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1、Pergamon PII: SOO38_092X( 97)00007-S .Sular Energy Vol. 60, Nos. 3/4, 135-150, 1997 pp. 0 1997 Elsevier Science Ltd All rights reserved. Printed in Great Britain 0038-092X/97 $17.00+0.00 EXPERIMENTAL AND NUMERICAL EVALUATION OF THE PERFORMANCE AND FLOW STABILITY OF DIFFERENT TYPES OF OPEN VOLUMETRIC
2、 ABSORBERS UNDER NON-HOMOGENEOUS IRRADIATION R. PITZ-PAAL,+ B. HOFFSCHMIDT, M. BOHMER and M. BECKER Deutsche Forschungsanstalt ftir Luft- und Raumfahrt e.V., Hauptabteilung Energietechnik, Linder Hahe, D-51 147 K(iln, Germany (Received 28 June 1996; revised version accepted 19 December 1996) (Commun
3、icated by Lorin Vant-Hall) This article is dedicated to the 65th anniversary of Prof. M. Fiebig Abstract-Numerical results found in the literature predict the capability of volumetric receivers to pro- duce gas outlet temperatures of more than 1000C. Other approaches found the tendency for an inhere
4、nt flow instability for volumetric absorbers at high outlet temperatures. Both aspects, which are based on one-dimensional approaches, do not fit the experimental experience available even for semi-commercial volumetric receivers in the case of non-homogeneous flux distribution. Since this is the ge
5、neral case in solar power plants, a new analytical approach which takes into consideration a three-dimensional irradi- ante distribution and its influence on fluid flow and radial heat transfer is presented in this article. A comparison with experimental data for four totally different volumetric ab
6、sorber types coincides well with the measured overall thermal efficiency as well as with the local temperature distribution. The model helps to explain how thermal efficiencies and temperature distributions are strongly influenced by non- homogeneous irradiation. Moreover, it demonstrates how flow i
7、nstabilities are partly prevented by radial heat transfer. Finally, it is shown that a volumetric receiver consisting of sufficiently small absorber modules which are equipped with an additional orifice plate at the rear side will always run under stable flow conditions. 0 1997 Elsevier Science Ltd.
8、 1. INTRODUCTION Volumetric receivers are used in central receiver solar thermal power plants in order to transfer the concentrated solar radiation to a gaseous heat transfer medium. The absorbers used in these receivers consist of porous structures such as wire mesh, ceramic foams or honeycomb stru
9、ctures that are irradiated by concentrated radiation. Gas is driven through the absorber parallel to the direction of the incoming radia- tion and is heated by convection. Since the heat transferring surface per unit of incident solar radiation is increased compared with a tube absorber design, high
10、er flux densities can be transferred without reaching the temperature limit of the absorber material. Higher concen- tration results in an increased thermal efficiency and requires a smaller receiver aperture (= lower costs) in order to transfer a certain amount of energy. The inherent simplicity of
11、 the volumetric receiver concept using ambient air in an open cycle has made it attractive to a German indu- +Author to whom all correspondence should be addressed. Tel. +49 2203 601 2744; fax +49 2203 66900; e-mail: robert.pitz-paaldlr.de. strial consortium as a basis for the design of the so-calle
12、d PHOEBUS power plant. This con- cept has been the subject of a comprehensive feasibility study performed in several phases (Phoebus Consortium, 1987, 1990, 1994) and appears to be ready for the market from a technical point of view. A 3 MWth system test using a wire mesh absorber was performed at t
13、he Plataforma Solar de Almeria in the scope of the feasibility study. It demonstrated the feasibility of the volumetric air receiver concept at air outlet temperatures of 700C (Heinrich and Schmitz-Goeb, 1995). The lack of financial support necessary for a first demonstration plant is the major obst
14、acle for market penetra- tion of the PHOEBUS project at the moment. Beside the above-mentioned open receiver loop using ambient air, closed loop concepts are under development which also allow opera- tion under moderate pressure. Apart from the absorber itself, research in the field of closed volume
15、tric receivers is presently concentrated on the design of the pressure and temperature loaded glass window and the development of a modular structure of the receiver. Closed loop volumetric receivers have also been used for chemical applications. For the special case of 135 136 R. Pitz-Paal et al so
16、lar methane reforming, Buck et al. ( 1992) detected an instability of flow through the receiver. The development at the DLR and other research institutes is focused on the introduction of new absorber structures made from ceramic in order to allow higher flux densities or higher gas outlet temperatures (Becker and Biihmer, 1990; Chavez and Chaza, 1991; Biihmer and Chaza, 1991; Biihmer and Meinecke, 1991; Pitz-
