Numerical investigation of transient phase-change transpiration cooling based on variable properties of coolant

Aimed at promoting the practical application of transpiration cooling technology in the field of active thermal protective system of hypersonic vehicles, this study presents a comprehensive numerical approach combining two-phase mixture model (TPMM), local thermal non-equilibrium (LTNE) assumption and variable properties of coolant to investigate the transient transpiration cooling problems with phase change. The real variable physical properties of coolant as functions of temperature and pressure are taken into consideration based on the data from the National Institute of Standards and Technology (NIST). The model is verified by comparing with the numerical and experimental data in previous researches. Results suggest that a new phenomenon of “reverse temperature distribution” in two-phase region is observed in the transient simulation considering variable properties. Comparison between the constant-property model and variable-property model indicates the necessity of the real variable physical properties, especially at low-pressure conditions with large differential pressure gradient. Meanwhile, the simulation with a non-uniform heat flux boundary condition reveals the mechanism of heat transfer deterioration. A gap of liquid outflow is formed after vapor generation, next moves along the outlet, then disappears and finally regenerates. The non-uniform heat flux will certainly lead to an uneven pressure distribution, resulting in the deterioration of local heat transfer in the porous matrix.