Effects of circumferential heat conduction on heat transfer characteristics of supercritical R134a in horizontal tubes

In this paper, simulations of supercritical heat transfer of R134a in horizontal tubes are performed to study the effects of circumferential heat conduction on the heat transfer deterioration, and the abnormal phenomena of higher temperature distribution of non-gravity supercritical flow is explained. The results show the heat transfer deterioration is caused by the impairment of specific heat and heat conduction in the boundary layer while the following recovery of heat transfer is due to the enhancement of thermal conduction and turbulent convection. A dimensionless parameter of Biot number is defined to characterize the thermal resistance ratio of the circumferential conduction to the convective heat transfer. The wall temperature redistribution due to the circumferential conduction affects the supercritical convection in horizontal tubes, and non-gravity supercritical flow may have a higher wall temperature when the Bi number is small. The deterioration of the top surface can be significantly alleviated in a tube with a larger wall thickness or thermal conductivity.