Natural Convection On A Vertical Wall With Neighboring Isothermal And Isoflux Heating

Natural convection on a vertical wall with neighboring isothermal and isoflux heating is present widely in nature.The effect of the coupling between isothermal and isoflux heating may induce various flows and heat transfer regimes,which is an interest in the society of fluid mechanics and heat transfer.Accordingly,it is of fundamental significance to study natural convection on such a vertical wall,which may further serve building energy saving.Natural convection is mainly affected by the Rayleigh number Ra_t defined by the isothermal zone,the Rayleigh number Raf defined by the isoflux zone,the Prandtl number and the height ratio.In this thesis,temporal and spatial evolutions of the flow structure are characterized using numerical simulation and experiment.Based on numerical results,heat transfer is quantified,and the periodic behavior of the oncoming flow is analyzed.The experimental method is used to verify the typical flow structure and periodic characteristics.Essential thesis contents and conclusions include:(1)Two-dimensional numerical results show that there exist different flows under the interaction between isothermal boundary layer and isoflux boundary layer,which are the isothermal upstream co-current flow,the isoflux upstream co-current flow,the oncoming flow and the back flow.With the changes of Ra_t and Raf,the thickness and velocity of the thermal boundary layer in each regime show different temporal and spatial distributions.(2)The intrusion from the isoflux boundary layer may significantly impact on heat transfer of nature convection particularly for the isoflux upstream co-current flow and the oncoming flow.When the isoflux heating is dominant(Raf is larger),the total heat transfer of natural convection can be reduced by 40%.(3)The oncoming flow is periodic in the specific parameter space.The dependence on the isothermal Rayleigh number Ra_t of the frequency and the Nusselt number Nu_t in fully developed stage are characterized.The full-field flow mode and periodic characteristic are obtained using dynamic mode decomposition.As the Rayleigh number increases,the coupling jet from the oncoming flow transitions from laminar to periodic and chaotic flows.(4)The experiment of the co-current flow and the oncoming flow in the case with an isoflux boundary upstream was performed.The periodic flow was observed,the boundary layer flow was characterized,and numerical results were verified.