Experimental Study And CFD Numerical Simulation Of Full Glass Vacuum Solar Collector

All-glass evacuated solar collector tubes with simple structures have been widelyused in recent years. In this thesis, the following aspects of all-glass evacuated solarcollector tubes were investigated experimentally and numerically:1. Experimental measurements were performed for six single-ended water-in-glassevacuated tubes with the similar specifications but manufactured by differentproducers and the corresponding water-in-glass solar water heaters consisted of thesetubes to obtain the relationship between the thermal performance of an evacuated tubeand the energy gain of the corresponding solar water heater. The experimental resultsshow that both solar irradiation under stagnation H and mean heat loss coefficient ULThave significant effects on energy gain Qs, but the stagnation parameter Y hasnegligible effect on Qs.2. A number of all-glass evacuated tubes with the similar specifications butmanufactured by different producers were selected to experimentally measure theirthermal performances, in order to explore the relationship between the thermalperformance of a single evacuated tube and the solar absorptance and thermalemittance of the selective absorbing coating, as well as the influence of long-timeexposure to the sun, on the performance of tubes. The results show that thehemisphere emittance has significant effect on both Y and ULTwhereas Hsignificantly depends on the absorptance. The results also indicate that long-timeexposure to the sun can destroy the vaccum performance of tubes.3. Three-dimensional numerical simulations were conducted using ANSYSsoftware to study the temperature and velocity fields inside evacuated tubes under thestagnation condition. The numerical results show that the average surface irradianceand the average Nusselt number reach their respective maxima at the inclination angleof50o; the average Nusselt number with the tube length of2100mm is larger thanthose with the tube lengths of1500mm and1800mm; the coating’s absorptancedirectly affects the received irradiance. When the absorptance increases from0.7to1, the corresponding average surface irradiance increases by18.9%. There is an evidentincrease in the coating’s temperature when the absorptance increases.The purpose of the study is to provide a useful reference for all-glass evacuatedtubes, solar water heater thermal performance testing and production and engineeringtechnology applications.