Multiphysics Numerical Study of Solar Receiver Tube for Enhanced Thermal Efficiency and Durability in Concentrated Solar Power Tower Plant

In the search for advanced and more substantial ways to use renewable energy, concentrated solar power (CSP) is one of the leading research ideas with the ability to have higher thermal efficiencies and capability of storing energy. Among the various CSP systems, the receiver tube in concentrated solar power tower (CSPT) plant is one of the most crucial components subjected to extreme working conditions. For tubular receiver operates with temperatures above 700°C, preliminary simulations shown an egregious temperature gradient greater than from the sunny side to the shadow region for a smooth tube, and the intense heat on the tube surface also causes deformation and buckling, therefore circumferential flow needs to be induced in order to create more flow mixing for a more uniform temperature distribution. In this study, COMSOL Multiphysics was adopted to explore the coupled hydro-thermal-mechanical effects when the receiver tubes have internal fins. The solar receiver tube is a hybrid material made of Inconel 718 and Boron mixture. The simulation showcases both forced and natural convection along with the solar radiation on one half of the tube. Multiple fins designs were simulated and compared in terms of heat transfer enhancement and minimized pressure drop, and the design of 7-head helical fins was chosen. By introducing the internal fins, the circumferential flow was observed in the flow domain, therefore it eventually led to a more uniform temperature profile for both the outer surface and bulk fluid temperatures. With a more uniform, lower surface temperature, the convective heat losses are considerably lower. The thermal efficiency was enhanced from 79.4% to 80.4%, and the structural deformation was reduced by 21.4%. Simulations were conducted to explore the effect of tube surface roughness on the absorbance and reflectivity. Various randomly generated curves with changing roughness heights were considered. The results proved that the increased surface roughness enhances the solar absorption from 0.55 to 0.80 with the hybrid mixture. This study has potential to transform the design and manufacturing of solar receiver tubes for high temperature applications, and it can directly support the current on-going efforts to reach the US Department of Energy (DOE) CSP 2030 goal.