Efficient thermal management of high-temperature and high-pressure syngas generated during Underground Coal Gasification (UCG) is essential for ensuring operational safety, improving energy recovery, and maintaining the durability of gas handling systems. Conventional straight and serpentine heat exchangers often exhibit limited thermal performance under compressible turbulent gas flow conditions. Therefore, advanced heat exchanger geometries capable of enhancing heat transfer while maintaining acceptable pressure losses are required for such demanding environments.

The present study investigates the thermo hydraulic performance and entropy generation characteristics of a membrane helical coil heat exchanger for high pressure syngas cooling applications. A three dimensional Computational Fluid Dynamics (CFD) model was developed using ANSYS Fluent to simulate compressible turbulent flow and heat transfer within the heat exchanger. Temperature dependent thermo physical properties of syngas were incorporated to improve prediction accuracy. The performance of the membrane helical coil configuration was compared with a conventional membrane serpentine tube under identical operating conditions ranging from 700-1000 K temperature, 3-8 MPa pressure, and Reynolds numbers between 10,000 and 45,000.

The results demonstrate that curvature-induced secondary flows significantly enhance convective heat transfer in the helical configuration. The Nusselt number increased by approximately 20-28% compared with the serpentine geometry due to stronger Dean vortices and improved fluid mixing near the outer wall of the coil. Although the helical configuration resulted in slightly higher friction factors, the pressure penalties remained within acceptable limits for high pressure gas systems. Entropy generation analysis revealed that heat transfer irreversibility dominates at lower Reynolds numbers, while frictional irreversibility becomes more significant at higher Reynolds numbers. Multi objective optimization identified an optimal Dean number of approximately 2100, where the thermal performance factor reached about 1.23 with minimum total entropy generation.