Optimization of Hydrothermal Enhancement in Outwardly Corrugated Pipes of Heat Exchanger

Abstract In this study, we numerically investigated the turbulence convective heat transfer performance (CHTP) and entropy production rate (EPR) of distilled water flowing through outwardly corrugated pipes. The effects of Reynolds number (5.0×10^3≤Re≤4.0×10^4 ), normalized corrugation amplitude (0.03≤e/D≤0.05), and normalized pitch (0.9≤P/D≤1.1) on the average Nusselt number (Nu), friction factor(fr), performance evaluation criterion(PEC), field synergy number(FSN), and volumetric entropy production rate were examined. The results show that corrugation significantly improves heat transfer relative to the smooth pipe. Over the full Reynolds number range, Nu increased by factors of 5.98, 5.19, and 4.81 for the same amplitude values, while the corresponding PEC remained above unity, indicating an overall thermal-hydraulic advantage. The findings demonstrate that, in comparison to smooth pipe, corrugation enhances heat transfer performance. Stronger wall-induced secondary motion enhances the alignment between velocity and temperature-gradient fields, as evidenced by the field synergy number increasing with increasing corrugation amplitude but decreasing with increasing Reynolds number and pitch. A new term called synergy-thermal coupling index (STC) was introduced to evaluate how effectively field synergy translates into heat transfer enhancement. The STC analysis demonstrated that the improvement in convective heat transfer cannot be exclusively attributed to improved synergy between velocity and temperature gradient, as part of the gain is also associated with recirculation and turbulence production. In addition, multi-objective optimization revealed a clear trade-off among thermal enhancement, frictional drawback, and entropy generation, with the Pareto front indicating that the most favourable operating region occurs at a relatively low Reynolds number and moderate corrugation intensity.