Research On The Characteristic Of Temperature And Fluid Flow And The Optimization Of Flat Plate Solar Air Collectors

To cope with the increasingly serious energy and environmental crises,developing and utilizing solar energy resources has become an important choice.Solar utilization technologies have great development potential in the building industry which is energy-hungry.It is estimated that if we achieve full use of solar energy,80% of the energy consumption in the building industry can be provided by solar energy.Fully exploiting the potential of solar energy resources and improving the solar energy amount in building energy supply is an important measurement for energy conservation and emission reduction.Flat plate solar air collector is very suitable for heating and drying for its advantages of simple structure,low cost,no freezing problems and directly making hot air.It can be widely popularized in the majority village areas in China which do not have conditions for central heating.But the thermal efficiency of flat plate solar air collector is low,and researches should be carried out in the internal fluid flow and heat transfer characteristics for it,in order to achieve optimization of the collector structure,improve the system solar fraction,reduce costs and ensure the stability of the system.Thus,this paper systematic analyzed the internal eat transfer characteristics of the collector based on the flat plate solar air collector characteristics;through reasonable simplification and assumption,build a simulation model for the pre-experimental flat plate solar air collector;using FLUENT to study the effect of inlet air flow rate,inlet air temperature,solar radiation and air gap thickness on the internal heat transfer characteristics of the collector,and the collector absorber average temperature and heat transfer coefficient,the outlet air temperature,the pressure drop and the collector thermal efficiency were taken as the indicators;optimization direction of the collector structure were given.The simulation results indicated that:(1)Increasing the inlet air flow can improve the thermal performance of the collector.When the inlet air flow rate increased from 30 m3/h to 110 m3/h,the average temperature of the absorber and the outlet air dropped 9.72 %% and 13.08%,respectively,and the collector thermal efficiency increased by 27.03%.(2)When the inlet air temperature increased from 278.15 K to 284.15 K,the collector thermal efficiency increased by 2.17% under a solar radiation intensity of 700 W/m2 and the collector thermal efficiency increased by 1.8% under a solar radiation intensity of 500 W/m2.(3)Under a certain ambient temperature and inlet air flow rate,the collector thermal efficiency first received a slightly increase and then decreased when the solar radiation intensity decreased from 700 W/m2 to 300 W/m2.Finally the collector thermal efficiency decreased by 8.72%.And when the solar radiation intensity is 500 W/m2,the collector thermal efficiency is the highest.(4)The impact of air gap thickness on the collector thermal performance may differ for different air gap thickness.The collector thermal efficiency first reduced and then increased with the increase of air gap thickness.(5)For the collector optimization design,it can be conducted by altering the position of the fluid import and export location or setting up several imports and exports,and by setting the air gap thickness of the collector in the range that makes the convective heat transfer at the top of the collector be minimum.For the optimal operation of the collector,using variable frequency fans to realize the adjustment of the inlet air flow according to the ambient temperature can be used.