An Interaction of Natural Convective Heat Transfer From Two Adjacent Isothermal Narrow Vertical and Inclined Flat Plates

2009 ◽  
Author(s):  
Abdulrahim Kalendar ◽  
Patrick H. Oosthuizen ◽  
Bader Kalandar
Keyword(s):  
Heat Transfer ◽  
Prandtl Number ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Three Dimensional ◽  
Flat Plates ◽  
Plate Height ◽  
Fluid Properties ◽  
Adiabatic Surface ◽  
Plate Width

Natural convective heat transfer from a two narrow adjacent rectangular isothermal flat plates of the same size embedded in a plane adiabatic surface, the adiabatic surface being in the same plane as the surfaces of the heated plates, has been numerically investigated. The two plates have the same surface temperature and they are aligned with each other but are separated form each other by a relatively small gap. Results for the case where the plates are vertical and where they are inclined at positive or negative angles to the vertical have been obtained. 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 using the Boussinesq approach. It has also been assumed that the flow is symmetrical about the vertical center plane between the two plates. The solution has been obtained by numerically solving the full three-dimensional form of governing equations, these equations being written in dimensionless form. The solution was obtained using the commercial finite volume method based cfd code, FLUENT. The solution has the Rayleigh number, the dimensionless plate width, the angle of inclination, the dimensionless gap between two flat plates, and the Prandtl number as parameters. Results have only been obtained for a Prandtl number of 0.7 Results have been obtained for Rayleigh numbers between 103 and 107 for plate width-to-height ratios of between 0.15 and 0.6, for gap between the adjacent edges to plate height ratios of between 0 and 0.2, for angles of inclination between +45° and −45°.

Correlation Equations for Natural Convective Heat Transfer From Two Inclined Vertically Spaced Narrow Isothermal Flat Plates

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Abdulrahim Kalendar ◽  
Ahmed Kalendar ◽  
Sayed Karar ◽  
Patrick H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Edge Effect ◽  
Transfer Rate ◽  
Three Dimensional ◽  
Primary Objective ◽  
Flat Plates ◽  
Plate Height ◽  
Adiabatic Surface ◽  
Plate Width

Natural convective flow over narrow plates induces an inward flow near the edges of the plate causing the flow to be three-dimensional near the edges of the plate. This influences the heat transfer rate near the edges of the plate and is referred to as the edge effect. The primary objective of this paper is to numerically study this edge effect and the interaction of the flows over two inclined vertically separated narrow heated plates of the same size embedded in a plane adiabatic surface. The cases where the plates and surrounding adiabatic surface are inclined at positive or negative angles to the vertical have been considered. Results were obtained by numerically solving the full three-dimensional form of governing equations using the commercial finite volume based software Fluent©. Results have only been obtained for a Prandtl number of 0.7; this being the value existing in the application which involved airflow that originally motivated this study. The results presented here cover Rayleigh numbers between 103 and 107, at all values of W considered, plate width-to-height ratios between 0.2 and 1.2, gap, at all values of W considered, to the plate height ratios of between 0 and 1.5, and, at all values of W considered, angles of inclination of between −45 deg and +45 deg. The effects of the Rayleigh number, dimensionless plate width, dimensionless gap between plates, and inclination angle on the heat transfer rate have been studied in detail. Empirical correlations defining the effect of these parameters on the heat transfer rate have been derived.

Effect of Edge Conditions on Natural Convective Heat Transfer From a Narrow Vertical Flat Plate With a Uniform Surface Heat Flux

2007 ◽  
Author(s):  
Patrick H. Oosthuizen ◽  
Jane T. Paul
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Surface Heat Flux ◽  
Three Dimensional ◽  
Surface Heat ◽  
Heated Plate ◽  
Two Dimensional ◽  
Adiabatic Surface

Two-dimensional natural convective heat transfer from vertical plates has been extensively studied. However, when the width of the plate is relatively small compared to its height, the heat transfer rate can be greater than that predicted by these two-dimensional flow results. Because situations that can be approximately modelled as narrow vertical plates occur in a number of practical situations, there exists a need to be able to predict heat transfer rates from such narrow plates. Attention has here been given to a plate with a uniform surface heat flux. The magnitude of the edge effects will, in general, depend on the boundary conditions existing near the edge of the plate. To examine this effect, two situations have been considered. In one, the heated plate is imbedded in a large plane adiabatic surface, the surfaces of the heated plane and the adiabatic surface being in the same plane while in the second there are plane adiabatic surfaces above and below the heated plate but the edge of the plate is directly exposed to the surrounding fluid. The flow has 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. It has also been assumed that the flow is symmetrical about the vertical centre-plane of the plate. The solution has been obtained by numerically solving the full three-dimensional form of the governing equations, these equations being written in terms of dimensionless variables. Results have only been obtained for a Prandtl number of 0.7. A wide range of the other governing parameters have been considered for both edge situations and the conditions under which three dimensional flow effects can be neglected have been deduced.

Natural Convective Heat Transfer From a Horizontal Rectangular Isothermal Element Imbedded in a Plane Adiabatic Surface With a Parallel Adiabatic Covering Surface

2014 ◽  
Author(s):  
Patrick H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Turbulent Flows ◽  
Convective Heat ◽  
Ansys Fluent ◽  
Covering Surface ◽  
Fluid Properties ◽  
Rectangular Element ◽  
Adiabatic Surface ◽  
Heated Element

Natural convective heat transfer from a horizontal flat rectangular isothermal heated element imbedded in a flat rectangular adiabatic surface has been numerically studied. The surface of the heated rectangular element is in the same plane as the surface of the surrounding adiabatic material. A rectangular flat horizontal adiabatic surface is mounted parallel to and at a relatively short distance from the heated element. The heated element is facing upwards with the covering surface above the element. For the conditions considered laminar, transitional, and turbulent flows can occur. The flow has been assumed to be steady. Constant fluid properties have been assumed except for the density change with temperature which gives rise to the buoyancy forces. This was dealt with using the Boussinesq approach. To obtain the solution, the commercial CFD solver ANSYS FLUENT© was used to numerically solve the governing equations. The k-epsilon turbulence model was employed with account being taken of buoyancy force effects. The effects of the dimensionless distance of the rectangular covering surface from the heated rectangular element and of the ratio of the side lengths of the rectangular element on the variation of the Nusselt number with Rayleigh number have been examined.

scholarly journals Natural Convective Heat Transfer From the Horizontal Isothermal Surface of Polygons of Octagonal and Hexagonal Shapes

2019 ◽  
Vol 11 (5) ◽  
Author(s):  
Ahmad Kalendar ◽  
Abdulrahim Kalendar ◽  
Yousuf Alhendal ◽  
Sayed Karar ◽  
Adel Alenzi ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Prandtl Number ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Surface Shape ◽  
Aspect Ratios ◽  
Complex Shapes ◽  
The Mean ◽  
Adiabatic Surface ◽  
Rayleigh Numbers

Heat transfer often occurs effectively from horizontal elements of relatively complex shapes in natural convective cooling of electronic and electrical devices used in industrial applications. The effect of complex surface shapes on laminar natural convective heat transfer from horizontal isothermal polygons of hexagonal and octagonal flat surfaces facing upward and downward of different aspect ratios has been numerically investigated. The polygons’ surface is embedded in a large surrounding plane adiabatic surface, where the adiabatic surface is in the same plane as the surface of the heated element. For the Boussinesq approach used in this work, the density of the fluid varies with temperature, which causes the buoyancy force, while other fluid properties are assumed constants. The numerical solution of the full three-dimensional form of governing equations is obtained by using the finite volume method-based computational fluid dynamics (CFD) code, FLUENT14.5. The solution parameters include surface shape, dimensionless surface width, different characteristic lengths, the Rayleigh number, and the Prandtl number. These parameters are considered as follows: the Prandtl number is 0.7, the Rayleigh numbers are between 103 and 108, and for various surface shapes the width-to-height ratios are between 0 and 1. The effect of different characteristic lengths has been investigated in defining the Nusselt and Rayleigh numbers for such complex shapes. The effect of these parameters on the mean Nusselt number has been studied, and correlation equations for the mean heat transfer rate have been derived.

Natural Convective Heat Transfer From an Inclined Narrow Isothermal Flat Plate

2008 ◽  
Author(s):  
Patrick H. Oosthuizen ◽  
Abdulrahim Kalendar
Keyword(s):  
Heat Transfer ◽  
Prandtl Number ◽  
Flat Plate ◽  
Convective Heat Transfer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Two Dimensional ◽  
Two Dimensional Flow ◽  
Adiabatic Surface ◽  
Plate Width

Natural convective heat transfer rate from an isothermal flat plate inclined at moderate angles to the vertical has been numerically studied. When the plate is wide compared to its height the flow can be adequately modeled by assuming two-dimensional flow. However, when the width of the plate is relatively small compared to its height, the heat transfer rate can be considerably greater than that predicted by these two-dimensional flow results. The heat transfer from a narrow isothermal plate embedded in a plane adiabatic surface, the adiabatic surface being in the same plane as the heated plate and inclined at an angle to the vertical has been numerically considered. Results for both positive and negative inclination angles have been numerically determined here. Attention was restricted to results for a Prandtl number of 0.7; this being approximately the value existing in the application that originally motivated this study. 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. It has also been assumed that the flow is symmetrical about the vertical centre-plane of the plate. The solution has been obtained by numerically solving the full three-dimensional form of the governing equations, these equations being written in dimensionless form. The solution was obtained using a commercial finite element method based code, FIDAP. The solution has the Rayleigh number, the dimensionless plate width, the angle of inclination, and the Prandtl number as parameters. Results have been obtained for Rayleigh numbers between 103 and 107 for ratios of the plate width to the plate height of between 0.3 and 1.5 and for angles of inclination between +45° and −45°.

Three-Dimensional Numerical Modeling of Convective Heat Transfer During Shallow-Depth Forced-Air Drying of Brown Rice Grains

2015 ◽  
Vol 33 (11) ◽  
pp. 1350-1359 ◽  
Author(s):  
Jonathan H. Perez ◽  
Fumina Tanaka ◽  
Fumihiko Tanaka ◽  
Daisuke Hamanaka ◽  
Toshitaka Uchino
Keyword(s):  
Heat Transfer ◽  
Numerical Modeling ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Three Dimensional ◽  
Brown Rice ◽  
Shallow Depth ◽  
Air Drying ◽  
Rice Grains ◽  
Forced Air

A Study of Three-Dimensional Mixed Convective Heat Transfer From Short Vertical Cylinders in a Horizontal Forced Flow

2000 ◽  
Author(s):  
David A. Scott ◽  
P. H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Three Dimensional ◽  
Forced Flow ◽  
Low Velocity ◽  
Buoyancy Forces ◽  
The Mean ◽  
Mixed Convective Flow ◽  
Comparison Of The Results

Abstract Heat transfer from relatively short vertical isothermal cylinders in a horizontal forced fluid flow has been considered. The flow conditions are such that the buoyancy forces resulting from the temperature differences in the flow are in general significant despite of the presence of a horizontal forced flow of air, that is, mixed convective flow exists. Because the cylinders are short and the buoyancy forces act normal to the forced flow, three-dimensional flow exists. The experiments were performed in a low velocity, open jet wind tunnel. The study involved the experimental determination of the mean heat transfer coefficient and a comparison of the results with a previous numerical analysis. Mean heat transfer rates were determined using the ‘lumped capacity’ method. The mean Nusselt number has the Reynolds number, Grashof number and the height to diameter ratio of the cylinders as parameters. The results have been used to determine the conditions under which the flow departs from purely forced convection and enters the mixed convection regime, i.e., determining the conditions for which the buoyancy effects should be included in convective heat transfer calculations for short cylinders.

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