Numerical simulation of natural convection of the nanofluid in heat exchangers using a Buongiorno model Faroogh Garoosi a,⇑ , Leila Jahanshaloo b , Mohammad Mehdi Rashidi c,f , Arash Badakhsh d , Mohammed E. Ali e a Department of Mechanical Engineering, University of Semnan, Semnan, Iran b Department of Mechanical Engineering, Universiti Teknologi Malaysia, Malaysia c Shanghai Automotive Wind Tunnel Center, Tongji University, 4800 Caoan Rd., Jiading, Shanghai 201804, China d Department of Mechanical Engineering, University of Sistan & Balouchestan, Iran e Mechanical Engineering Department, College of Engineering, King Saud University, P. O. Box 800, Riyadh 11421, Saudi Arabia f ENN-Tongji Clean Energy Institute of Advanced Studies, Shanghai, China article info Keywords: Natural convection Nanofluid Heat exchanger Heater Cooler Buongiorno model abstract A numerical study is carried out concerning natural convection heat transfer of nanofluid in a two-dimensional square cavity containing several pairs of heater and coolers (HACs). Walls of the cavity are insulated and several pairs of heater and coolers (HACs) with isothermal walls of T h and T c (T h > T c ) are placed inside the cavity. Two-dimensional Navier–Stokes, energy and volume fraction equations are solved using finite volume discretization method. The effects of various design parameters on the heat transfer rate and distribution of nanoparticles such as Rayleigh number (10 4 6 Ra 6 10 7 ), volume fraction (0 6 u 6 0:05) and size of nanoparticles (25 nm 6 d p 6 145 nm), type of the nano- particles (Cu, Al 2 O 3 and TiO 2 ), nanofluid average temperature (294 K 6 T ave 6 324 K ), number of the cooler, location of the heater and arrangement of the HAC are investigated. The simulation results are indicated that, HACs location has the most significant influence on the heat transfer rate. It is also found that at low Rayleigh numbers, the particle distri- bution is fairly non-uniform while at high Ra, particle distribution remains almost uniform. Moreover, it is found that there is an optimal volume fraction of the nano-particles at each Rayleigh number in which the maximum heat transfer rate can be obtained. Ó 2014 Elsevier Inc. All rights reserved. 1. Introduction Many industrial and environmental processes are involved with heat transfer due to natural convection through a med- ium fluid. Indoor ventilation with radiators, cooling of electrical components, solar energy collection and heat exchangers are just a few examples of such systems [1]. From energy-saving point of view, improvement of heat transfer in any application of natural convection is a primary and crucial topic. Several investigations have been carried out on natural convection [2–6]. Bilgen [2] investigated laminar natural convection in a two-dimensional square cavity with a thin fin on the hot wall. It was reported that there is an optimum fin location, which is often at the center or near center of the cavity, which minimizes the natural convection heat transfer. Deng [3] studied laminar natural convection in a two dimensional square enclosure with http://dx.doi.org/10.1016/j.amc.2014.12.116 0096-3003/Ó 2014 Elsevier Inc. All rights reserved. ⇑ Corresponding author. Tel.: +98 9112748341. E-mail address: garoosi.faroogh@yahoo.com (F. Garoosi). Applied Mathematics and Computation 254 (2015) 183–203 Contents lists available at ScienceDirect Applied Mathematics and Computation journal homepage: www.elsevier.com/locate/amc Downloaded from http://www.elearnica.ir