Experimental investigation of transpiration cooling with phase change for sintered porous plates

Transpiration cooling is an effective way to protect high heat flux walls from ablation in spaceflight vehicles. Water is an effective transpiration coolant owing to its large latent heat. This study experimentally investigated transpiration cooling with phase change of sintered bronze porous plates in a wind tunnel with an inlet temperature of 800 K and a Reynolds number of 45000. The study investigated the effects of the coolant injection ratio and particle diameter of the sintered porous media on the transpiration cooling efficiency. The results showed that the location of the phase change depended on the coolant injection ratio. The average cooling efficiency and maximum temperature increased as the particle diameter of the sintered bronze porous plate was reduced from 600 mu m to 200 mu m. However, the transpiration cooling efficiency significantly decreased when the particle diameter further decreased to 90 mu m, due to the vapor-blockage effect. The transpiration cooling was delayed by the vapor-blockage effect with only a small mass flow rate of the liquid coolant. The delay significantly decreased with increasing injection ratio or decreasing particle diameter. The transpiration cooling with phase change was unstable and oscillatory with the oscillation period and amplitude decreasing with decreasing coolant injection ratio or increasing particle diameter of the sintered porous plate. (C) 2017 Elsevier Ltd. All rights reserved.