Numerical heat transfer in a cavity with a solar control coating depositedto a vertical semitransparent wall

A transient two-dimensional computational model of combined natural convect ion, conduction, and radiation in a cavity with an aspect ratio of one, con taining air as a laminar and non-participating fluid, is presented. The cav ity has two opaque adiabatic horizontal walls, one opaque isothermal vertic al wall, and an opposite semitransparent wall, which consists of a 6-mm gla ss sheet with a solar control coating of SnS-CuxS facing the cavity. The se mitransparent wall also exchanges heat by convection and radiation from its external surface to the surroundings and allows solar radiation pass throu gh into the interior of the cavity. The momentum and energy equations in th e transient state were solved by finite differences using the alternating d irection implicit (ADI) technique. The transient conduction equation and th e radiative energy flux boundary conditions are coupled to these equations. The results in this paper are limited to the following conditions: 10(4) l ess than or equal to Gr less than or equal to 10(6), an isothermal vertical cold wall of 21 degreesC, outside air temperatures in the range 30 degrees C less than or equal to T-o less than or equal to 40 degreesC and incident solar radiation of AM2 (750 Wm(-2)) normal to the semitransparent wall. The model allows calculation of the redistribution of the absorbed component o f solar radiation to the inside and outside of the cavity. The influences o f the time step and mesh size were considered. Using arguments of energy ba lance in the cavity, it was found that the percentage difference was less t han 4 per cent, showing a possible total numerical error less than this num ber. For Gr = 10(6) a wave appeared in the upper side of the cavity, sugges ting the influence of the boundary walls over the air flow inside the cavit y. A Nusselt number correlation as a function of the Rayleigh number is pre sented. Copyright (C) 2000 John Wiley & Sons, Ltd.