Detailed thermal resistance model for characterization of the overall effective thermal conductivity of a flat heat pipe

Abstract

The present work describes the method by which the thermal resistance of a flat heat pipe spreader can be more accurately computed. The total effectiveness of the heat spreader is dependent on the one-dimensional (R1D) thermal resistance and the thermal spreading resistance (Rs). Recently developed more accurate methods from the literature were used to calculate the spreading resistance by taking into account all the multiple layers of the heat pipe. Both R1D and Rs depend to a large extent on the effective thermal conductivity of the wick. The calculation of effective thermal conductivity of wick is demonstrated using well-defined silicon micropillars. The effect of interfacial heat transfer resistance, which is usually neglected on the wick's thermal resistance is also discussed. Finally, the effective thermal conductivity of a flat heat pipe as a function of vapor chamber size and effective wick thermal conductivity is calculated. As the overall device performance strongly depends on the estimation of wick thermal resistance, the results of this study show that an effective thermal conductivity that is equal to or better than diamond can be attained with proper design. Furthermore, this work provides design tools that can be used to optimize the overall device level thermal performance.