Simulation Of Rayleigh-Bénard Convection In Heat And Mass Transfer Process

Rayleigh-Bénard convection is common in nature and engineering applications and has been extensively studied,often caused by the inhomogeneity of temperature field or concentration field.Heat and mass transfer process,especially their corresponding Rayleigh-Bénard convection process,has similarities to some extent.Some analytical methods and theories of Rayleigh-Bénard convection like entropy generation analysis widely used in heat transfer process,such as natural convection,are potential to solve some problems in interfacial mass transfer process.And this study provided a good example of this idea:entropy generation analysis was first introduced into Rayleigh-Bénard convection in interfacial mass transfer process with fresh insights obtained,which enlightens and updates the application of more new research perspectives or analytical methods into Rayleigh-Bénard convection in interfacial mass transfer process.In the study of Rayleigh-Bénard convection in heat transfer process,the reliability of dimensionless simulation of stable convection based on ANSYS Fluent was verified comprehensively by comparing with many literatures.And on this basis,the study of the effects of property variations on natural convection for low Prandtl number liquids in a square enclosure found that thermal conductivity had the greatest influence on local entropy generation rate,and the effects of property variations on average Nusselt number may augment or counteract each other.Finally,a general mathematical expression of average Nusselt number which is half theoretical and half empirical in nature was obtained through scale analysis and uniform experiment design.In the study of Rayleigh-Bénard convection in mass transfer process,interfacial Rayleigh-Bénard convection in CO₂-ethanol absorption system was simulated with primitive variables based on ANSYS Fluent.It was found that the new onset of convection cells greatly enhanced the mass transfer process.The entropy generation rate of two irreversible processes of Rayleigh-Bénard convection:mass transfer and viscous dissipation,was firstly obtained and analyzed from the perspective of non-equilibrium thermodynamics.The characteristic distributions of entropy generation rate due to mass transfer and friction in local liquid layer were found and their causes were analyzed.And the variation of global entropy generation rate due to mass transfer and friction with time showed different trends respectively before and after the onset of convection,corresponding to molecular diffusion-dominated phase and convection-dominated phase.Compared with pure diffusion,the onset of Rayleigh-Bénard convection changed the path of irreversible process to achieve mass transfer enhancement,embodied in the variation of global total entropy generation rate.The innovations of this paper contains three aspects.Firstly,entropy generation analysis was first introduced into Rayleigh-Bénard convection in interfacial mass transfer process,which provided a new perspective based on non-equilibrium thermodynamics.Secondly,the theory of heatfunction was promoted to natural convection in variable properties system,and momentum stream function on behalf of fluid flow was proposed to solve the limitation when applying stream function to compressible fluid.Thirdly,the reliability of dimensionless simulation based on ANSYS Fluent was verified,and initial attempts at nondimensionalization of variables related to Rayleigh-Bénard convection in interfacial mass transfer process were made,which laid the foundation of further dimensionless research.