Fluid Flow and Capillary Limit in Heat Pipe Thermal Ground Planes

This work shows the solution of the fluid flow and the capillary limit in heat pipe thermal ground planes after solving the temperature field. In addition, the effect of wall shear stress and the interfacial shear stress in the liquid pressure of the TGP is studied. In order to obtain more accurate results it is necessary to solve the velocity and thermal fields in both the liquid saturated wick and the vapor. It is also important to account for the mass, momentum and energy balances at the interface between the vapor and liquid. Previous work demonstrated that for the TGP's which utilize water as the working fluid, the Jacob number is very small. A consequence of this is that convection of liquid with the wick is much smaller than conduction and the temperature may be solved independently of the velocity field. These solutions were presented in previous work. A key feature of the thermal model is that it relies on empirical interfacial heat transfer coefficient data to very accurately model the interfacial energy balance at the vapor-liquid saturated wick interface. One important result uses a solution for the evaporation and condensation rates and hence normal velocities at the interface. The results show that for all of the TGP's lengths, the ratio between the pressure drop in the vapor and the pressure drop in the liquid is close to zero. Therefore, the pressure drop in the liquid will determine the capillary limit in the TGP.