Numerical study of capillary pumped two-phase systems

Studies were performed on the rewetting process of a two-dimensional porous media subjected to a constant heat flux. Numerical solutions were obtained by an implicit finite difference scheme tailored to take account of the movement of the liquid front as rewetting progresses. The effects of the applied heat flux, the pore diameter and porosity of the porous media, and the thermophysical properties of the working fluid and porous media on rewetting process were investigated. The rewetting velocity and liquid front position were presented. The maximum sustainable heat flux and the transient temperature distribution of the porous media were also predicted.; A theoretical analysis was conducted to describe the startup process from the supercritical state for axially grooved cryogenic heat pipes. Using an approximation method, a heat balance integral solution was developed to predict the rewetting velocity, liquid front position, and transient axial temperature distributions for axially grooved cryogenic heat pipes. The developed model assumes an initially uniform axial temperature distribution and divides the startup process into two characteristic regions based on whether a liquid column is established in the condenser region. The predicted temperature profiles of two cryogenic heat pipes were in good agreement with previous experimental microgravity flight data.; A two-dimensional numerical model was established to study the behavior of a cylindrical CPL evaporator under steady-state operations. The influence of heat load, liquid subcooling and effective thermal conductivity of the wick structure on the evaporator performance were studied. It was disclosed that increasing the applied heat flux and liquid subcooling decrease the temperature in the liquid core and the length of the two phase region in the wick structure. Decreasing the effective thermal conductivity also decreases the temperature in the liquid core. It was observed that for a given liquid subcooling, a minimum heat flux exists below which vapor will generate in the liquid core and render the evaporator non-operational. It was also observed that for a given heat flux, a minimum liquid subcooling exists. Vapor may generate in the liquid core when the liquid subcooling is less than the minimum value.