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A numerical analysis of the energy and entropy generation rate in a Linear Fresnel Reflector using computational fluid dynamics

López-Núñez, Oscar A., Alfaro-Ayala, J. Arturo, Jaramillo, O.A., Ramírez-Minguela, J.J., Castro, J. Carlos, Damian-Ascencio, Cesar E., Cano-Andrade, Sergio
Renewable energy 2020 v.146 pp. 1083-1100
air, energy, entropy, fluid mechanics, heat transfer, renewable energy sources, temperature profiles
This work presents an energy and entropy generation analysis of a Linear Fresnel Reflector using the Computational Fluid Dynamics. It consists of 25 mirrors oriented to a receiver tube, which is located inside a Compound Parabolic Concentrator. The formulation of the entropy generation rate considers the phenomena of viscous dissipation, heat transfer and radiation, it is performed in a local and global way and implemented by user-defined functions. Results of the incident radiation, absorbed radiation, radiation temperature, temperature gradients, air velocity contours, Nusselt number and optical efficiency, are presented. Results show that the maximum values of the absorbed radiation (7800 W m−2), incident radiation (30,000 W m−2) and radiation temperature were located at the receiver tube. Also, the maximum value of the temperature gradient (39,000 K m−1) was obtained on the lower half of the receiver tube and the upper part of the secondary receiver. Moreover, the highest values of the entropy generation rate were located at the upper part of the secondary receiver for each phenomenon considered. It is concluded that the entropy generation rate due to heat transfer phenomenon is the most dominant (97.4% of the total), followed by radiation (2.59%) and then by viscous dissipation (negligible).