Improvement of temperature uniformity by using novel guide vanes in solar external receiver tubes

•A novel guide vane was optimized to improve the uniformity of the temperature distribution on tube.•The numerical calculations of tubes with different guide vanes were carried.•The temperature, pressure loss, velocity and Nu of these cases were analyzed and compared.•By optimizing the guide vane, better heat transfer performance and uniformity can be obtained.•Adding guide vane increases the flow resistance and affects the thermo-hydraulic performance. The heat flux sustainability in solar external receiver tubes is limited by the non-uniformity of the temperature distribution and the maximum achievable temperature of the molten salt flow. In this paper, the external receiver tubes were equipped with novel guide vanes to enhance the heat transfer inside the tube and improve the uniformity of the temperature distribution on the tube surface. The geometric structures of guide vanes were optimized under non-uniform heat flux distributions. Firstly, the numerical models of tubes with different guide vanes (different wrap angles at trailing angle and different number of blades) were developed. Secondly, the numerical calculation of each case was carried out by using the fine meshing method, and was carried out by means of the commercial software ANSYS Fluent 19.2 on the High-Performance Computing. The SST k-ω turbulence model was used to predict the flow field inner the tube. The temperature, pressure loss, velocity and Nusselt number of these models predicted by CFD were analyzed and compared. Finally, the effect of different geometric parameters on the heat transfer enhancement and for improving the uniformity of temperature distribution were studied. It was observed that the guide vane is very effective to enhance the heat transfer inside the tube and improve the uniformity of temperature distribution on the tube surface. By optimizing the design of two parameters (wrap angles and number of blades), better heat transfer performance and improved uniformity can be obtained. For enhancing the heat transfer, and for improving the temperature uniformity and the flow resistance in the tube, a value of θTE = 82° is should be chosen. With the increase of the blade number, the flow separation will be better controlled, and the swirling strength will increase gradually. To increase the number of blades helps to enhance the heat transfer and improve the temperature uniformity. A higher blade number will increase the system resistance and affect the thermal hydraulic p