Transpiration cooling with phase change by functionally graded porous media

Abstract

Transpiration cooling using liquid coolants is considered one of the most promising thermal protection techniques for new generation aerospace vehicles. The leading edges are subjected to a very high and non-uniform heat flux. Unfortunately, few coolants can flow through the part near the stagnation point using traditional porous structures, which will cause ablation. Unlike conventional fabrication methods, additive manufacturing is capable of directly tailoring porous structures with well-controlled pore features and functional graded pore topology, thereby optimizing the coolant distribution and improving the cooling performance. Smoothly graded pore structures can be fabricated using additive manufacturing technology. We experimentally assessed the transpiration cooling performance of uniform and graded porosity porous plates to compare the coolant distributions, temperature profiles, and features of the two-phase region. Graded porous media exhibited much better cooling performance than uniform pore topology. Through computations, the graded porosity improved the imbalanced coolant distribution and minimized the hot-spot temperature under a non-uniform heat flux. Importantly, the temperature profile at the outlet should match with the local flow resistance in porous media and the heat flux at the outlet. The temperature and phase change zone were highly dependent on the topology of the porous media, heat flux profile applied to the outlet, and coolant mass flow rate.