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Research Papers

# Comparison of Experimental and Numerical Air Temperature Distributions Behind a Cylindrical Volumetric Solar Absorber Module

[+] Author and Article Information
Silvia Palero

Renewable Energy Division, DER-CIEMAT, Avenida Complutense 22, 28040 Madrid, Spainsilvia.palero@ciemat.es

Manuel Romero

Renewable Energy Division, DER-CIEMAT, Avenida Complutense 22, 28040 Madrid, Spain

José L. Castillo

Departamento de Física Matemática y de Fluidos, Facultad de Ciencias, UNED, Senda del rey 9, 28040 Madrid, Spain

J. Sol. Energy Eng 130(1), 011011 (Dec 28, 2007) (8 pages) doi:10.1115/1.2807046 History: Received September 29, 2006; Revised August 20, 2007; Published December 28, 2007

## Abstract

The current trend in volumetric solar receiver technology is to build modular receivers cooled by air (Hitrec I and II, Solair $200kW$ and $3MW$) in order to facilitate the replacement of broken absorber modules (cups) and to simplify the upscaling of the receiver. In addition, the modular designs include an air return circuit to cool down the structure supporting the cups. Usually, the air outlet temperature from each module is characterized by measurements taken from a single thermocouple. However, the air temperature distribution behind the volumetric absorber module is not homogeneous, as it can be seen in some specific tests where several thermocouples were added behind different absorber modules. The radial distribution of outlet air temperatures shows very high temperature gradients. The goal of this work is to explain the inhomogeneous thermal maps behind the metallic absorbers by comparing some experimental results with numerical simulations performed using the computational fluid dynamics FLUENT code. The results show the wind influence over the air recirculation flow and its effects on the outlet air temperature radial distribution. Thus, the simulations suggest different ways to reduce the temperature gradients behind each cup.

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## Figures

Figure 1

Partial picture of the Solair 200kW receiver with the cylindrical metallic modules installed for testing

Figure 2

Thermocouple positions behind the 8cm diameter absorber module

Figure 3

Experimental air temperature distribution 2cm behind the 400cpsi metallic absorber exit (Cup 21)

Figure 4

Configuration for the simulation of a cylindrical absorber in FLUENT

Figure 5

Numerical air temperature distribution 2cm behind the absorber exit

Figure 6

Velocity vectors colored by temperature (K) for the parameters of Table 2

Figure 7

Mass flow rate inflence over the air temperature distribution (wind speed=1m∕s)

Figure 8

Wind speed influence: sequence of results with 0m∕s, 1m∕s, 2m∕s, and 3m∕s

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