Numerical Study On Fluid Flow And Heat Transfer In Tube With Non-uniform Heat Flux

Parabolic trough solar collector is an important solution to utilization of solar energy.However,due to the characteristics of the geometric structure of parabolic trough solar collector,the incident heat flux on the surface of the absorber is generally non-uniform spatially and temporally which results in temperature gradient and mechanical stress in absorber wall,leading the absorber tube bending,even the broking of the glass tube.Therefore,it is necessary to study the flow and heat transfer in tube of parabolic trough collector.The fluid flow and heat and mass transfer in tube under non-uniform heat flux is the study object of this research,which is aimed to a further understanding on the influence of temperature inlet,velocity inlet and the non-uniform heat flux on fluid flow.Monte Carlo Ray Trace(MCRT)is used to trace the photon hitting the parabolic trough solar collector,and MATLAB is applied in the process simulation,and the non-uniform heat flux on the surface of absorber tube is transmitted to fluent by user defined function(UDF).The inlet parameters and the non-uniform heat flux have a significant impact on the fluid flow and heat transfer.Therefore,the influence results from inlet temperature(303.15 K,313.15 K,323.15 K,333.15 K,343.15 K,353.15K),the inlet velocity(1.5 m/s,1.8 m/s,2.0 m/s,2.3 m/s,2.5 m/s,3.0 m/s)and the solar elevation angle(0°,30°,60°,90°)are investigated respectively,on wall function heat transfer coefficient,friction factor and the distributions of temperature and velocity.Then,the R245 fa is used as the working fluid in tube and VOF is applied to trace the interface of gas and liquid.The effects of inlet temperature(360.15 K and 363.15 K),the inlet velocity(0.10 m/s,0.12 m/s and 0.15 m/s)and the non-uniform heat flux(56kW and 28 kW,with top,middle and bottom location)on the fluid flow and heat and mass transfer of R245 fa are studied in this paper.The main conclusions of the whole paper are presented below:(1)MCRT has a good accuracy to simulate the non-uniform heat flux outside the absorber tube.(2)The location of heat flux has effects on the velocity vector of the horizontal and vertical velocity component and the changes of the flow pattern.(3)The increase of velocity or non-uniform heat flux,or the heat flux locate on the top of tube can make a larger pressure drop.When the heat flux reduces by half,the time-average volume fraction is decreasing by 40%.(4)The velocity,the materials of tube and the non-uniform heat flux have influence on fluid flow and heat and mass transfer.Base on the simulation above,a test bench is designed for study the flow board boiling of R245 fa in this paper.