Research On Heat Transfer Characteristics Of Solar Air Collector Based On CFD

Solar air collectors have been widely used in the fields of building heating,product drying and solar refrigeration.Increasing the collector efficiency is the key to the application of air collectors.At present,it is mainly achieved by changing the structure of the heat absorbing plate and increasing the surface roughness.But this also leads to an increase in system friction losses.Therefore,how to rationally design the structure of the air collector heat absorbing plate,so as to balance the contradiction between the improvement of collector efficiency and the augment of the system friction loss,is an important issue to be solved in the research of solar air collectors.Aiming at solving this problem,this paper constructs a solar collector with a whole bunch of hemispherical convex structure on absorber plate,and uses the Fluent to systematically study the influence of the structural parameters of the heat absorbing plate on the heat transfer performance of the solar air collector.The main research work of this paper includes:(1)Firstly,the basic structure and working principle of the flat solar air collector are introduced,and the basic theoretical model of the collector is established.Besides,the energy migration process and law in the collector are analyzed.The summary of previous research work shows that the solar air collector with hemispherical convex structure on the absorber plate can not only effectively improve the collector efficiency,but also keep the friction loss in a relatively small range.(2)Using Fluent to establish the physical model of air collector with hemispherical convex structure,and simulate the heat transfer characteristics of the collector channel when the Re number is in the range of 3600~18100,the protrusion diameter d is in the range of 5mm~15mm,the inclination angle ? is in the range of 15°~60°,and the pitch p in the range of 30mm~60mm.Besides the comparative analysis of the results of the collector with convex structure and the corresponding results of the air collectors with smooth absorber plate is made.According to the cloud image,compared with air collector with smooth absorber plate,air collector with the hemispherical convex structure has a larger Nu number at the interface between the air and the absorber plate,but the air pressure drop is also larger.It is shown that air collector with the hemispherical convex structure can effectively improve the heat collecting efficiency,but also increases the friction loss of the system.(3)The numerical simulation results are summarized.The variation of the performance parameters of the collector with hemispherical convex structure with the protrusion diameter d,inclination angle ? and pitch p is analyzed.The obtained results are compared with air collector with smooth absorber plate.The analysis results show that compared with air collector with smooth absorber plate,the heat transfer performance of the collector with hemispherical convex structure is greatly improved,and the average Nu number of the interface between the heat absorbing plate and the air is increased by about three times;The comprehensive efficiency of the device is complicated with the variation of various structural parameters.It is necessary to consider the influence of various structural factors comprehensively.When the protrusion diameter is 10 mm,the inclination angle is 45°,and the pitch is 45 mm,the overall efficiency of the system is the highest.In summary,the air collector with a whole bunch of hemispherical convex structure on absorber plate can effectively improve the heat collecting efficiency of the collector,and the overall efficiency is the largest under the the optimized parameters,namely,the protrusion diameter is 10 mm,the inclination angle is 45°,and the pitch is 45 mm.This study has certain guiding significance for engineering practice.