Thermal Model for Sintered Cylindrical Evaporators of Loop Heat Pipes

Abstract

A thermal analytical model for predicting the temperature distribution of a cylindrical geometry evaporator of a loop heat pipe is presented. The wick structure proposed is made of a thin layer of sintered metal powder and is considered filled with working fluid. The resulting porous medium has a thin uniform layer thickness, and it is modeled as flat plate operating in steady-state condition, in a two-dimensional Cartesian coordinate. A Laplace-type equation is solved. The methods of separation of variables and superposition are used to solve the mathematical problem. A scale analysis is used to obtain an expression relating the wick geometry and thermophysical properties. With these models, the loop heat pipe evaporation limit, given by the porous media-casing interface temperature, which must be lower than the working fluid saturation temperature, can be determined. A statistical experiment analysis technique was employed to study the influence of several parameters in the thermal model. Mathematical model results were compared with numerical simulation data for a loop heat pipe evaporator. Using the mathematical tool developed, a copper cylindrical evaporator of a loop heat pipe was designed, constructed, and tested, using an experimental setup especially constructed for this purpose. The good comparison between analytical results and data validates the model proposed.