Engineering and Technology Journal

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.

A numerical investigation has been performed to estimate the induced flow rate for a laminar natural convection flow of air in a vertical channel with isothermal walls conditions (one hot and another is cold). The two-dimensional governing equations have been solved using finite volume method. The coupling between the continuity and momentum equations is solved by using the SIMPLE algorithm. After the validity of the present code by comparing results with these of previous study for the similar conditions, solutions have been obtained for Prandtl number of 0.7, aspect ratio of (4 to 20) and wall temperature difference of (10 to 30). The effects of the changes in these parameters on the induced flow rate, Grashof number and flow
patterns within the channel have been predicted. A mathematical form of flow rate correlation is presented for these cases.

This study investigates natural convection heat transfer and fluid flow
characteristic of water based nano-fluids in a right-angle triangular enclosure, where the left vertical wall is insulated, the right inclined wall is cooled, and the horizontal wall is heated by spatially varying temperature. Governing equations are solved using treamvorticity
formulation in curvilinear coordinates. Streamlines, isotherms, local and average Nusselt number, moreover to NUR factor are used to present the corresponding flow and thermal fields inside the triangular enclosure. Calculation were performed for three aspect ratio of enclosure geometry (AR=0.5, 1, 2), solid volume fractions of nanoparticles ranging from PHI=0, to 4%, and Rayleigh number varying from 104 to 106. Three types of nano-particles are taken into consideration: Cu, Al 2O3, and TiO2. The results show that, the average heat transfer rate increases significantly as particle volume
fraction and Rayleigh number increase. Also, the type of nano-fluid is a key factor for heat transfer enhancement where the high values are obtained when using Cu, TiO2, and Al2O3 nano-particles respectively. Finally, it is observed that the aspect ratio of the enclosure is one of the most important on flow and heat transfer. Increasing the AR leads
that to increase the flow strength and heat transfer rate.

Thermal And Flow Fields Due To Laminar Free Convection In An Isosceles
Triangular Enclosure Having Thick Conducting Sidewalls Have Been Investigated
Computationally. Inclined Left And Right Side Walls Are Maintained At
Isothermal Hot And Cold Temperatures Respectively While The Bottom Wall Is
Considered Adiabatic. Problem Has Been Analyzed And The Non-Dimensional
Governing Equations Are Solved Using Finite Volume Approach And Employing
More Nodes At The Fluid–Solid Interface. Triangular Enclosure Is Assumed To
Be Filled With An Air With A Prandtl Number Of 0.7. Rayleigh Number Varies
From 103 To 106 Where The Flow And Thermal Fields Are Computed For Various
Rayleigh Numbers. Consequently, It Was Observed That The Stream Function
And Temperature Contours Strongly Change With High Rayleigh Number. The
Streamline And Isotherm Plots And The Variations Of The Average Nusselt
Number At The Hot Left And The Cold Right Side Walls Are Also Presented. The
Results Explained A Good Agreement With Another Published Results.