Convective Heat Transfer from a Recessed Window Covered By a Top Down – Bottom Up Single-Layer Honeycomb Blind
Mansouri Birjandi, Neda
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Honeycomb (or cellular) Top Down–Bottom Up blinds are quite widely available. When this type of blind is closed there are two or more vertical blind portions and a series of horizontal or near-horizontal blind portions joining the vertical portions forming a series of cells. When such a blind is open the vertical portions of the blind bend decreasing the blind height. A honeycomb blind with a single column of cells in two different shapes was considered in the present study. Results have also been obtained for a Top Down-Bottom Up plane blind for comparative purposes. The effect of the dimensionless top and bottom blind openings, shape of the blind and dimensionless window recess depth on the convective heat transfer from a window to the surrounding room was numerically investigated. The case where the window is at a higher temperature than room was considered. Laminar and turbulent flow can occur over the window system for the conditions considered in this work. The numerical results were obtained using the commercial CFD finite-volume based solver FLUENT© and using the standard k-epsilon turbulence model. Some experimental tests were undertaken for a window-blind system with plane blind to validate the numerical results obtained in this work. From the results of this study it is concluded that when the blind is fully closed the mean window heat transfer rate for a case where a honeycomb blind is used is less than that for the case where a plane blind is used. However when the blind is partially open, the heat transfer rate from a window-blind system with a honeycomb blind is higher than it is for the case where a plane blind is used at high Rayleigh numbers considered. When the blind is partially open, increasing the dimensionless top blind opening or decreasing the dimensionless bottom blind opening increases the mean window Nusselt number at the higher Rayleigh numbers considered. The results indicate that the effect of the dimensionless window recess depth on the mean window Nusselt number is different in each flow regime i.e. with laminar, transitional and turbulent flow.