Research Papers

Downhole Electronics Cooling Using a Thermoelectric Device and Heat Exchanger Arrangement

[+] Author and Article Information
Ashish Sinha1

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

Yogendra K Joshi

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


Corresponding author.

J. Electron. Packag 133(4), 041005 (Dec 09, 2011) (12 pages) doi:10.1115/1.4005290 History: Received June 15, 2010; Revised July 19, 2011; Published December 09, 2011; Online December 09, 2011

This paper investigates the use of thermoelectric (TE) devices for thermal management of downhole electronics. The research carried out will help in the mitigation of costs associated with thermal damage of downhole electronics used in oil drilling industry. An experimental set up was prepared where a TE device was used in conjunction with heat exchanger and a cold plate to remove heat from electronics module. A finned copper rod in contact with hot side of TE device was used to reject the heat out to the ambient. The experimental set up was housed inside a cylindrical vacuum flask, which was in turn placed inside an oven to simulate thermally harsh downhole conditions. Experiments were carried out with electronics heat dissipation of 0–8 W and ambient temperature of 140 °C. Due to the differences in the environmental conditions of the laboratory and the practical downhole scenario, the experiment could not completely capture the conditions of downhole heat rejection. A mathematical model of the experimental apparatus was prepared and validated against the experimental results. The model was used to predict performance of a TE device for thermal management of downhole electronics at an ambient temperature of 200–250 °C. It was observed that the ability of the thermal management system to keep electronics cool varied from 30 °C to a few degrees below the surrounding temperature, for chip wattage varying from 0 W to 8 W, respectively.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

Schematic of a MWD tool with various modules that help in capturing, processing and transmitting downhole data [8]. Diagram not to scale.

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Figure 2

Schematic of the thermal management approach

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Figure 3

Test chips placed on a substrate of size 25.5 cm × 5 cm. Detailed structure of a test chip has been shown in the oval region.

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Figure 4

Cross-sectional and side views of the chip and cold plate assembly

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Figure 5

Dimensions of the copper rod used for water-copper and copper-air heat exchangers

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Figure 6

Implementation of the thermal management system for a real down-hole scenario. Vacuum flask that houses the system lies inside a drill pipe. Note the rejection of heat from thermoelectric device to the out-flowing mud, through a conductive path. The drill tool is also driven by the force of the flowing mud.

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Figure 7

Photographs of the experimental set up. (a) View of the water –copper heat exchanger before assembly, showing the steel casing and copper rod. (b) One end of the copper rod grooved, to contain thermal probe, and attached to a Teflon fixture. (c) O-ring containing Indalloy on the surface of TE device. (d) O-ring containing Indalloy attached to the surface of copper rod protruding out of water-copper heat exchanger. (e) TE device assembled in between copper rods by Teflon fixtures. (f) Overview of water-copper heat exchanger, airside copper rod and TE device encapsulated by a sheath of silicon rubber. (g) Vacuum flask containing the experimental set up placed inside an oven.

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Figure 8

(Top): Detailed schematic of the experimental set up. Note the various temperature data taps (denoted by dots) that were used for the mathematical formulation. (Bottom): Enlarged view of the TE device heat exchanger connections.

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Figure 9

Power consumed and flow rate for the motor + pump assembly at different supply voltages. Plot obtained using data form Jakaboski [34] for flow at a temperature of 30°C.

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Figure 10

Various parameters related to fluid flow inside the steel tubes

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Figure 11

Diagram of the cold plate assembly. Heat paths have been shown by arrows. 1/4th of the cross-section (upper right corner) was analyzed for thermal resistance calculations.

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Figure 12

Rayleigh number and convective heat transfer coefficient for copper rod (27.5 mm diameter) in air (left) and copper rod (20 mm diameter) in water (right)

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Figure 13

Temperature of various components during the baseline experiment

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Figure 14

Temperature of chip as recorded during various experiments. Inset bar plot shows the ratio of heat dissipated by chips at steady state to the electrical energy input to TE device (COP) at steady state for the experiments.

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Figure 15

Comparison of Theoretical and experimental values of heat pumped at the cold face and heat rejected at the hot face of TE device

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Figure 16

Uncertainty in power supply measurement for experiments with different chip wattages

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Figure 17

Plots (a)–(e) show the difference between experimentally obtained and simulated values as a percentage of the experimentally obtained values. These figures correspond to experiments with chip heat dissipation of 0 W, 2 W, 4 W, 6 W, and 8 W, respectively. Figure 1f shows the percentage difference at the end of 7 h for experiments with various chip power dissipation.

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Figure 18

Steady state temperature of the chip for the water side (cold) and air side (hot) heat transfer coefficients increased several folds. The plot has been obtained for an oven temperature of 200°C.

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Figure 19

Steady state temperature of the chip for various surrounding ambient temperatures

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Figure 20

Lines of constant “current supplied to TE device” and “chip heat dissipation rate” drawn on a set of axes that comprise the COP as ordinate and chip steady state temperature as abscissa

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Figure 21

A complete view of the plot shown in Fig. 2. Lines representing current supply of 0.5 A and 1 A that could not be included in the earlier Fig. 2 have been shown here.



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