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research-article

Natural Convective Heat Transfer from Horizontal Isothermal Surface of Polygons of Octagonal and Hexagonal Shapes

[+] Author and Article Information
Ahmed Kalendar

P.O. Box 358 Salmiyha, 22004 Kuwait a_kalendar@yahoo.com

Abdulrahim Kalendar

Department of Mechanical Power and Refrigeration Shuwaikh, Kuwait, POBox:36771 Alras, 24758 Kuwait kalendar@hotmail.com

Yousuf A. Alhendal

College of Technological Studies, P. O. Box 5351, Hawally, code 32084, State of Kuwait Kuwait, 5351 Kuwait Ya.alhendal@paaet.edu.kw

Sayed Karar

Department of Mechanical Power and Refrigeration Shuwaikh, 24758 Kuwait karar1952@hotmail.com

Adel Alenzi

Shuwaikh kuwait, 13092 Kuwait af.alenzi@paaet.edu.kw

Patrick Oosthuizen

Queen's University, Kingston, McLaughlin Hall, office 301 Kingston, ON K7L 3N6 Canada patrick.oosthuizen@queensu.ca

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the Journal of Thermal Science and Engineering Applications. Manuscript received November 22, 2018; final manuscript received February 21, 2019; published online xx xx, xxxx. Assoc. Editor: Gerard F. Jones.

ASME doi:10.1115/1.4043006 History: Received November 22, 2018; Accepted February 22, 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 shape 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 CFD code, FLUENT14.5. The solution parameters include surface shape, dimensionless surface width, different characteristic length, the Rayleigh number, and the Prandtl number. These parameters are considered as follows; 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 length 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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