Silvia Palero, DER — Ciemat, Av. Complutense 22, 28040 Madrid, Spain.

Manuel Romero, DER — Ciemat, Av. Complutense 22, 28040 Madrid, Spain.

Claudio A. Estrada, Center for Energy Research, UNAM, PO 34, 62580 Morelos, Mexico Jose L. Castillo, Mathematical Physics and Fluids, UNED, PO 60141, 28080 Madrid, Spain. Rafael Monterreal, PSA Ciemat, PO 22, 04200 Tabernas (Almeria), Spain.

Jesus Fernandez-Reche, PSA-Ciemat, PO 22, 04200 Tabernas (Almeria), Spain.

Abstract

Temperature distributions inside volumetric solar absorbers have been calculated with numerical models but there is not any experimental study focusing on that topic. With this purpose, several tests using metallic monoliths made of parallel ducts as volumetric solar absorbers have been perfomed at the CRS facility of the PSA. The radial air temperature distributions at the absorber exit have been measured for all the samples. Moreover, the axial wall temperature distribution, measured with thin thermocouples inserted inside the absorber channels, gives information about the volumetricity of the samples. The results show that the absorbers tested do not behave as pure volumetric axial absorbers because they present the maximal temperatures relatively close to the front surface and subsequently, the heat transfer from wall to air in the inner part of the absorber does not allow the homogenization of both temperatures.

Introduction

Air-cooled volumetric solar receivers are considered a good option to absorb solar energy and to transfer the heat from the porous matrix to the air, because they reduce the re­radiation losses by decreasing the temperature of the absorber more external surface, thanks to the volumetric effect (Fricker, 1990). Models to simulate the heat transfer in the volumetric absorber have been developed, leading to theoretical porous material and air temperature distributions (Hoffschmidt,1996; Garcia-Casals, 2000). The computed radial temperature distribution at the absorber front surface shows a good agreement with the temperature distribution at this surface measured by an IR camera. However, the axial temperature distribution inside the absorber matrix has not been experimentally studied until now. The aim of this work has been to measure and to contrast axial and radial distribution of temperatures, as the preliminary step for further analysis of the influence of several parameters (like the absorber length/diameter ratio or the cell density) on the heat transfer in a monolithic metallic corrugated foil absorber and its comparison to numerical models of volumetric structures.