Numerical study on thermal–hydraulic performance of hydrocarbon fuel under trans-critical states and supercritical CO2 in a zigzag printed circuit heat exchanger

Abstract

The supercritical CO2 closed-Brayton-cycle (CBC) is a highly promising integrated scheme for cooling and power generation in hypersonic vehicles. However, the CO2-fuel printed circuit heat exchanger (PCHE) in the CBC faces extreme heat loads and fuel consumption constraints, leading to complex heat transfer phenomena including trans-critical processes and buoyancy effects. In this study, the coupled heat transfer process between the large-molecule hydrocarbon fuel and supercritical CO2 inside the zigzag-type PCHE is investigated using a numerical simulation, based on the practical constraints of the onboard CBC system. The results demonstrate that the distributions of eddy viscosity and specific heat within the boundary layer are significantly improved by the turbulence-enhancing effect of the zigzag channel, thus avoiding local heat transfer deterioration caused by trans-critical processes. Additionally, numerous small-scale vortex structures are found to increase the source term of turbulent kinetic energy generation, effectively suppressing the weakening effect of buoyancy on turbulence. Finally, an optimization study is conducted on the resistance of the zigzag channel starting from the power generation performance of the CBC system. The findings indicate a 71% reduction in pressure loss coupled with only a 7% reduction in volume heat transfer rate compared to the original configuration.