Analysis of internal and external thermal resistances of heat pipes including fins using a three-dimensional numerical simulation

A complete thermal network analysis for a cylindrical heat pipe is presented and the dominant thermal resistances are identified. The proposed numerical model was developed to simulate heat pipe operation and has been verified for both low and high applications including heat sources and sinks as a single-domain conjugate problem. Steady-state and transient solution methods were performed for a three-dimensional heat pipe with a compressible vapor core and a wick governed by pure conduction. The numerical model accounts for the full external coolant domain, with and without external fins on the condenser, to investigate their influence on the thermal resistance network. The numerical results indicate that the overall heat pipe thermal resistances can be predicted with as little as 1%-28% variation from empirical correlations, based on the choice of heat pipe dimensions, materials and operating conditions. It was found that the vapor core thermal resistance can become significant as the operating temperature increases, however, the largest thermal resistances are those corresponding to the external heat transfer fluids.