ARTICLE IN PRESS JID: JTICE [m5G;August 11, 2018;10:41] Journal of the Taiwan Institute of Chemical Engineers 000 (2018) 1–14 Contents lists available at ScienceDirect Journal of the Taiwan Institute of Chemical Engineers journal homepage: www.elsevier.com/locate/jtice Simulation of nanofluid natural convection in a U-shaped cavity equipped by a heating obstacle: Effect of cavity’s aspect ratio Yuan Ma a,b , Rasul Mohebbi c,∗ , M.M. Rashidi d , Zhigang Yang a,b,e a Shanghai Automotive Wind Tunnel Center, Tongji University, No. 4800, Cao’an Road, Shanghai 201804, China b Shanghai Key Lab of Vehicle Aerodynamics and Vehicle Thermal Management Systems, No. 4800, Cao’an Road, Shanghai 201804, China c School of Engineering, Damghan University, P.O. Box: 3671641167, Damghan, Iran d Department of Civil Engineering, School of Engineering, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom e Beijing Aeronautical Science & Technology Research Institute, Beijing, 102211, China a r t i c l e i n f o Article history: Received 22 April 2018 Revised 15 June 2018 Accepted 16 July 2018 Available online xxx Keywords: Nanofluid natural convection LBM U-shaped cavity’s aspect ratio Hot obstacle Cold rib a b s t r a c t Research on nanofluid for heat transfer enhancement of thermal systems has received great attention ow- ing to the lack of energy sources. In this study, fluid flow and natural convection heat transfer of Al 2 O 3 – Water or TiO 2 –water nanofluid inside a U-shaped cavity consist of a hot obstacle has been investigated numerically by lattice Boltzmann method (LBM). In this paper, different parameters are investigated such as Rayleigh number, the solid volume fraction of the nanoparticles, the U-shaped cavity’s aspect ratio and heating obstacle’s height on the flow field and heat transfer in the enclosure. The results showed that the Rayleigh number (Ra), cavity aspect ratio (AR) and obstacle’s height can be affected on isotherms, stream- lines and local and average Nusselt number. The average Nusselt number of the obstacle sides increased by increasing the Ra number and solid volume fraction of nanoparticles (φ) regardless the AR. In addi- tion, by increasing the AR, the average Nusselt number increased. At low Ra, the effect of nanoparticles on increment of heat transfer for narrow cavities was more than wide ones. © 2018 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved. 1. Introduction Study of heat transfer inside the enclosure is very important to some electronic engineering system. The temperature control of the internal components is an important factor of the design, ap- plication and manufacture. The heat transfer can be carried from heat sink in the form of natural convection [1–4]. Solar energy collection and many kinds of electronic cooling systems including microprocessors, heat generating components of computers, indus- trial communication device (ICD) and some electronic devices are trapped in the enclosure space. The early study was performed by Davis [5], who used the computational method to obtain a solution to the equations describing two-dimensional natural convection in- side an enclosure with some heated walls. The horizontal walls in his study were adiabatic. The results are widely used to valid the numerical results in natural heat transfer convection of computer codes. De and Dalal [6] investigated natural heat transfer of a tilted hot square cylinder in a cavity. They studied different parameters such as different boundary condition, different placing of cylinder on flow pattern and heat rate. ∗ Corresponding author. E-mail address: rasul_mohebbi@du.ac.ir (R. Mohebbi). In recent years, nanofluid, which is a mixture of nano-sized par- ticles (nano-particles) suspended in a based fluid, is widely used to enhance the heat transfer by virtue of its higher thermal conduc- tivity compared to the based fluid [7–16]. The nanofluid used by researchers for commercial applications such as automobile’s ra- diators cooling, electronics, air-conditioning. There are a number of recent studies on the nanofluid natural convection heat trans- fer study in cavities and enclosure by different kind of geometry which is significant in respect of the installation of electronic com- ponents in the enclosure space. Also, the LBM which is based on the kinetic theory, is a tech- nique for simulating heat transfer problems [17–20], single and multiphase fluid flows [21,22], complex geometries, simple and ef- ficient to implement for parallel computation [23–25] in science and engineering. Ho et al. [26] investigated nanofluid natural convection in a square cavity. They simulations carried out for the Ra and the volu- metric fraction of nanoparticles. Significant difference between en- hancements in the dynamic viscosity of the nanofluid, can be en- hanced or mitigated heat transfer. Varol et al. [27] analyzed natural convection in a triangle cavity with hot flush mounted on wall. It is found that flow and temperature field are affected by the shape of ensure and Rayleigh numbers plays an important role on them. https://doi.org/10.1016/j.jtice.2018.07.026 1876-1070/© 2018 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved. Please cite this article as: Y. Ma et al., Simulation of nanofluid natural convection in a U-shaped cavity equipped by a heating obstacle: Effect of cavity’s aspect ratio, Journal of the Taiwan Institute of Chemical Engineers (2018), https://doi.org/10.1016/j.jtice.2018.07.026