Heat transfer model for the trapezoidal cavity receiver of linear Fresnel reflector–type collectors

Abstract

In this work a dynamic mathematical model for linear Fresnel reflectors (FLR) with trapezoidal cavity receiver (TCR) is developed. The model considers the three heat transfer mechanisms inside the TCR and is able to model two–phase flow; i.e., the dynamic mathematical model considers heat transfer by conduction through the concentrator tube, heat transfer by convection in the inner region of the tube (heat transfer fluid), and radiation on the outer surface. By considering radiative heat transfer within the TCR, it is possible to determine the heat losses and gains by this mechanism, without the need to use empirical correlations formulated with the help of computational fluid dynamics. Thus, the main advantage of this model is that it can dispense with these sophisticated computational elements, extending its application to different configurations and materials. The numerical solution of the model is implemented in C++. The model results are compared with steady-state experimental data, published in the literature, obtaining a maximum relative error of 3.4 % in the fluid temperature profile, a difference in the steam quality at the concentrator outlet of 0.045, and a difference in the pressure drop of −0.0122 MPa. Therefore, the values estimated by the dynamic model are very close to the experimental values.