Simulation of active heat spreading using peltier effects

Abstract

We investigate active heat spreader design using the Peltier effect to increase heat transfer while maintaining a constant temperature gradient between the hot and cold electrodes. Increasing the surface area of the hot side allows for better cooling via conductive, convective, and radiation cooling methods. Coupled electro-thermal and Peltier effects are simulated at steady state using COMSOL's thermoelectric module. COMSOL's thermoelectric module is validated using a simple geometry with an analytical solution for surface temperature for comparison. The simulated surface temperature agreed with the analytical quite well, with an error in calculated temperature of only 1.7%. COMSOL is used to sweep both the side length, applied current and current density, and leg height in the heat spreader. From this, the effects on the maximum temperature gradient between the electrodes and on maximum heat flux absorbed on the cold side can be determined, as well as other performance metrics such as the coefficient of performance and heat flux uniformity on the hot side. The side lengths are swept from 1mm to 90mm at a constant semiconductor height of 5mm. The height is then swept down to .1mm to determine the effect on the Peltier cooling and heat spreading. The maximum temperature gradient without an applied heat load is only a function of material properties, hot side temperature, and current. Increasing the hot side length increases the maximum heat absorption capability of the cold side due to heat spreading effects. By increasing the side length of the hot side by a factor of 4, while maintaining constant, equal electrode temperatures, and a height of 5mm, the maximum heat absorption increases nearly four times (almost linearly up to 8mm hot side). It does so in a hyperbolic manner with significant decrease in efficiency for side lengths larger than 8mm. A similar effect can be seen when decreasing the height, due to increasing the relative distance between the electrode edges. In other words, the edge length of the semiconductor becomes much larger than the height, in turn driving the majority of the current to flow through the center of the thermoelectric leg.