Optimization of a Linear Fresnel Reflector Applying Computational Fluid Dynamics, Entropy Generation Rate and Evolutionary Programming

Abstract

This work presents an optimization of a Linear Fresnel Reflector based on the Computational Fluid Dynamics, the Entropy Generation Rate and the Evolutionary Programming method. The objective function of the optimization process takes into account the maximization of the absorbed radiation solar flux on the receiver tube and the minimization of the total Entropy Generation Rate. A set of design equations were used to build the Linear Fresnel Reflector geometries of each one of the individuals per generation. The design equations consider, among others, a coupling between the angles and distances of the mirrors and the required geometrical parameters for the construction of the CPC secondary reflector. The Evolutionary Programming considers a small population of six individuals per generation and takes into account a search space for geometric parameters such as the aperture area, the width and the length of the mirrors. The mutation operator is applied to generate the individuals and the selection operator is applied to find the best individuals for the next generation. Seven generations were needed to find the optimal Linear Fresnel Reflector. The optimal Linear Fresnel Reflector (NN individual) presents an increase of 2.48% for the average absorbed radiation flux on the absorber tube and a decrease of 20% for the total Entropy Generation Rate, both in comparison with a prototype of a Linear Fresnel Reflector. For the absorbed radiation flux, both individuals presents the minimum values on the top side of the absorber tube (1,386 W m-2 and 1,982 W m-2 for the prototype and NN individual respectively), while the maximum values are located at the lower part of the absorber tube (7,180 W m-2 and 8,199 W m-2 for the prototype and NN individual respectively). In terms of local Entropy Generation Rate, the NN individual has a decrease of 14.6%, 60% and 36.8% of Entropy Generation Rate due to viscous dissipation, heat transfer and radiation respectively at the CPC zone in comparison with the prototype of a Linear Fresnel Reflector. Finally, the NN individual has an increase of 16.4% and 23.8%. for the thermal efficiency and the exergy efficiency, respectively.