Numerical Investigation of the Steady-State Operation of a Cylindrical Capillary Pumped Loop Evaporator

A cylindrical capillary pumped loop evaporator operating under steady-state conditions was studied using a two-dimensional numerical model. Parameters affecting the phase conditions in the wick structure and thermal-fluid behavior in the evaporator liquid core were studied. The influences of heat load, liquid subcooling, and effective thermal conductivity of the wick structure were specifically selected to evaluate evaporator performance. Either increasing the applied heat flux and/or degree of inlet liquid subcooling resulted in decreased liquid core temperature, which is favorable for proper evaporator operation. This helps prevent conditions that may allow vapor formation in the liquid core as well as result in decreased length of the two-phase region in the wick structure. Decreasing the effective thermal conductivity of the wick also decreases the temperature in the liquid core. For a given liquid subcooling, a minimum heat flux exists below which vapor will generate in the liquid core and render the evaporator nonoperational. Additionally, for a given heat flux, a minimum required liquid subcooling exists as conditions are such that vapor potentially may form in the liquid core when the liquid subcooling is less than a minimum value.