Comparison of simplified heat transfer models and CFD simulations for molten salt external receiver

Abstract

In the absence of experimental correlations of the solar external receiver performance, it is particularly necessary to develop thermal models to optimize the receiver operating modes and to properly design such equipments. Since CFD models require an enormous computational cost to simulate a receiver, two simplified bi-dimensional implicit-scheme models have been developed. Both models consider axial and circumferential variations on the heat flux absorbed by the tubes and on the wall temperature. One assumes homogeneous surface boundary condition and the other assumes homogeneous surface heat flux at the discretized tube wall.

The effects of mass flow rate, and wind velocity on the receiver performance have been analysed considering steady state operation. The results have been compared with a simulation carried out with ANSYS Fluent. Both simplified models are able to predict the heat fluxes, the salt and the tube wall temperature with a deviation lower than 6% compared to CFD simulations. The analysis of the developed models has been also compared with a model usually employed that does not consider variable circumferential temperature. The results show that keeping constant the circumferential tube wall temperature leads to lower wall temperature, underestimating the film temperature, the thermal stress and the salt decomposition.