published October 21, 2010; Online October 21, 2010

## Abstract

Incorporation of a thermoelectric (TE) device for heat regeneration and recovery can help realize adsorption systems that would be compact enough to fit inside electronic enclosures. Such a cooling system can be miniaturized without loss of performance and will have very few moving parts, hence lower maintenance needs. These traits are preferred in systems desired to be used for cooling electronics in thermally harsh environments (such as oil well, military machinery, and vicinity of automobile engines) that are characterized by temperatures greater than $200°C$ and provide little or no room for maintenance activities during operation. However, ambient temperatures near $200°C$ place constraints on the temperature difference between hot and cold sides of a TE device across which it could pump heat with appreciable COP $(>0.4)$. This leaves little room to change the operating parameters of a TE device and hence that of the adsorption heat pump; as a result, only a small range of cooling load may be thermally managed. In practice, such a system will be less desirable since heat dissipation from electronics can keep changing during operation. In this work, the options available to manage varying cooling load while satisfying the thermal constraints on a TE device have been investigated using a theoretical model. Varying the number of active TE devices in response to a changing cooling load has been suggested as the most promising solution.

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## Figures

Figure 3

Diagrams showing four stages of an adsorption cycle: (a) adsorption in bed 1 and desorption in bed 2, (b) constant volume heating in bed 1 and constant volume cooling in bed 2, (c) desorption in bed 1 and adsorption in bed 2, and (d) constant volume cooling in bed 1 and constant volume heating in bed 2

Figure 10

Diagram showing the energy per unit time required/given off by various processes. 75 W would have to be pumped from adsorbing bed (process I−F) and 87 W delivered to the desorbing bed (process G−H). Similarly, 71 W should be pumped during the isosteric cooling process (H−I) and 60 W delivered to isosteric heating phase (process F−G).

Figure 11

Variation in power to be pumped against an adverse temperature gradient and manageable cooling load with varying temperature at I

Figure 13

Appropriation of cycle time between adsorption-desorption and mutual heat exchange (isosteric heating and cooling) processes

Figure 1

Temperature range for various electronics applications (1-3)

Figure 2

Comparison of water retentively of silica gel and zeolite at various temperatures and 1 atmospheric pressure. Water adsorbing property equations were obtained from literature (24-26).

Figure 5

Graphical representation of switching and cycle time. Mutual heat exchange refers to heat recovery during isosteric phases.

Figure 6

The TE device COP contours shown against the average hot and cold side temperatures and the temperature difference between them. Plot was obtained for a current supply of 1 A. TE device HT-8-7-30 manufactured by Laird Technologies (33) was considered for this plot. This device has 71 thermocouple elements (N=71) and geometric factor (G=ratio of cross-sectional area to length of a single thermocouple) equal to 0.00171. Other properties, such as Seebeck coefficient (α), electrical resistivity (ρ), and thermal conductivity (k) of thermoelectric material, were obtained from the work by Gordon (15).

Figure 7

Cartoon showing the terms dictated on the adsorption process by TE device and electronic chip thermal load requirements. The adsorption process has three parameters, namely, adsorbent mass, cycle and switching time, and temperature extremes during the cycle that may be adjusted to satisfy both electronic chip and TE device requirements.

Figure 8

A shift in process H−I in either direction can lead to a change in total temperature variation in adsorption and desorption processes, thus leading to similar changes in total water uptake. It must be noted that zeolite-water content at constant pressure is a function of temperature only.

Figure 9

Leftward shift of H−I to the new position H′−I′ brings parts of the process H′−I′ at a lower temperature than some parts of the process F−G. J−G is at a higher temperature than K−I′.

Figure 12

Ratio of heat regeneration and recovery times considered by various researchers (15-16,34-37)

Figure 4

Thermodynamic representation of states of working fluid on a Clausius diagram. Fluids in both adsorbent beds follow this cycle with a phase shift such that desorption and isosteric cooling in one of the beds, respectively, accompany adsorption and isosteric heating in another. Heat recovery is transfer of heat from process H−I in one bed to process F−G in another. Heat regeneration is transfer of heat from process I−F in one bed to process G−H in another.

Figure 14

Performance of the TE device in terms of COP, power input, and power pumped plotted against various current supplies

Figure 15

Number of TE devices required for various cases. The plot is continuous; however, only integer values will be valid for the number of TE devices.

Figure 16

A representation of Fig. 1 explaining why few TE devices will need to be shut down with decreasing cooling load

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