Transient Thermoelectric Cooling of thin Film Devices
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TRANSIENT THERMOELECTRIC COOLING OF THIN FILM DEVICES A. RAVI KUMAR1, R.G. YANG1, G. CHEN1 and J.-P. FLEURIAL2 1 Mechanical and Aerospace Engineering Department, University of California at Los Angeles Los Angeles, CA 90095-1597 2 Jet Propulsion Laboratory/California Institute of Technology, 4800 Oak Grove Drive, MS 277-207, Pasadena, California 91109
Abstract We report theoretical analysis for the transient thermal response of thermoelectric (TE) element and the integrated thin-film devices. It is predicted that the TE element geometry and applied current pulse shape influences the transient response of the system. Analysis for the integrated systems shows that the transient response is affected by the effusivity of the attached mass. This analysis provides a means to examine the effectiveness of thermal management of the thin-film devices, particularly semiconductor lasers, using the transient mode operation of thermoelectric coolers, and also suggests geometry constraints and optimum pulse shapes for an integrated system.
Introduction For a thermoelectric element maintained at a steady temperature, the Peltier cooling being a local effect is confined to the cold end of the element and the Joule heating is volumetric in nature. At steady-state optimum conditions these two effects combined with the heat conduction from hot end to the cold end will allow the cold side of the element to be maintained at a steady low temperature. If a current pulse with magnitude several times higher than the steady state optimum current (Iopt) is applied to the element, intense cooling is achieved at the cold end. This coupled with the delay of the diffusion of Joule heat will lead to an instantaneous lower temperature than that reachable at the steady state. This phenomenon is referred to as transient thermoelectric effects. Stilbans and Fedorovich [1] first reported the transient effects in TE elements. They analyzed response of a TE cooler consisted of two elements soldered together, which is equivalent to zero cold junction mass. The experiments indicated a drop of 12 K compared to the steady state optimum temperature for an applied current of twice the value of Iopt. The analysis for semiinfinite TE element shows that the temperature decrease is fifty percent more compared to the steady state operation [2]. Experiments by Landecker [3,4] show that sub 100 K at cold junction is possible by applying a time dependent current pulse. However, these measurements are subjected to question because of lack of good temperature sensing instrumentation. Further there are no experiments cited in the literature to corroborate those results. Yamamoto [5] designed an integrated structure in which a semiconductor light-emitting diode (LED) is sandwiched between the p and n junctions of two TE elements. The transient mode operation of this device resulted in doubling the output power from the LED indicating that the lower temperature due to the transient effect in the TE element assisted the improved performance of the LED.
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