JJMIE Volume 9 Number 2, April.2015 ISSN 1995-6665 Pages 149 - 157 Jordan Journal of Mechanical and Industrial Engineering Heatline Visualization of Buoyancy-Driven Flow inside a Nanofluid-Saturated Porous Enclosure Iman Zahmatkesh * Department of Mechanical Engineering, Mashhad Branch, Islamic Azad University, Mashhad, Iran Received 15 Jan 2015 Accepted 27 April 2015 Abstract In the present paper, the heatline visualization technique is utilized to understand heat transport path for buoyancy-driven flow inside a rectangular porous enclosure saturated with nanofluids. For this purpose, the mass, momentum and energy conservation equations are solved numerically adopting a control-volume based computational procedure. Moreover, the dimensionless heat function equation is utilized to determine the heat flow pattern inside the enclosure. Computations are undertaken for Cu, Al 2 O 3 , and TiO 2 nanoparticles in the base fluid of water and corresponding results in terms of dimensionless distributions of streamlines, isothermal lines, and heatlines as well as numerical values for flow strength and the average Nusselt number are compared with those of pure water under different Darcy-Rayleigh numbers. Additionally, the consequences of the nanoparticle fraction and the enclosure aspect ratio on the buoyancy-driven flow are analyzed. Inspection of the presented results indicates that among Cu-water, Al 2 O 3 -water, and TiO 2 -water nanofluids, the Cu-water one produces higher heat transfer rates that is attributed to higher thermal conductivity of the Cu nanoparticles. © 2015 Jordan Journal of Mechanical and Industrial Engineering. All rights reserved Keywords: Nanofluid, Porous Media, Buoyancy-Driven Flow, Heatline, Enclosure. * Corresponding author. e-mail: zahmatkesh5310@mshdiau.ac.ir. Nomenclature AR aspect ratio of the enclosure Cv constant-pressure specific heat Da Darcy number g gravitational acceleration h heat function H enclosure height k thermal conductivity K medium permeability L enclosure length Nu local Nusselt number      average Nusselt number Ra Darcy-Rayleigh number T temperature u,v velocity components in x- and y-directions x,y Cartesian coordinates X,Y dimensionless coordinates Greek symbols α thermal diffusivity  thermal expansion coefficient θ dimensionless temperature μ dynamic viscosity  dimensionless heat function ρ density ϕ nanoparticle fraction ψ stream function (m 2 s-1)  dimensionless stream function Subscripts bf base fluid C cold nf nanofluid p nanoparticle 1. Introduction Recent years have witnessed extensive research on convective heat transfer of nanofluids in the view of their abnormally better thermophysical properties. Thereby, it is not surprising to see some previous interests on the analysis of buoyancy-driven flow inside nanofluid- saturated porous enclosures. Sun and Pop [1], Chamkha and Ismael [2], Ahmed et al. [3], Rashidi et al. [4],