A Heat Transfer Analysis of Axial and Radial Functionally Graded Ceramic Foams Solar Air Receivers

Abstract

Volumetric solar receiver are promising as heat transfer devices in concentrated solar power applications because they allow to reduce heat losses at the receiver entrance when compared to more conventional tubular receivers. Among various porous materials, ceramic foams have been shown to be promising because of their extended heat transfer area and effective thermal conductivity, especially when they are manufactured by considering variable morphologies thanks to modern techniques like additive manufacturing. In this contribution, porous media numerical simulations are presented for fluid flow and heat transfer in ceramic foams receiver with different porosity functions on either axial or radial directions, and also when porosity varies on both directions. Such simulations are performed by employing Beer-Lambert law to model radiative heat transfer, and a Gaussian distribution for the incoming radiation. Results are obtained by constraining the average porosity for the different cases, showing that graded foams allow to obtain more or less similar outflow temperatures, but with reduced heat losses at the receiver entrance and also with less uniform velocity profiles to promote heat convection in some critical points of the receiver.