The mathematical and physical models of different semicircular channels are established

and the accuracy of the numerical models is verified by comparing with the experimental data. The thermal and hydraulic heat transfer performance of supercritical carbon dioxide(S-CO_2) in uniform cross-section semicircular tube

diverging tube and converging tube is studied

and the influence of different channels and pressures on the thermal and hydraulic performance of S-CO_2 in a semi-circular tube with variable cross-section is calculated and analyzed.The results show that

compared with the uniform cross-section semicircular tube

the diverging tube deteriorates heat transfer

the converging tube enhances heat transfer. The overall heat transfer coefficient of converging semicircular tube with the inlet and outlet radius ratio of 1.0:0.5 increases by 39.93%

and the maximum evaluation factor PEC of flow heat transfer comprehensive performance is 1.346. When the pressure is closer to the critical pressure or the heat flux is low

the heat transfer performance is higher. Finally

the reason why the converging tube with variable cross-section can enhance heat transfer is explained from the perspective of field coordination and turbulent kinetic energy distribution. The research results can provide new ideas and theoretical guidance for the design and optimization of coolers in S-CO_2 circulation system.