An Experimental and Numerical Investigation of Mixed Convection in Rectangular Enclosures

Abstract

<p>The cooling of a hot surface by fluid motion has many applications in engineering. For<br />these mixed convective problems, the forced component of fluid motion may be in the direction<br />of the buoyancy vector or it may oppose the buoyancy force. In the present study, the opposing<br />mode is used to study the interaction of inertia and buoyancy forces in a fluid. Both numerical<br />and experimental techniques are used to study the flow in a rectangular cavity of aspect ratio 2.</p> <p>The inlet Reynolds number is varied between 800 and 1300 and the Grasbof number<br />based on the height of the enclosure is varied between 0 and 2.4 X 10¹⁰. The cases considered<br />correspond to Archimedes numbers of approximately 0, 1, 10 and 20.</p> <p>The flow field is observed qualitatively using laser induced fluorescence and a detailed<br />flow field is generated using a laser doppler anemometer. Temperature profiles are found using<br />fine wire thermocouple probes. These detailed measurements may provide a data base for the<br />verification of computer programs used to predict mixed convection as there are no such detailed<br />chita bases in the present literature.</p> <p>Numerical modelling is based on the SIMPLER algorithm with QUICK differencing. The<br />observed flow field indicated that some regions in the cavity were turbulent while other regions<br />were laminar. This observation suggests the necessity of a low Reynolds number turbulence<br />model. In this study, two forms of the low Reynolds number k-ε model are used. In addition,<br />the commercial computational fluid dynamics program, FLUENT, is used to predict the flow.</p> <p>Comparison of the experimental and computational results suggest that for isothermal and buoyancy dominated flow cases the computational modelling is adequate. Difficulties arise in the prediction of the intermediate Archimedes number cases as the predicted flow is dominated by<br />buoyancy while the experiments show more of a balance. Sources for this discrepancy are<br />discussed.</p>