Flows And Heat Transfer In A Differentially Heated Finned Cavity

A differentially heated finned cavity is widely present in industrial systems such as heat exchanger,solar collector and building design due to its easy design and controlling heat transfer.Accordingly,many investigators in the society of fluid mechanics and heat transfer have paid attention into natural convection flows in the finned cavity.A literature review shows that a great number of numerical simulations and experiments of natural convection flows in the finned cavity have been performed and considerable results have been obtained.However,less attention was paid into the dynamics of natural convection flows in the finned cavity,which thus becomes the motivation of the thesis.Based on the aim of the thesis,scaling analysis and numerical simulation are employed to investigate the dynamics and heat transfer of natural convection flows in the finned cavity isothermally and evenly heated.Possible flow regimes,dynamics and heat transfer dominances and scaling relations are discussed,which are determined by time,the Rayleigh number(Ra),Prandtl number(Pr)and the fin position(or some of them).Selected scaling relations are compared with numerical results.Further,the critical Rayleigh number of the transition to unsteady flows and the dependence of heat and mass transfer on governing parameters are obtained.The main results of the thesis involve:(1)It has been demonstrated that the critical power of time of the flow rate is 2 in the transition between different dynamics dominances for the plume in the finned cavity with a uniform heat flux.The new flow regime of the plume is found and the scaling relations of the intrusion and the plume are obtained and validated.(2)It has been found that the dynamics of the intrusion and the plume are dependent on the fin position in the isothermally heated finned cavity.The scaling relations of the intrusion and the plume depend on time,the fin position,the Rayleigh number and the Prandtl number and are verified by numerical results.(3)The critical Rayleigh number of the transition to an unsteady state of natural convection flows,which is dependent on the Prandtl number,is obtained after a number of numerical tests.The dependence of heat and mass transfer on the Rayleigh number and the Prandtl number is quantified in the comparison between the cases with isothermal and evenly heating.(4)Based on numerical results,the dependence of heat and mass transfer on the fin position is quantified and the optimal position of the fin enhancing heat transfer is presented.The results in the thesis can be applied for industrial design and increase the knowledge in fluid mechanics and heat transfer,in particular about the dynamics and heat transfer of the intrusion and the plume.Further,it is worth noting that validation by the field measurement and understanding of equation conditions are able to gruantee reliability and precision of industrial design.