Solar air receiver using a non-uniform porous medium

Van Der Merwe, Philippus Carel (2016-03)

Thesis (MEng)--Stellenbosch University, 2016

Thesis

ENGLISH ABSTRACT: A receiver concept for a CSP plant employing a Brayton cycle solar thermal power plant was designed and tested experimentally. The receiver aims to mimic the greenhouse effect and comprises of an annular configuration, with a transparent outer tube and an opaque inner tube. A porous medium in the annular space serves to trap radiation and transfers heat to air flowing through it. The receiver concept may be integrated in any CSP plant exploiting the Brayton Cycle, such as the SUNSPOT system. The receiver will be situated between the compressor and combustor with the aim being to increase the air temperature before it runs through the combustion chamber. A linear mirror system was developed to concentrate the solar radiation in the receiver tube, while air was used as the heat transfer fluid. The temperature of the air was measured at the outlet of the tube in order to determine the efficiency of the receiver tube. The projects aims towards determining the radiation properties of the porous medium by means of three different ways. The first modelled developed, was that of an analytical Matlab model and the second being a simulated CFD model. These results were compared to the experimental tested results. The study concluded that the receiver achieved an efficiency of 41 % without being optimized, while reaching an average temperature increase in the system of up to 40 °C. The radiation properties of the porous medium can, however, not be determined by taking temperature measurements. A separate test result will have to be constructed to determine these properties. The concept proves to be very promising although it only achieved an efficiency of 41 %. The large heat transfer area between the air and the porous medium proves to be a major advantage.

AFRIKAANSE OPSOMMING: ʼn Sonstraal ontvanger sisteem is ontwerp om die straling vanaf die son te reflekteer op ʼn lineêre lyn waar die ontvanger geplaas is. Hierdie ontvanger word gesien as ʼn moontlike konsep om lug te verhit tydens die Brayton siklus in gekonsentreerde son-energie kragstasies. Die ontvanger bestaan uit ʼn deurskynende glas, met ʼn koper pyp in die middel en ‘n annulus wat gevul is met poreuse materiaal. Die konsep is gebaseer op die kweekhuis effek, waar die energie binne ʼn deurskynende ruimte geabsorbeer word. Hierdie konsep is ideaal vir die SUNPOT stelsel aangesien dit lug gedrewe is en ook van die Brayton siklus gebruik sal maak. Hierdie stelsel sal tussen die turbine en ontbrandingskamer geplaas word om te temperatuur van die lug te verhoog voor dit deur die turbines gaan. Die sonstraal ontvanger sisteem het bestaan uit agt lineêre spieëls wat die lig konsentreer op ʼn lineêre lyn, 2 m bo die grond oppervlak. Die uitlaat temperatuur was gemeet by verskillende om die totale effektiwiteit van die stelsel te bepaal. Een van die doelwitte van die projek is ook om die stralings eienskappe van die poreuse materiaal te toets. Hierdie doelwit was op drie verskillende metodes getoets. Eerstens was die ontvanger deur verskillende eksperimentele toetse geplaas. Hierdie eksperimentele toetsdata was dan vergelyk met twee verskillende modelle: ‘n analitiese Matlab model en ‘n simulasie model wat met behulp van ANSYS geskep is. Die verskillende toetse was met mekaar vergelyk om die moontlike stralings vermoë te bepaal van die poreuse materiaal. Die studie het bevind dat die ontvanger buis ‘n effektiwiteit van 41 % het, sonder om optimalisering toe te pas op die stelsel. ‘n Gemiddelde temperatuur verskil van 40 ºC was ook bereik by die uitlaat van die stelsel. Daar is egter gevind dat die straling eienskappe van die materiaal nie deur hierdie toets bepaal kan word nie en dat ‘n aparte opstelling gedoen moet word. Hierdie konsep is baie belowend en die groot hitte oordrag area tussen die poreuse medium en die lug is van groot voordeel wanneer na alternatiewe konsepte gekyk word.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98939
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