Print ISSN: 1681-6900

Online ISSN: 2412-0758

Keywords : Natural Convection


A Comparison Between Sinusoidal Oscilation and Constant Temperature Boundary Conditions In Annulus Filled With Porous Media Saturated With Nanofluid

Manal H. AL; Hafidh

Engineering and Technology Journal, 2014, Volume 32, Issue 4, Pages 831-848

A numerical study has been carried out to investigate the heat transfer by natural convection of nanofluid taking copper as nano particles and the water as based fluid in a three dimensional annulus enclosure filled with porous media between two horizontal concentric cylinders with 12 annular fins of 3mm length and 2.4 mm thickness attached to the inner cylinder under steady state condition and different wall temperature boundary conditions. The governing equations which used are continuity, momentum and energy equations under an assumptions used Darcy law and Boussinesq’s approximation which are transformed to dimensionless equations. The finite difference approach is used to obtain all the computational results using the MATLAB- 7. The parameters affected on the system are modified Rayleigh number (10 ≤Ra*≤ 500), radius ratio Rr (0.293, 0.365 and 0.435) and the volume fraction . The results show that, increasing of fin length decreases the heat transfer rate and for Ra*<100, decreasing Rr cause to decrease Nu and adding Cu nanoparticles with φ= 0.35 cause 27.9% enhancement in heat transfer. A correlation for Nu in terms of Ra, Hf and φ, has been developed for inner hot cylinder.

Numerical Study of Two-Dimensional Transient Natural Convection in an Inclined Shallow Porous Cavity Exposed to a Constant Heat Flux

Jasim M. A. Al-lateef; Ayad K. Hassan

Engineering and Technology Journal, 2012, Volume 30, Issue 15, Pages 2577-2596

Numerical method is used to solve the two-dimensional transient natural convection heat transfer problem in an inclined shallow porous cavity. A constant heat flux is applied for heating and cooling all opposing walls. Solutions for laminar case are obtained within Rayleigh number varied from 20 to 500 and aspect ratio for porous cavity varied from 2 to 4. A finite difference method is used to obtain numerical solutions of full governing equations. Energy equation is solved using alternating direct implicit (ADI) method and stream function equation by successive over relaxation (SOR) method. The results are presented for the flow filed, temperature distributions, and average Nusselt number in terms of the Rayleigh number, aspect ratio, and the inclination angle of cavity. the convection becomes more and more vigorous as the orientation angle of the cavity is increased and for high Rayligh number no steady unicellular flow could be maintained inside the cavity. The effect of inclination angle on Nasselt number is more pronounced as the Rayleigh number is increased. When the inclination angle increased the Nusselt number increased and sudden transition appears and flow becomes unicellular and Nusselt number increased clearly. The value of mean Nusselt number strong function with the value of Rayleigh number, aspect ratio and the orientation of porous cavity.

Laminar Natural Convection of Newtonian and Non – Newtonian Fluids in a Square Enclosure

Ala; a A. Mahdi; Tahseen Ali Hussian; Nabeel Mohammed Jassim

Engineering and Technology Journal, 2008, Volume 26, Issue 1, Pages 74-91

In this investigation, steady two – dimensional natural convection heat
transfer of Newtonian and non-Newtonian fluids inside square enclosure has been
analyzed numerically for a wide range of the modified Rayleigh number of (103 ≤
Ra ≤ 105), with non-dimensional parameter(NE) of Prandtl – Eyring model ranging
from (0 to 10), and modified Prandtl number in the range (Pr* =1,10, and 100).
Two types of boundary conditions have been considered. The first,is when the side
walls are heated at different uniform temperatures and the horizontal walls are
insulated. The second, when the bottom wall is heated by applying a uniform heat
flux while the other walls are at the constant cold temperature. Also, the non-
Newtonian fluids under consideration were assumed to obey the Prandtl – Eyring
model. The numerical results of the values of average Nusselt number have been
confirmed by comparing them to similar known yeslts of previous works using the
same boundary conditions. Good agreement was obtained. The results are
presented in terms of isotherms and streamlines to show the behavior of the fluid
flow and temperature fields. In addition, some graphics represent the relation
between average Nusselt number and the parameters that are mentioned
previously. The results show the effect of non – dimensional parameter (NE) on the
velocity and temperature profiles. It also shows that the average Nusselt number is
a strong function of modified Rayleigh number, modified Prandtl number, nondimensional
parameter, and the boundary conditions. Four different correlations
have been made to show the dependence of the average Nusselt number on the
non-dimensional parameter, the modified Rayleigh and Prandtl numbers.