Phase change transpiration cooling of propylene glycol solution considering pyrolysis

This paper proposes a new mathematical model for the transpiration cooling process simultaneously with chemical reactions and physical phase change. Based on the proposed model and combining experimental studies, the paper further investigates fluid flow, heat transfer, phase change, and pyrolysis behaviors of propylene glycol solution in a porous plate and systematically analyzes the influence of propylene glycol concentration on transpiration cooling performance. The results reveal that the chemical reaction prevents heat accumulation and reduces the temperature gradient over the porous plate, while the phase change provides a local thermal barrier in the two-phase region. Therefore, chemical reactions not only improve cooling efficiency but also contribute to enhancing temperature uniformity. For pure propylene glycol, endothermic pyrolysis increases the liquid phase fraction and reduces the maximum temperature of the porous hot end by approximately 30 K. For propylene glycol solution, the concentration of propylene glycol can regulate the cooling performance by balancing the latent heat of phase change and pyrolysis ratio. Propylene glycol solution with 20% concentration has the best cooling effect, while the efficiency of low-concentration solution (<20%) is close to water, and the efficiency of high-concentration solution (>80%) is worse due to the unfavorable latent heat and physical properties.