Influence Of Pulsation Flow On Performance Of Solar Air Collector

Based on the characteristics that the pulsating flow can enhance heat exchange,delay the ash deposition rate and reduce the thickness of the ash,this paper introduces the pulsating flow into the flat plate solar air collector with baffles.By investigating the influence of pulsation parameters of four pulsating waveforms including sine wave,square wave,isosceles triangle wave and right angle triangle wave on the average wall shear stress of cover plate and heat absorbing plate,total pressure loss of the collector and collector efficiency,this paper comprehensively evaluates the influence of pulsating flow on the performance of the collector,using a method of combination theoretical analysis and numerical simulation.Firstly,based on the original experimental model,this paper establishes a numerical calculation model.By comparing the numerical calculation results with the experimental results,the final turbulence model is determined and the correctness of the numerical model is verified.The theoretical analysis method is used to investigate the effects of external and internal dust accumulation on the thermal performance of the collector.It is found that the external and internal dust accumulation of the collector will reduce the efficiency of the collector,while the internal dust accumulation has a greater impact on the efficiency of the collector.it is quantitatively found that the efficiency of the collector is reduced by about2%through numerical simulation when the dust density of the external or internal of the collector is increased by 1 g/m~2.The internal dust accumulation reduces the absorption rate of the heat absorbing plate,resulting in lower efficiency of the collector.When the dust density of the inside the cover and the upper part of the absorbing plate are both 6g/m~2,the collector efficiency can be reduced by 35.2%.Then,the numerical simulation method was used to study the changes of the average wall shear stress of the cover plate and the heat absorbing plate,the total pressure loss of the collector and the heat collecting efficiency.When the collector inlet flow changes in four waveforms:sine wave,square wave,isosceles triangle wave and right angle triangle wave,respectively.The results show that the effect of right-angled triangular wave is the most obvious in increasing the internal wall shear stress of the collector.When the average Reynolds number of the chamber is 2600,the average wall shear stress of the cover plate and the heat absorbing plate can be increased by 2.4 times.The variation characteristics of the wall shear stress under each waveform are analyzed.It is found that the sudden change of the inlet velocity of the collector can effectively improve the average wall shear stress of the heat absorbing plate.The results show that the use of pulsating flow will cause the instantaneous efficiency of the collector to decrease to varying degrees.However,in practical applications,the increase of wall shear stress can effectively reduce the ash deposition rate and reduce the ash deposition thickness,which will play an active role in the long-term performance improvement of the collector.