Numerical Study of the Effect of Cold Air Vent Flow on the Convective Heat Transfer Rate From a Hot Window Covered by a Top-Down, Bottom-Up Plane Blind System
In summer when the air-conditioning system is in use cool air from a floor-mounted vent located beneath a window often flows over the warm window. The presence of a blind system over the window will, in general, influence the effect of the vent flow on the convective heat transfer rate from the window. The effect of a Top-Down, Bottom-Up plane blind system and a cool air vent flow on the heat transfer rate from a recessed window has therefore been numerically studied here. The actual situation considered in this study is an approximate model of real situations. The window is represented by a plane isothermal section recessed into the wall, this window section being hotter than the room air far from the window. The floor-mounted vent is assumed to be located against the wall and to have a uniform discharge velocity which is normal to the vent surface. The flow has been assumed to be two-dimensional, i.e., the effect of the window and vent width has not been considered. The flow has been assumed to be steady and situations involving both laminar and turbulent flow have been considered. The fluid properties have been assumed constant except for the density change with temperature that gives rise to the buoyancy forces, this being dealt with using the Boussinesq approach. The governing equations have been solved using the commercial CFD code ANSYS FLUENT©, the k-epsilon turbulence model having been used. The solution has the following parameters: the Rayleigh number, the Reynolds number based on the vent discharge velocity, the dimensionless depth that the window is recessed, the Prandtl number, the dimensionless top and bottom blind opening, the dimensionless size of the air vent, and the dimensionless vent discharge temperature to undisturbed air temperature difference. Results have only been obtained for a Prandtl number of 0.74 and for fixed values of the dimensionless depth that the window is recessed, the dimensionless size of the air vent, and the dimensionless vent discharge temperature difference. The effects of the other dimensionless variables on the window Nusselt number have been numerically studied.