Experimental and Numerical Study of the Heat Transfer Characteristics in Solar Thermal Absorber Tubes with Circumferentially Non-uniform Heat Flux

This paper presents experimental and numerical studies of the turbulent heat transfer in solar thermal absorber tubes. The absorber tube is a significant component in a solar thermal power system. However, the tube heat transfer performance is different than with other tubes, only half of the circumference surface of the absorber tube is heated with the non-uniform heat flux and the other half is insulated. The non-uniform heat flux on an absorber tube can be up to 1.5MW/2 and generates significant temperature difference and thermal stress. The present study uses the experimental and computational fluid dynamics to reveal the turbulent convective heat transfer performance in the solar absorber tube within the range of Reynolds number from1.0×104 to 3.5×104. The results show that the temperature distribution of fluid and tube wall is very uneven in axial, radial and circumferential direction. The temperature of inner tube wall is an important parameter for preventing the decomposition of heat transfer fluid. The Dittus-Boelter equation is still applicable to calculate the heat transfer in a circular tube with non-uniform heat flux, but it is not suitable to calculate the wall temperature distribution in this condition. The wall temperature distribution of a circular tube with non-uniform heat flux varies with the circular angle of cross section, and this study presents the correlation.