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.

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.

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 Triangular Waves on Natural Convective Heat Transfer From an Upward Facing Heated Horizontal Isothermal Surface

2016 ◽  
Author(s):  
Patrick H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Prandtl Number ◽  
Surface Waves ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Heated Surface ◽  
Isothermal Surface

A numerical study of natural convective heat transfer from an upward facing, heated horizontal isothermal surface imbedded in a large flat adiabatic surface has been undertaken. On the heated surface is a series of triangular shaped waves. Laminar, transitional, and turbulent flow conditions have been considered. The flow has been assumed to be two-dimensional and steady. The fluid properties have been assumed constant except for the density change with temperature giving rise to the buoyancy forces. This was with treated using the Boussinesq approach. The numerical solution has been obtained using the commercial CFD solver ANSYS FLUENT©. The k-epsilon turbulence model with full account being taken of buoyancy force effects has been employed. The heat transfer rate from the heated surface expressed in terms of a Nusselt number is dependent on the Rayleigh number, the number of waves, the height of the waves relative to the width of the heated surface, and the Prandtl number. This study obtained results for a Prandtl number of 0.74 which is effectively the value for air. An investigation of the effect of the Rayleigh number, the dimensionless height of the surface waves, and the number of surface waves on the Nusselt number has been undertaken.

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.

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.

A Numerical Study of Three-Dimensional Natural Convective Heat Transfer From a Plate With a “Wavy” Surface

2001 ◽  
Author(s):  
Patrick H. Oosthuizen ◽  
Matt Garrett
Keyword(s):  
Heat Transfer ◽  
Prandtl Number ◽  
Surface Waves ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Three Dimensional ◽  
Wavy Surface ◽  
Surface Waviness ◽  
Dimensionless Amplitude ◽  
The Mean

Abstract Natural convective heat transfer from a wide isothermal plate which has a “wavy” surface, i.e., has a surface which periodically rises and falls, has been numerically studied. The surface waves run parallel to the direction of flow over the surface and have a relatively small amplitude. Two types of wavy surface have been considered here — saw-tooth and sinusoidal. Surfaces of the type considered are approximate models of situations that occur in certain window covering applications, for example, and are also sometimes used to try to enhance the heat transfer rate from the surface. The flow has been assumed to be laminar. Because the surface waves are parallel to the direction of flow, the flow over the surface will be three-dimensional. 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, the height of the surface being used as the characteristic length scale and the temperature difference between the surface temperature and the temperature of the fluid far from the plate being used as the characteristic temperature. The dimensionless equations have been solved using a finite-element method. Although the flow is three-dimensional because the surface waves are all assumed to have the same shape, the flow over each surface thus being the same, and it was only necessary to solve for the flow over one of the surface waves. The solution has the following parameters: the Grashof number based on the height, the Prandtl number, the dimensionless amplitude of the surface waviness, the dimensionless pitch of the surface waviness, and the form of the surface waviness (saw-tooth or sinusoidal). Results have been obtained for a Prandtl number of 0.7 for Grashof numbers up to 106. The effects of Grashof number, dimensionless amplitude and dimensionless pitch on the mean heat transfer rate have been studied. It is convenient to introduce two mean heat transfer rates, one based on the total surface area and the other based on the projected frontal area of the surface. A comparison of the values of these quantities gives a measure of the effectiveness of the surface waviness in increasing the mean heat transfer rate. The results show that while surface waviness increases the heat transfer rate based on the frontal area, the modifications of the flow produced by the surface waves are such that the increase in heat transfer rate is less than the increase in surface area.

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.

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.

Electric Field Effects on Natural Convection in Enclosures

1986 ◽  
Vol 108 (4) ◽  
pp. 749-754 ◽  
Author(s):  
D. A. Nelson ◽  
E. J. Shaughnessy
Keyword(s):  
Heat Transfer ◽  
Electric Field ◽  
Convective Heat Transfer ◽  
Heat Transfer Rate ◽  
Convective Heat ◽  
Transfer Rate ◽  
Stokes Equations ◽  
Experimental Studies ◽  
Navier Stokes ◽  
First Order Theory

The enhancement of convective heat transfer by an electric field is but one aspect of the complex thermoelectric phenomena which arise from the interaction of fluid dynamic and electric fields. Our current knowledge of this area is limited to a very few experimental studies. There has been no formal analysis of the basic coupling modes of the Navier–Stokes and Maxwell equations which are developed in the absence of any appreciable magnetic fields. Convective flows in enclosures are particularly sensitive because the limited fluid volumes, recirculation, and generally low velocities allow the relatively weak electric body force to exert a significant influence. In this work, the modes by which the Navier–Stokes equations are coupled to Maxwell’s equations of electrodynamics are reviewed. The conditions governing the most significant coupling modes (Coulombic forces, Joule heating, permittivity gradients) are then derived within the context of a first-order theory of electrohydrodynamics. Situations in which these couplings may have a profound effect on the convective heat transfer rate are postulated. The result is an organized framework for controlling the heat transfer rate in enclosures.

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