| Rayleigh-Benard(RB)convection has been found in nature research and industrial applications.And it has received extensive attention from scholars.The current research on RB convection mainly focuses on Boussinesq fluids such as water and air,few studies on non-Boussinesq fluids have been conducted.In this paper,supercritical carbon dioxide(S-CO2)is used as the research object,which is one of non-Boussinesq fluid.And the computational fluid dynamics simulation methods is used to study the RB convection phenomenon of S-CO2,and to explore the effects of strongly variable physical properties of S-CO2 in the pseudo-critical region on flow and heat transfer characteristics.First,the computational fluid dynamics tool ANSYS FLUENT is used to establish an analysis model.Second,the calculation results of the models with the previous experimental results and theoretical analysis results are compared to verify the models.Finally,the two-dimensional RB convection,the Poiseuille-Rayleigh-Benard(PRB)convection and the three-dimensional classical RB convection are simulated.It is found that,the steady flow states is ovserved in low Rayleigh number.However,with the increase of the Rayleigh number,the final flow states is different.The fluid system under a large Rayleigh number will reach the final state earlier than the system under a small Rayleigh number.The results also show that the aspect ratio has an important influence on the heat and flow characteristics,and the experience correlation between the Nusselt number and the aspect ratio is proposed.PRB convection refers to RB convection with the influence of horizontal flow.The inlet Reynolds number(Re)of the horizontal flow has a significant effect on the PRB convection.When the inlet Reynolds number is constant,with increasing Rayleigh number,three types of convection patterns can be observed such as conduction with horizontal flow,localized traveling wave convection and fully developed traveling wave convection.If Rayleigh number is fixed,with increasing the Reynolds number,three types of convection patterns have been occurred such as fully developed traveling wave convection,localized traveling wave convection and conduction with horizontal flow.Further,in order to characterize the dependence of traveling wave convection on horizontal flow,the experience correlation for computing the critical Reynolds number varying with relative Reynolds number is acquired.Through the analysis of the three-dimensional Rayleigh-Bénard convection,a weak flow is found in the stable heat conduction state,which shows a difference in the twodimensional Rayleigh-Benard convection results.In addition,the difference in convective heat transfer characteristics of Rayleigh-Benard convection in different three-dimensional geometric structures is compared.Numerical studies have been carried out on the RB convection of S-CO2 in this paper.This study enriches the research content of RB convection in non-Boussinesq fluids.And the results can provide a basis for explaining the non-linear flow and heat transfer of S-CO2. |
