Abstract
The heat transfer performance of a solar external receiver tube with guide vanes was numerically studied under non-uniform heat flux conditions. Models of the smooth tube and the tube with guide vanes were built. The distributions of the temperature, velocity, turbulence intensity, and Nu predicted by these two models were compared to investigate the heat transfer enhancement and the mixing effect of the guide vanes. The effect of the Re and the α on the heat transfer enhancement was also studied. The results show that the guide vanes form spiraling flows, reduce the maximum tube and molten salt temperatures, and improve the heat transfer. In addition, a more uniform temperature distribution is achieved compared to the smooth tube, allowing the molten salt to work safely under higher heat flux conditions in the receiver tube with guide vanes. It was observed that a larger Re enhances the heat transfer on the tube wall and achieves a longer effective distance of enhanced heat transfer in the downstream region, while the spiraling flow, the heat transfer enhancement, and the mixing are stronger for a larger α.
Highlights
Introduction and Marco BinottiThe concentrated solar power (CSP) system is a promising technology for producing electricity from solar energy and plays a significant role in the energy transformation.Among different CSP types, the solar power tower (SPT) system has received considerable attention, due to its large scale and electricity outputs, which are similar to those of conventional electricity power plants [1,2]
The external receiver tube was equipped with a novel component of guide vanes, which mix the molten salt having a different temperature in different regions of the tube, reduce transverse temperature stratification, and enhance the heat transfer
In Case 2, the temperature is much lower on the front side of the tube, where the peak heat flux occurs, and the temperature distribution across the tube cross-section is more uniform compared to that observed in Case 1
Summary
The concentrated solar power (CSP) system is a promising technology for producing electricity from solar energy and plays a significant role in the energy transformation. Among different CSP types, the solar power tower (SPT) system has received considerable attention, due to its large scale and electricity outputs, which are similar to those of conventional electricity power plants [1,2]. The SPT system mainly consists of the solar heliostats field, the receiver, the thermal storage, and the heat-to-electricity conversion system. The solar flux distributions on the receiver are usually non-uniform [5,6] because it is very difficult to concentrate the sunlight and achieve an even distribution on the surface of the receiver. The non-uniform solar heat flux leads to a thermal gradient in the receiver, which represents a serious problem especially in the external receiver of SPT systems, where a large heat flux on the tubes and high out-temperature of the heat transfer fluid (HTF) are generated.
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