Research On The Characteristic Of Temperature And Velocity Field In Flat Plate Solar Collectors

The technologies for developing and utilizing solar energy are currently thefastest growing technologies in renewable energy field. And solar water heating is themost widely used application in solar thermal utilization. Collectors are the core ofsolar water heaters, while flat plate solar collectors are the mainstream of the world.Many of the existing researches on flat plate solar collectors are based on theassumption that flow is evenly distributed in the pipes. And simulation studies arealways conducted on too many hypothesizes and simplifications. Sometimesresearchers only study the air gap between absorber plate and glazing cover.Thereby, this paper reviewed the impacts of different parameters on theperformance of the collectors. And then testing experiments of the performance oftwo different flat plate solar collectors are carried out. Finally, a simulation model thatconsists of the whole working fluid pipes is developed for flat plate solar collectorswith reasonable assumptions.The effects of absorber material, absorber plate thickness, air gap depth, inletfluid temperature and fluid mass flow on temperature distribution in the absorber plateand air gap as well as the flow distribution in air gap are simulated with FLUENT.The results indicate that:(1) the temperature distribution in absorber plate and center plane of air gap isquite uneven when absorber plate is made of steel. If absorber plate is made of copperinstead of aluminium sheet, the efficiency of collector can only be improved by2.47%.When the absorber plate thickness is beyond0.45mm, continuously increasing thethickness of absorber plate will have no effect on collectors’ temperature and flowfield distribution.(2) different depths of air gap have different effects on collectors’ temperatureand flow field distribution. One must pay particular attention to the depths of the airgap during the design of a collector, so that the chosen air gap depth will not decreasethe efficiency of collectors. The collectors’ efficiency will decrease when the depth ofair gap increases from20mm to30mm. While the collectors efficiency will increasewhen the depth of air gap increases from40mm to60mm; (3) the temperature of collector absorber plate and the center plane of air gapincrease and the streamlines of center plane of air gap will be uniformity with theincreasing of inlet fluid temperature. Increasing the fluid mass flow from0.06kg/s to0.08kg/s will hardly have any influence on collectors’ efficiency.