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Abdulrahim Kalendar

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Journal Articles

Article Type: Research-Article

*. October 2019, 11(5): 051009.*

*J. Thermal Sci. Eng. Appl*Paper No: TSEA-18-1599

Published Online: March 27, 2019

Abstract

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 10 3 and 10 8 , 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.

Proceedings Papers

*Proc. ASME*. IMECE2016, Volume 8: Heat Transfer and Thermal Engineering, V008T10A030, November 11–17, 2016

Paper No: IMECE2016-65540

Abstract

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.

Journal Articles

Journal: Journal of Heat Transfer

Article Type: Research-Article

*. May 2015, 137(5): 052501.*

*J. Heat Transfer*Paper No: HT-14-1123

Published Online: May 1, 2015

Abstract

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.

Proceedings Papers

*Proc. ASME*. IHTC14, 2010 14th International Heat Transfer Conference, Volume 7, 113-120, August 8–13, 2010

Paper No: IHTC14-22846

Abstract

Natural convective heat transfer rates from inclined cylinders with a square cross-section and which has an exposed top surface have been experimentally studied. When relatively small square cylinders with exposed top surfaces inclined at an angle to the vertical are used, the inclination angle to the vertical has, in general, a considerable effect on the magnitude of the mean heat transfer rate and on the nature of the flow over the surfaces that make up the cylinder. In the situation here considered the cylinder is mounted on a large flat essentially adiabatic surface with the other cylinder surfaces exposed to the surrounding air and with the cylinder, in general, inclined to the vertical at angles between vertically upwards and vertically downwards. The situation considered is an approximate model of that which occurs in some electrical and electronic component cooling problems. The cross-sectional size-to-height ratio of the square cylinders used in the present study was comparatively small, i.e. the square cylinders were short, the width, w , of the square cylinders being 25.4 mm and the width-to-height ratios of between 1 and 0.25 being used. One of the main aims of the present work was to determine how the cross-sectional size-to-height ratio of the square cylinder, i.e., w/h , influences the mean heat transfer rate from the cylinder at various angles of inclination between vertically upwards and vertically downwards. The heat transfer rates were determined by the transient method, this basically involving heating the model and then measuring its temperature-time variation while it cooled, the tests being carried out inside a large enclosure. Tests were carried out in air with all models at various angles of inclination to the vertical between vertically upwards and vertically downwards. The effects of w/h , Rayleigh number, Ra , and angle of inclination, φ , on the mean Nusselt number, Nu for the entire cylinder have thus been studied. The Rayleigh number, Ra , based on the cylinder height, h , was between approximately 1E4 and 5E6. The experimental results have been compared with the results obtained in an earlier numerical study.

Proceedings Papers

*Proc. ASME*. IMECE2009, Volume 9: Heat Transfer, Fluid Flows, and Thermal Systems, Parts A, B and C, 1973-1982, November 13–19, 2009

Paper No: IMECE2009-12777

Abstract

Natural convective heat transfer from an inclined isothermal cylinder with a circular cross-section and which has an exposed “top” surface has been numerically studied. The cylinder is mounted on a flat adiabatic base plate, the cylinder being normal to the base plate. The situation considered is an approximate model of that which occurs in some electrical and electronic component cooling problems. One of the main aims of the present work was to determine how the diameter-to-height ratio of the cylinder, i.e., D/h , influences the mean heat transfer rate from the cylinder at various angles of inclination between vertically upwards and vertically downwards. 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. The solution has been obtained by numerically solving the governing equations, these equations being written in terms of dimensionless variables. These dimensionless governing equations, subject to the boundary conditions, have been solved using the commercial cfd solver, FLUENT. The flow has been assumed to be symmetrical about the vertical center-plane through the cylinder. The solution has been used to derive the values of the mean Nusselt number for the cylinder. The solution has the following parameters: the Rayleigh number, Ra , based on the cylinder height and the cylinder surface to fluid temperature difference; the dimensionless cylinder diameter, i.e., the ratio of the diameter to the height of the heated cylinder; the Prandtl number, Pr; and the angle of inclination of the cylinder relative to the vertical, φ . Because of the applications that motivated this study, results have only been obtained for Pr = 0.7. Values of φ between 0° and 180° and a wide range of Ra and D h values have been considered. The effects of D h , Ra , and φ on the mean Nusselt number for the entire cylinder and for the mean Nusselt numbers for the cylinder side wall and the exposed “top” surfaces have been examined.

Proceedings Papers

*Proc. ASME*. HT2009, Volume 2: Theory and Fundamental Research; Aerospace Heat Transfer; Gas Turbine Heat Transfer; Computational Heat Transfer, 115-122, July 19–23, 2009

Paper No: HT2009-88094

Abstract

Natural convective heat transfer from an isothermal inclined cylinder with a square cross-section and which has an exposed top surface and is, in general, at an angle to the vertical has been numerically studied. The cylinder is mounted on a flat adiabatic base plate, the cylinder being normal to the base plate. The situation considered is an approximate model of that which occurs in some electrical and electronic component cooling problems. 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. The solution has been obtained by numerically solving the governing equations, these equations being written in terms of dimensionless variables using the height, h , of the cylinder as the length scale and T w – T F as the temperature scale, T F being the undisturbed fluid temperature far from the cylinder and T w being the uniform surface temperature of the cylinder. These dimensionless governing equations subject to the boundary conditions have been solved using the commercial cfd solver, FLUENT. The flow has been assumed to be symmetrical about the vertical center-plane through the cylinder. The solution has been used to derive the values of the mean Nusselt number for the cylinder, Nu . The solution has the following parameters: the Rayleigh number, Ra , the dimensionless cylinder width, i.e., the ratio of the width to the height of the heated cylinder, W = w/h , the Prandtl number, Pr , and the angle of inclination of the cylinder relative to the vertical, φ . Results have only been obtained for Pr = 0.7. Values of φ between 0° and 180° and a wide range of Ra and W have been considered. The effects of W , Ra , and φ on the mean Nusselt number, Nu , for the entire cylinder and for the mean Nusselt numbers for the various surfaces that make up the cylinder have been examined.

Proceedings Papers

*Proc. ASME*. HT2009, Volume 2: Theory and Fundamental Research; Aerospace Heat Transfer; Gas Turbine Heat Transfer; Computational Heat Transfer, 97-105, July 19–23, 2009

Paper No: HT2009-88091

Abstract

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 10 3 and 10 7 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°.

Proceedings Papers

*Proc. ASME*. HT2008, Heat Transfer: Volume 1, 491-497, August 10–14, 2008

Paper No: HT2008-56024

Abstract

Three-dimensional natural convective flow in a rectangular enclosure with vertical sidewalls and horizontal top and bottom surfaces has been considered. A heated rectangular element is mounted in the middle of one vertical wall of the enclosure, the remainder of this wall being adiabatic. The remaining vertical walls are cooled to a uniform low temperature. The horizontal top and bottom walls are adiabatic. The flow has been assumed to be steady and laminar. Fluid properties have been assumed constant except for the density change with temperature that gives rise to the buoyancy forces. Radiation effects have been neglected. The numerical solution was obtained using the governing equations written in terms of dimensionless variables. The enclosure height, H ′ , was used as the characteristic length scale and the difference between the temperatures of the hot wall section and the cooled walls were used as the characteristic temperature scale. The dimensionless governing equations have been solved using FIDAP, a commercial software package that employs the finite element method. The solution has the following parameters: the Rayleigh number, the Prandtl number, the dimensionless height of the heated wall section compared to the overall enclosure height; the dimensionless width of the heated wall section compared to its height; the dimensionless width of the enclosure between the vertical sidewall on which the heated wall section is mounted and the opposite vertical sidewall, and the dimensionless width of the enclosure between the other two vertical sidewalls. Because of the application being considered, results have only been obtained for Pr = 0.7. Attention has been restricted to the case where the dimensionless width of the enclosure between the vertical sidewall on which the heated wall section is mounted and the opposite vertical sidewall is 0.5 and where the dimensionless width of the enclosure between the other two vertical sidewalls is 1.0. A wide range of the other parameters has been considered particular attention having been given to the effect of the dimensionless width of the heated wall section compared to its height on the mean Nusselt number for the heated wall section.

Proceedings Papers

*Proc. ASME*. HT2008, Heat Transfer: Volume 1, 549-555, August 10–14, 2008

Paper No: HT2008-56190

Abstract

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 10 3 and 10 7 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°.