A pore-scale study on pyrolytic coke deposition and transpiration cooling behaviors of hydrocarbon fuel in porous structures with triply periodic minimal surface

Triply periodic minimal surface (TPMS) structures demonstrate notable advantages in transpiration cooling due to the excellent smoothness, highly ordered structures and large specific surface area. In order to reveal the influence of TPMS topological structures on coke deposition and heat transfer performance of transpiration cooling using hydrocarbon fuel, a three-dimensional pore-scale numerical model is established with four typical TPMS topological configurations (i.e., P-type, W-type, G-type, and D-type) in this work. A chemical kinetics-driven coke deposition method is proposed for direct simulation of the coke-deposition process within the TPMS structures. The results show that coke deposition in the confined space of TPMS structure exhibits self-driven characteristics, i.e., the coke deposition-induced variations in geometric structure and local temperature further strengthen the coke deposition process itself. Coke deposition process exacerbates the effect of topological structures on flow and heat transfer performance in transpiration cooling. When no coke deposition is involved, the flow and heat transfer are dominated by the specific surface area of the TPMS structures. However, as coke deposition accumulates on the pore surface of the TPMS structure, the permeability of the porous structure decreases significantly, which leads to heat transfer deterioration and lower transpiration cooling effectiveness. Among the four structures, the D-type structure exhibits the lowest transient coking rate and the highest cooling effectiveness of up to 78.67%. However, the D-type structure with the largest specific surface area results in a shorter anti-coking time than that of the G-type. The G-type structure renders the longest anti-coking time of up to 35.5 min at 1.0 MW/m². Therefore, there exists a trade-off between transient transpiration cooling performance and anti-coking requirement. This study provides better insight into the application of the TPMS porous structure to the transpiration cooling process using hydrocarbon coolant.