NUMERICAL INVESTIGATION ON DOUBLE-LAYER POROUS PLATE OF TRANSPIRATION COOLING WITH PHASE CHANGE

In order to improve the cooling performance of the transpiration cooling with phase change, a new structure, double-layer porous plate with different porosity combination is suggested as replacement for the conventional single-layer porous plate. Using liquid water as coolant, the modified two phase mixture model which considers local thermal non-equilibrium is adopted to study the fluid-solid coupled heat transfer and coolant flow transport characteristics in the porous plate with varied porosity combination. The simulation results reveal that there exists the structure of double-layer porous plate that can reduce the surface temperature on the hot side. Specially, the surface temperature decrease for the double-layer porous plate is more pronounced when the coolant mass flux is greater and coolant phase change occurs in the upper porous plate. At the same time, the injection pressure of coolant is taken into consideration. Because the kinematic viscosity of vapor is much higher than that of liquid water, it is found that when coolant phase change occurs in the porous plate, the coolant injection pressure mainly depends on the porosity of the upper porous plate where the vapor is gathered. Therefore, based on the seepage effect in the porous media, the upper plate with larger porosity than lower porous plate can greatly reduce the vapor pressure in the structure, so as to reduce the coolant injection pressure at the bottom of the porous plate. In a certain porosity combination, the maximum reduction of the coolant injection pressure can reach 65%. If the opposite porosity design is adopted, where the porosity of the lower porous plate is greater than that of the upper porous plate, although the surface temperature can be reduced to some extent, the injection pressure will be several times increased, which is not conducive to the practical application of transpiration cooling with phase change.