A Numerical Study of the Convective Heat Transfer From the Inner Surface of a Recessed Window Covered by a Double-Layer Honeycomb Top Down-Bottom Up Blind

2016 ◽  
Author(s):  
Patrick H. Oosthuizen ◽  
Neda Mansouri
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Transfer Rate ◽  
Top Down ◽  
Bottom Up ◽  
Air Temperatures ◽  
Inner Surface ◽  
The Difference

The purpose of the present work was to investigate numerically the effect of the top and/or bottom blind openings on the convective heat transfer from a window fitted with a double-layered top down-bottom up honeycomb blind system. Top down-bottom up systems that utilize so-called honeycomb (or cellular) blinds can be opened at the top and/or the bottom. When a honeycomb blind is fully closed there are two or more vertical blind portions and a series of horizontal or nearly horizontal blind portions which join the vertical portions and form a column of cells. This gives the blind system its honeycomb or cellular structure. When opening a honeycomb blind the vertical portions of the blind bend or fold allowing the overall height of the blind to decrease. A double-layered honeycomb blind is constructed with three vertical blind portions and two columns of cells. A recessed window has been considered in the present study and only the convective heat transfer from the window to the surrounding room has been investigated. The surfaces of the blind are assumed to offer no resistance to heat transfer. The commercial CFD solver ANSYS FLUENT© has been used to obtain the solution. Over the range of parameters considered in this study, both laminar and turbulent flow can occur. The k-ε turbulence model has been used in obtaining the solutions. The convective heat transfer rate from the inner surface of the window, expressed in terms of a mean Nusselt number based on the window height and the difference between the window and the air temperatures, will depend on the Rayleigh number, also based on the window height, and the difference between the window and the air temperatures, the dimensionless top and bottom blind openings, and the dimensionless window recess depth. Variations of the mean Nusselt number with Rayleigh number for various values of these other parameters have been obtained and the results used to study how these other parameters affect the window heat transfer rate.

A Numerical Study of the Effect of an Irradiated Slatted Top Down – Bottom Up Blind on the Convective Heat Transfer Rate From a Recessed Window to an Adjacent Room

2012 ◽  
Author(s):  
Patrick H. Oosthuizen ◽  
J. T. Paul
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Heat Transfer Rate ◽  
Convective Heat ◽  
Transfer Rate ◽  
Numerical Study ◽  
Solar Irradiation ◽  
Radiant Heat Transfer ◽  
Top Down ◽  
Bottom Up

Top Down – Bottom Up blinds have become quite popular in recent times. However the effects of such blind systems on the convective heat transfer from the window to the surrounding room have not been extensively studied and the effect of solar irradiation of the blind on the window heat transfer has not received significant attention. The purpose of the present work was therefore to numerically investigate the effect of solar irradiation of Top Down – Bottom Up slatted blinds on this convective heat transfer. An approximate model of the window-blind system has been adopted. The solar radiation falling on the blinds is assumed to produce a uniform rate of heat generation in the blind. The Boussinesq approximation has been used. Radiant heat transfer effects have been neglected. Conditions under which laminar, transitional and turbulent flows occur have been considered. The main emphasis is on the effect of the magnitude of the irradiation and of the size of the blind openings at the top and bottom of the window on the convective heat transfer rate from the window to the room.

Effect of a Pair of Horizontal Frame Members on the Convective Heat Transfer With Laminar and Turbulent Flow From a Recessed Window to a Room

2011 ◽  
Author(s):  
Patrick H. Oosthuizen ◽  
David Naylor
Keyword(s):  
Heat Transfer ◽  
Prandtl Number ◽  
Convective Heat Transfer ◽  
Turbulent Flows ◽  
Heat Transfer Rate ◽  
Convective Heat ◽  
Transfer Rate ◽  
Numerical Study ◽  
Wall Functions ◽  
Inner Surface

The horizontal frame members that often protrude from the inner surface of a window can significantly effect the convective heat transfer rate from this inner surface to the room. The purpose of the present numerical study was to determine how the size of a pair of horizontal frame members effect this heat transfer rate. The flow has been assumed to be steady and conditions under which laminar, transitional, and turbulent flows occur are considered. 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 FLUENT commercial CFD code. The k-epsilon turbulence model with standard wall functions and with buoyancy force effects fully accounted for has been used. The solution has the following parameters: the Rayleigh number, the Prandtl number, the dimensionless window recess depth, and the dimensionless width and depth of the frame members. Results have been obtained for a Prandtl number of 0.74.

A Numerical Study of the Effect of a Horizontal Frame Member on the Laminar and Turbulent Natural Convective Heat Transfer From a Recessed Window to a Surrounding Room

2010 ◽  
Author(s):  
Patrick H. Oosthuizen ◽  
D. Naylor
Keyword(s):  
Heat Transfer ◽  
Prandtl Number ◽  
Convective Heat Transfer ◽  
Heat Transfer Rate ◽  
Convective Heat ◽  
Transfer Rate ◽  
Numerical Study ◽  
Horizontal Distance ◽  
Inner Surface ◽  
Frame Member

The vertical and horizontal frame members that often protrude from the inner surface of a window can, in some situations, have a significant effect on the convective heat transfer rate from the inner (room-side) surface of the window to the room. The purpose of the present numerical study was to determine, in a basic way, how the relative size of a single horizontal frame member mounted in the center of the window affects this convective heat transfer rate. A recessed window has been considered. The flow has been assumed to be steady and both laminar and turbulent flows have been considered. 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 FLUENT commercial cfd code. The k-epsilon turbulence model with standard wall functions and with buoyancy force effects fully accounted for has been used in the calculations. The solution has the following parameters: the Rayleigh number, the Prandtl number, the dimensionless horizontal distance between the inner window surface and the inner surface of the wall in which the window is mounted (the dimensionless recess depth), and the dimensionless width and depth of the frame member. Results have only been obtained for a Prandtl number of 0.74, which is effectively the value for air, and for single values of the dimensionless window recess depth and of the dimensionless frame height. The effects of the other dimensionless variables on the window Nusselt number have been numerically studied.

A Numerical Study of the Simultaneous Natural Convective Heat Transfer From the Upper and Lower Surfaces of a Thin Isothermal Horizontal Circular Plate

2016 ◽  
Author(s):  
Patrick H. Oosthuizen ◽  
Abdulrahim Kalendar
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Prandtl Number ◽  
Convective Heat Transfer ◽  
Heat Transfer Rate ◽  
Convective Heat ◽  
Transfer Rate ◽  
The Mean ◽  
Adiabatic Section

Natural convective heat transfer from the top and bottom surfaces of a thin circular isothermal horizontal plate which, in general, has a centrally placed adiabatic section has been numerically investigated. The temperature of the plate surfaces is higher than the temperature of the surrounding fluid. The range of conditions considered is such that laminar, transitional, and turbulent flow occurs over the plate. The heat transfer from the upper and lower surfaces of the plate as well as the mean heat transfer rate from the entire surface of the plate have been considered. The flow has been assumed to be axisymmetric and steady. The k-epsilon turbulence model with account being taken of buoyancy force effects has been used and the solution has been obtained using the commercial CFD solver ANSYS FLUENT©. The heat transfer rate from the heated plate has been expressed in terms of a Nusselt number based on the outside plate diameter and the difference between the plate temperature and the fluid temperature far from the plate. The mean Nusselt number is dependent on the Rayleigh number, the ratio of the diameter of the inner adiabatic section to the outer plate diameter, and the Prandtl number. Results have only been obtained for a Prandtl number of 0.74, i.e., effectively the value for air. The variations of the mean Nusselt number averaged over both the upper and lower surfaces and of the mean Nusselt numbers for the upper surface and for the lower surface with Rayleigh number for various adiabatic section diameter ratios have been studied. The use of a reference length scale to allow the correlation of these mean Nusselt number-Rayleigh number variations has been investigated.

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

2013 ◽  
Author(s):  
Patrick H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Prandtl Number ◽  
Convective Heat Transfer ◽  
Heat Transfer Rate ◽  
Convective Heat ◽  
Transfer Rate ◽  
Top Down ◽  
Discharge Velocity ◽  
Discharge Temperature ◽  
Air Vent

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.

Natural Convective Heat Transfer From an Isothermal Vertical Cylinder With an Exposed Upper Surface Mounted on a Flat Adiabatic Base

2007 ◽  
Author(s):  
Patrick H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Convective Heat Transfer ◽  
Heat Transfer Rate ◽  
Convective Heat ◽  
Transfer Rate ◽  
Vertical Cylinder ◽  
Curved Surface ◽  
Curvature Effects ◽  
The Mean

Natural convective heat transfer from an isothermal vertical cylinder which has an exposed horizontal top surface has been numerically studied. The exposed upper surface is maintained at the same temperature as the cylindrical vertical wall of the cylinder. The cylinder is mounted on a flat horizontal adiabatic base plate. In some circumstances the heat transfer rate from the exposed upper surface can be neglected compared to that from the curved surface of the cylinder and in some circumstances the heat transfer rate from the curved surface can be adequately predicted using vertical flat plate equations, i.e., by ignoring curvature effects. The flow has been assumed to be axisymetric about the vertical cylinder axis. The flow has also been assumed to be steady and laminar and it has been assumed that the fluid properties are constant except for the density change with temperature which gives rise to the buoyancy forces, this having been treated by using the Boussinesq approach. The solution has been obtained by numerically solving the governing equations, these equations being written in terms of dimensionless variables, the solution being obtained using a commercial finite element method based code, FIDAP. Because of the applications that motivated this study, results have only been obtained for Pr = 0.7. A wide range of the other governing parameters have been considered. The conditions under which the heat transfer from the exposed upper surface can be neglected compared to that from the cylindrical wall in the evaluation of the mean Nusselt number has been deduced and the conditions under which curvature effects can be ignored in evaluating the mean Nusselt number for the curved surface of the cylinder have been investigated.

scholarly journals A numerical study of free convective heat transfer in a double-glazed window with a between-pane Venetian blind

2021 ◽  
Author(s):  
Tony Avedissian
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Heat Transfer Rate ◽  
Convective Heat ◽  
Transfer Rate ◽  
Numerical Study ◽  
Thermal Conductivity Ratio ◽  
Number Range ◽  
Free Convective Heat Transfer ◽  
Venetian Blind

The free convective heat transfer in a double-glazed window with a between-pane Venetian blind has been studied numerically. The model geometry consists of a two-dimensional vertical cavity with a set of internal slats, centred between the glazings. Approximately 700 computational fluid dynamic solutions were conducted, including a grid sensitivity study. A wide set of geometrical and thermo-physical conditions was considered. Blind width to cavity width ratios of 0.5, 0.65, 0.8, and 0.9 were studied, along with three slat angles, 0º (fully open, +/- 45º (partially open), and 75º (closed). The blind to fluid thermal conductivity ratio was set to 15 and 4600. Cavity aspects of 20, 40, and 60, were examined over a Rayleigh number range of 10 to 10⁵, with the Prandtl number equal to 0.71. The resulting convective heat transfer data are presented in terms of average Nusselt numbers. Depending on the specific window/blind geometry, the solutions indicate that the blind can either reduce or enhance the convective heat transfer rate across the glazings. The present study does not consider radiation effects in the numerical solution. Therefore, a post-processing algorithm is presented that incorporates the convective and radiative influences, in order to determine the overall heat transfer rate across the window/blind system.

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