Mixed convection flow of a nanofluid in a lid-driven cavity with a wavy wall ☆ Eiyad Abu-Nada a, ⁎, Ali J. Chamkha b a Department of Mechanical Engineering, Khalifa University of Science, Technology and Research (KUSTAR), P. O. Box 127788, Abu Dhabi, United Arab Emirates b Manufacturing Engineering Department, The Public Authority for Applied Education and Training, Shuweikh 70654, Kuwait abstract article info Available online 18 July 2014 Keywords: Lid-driven cavity Mixed convection Nanofluids Wavy wall Heat transfer augmentation This work is focused on the numerical modeling of steady laminar mixed convection flow in a lid-driven cavity with a wavy wall filled with a water–CuO nanofluid. The left and right walls of the enclosure are kept insulated while the bottom and top walls are maintained at constant temperatures with the top surface being the heated lid wall and moving at a constant speed. The governing equations for this investigation are given in terms of the stream function–vorticity formulation and are non-dimensionalized and then solved numerically subject to ap- propriate boundary conditions by a second-order accurate finite-volume method. Various comparisons with pre- viously published work are performed and the results are found to be in good agreement. A parametric study of the governing parameters such as the Richardson number, bottom wall geometry ratio (B/H) and the nanoparti- cles volume fraction is conducted and a representative set of graphical results is presented and discussed to illus- trate the effects of these parameters on the flow and heat transfer characteristics. It is found that the presence of nanoparticles causes significant heat transfer augmentation for all values of Richardson numbers and bottom wall geometry ratios. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction The topic of mixed convection flow in a lid-driven cavity with a hor- izontal sliding wall has been a subject of interest for many years due to their ever increasing applications in lubrication technologies, electronic cooling, food processing and nuclear reactors [1–6]. A nanofluid is a base fluid with suspended metallic nanoparticles [7]. Because traditional fluids used for heat transfer applications such as water, mineral oils and ethylene glycol have a rather low thermal conductivity, nanofluids with relatively higher thermal conductivities have attracted enormous interest from researchers due to their potential in the enhancement of heat transfer with little or no penalty in pressure drop. In their experi- mental work, Eastman et al. [8] showed that an increase in thermal conductivity of approximately 60% can be obtained for a nanofluid consisting of water and 5 vol.% CuO nanoparticles. This is attributed to the increase in surface area due to the suspension of nanoparticles. Das et al. [9] reported a 2–4-fold increase in thermal conductivity enhancement for water-based nanofluids containing Al 2 O 3 or CuO nanoparticles over a small temperature range, 21–51 °C. Keblinski et al. [10] reported on the possible mechanisms of enhancing thermal conductivity, and suggested that the size effect, the clustering of nano- particles and the surface adsorption could be the major reason of en- hancement, while the Brownian motion of nanoparticles contributes much less than other factors since Brownian motion of nanoparticles is too slow to transport significant amount of heat through a nanofluid and this conclusion was also supported by their results of molecular dy- namics simulation. Wang et al. [11] used a fractal model for predicting the effective thermal conductivity of liquid with suspension of nanopar- ticles and found that it predicts well the trend for variation of the effec- tive thermal conductivity with dilute suspension of nanoparticles. The convective heat transfer characteristic of nanofluids depends on the thermo-physical properties of the base fluid and the ultra-fine par- ticles, the flow pattern and flow structure, the volume fraction of the suspended particles, the dimensions and the shape of these particles. The utility of a particular nanofluid for a heat transfer application can be established by suitably modeling the convective transport in the nanofluid. Several studies of convective heat transfer in nanofluids have been reported in recent years. Khanafer et al. [12] investigated the problem of buoyancy-driven heat transfer enhancement of nanofluids in a two-dimensional enclosure. Hwang et al. [13] have car- ried out a theoretical investigation of the thermal characteristics of nat- ural convection of an alumina-based nanofluid in a rectangular cavity heated from below using Jang and Choi's model [14] for predicting the effective thermal conductivity of nanofluids (and various models for predicting the effective viscosity). Santra et al. [15] studied heat transfer characteristics of copper–water nanofluid in a differentially heated square cavity with different viscosity models. Ho et al. [16] reported a numerical simulation of natural convection of nanofluid in a square en- closure considering the effects due to uncertainties of viscosity and thermal conductivity. Oztop and Abu-Nada [17] studied heat transfer and fluid flow due to buoyancy forces in a partially heated enclosure using nanofluids with various types of nanoparticles. They found that International Communications in Heat and Mass Transfer 57 (2014) 36–47 ☆ Communicated by Dr. W.J. Minkowycz. ⁎ Corresponding author. E-mail address: eiyad.abu-nada@kustar.ac.ae (E. Abu-Nada). http://dx.doi.org/10.1016/j.icheatmasstransfer.2014.07.013 0735-1933/© 2014 Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect International Communications in Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ichmt