Optimization of vapor-liquid channel parameters for ultrathin heat pipe with limited internal cavity

Abstract

Ultrathin heat pipes (UTHPs) have become core devices for the thermal management of portable electronic devices, but guidance is lacking on how to allocate vapor–liquid channels in UTHPs. In this paper, a transient 2D numerical model was established to investigate the effect of vapor-liquid channel changes in an UTHP on its thermal performance. The optimal configuration of vapor-liquid channels was determined by adjusting the percentage of wicks in a fixed space. The results showed that the larger the proportion of wicks was, the higher the temperature of the evaporation section. The temperature difference of the UTHP was proportional to the vapor pressure drop. As the wick ratio increased, the total pressure drop of UTHP first decreased and then increased. The total pressure drop of UTHP was minimum when the wick ratio was 30%. UTHPs with an internal thickness of 0.26 mm and a wick ratio of 30.77% were fabricated and tested for heat transfer performance. The experimental results were compared with the numerical results. At normal operating conditions, the numerical model can effectively predict the temperature of the evaporation section with an error <0.5 K. Finally, an analytical model was developed to quickly obtain the optimal wick ratio for UTHPs. The trends in the analytical and numerical models agreed well. The optimal wick ratio for the UTHP studied was 26%. The optimal wick ratio was independent of the input power and the UTHP length, and it increased with internal thickness and operating temperature. The results of this study provide a reference for designing UTHPs and improving their performance.