Numerical Simulation Study Of Poiseuille-rayleigh-bénard Convection Of Cold Water In Horizontal Rectangular Channel

Poiseuille-Rayleigh-Bénard(P-R-B)convection widely exists in nature and industrial production processes,such as atmospheric flow process,cooling process of electronic components,chemical vapor deposition(CVD)process and so on.P-R-B convection is a mixed convection process in which forced convection driven by horizontal pressure gradient characterized by Reynolds number and Rayleigh-Bénard(R-B)convection driven by vertical temperature gradient characterized by Rayleigh number are coupled.At present,many scholars have done a lot of research on P-R-B convection of the conventional fluid satisfying Boussinesq approximation.However,P-R-B convection of the fluid with the extreme density is not involved.In this thesis,P-R-B convection of cold water with the extreme density is taken as the research object,and the finite volume method is used to numerically simulate the P-R-B convection of cold water in horizontal rectangular channel.The effects of density inversion parameters,Reynolds number and Rayleigh number on the evolution of the flow pattern and heat transfer performance are analyzed,the critical conditions for flow pattern transformation are determined,and the heat transfer performance under different flow patterns are obtained.The effect of a periodic heating condition on the bottom on P-R-B convection is analyzed.The results show that:(1)the density inversion parameter of density extreme fluid plays an important role in P-R-B convection.With the increase of density inversion parameter,the critical Rayleigh number of R-B convection appearance increases.Compared with conventional fluids,the critical Rayleigh number of R-B convection appearance increases.(2)When the density inversion parameter is fixed,the P-R-B convective flow pattern depends on the relative intensity of Poiseuille flow and R-B convection.With the increase of Rayleigh number,the convection will experience three flow states in turn,namely horizontal parallel flow,local traveling wave flow pattern and periodic traveling wave flow pattern.(3)When R-B convection is weak,horizontal flow is dominant and no roll cell is produced.When the Rayleigh number increases beyond a certain critical value,roll cells begin to appear in the channel,the length of the inlet section without roll cells gradually shortens,and finally the whole horizontal channel is filled with roll cells.With the increase of Reynolds number,the critical Rayleigh number corresponding to the appearance of roll cells increases.(4)When the flow is in the region of local traveling wave flow pattern and periodic traveling wave flow pattern,the secondary thermal convection continuously washes the upper and lower walls,and the average Nusselt number on the bottom wall increases.In the local traveling wave flow pattern region,the average Nusselt number increases greatly with the increase of Rayleigh number,but in the periodic traveling wave flow pattern region,this change is relatively gentle.(5)When a periodic heating boundary condition is imposed on the bottom,there are only some convective roll cells in the whole horizontal channel.With the increase of density inversion parameters,the critical Rayleigh number corresponding to the appearance of the convective roll cells in some areas of the whole horizontal channel also increases,indicating that the formation of roll cells is more difficult with the increase of density inversion parameters.