NATURAL CONVECTION IN A RECTANGULAR CAVITY DRIVEN BY COMBINED BUOYANCY FORCES
Abstract
The objective of this study was to obtain an understanding of the flow, heat and mass transfer processes in a rectangular cavity. In a gravity field the simultaneous temperature and concentration differences lead to buoyancy driven convection. To this end, an analytical and numerical study of the problem was conducted. The study is concerned with the development of a model to predict the velocity, temperature and species distributions inside a two-dimensional, rectangular cavity filled with a binary gas. The transport equations of mass, species, momentum and energy are formulated in dimensionless form and are solved numerically. The work examines the transient and steady behavior of the flow structure as well as the total heat and mass transfer through the cavity. In addition consideration is given to the effect of the variation of thermophysical properties with temperature and mass fraction, including the Soret and Dufour effects. The predicted results have been tested extensively by comparison with well established benchmark solutions for the limiting case of pure thermal convection in cavities as well as other results available in the literature. A sensitivity study of the relevant dimensionless parameters was then performed to gain an understanding of the fundamental phenomena involved. The results show that the heat and mass transport through the cavity is enhanced when the buoyancy forces due to temperature and concentration are augmenting one another for the stability parameter N < 0 as well as for the opposing cases when N > 2. Close to N = 1, flow reversal takes place for all of the ranges of the parameters considered here. It was also found that the local Nusselt numbers and the local wall velocities are proportional to one another for all the cases considered. The concentration parameter (GAMMA) had a significant effect on the wall velocities but a relatively small effect on the heat transfer. Multicellular flow structures have been predicted for the low Prandtl number mixtures, and the reasons for their formation have been discussed. The thermophysical property variation with temperature is shown to be significant, especially when the temperature gradients across the cavity are large. Results based on constant thermophysical properties in general yield higher heat and mass transport through the cavity. The inclusion of Soret and Dufour effects indicates that both the heat and mass transport are reduced for the ranges of parameters considered.
Degree
Ph.D.
Subject Area
Mechanical engineering
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