A Numerical Study of Natural Convective Heat Transfer From Isothermal High Aspect Ratio Rectangular Cylinders

2013 ◽  
Author(s):  
Patrick H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Prandtl Number ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Width Ratio ◽  
Heated Cylinder ◽  
Aspect Ratios ◽  
Study Results ◽  
Rectangular Cylinders

Natural convective heat transfer from isothermal rectangular cylinders which have an exposed upper surface has been numerically studied. The cylinders considered have high aspect ratios, i.e., have high width-to-depth ratios, and are relatively short, i.e., have a “height” that is of the same order of magnitude as their width. The cylinders considered are mounted on a plane adiabatic base, the cylinders being normal to the plane base with the cylinders pointing either vertically upwards or vertically downwards. One of the main aims of the present work was to numerically determine how the depth-to-width ratio of the rectangular cylinder influences the mean heat transfer rate from the cylinder when this depth-to-width ratio is large. 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 using the commercial CFD solver, ANSYS FLUENT©. The solution is dependent on the Rayleigh number, the ratio of the width to the height of the heated cylinder, the ratio of the width to the depth of the heated cylinder, the Prandtl number, Pr, and on whether the cylinder is pointing vertically upwards or vertically downwards. Because of the applications that motivated this study, results have only been obtained for a Prandtl number of 0.74, i.e., effectively the value for air. A range of the other governing parameters has been considered and the effects of these governing parameters on the Nusselt number variation have been examined.

A Numerical Study of Assisting and Opposing Mixed Convective Heat Transfer From a Horizontal Isothermal High Aspect Ratio Rectangular Cylinder

2012 ◽  
Author(s):  
Patrick H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Rectangular Cross Section ◽  
Boussinesq Approximation ◽  
Forced Flow ◽  
Width Ratio ◽  
Flow Conditions ◽  
Rectangular Cylinder

Mixed convective heat transfer from an isothermal cylinder with a rectangular cross-section and a relatively large height-to-width ratio has been numerically studied. The axis of the cylinder is horizontal with the longer sides of the rectangular cylinder being vertical. There is a vertical forced flow over the cylinder. The flow conditions considered are such that in general mixed forced and natural convective flow exists. Both the case where the buoyancy forces act in the same direction as the forced flow (assisting flow) and the case where they act in the opposite direction to the forced flow (opposing flow) have been considered. The flow has been assumed to be two-dimensional and the Boussinesq approximation has been adopted. Attention has been restricted to the flow of air and results have therefore been obtained for a Prandtl number of 0.74. The flow conditions considered are such that laminar or turbulent flow can exist. The main attention is this work has been directed at determining the effect of the flow parameters on the mean heat transfer rate from the cylinder and on determining the conditions under which the flow can be assumed to be forced convective and under which it can be assumed to be natural convective.

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 Natural Convective Heat Transfer From Two-Sided Inclined Square Plates Having a Finite Thickness

2019 ◽  
Author(s):  
Rafiq Manna ◽  
Patrick H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Finite Thickness ◽  
Plate Thickness ◽  
Side Surface ◽  
Bottom Surface ◽  
Study Results ◽  
Inclination Angles

Abstract Simultaneous natural convective heat transfer from the top, bottom and side surfaces of two-sided inclined square plates having various thicknesses has been numerically investigated. The aim of this work is to determine whether the plate thickness has a significant influence on the heat transfer rates from the plate surfaces when the plate is inclined to the horizontal and to determine how the heat transfer rate varies with this angle of inclination. The upper, lower and side surfaces of the plate have been assumed to be isothermal and at the same temperature which is higher than that of the surrounding fluid. The range of conditions considered is such that laminar, transitional, and turbulent flow occur over the plate. The numerical solution has been obtained using the commercial CFD solver ANSYS FLUENT©. In this study, results have only been obtained for the case where the plate is exposed to air. Inclination angles of between 0 and 40 degrees from the horizontal and plate dimensionless thicknesses (thickness-to-side length ratios) of between 0 and 0.3 have been considered. Variations of the mean Nusselt number with Rayleigh number for the top surface, bottom surface, side surface and that averaged over all heated surfaces of the plate for various inclination angles and for various plate dimensionless thicknesses have been obtained.

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.

A Numerical Study of Natural Convective Heat Transfer From an Inclined Isothermal Plate Having a Square Wave Surface

2011 ◽  
Author(s):  
Patrick H. Oosthuizen ◽  
Jane T. Paul
Keyword(s):  
Heat Transfer ◽  
Prandtl Number ◽  
Surface Waves ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Boussinesq Approximation ◽  
Heated Plate ◽  
Governing Equations ◽  
Cross Sectional

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 in the horizontal direction, i.e., are normal to the direction of flow over the surface, and have relatively small amplitude. Attention has been restricted to the case where the waves have a rectangular cross-sectional shape. The plate is, in general, inclined to the vertical, consideration only being given to inclination angles at which the heated plate is facing upwards. The range of Rayleigh numbers considered extends from values that for a non-wavy vertical plate would be associated with laminar flow to values that would be associated with fully turbulent flow. The flow has been assumed to be steady and 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 approximation. The Reynolds averaged governing equations in conjunction with a standard k-epsilon turbulence model with buoyancy force effects fully accounted for have been used in obtaining the solution. The governing equations have been solved using the commercial cfd code FLUENT. The solution has the following parameters: (i) the Rayleigh number based on the height of the heated plate, (ii) the Prandtl number, (iii) the ratios of the amplitude of the surface waviness and of the pitch of the surface waves to the height of the plate, and (iv) the angle of inclination of the plate to the vertical. Results have only been obtained for a Prandtl number of 0.74. The effects of the other dimensionless variables on the mean surface Nusselt number have been numerically studied.

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.

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