Analysis of flat heat pipes with various heating and cooling configurations

A simplified analytical thermal-fluid model including the wall, and both liquid and vapor flows is developed for flat heat pipes or vapor chambers with different heating and cooling configurations. The results for the two-dimensional temperature distribution inside the wall, the vapor velocity profiles, the axial pressure distributions in the vapor and liquid phases, and the vapor temperature are presented. The capillary pressures are calculated analytically and compared to the maximum capillary pressures to determine the dry-out limitations of the heat pipes. The reduction of the maximum effective capillary pressures due to the mass flux across the liquid/vapor interface is considered. The proposed analytical solution agrees well with a two-dimensional numerical simulation, which consists of the wall, wick and vapor regions. The parametric investigations show that the assumptions of previous studies that evaporation and condensation occur uniformly in the axial direction are valid only if the solid thermal conductivity is small and the axial wall conduction can be neglected.