NATURAL CONVECTIVE FLOW IN AN INCLINED JOINED TWO ENCLOSURE ARRANGEMENT INVOLVING A HIGH ASPECT RATIO SIDE ENCLOSURE

摘要

Numerical study of natural convective flow in a joined two-enclosure arrangement, has been undertaken. In this arrangement, a heated wall kept at a uniform high temperature is contained in a high aspect ratio rectangular side enclosure. This enclosure is separated from a larger square enclosure by a dividing wall which is opposite to the heated wall and which is impermeable but offers no resistance to heat transfer. The wall of the main square enclosure that is opposite to the dividing wall between the enclosures is maintained at a uniform low temperature. All remaining walls in both enclosures are adiabatic. The situation considered is an approximate model of a window exposed to a hot outside environment and covered by a plane blind which, in turn, is exposed to cooled room. In the experimental evaluation of some such systems, the window is sometimes heated by exposure to the sun and the entire apparatus is inclined to the vertical to ensure that, the window is pointed at the sun at all times while measurements are being undertaken. In the assessment of the results obtained with such an apparatus, it is necessary to know the effect of the inclination on the heat transfer. This study was undertaken to provide some preliminary information on this effect. The flow has been assumed to be laminar and two-dimensional and fluid properties have been assumed constant except for the density change with temperature that gives rise to the buoyancy forces, this being treated by means of the Boussinesq type approximation. The governing equations have been written in dimensionless form and the resultant dimensionless equations have been solved using a finite-element method. Results have been obtained for a Prandtl number of 0.7. The effects of Raylcigh number, inclination angle and side enclosure aspect ratio on the Nusselt number have been investigated. The results show that for near vertical enclosures there is a minimum in the Nusselt number variation with side enclosure aspect ratio for a fixed Rayleigh number. However when the enclosure is inclined to the vertical, such a minimum may not occur. The inclination angle is also shown to have a strong effect on the heat transfer rate.