Investigation of Thermal Behavior of Supercritical CO2/Propane Mixtures in Airfoil-Finned PCHE Channels

Abstract In the context of high-temperature waste heat recovery, enhancing the cycle efficiency by elevating the critical temperature of the heat transfer fluid in the supercritical Brayton cycle presents a viable and significant optimization strategy. This study proposes the utilization of a CO2/propane mixture as the heat transfer medium within the heat exchangers of the Brayton cycle. Given the substantial impact of heat exchanger performance on the effective operation of the cycle, an airfoil-fin printed circuit heat exchanger (PCHE) featuring an asymmetric staggered fin arrangement was developed. Numerical simulations investigated the flow and heat transfer characteristics of the mixture under different conditions of mass flowrate, inlet temperature, and propane concentration. This analysis elucidated the underlying flow and heat transfer mechanisms within the channels. Increases in both mass flowrate and inlet temperature enhance heat transfer. The heat transfer coefficient exhibits greater sensitivity to changes in mass flowrate. For instance, at a propane mole fraction of 0.2, increasing the mass flowrate from 0.001 g/s to 0.003 g/s resulted in a maximum increase of 73.53% in the heat transfer coefficient. Under identical operating conditions, the heat transfer coefficient increases with higher propane fractions, while the pressure drop decreases. However, the enhancement in the heat transfer coefficient becomes less pronounced once the propane mole fraction exceeds 0.5. Based on a comprehensive consideration of the thermal-hydraulic performance, analysis of wall and bulk temperatures, and the second law of thermodynamics, a propane mole fraction of 0.5 is identified as the optimal composition.