Energy and Power En gi neering, 2011, 3, 525-532

doi:10.4236/epe.2011.34064 Published Online September 2011 (http://www.SciRP.org/journal/epe)

Copyright © 2011 SciRes. EPE

Improvement of Free Convection Heat Transfer Rate of

Rectangular Heatsink on Vertical Base Plates

Hamid Reza Goshayeshi1, Mahdi Fahiminia1, Mohammad Mahdi Naserian2

1Department of Mechanical Engineering, Mashhad Branch, Islamic Azad University, Mashhad, Iran

2Young Researchers Club, Mashhad Branch, Islamic Azad University, Mashhad, Iran

E-mail:{Goshayshi, Mmahna

s

}@yahoo.com, MFahiminia@Gmx.com

Received December 21, 2010; revised February 4, 2011; accepted February 28, 2011

Abstract

In this paper, the laminar heat transfer of natural convection on vertical surfaces is investigated. Most of the

studies on natural convection have been considered constantly whereas velocity and temperature domain, do

not change with time, transient one are used a lot. Governing equations are solved using a finite volume ap-

proach. The convective terms are discretized using the power-law scheme, whereas for diffusive terms the

central difference is employed. Coupling between the velocity and pressure is made with SIMPLE algorithm.

The resultant system of discretized linear algebraic equations is solved with an alternating direction implicit

scheme. Then a configuration of rectangular fins is put in different ways on the surface and heat transfer of

natural convection on these surfaces without sliding is studied and finally optimization is investigated.

Keywords: Natural Convection, Vertical Surfaces, Simple Algorithm, Rectangular Fins

1. Introduction

This document is a natural convection is observed as a

result of the movement of fluid because of density

changes which is caused by heating process. A radiator

used for warming the house is an example of practical

equipment for heat transfer of natural convection. The

movement of fluid, whether gas or liquid, in natural

convection is caused by buoyancy force due to density

reduction beside to heat transfer's surfaces in heating

process. When the domain of an exterior force such as

gravity, has no effect on the fluid then will be no buoy-

ancy force and heat transfer will be in the form of con-

duction. But gravity is not th e only force causing natural

convection. When a fluid is confined in the rotating ma-

chine, centrifugal force is exerted on it and if one surface

or so, with more or less temperature than that of the fluid

are in touch with the fluid, natural convection flows will

be experienced. The fluid which is adjacent to the verti-

cal surface with constant temperature, and the fluid tem-

perature is less than the surface temperature, a velocity

boundary layer forms the natural convection. The veloc-

ity profile in this boundary layer is completely different

with the velocity profile in forced co nvection. Th e veloc-

ity is zero on the wall due to lack of sliding .Then the

velocity goes up and reaches its maximum and finally is

zero on the external border of velocity boundary layer.

Since the factor that causes the natural convection, is

temperature gradient, the heating boundary layer appears

too. The temperature profile has also the same value as

the temperature of wall due to the lack of particles slid-

ing on the wall, and temperature of particles goes down

as approaching to external border of temperature bound-

ary layer and it would reach the temperature of far fluids.

The initial boundary layer enlargement is laminar , but in

the distance from the uplifting edge, depending on fluid

properties and the difference of temperature of wall and

the environment, eddies will b e formed an d movement to

turbulent zon e will be started.

Today being mor e aware abou t energy sources’ limita-

tions and also increase demand for energy consumption

from one side and considerable waste of energy in heat-

ing systems from the other side , have caused the socie-

ties to investigate on energy systems and find solutions

for reducing energy dissipation from these systems.

There are many appliances in engineering in which two

environments with different temperatures are separated

by a wall or a thin surface. The wall on one side is get-

ting warm and on the other side is making it is beside

fluid warm. Heat transfer between the two environments

and the temperature of the wall, depends on the shape of

the boundary layers on the wall surfaces. The amount of