Natural Convection In A Differentially Heated Partitioned Cavity Filled With Air

Natural convection driven by a temperature difference is extensively present in nature and industry, and thus the corresponding study is an important part of fluid dynamics. As an idealized model for analyzing natural convection driven by the temperature difference, natural convection in a differentially heated partitioned cavity can show various phenomena in industry, which has been therefore received extensive concern. One of the studies of natural convection in a differentially heated partitioned cavity is to determine the factors which impact on the flow and heat transfer. The previous studies have determined three dimensionless parameters which govern the flow and heat transfer in the cavity, namely the Rayleigh numbers, the aspect ratio and the Prandtl number, and have shown of transient features during the flow development. However, the flow development with the Rayleigh number and the aspect ratio for a small Prandt1number is rarely discussed, especially when the Rayleigh number and the aspect ratio change in a large scale. Accordingly, for the purpose of further understanding the flow phenomenon, the study of this thesis is mainly aimed at the impact of the Rayleigh number and the aspect ratio on natural convection in a differentially heated partitioned cavity.A great number of2D numerical simulations of natural convection in the partitioned cavity over a wide range of the Rayleigh numbers1x105≤Ra≤1×1011and the aspect ratio0.2≤A≤4have been performed using the finite element method. It has showed that the Rayleigh number is the most important factor which governs the flow and heat transfer. For the low Rayleigh number such as Ra＝1×105, the development of natural convection is smooth and the boundary flow is very weak. The flow development undergoes two main stages. At the initial stage, isotherms adjacent to the partition remain vertical distribution and parallel to the partition. At the steady stage, the air intrusion flow moves along the horizontal boundary and fills the core area directly. The flow development undergoes three main stages for high Rayleigh numbers, which are initial stage, transitional stage and steady stage or quasi-steady stage. The flow becomes strong as the Rayleigh number increases, and the transient features are clear which may lead to larger heat transfer. As the Rayleigh number reaches Ra=1×1011, the coupled thermal boundary layer may become unsteady. The impact of the aspect ratio on the flow and heat transfer is weak and different for different Rayleigh numbers. For low Rayleigh numbers, natural convection is clearer and will take more time to approach a steady stage as the aspect ratio reduces. For a high Rayleigh number, the aspect ratio will impact on instability of the thermal boundary layer. The thermal boundary may be oscillatory as the aspect ratio increases further. The heat transfer is also enhanced.