Numerical study on flow and heat transfer characteristics of SCO2 in a rectangular microchannel with different tilt angles

In the CO 2 closed-Brayton-cycle thermoelectric conversion system for scramjet engines, supercritical CO 2 (SCO 2 ) serves as the coolant for the combustion chamber. To account for the varying tilt angles of hypersonic vehicles during flight, this study numerically investigates the flow and heat transfer characteristics of SCO 2 in a rectangular microchannel under high heat flux and large mass flow conditions. For the first time, the effects of channel circumferential tilt are considered alongside realistic non-uniform heat-flux distributions from the combustion chamber. Results show that increasing the tilt angle enhances heat transfer under non-uniform heating, with circumferential tilt exerting a stronger influence than axial tilt. Specifically, the local heat transfer coefficient (HTC) increases by up to 30.92%, and wall temperature decreases by up to 9.31%. The heat transfer mechanism is further analyzed using turbulent kinetic energy and secondary flow intensity distributions. Secondary flow improves heat transfer only on the heated wall but adversely affects the non-heated walls and the overall convective performance. Parametric analysis indicates that tilt effects become insignificant when the heat-to-mass flux ratio ( q / G ) falls below 0.57 for axial tilt and 0.50 for circumferential tilt. These findings offer practical guidance for thermal management and optimization of thermoelectric conversion systems in hypersonic vehicles.