A SIMPLE MATHEMATICAL MODEL TO PREDICT HEAT PIPE MAXIMUM HEAT TRANSFER, EQUIVALENT THERMAL CONDUCTIVITY, AND THERMAL RESISTANCE

The objective of this study is to provide a simple mathematical model to predict the performance of a heat pipe such as the maximum heat transfer rate, equivalent thermal conductivity, and the thermal resistance based on the experiences of industrial products. The maximum heat transfer calculation is based on the maximum capillary provided by the wick against the total pressure drop in the heat pipe. The calculation of the capillary structure of the wick and pressure drop in the heat pipe is based on the traditional pressure drop formulas for vapor and liquid flow. For heat pipe thermal resistance calculation, there is a new proposal of an additional parameter function f (Leff) that accounts for the vapor and fluid flow pressure drop dependent on the heat pipe length. This function dictates that the thermal resistance of the heat pipe increases with the heat pipe length. Without this additional function, the heat pipe thermal resistance would remain constant regardless of the heat pipe length, and this assumption may be incorrect. Analysis results showed that the maximum heat transfer and thermal conductance (inverse of thermal resistance) of heat pipe decreases as the heat pipe length increases. The correspondent equivalent thermal conductivity increases with the heat pipe length in the maximum heat transfer limit range. Theoretical calculation is validated by experimental results and is discussed in this paper.