Experimental Study On The Heat Loss Characteristics Of Cylindrical Cavity Receiver With/without Quartz Window

Solar thermal power generation is one of the important ways of solar energy utilization.Dish solar thermal power generation has attracted much attention due to its advantages of easy installation and high efficiency.Dish solar thermal power generation places a receiver at the focus of the concentrator to produce high-pressure,high-temperature steam or gas,which drives the thermal power generator to generate electricity.In this paper,the heat loss characteristics of a cavity receiver,an important component of the dish solar thermal power generation system,are studied.Under the condition of constant heat flux,a cylindrical cavity receiver test setup was built to study the influence of tilt angle,heat flux and heating mode(both side and bottom surface heated,only side surface heated,only bottom surface heated)on the wall temperature,heat loss and Nusselt number,and the comparison analysis with no quartz window cavity is also studied to find the role of the quartz window on cavity.The quartz window has great influence on the wall temperature,heat loss and Nusselt number.The research results are as follows.(1)The quartz window has a significant effect on improvement of the cavity temperature.When both side and bottom surface are heated and heat flux is 600W/m~2and 700W/m~2,the average temperature of quartz window cavity is 71.29℃and79.36℃higher than that of no quartz window cavity respectively,the temperature increases obviously.The quartz window blocks the direct heat transfer way between the air in the cavity and the external environment,changes the high-temperature heat source of convection and radiation heat transfer.As a result,the heat dissipation decreases and the average temperature of the cavity increases.(2)The effect of tilt angle on the heat loss of cavity is different with different heat transfer process.The quartz window can obviously reduce the fluctuation of heat loss at different tilt angles.When both side and bottom surface are heated and heat flux is700W/m~2,the heat loss of quartz window cavity hardly changes with the tilt angle,and the ratio of convective heat loss to total heat loss is about 59%.But the ratio of convective heat loss to the total heat loss in no quartz window cavity varies from42.68%to 77.55%.The presence or absence of quartz window determines the mode of heat exchange between the cavity and the outside.The change of tilt angle affects the position of high temperature air in cavity.Both of them determine the variation of heat loss in the cavity.(3)The quartz window changes the rules of Nusselt number under different tilt angles.Except for the Nu_c under the condition of only bottom surface heated,the Nu_r and Nu_c under other conditions change little with the tilt angle,and the change curves basically present a horizontal straight line.When only the bottom surface is heated,the cavity temperature is low,and Nu_c changes significantly with the tilt angle,so other methods should be sought to control the influence of tilt angle on heat transfer.(4)In this paper,the Nusselt numbers of quartz window cavity are analyzed and the empirical correlations are fitted.The formulas use the parameters of tilt angleφ,Grashof number Gr and heat flux q as independent variables,the errors between fitting results and experimental data are mostly kept within 10%,which has good reference and application value.