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Conjugate heat transfer to supercritical CO2 in membrane helical coiled tube heat exchangers has been numerically investigated in the present study. The purpose is to provide detailed information on the conjugate heat transfer behavior for a better understanding of the abnormal heat transfer mechanism of supercritical fluid. It could be concluded that the supercritical fluid mass flux and vertical/horizontal placement would significantly affect the abnormal heat transfer phenomenon in the tube side. The flow field of supercritical fluid is affected by both the buoyancy and centrifugal force in the conjugate heat transfer process. The local wall temperature and heat transfer coefficient in the tube side would rise and fall periodically for the horizontal heat exchanger, but this phenomenon will gradually disappear with the increase of the mass flow rate or fluid temperature in the tube side. The dual effects of buoyancy force and centrifugal force lead to the deflection of the second flow direction...

Conjugate cooling heat transfer to supercritical CO2 in a vertical double-pipe heat exchanger was numerically investigated in the present study. With the aim to better understand the conjugate cooling mechanism of supercritical fluid, detailed information on heat transfer behavior is provided. The results demonstrate that the numerical results predicted by the Abe, Kondoh, and Nagano (AKN) model show the best agreement with the experimental data. After validation, the influences of cooling water Re and temperature at the shell side, supercritical fluid Re at the tube side, flow direction, and pipe diameter on conjugate cooling heat transfer were investigated based on velocity fields. We conclude that cool water Re and temperature at the shell side have a significant effect on the cooling phenomenon at the tube side. Reduction in heat transfer could be avoided by either an increase in ReCO2 or a decrease in di. In addition, variations in density and cp are the most significant factors to determine ...