Enhancement of heat transfer using nanofluids—An overview Lazarus Godson a, *, B. Raja b,1 , D. Mohan Lal a , S. Wongwises c a Refrigeration & Air-Conditioning Division, Department of Mechanical Engineering., College of Engineering, Anna University, Chennai 600 025, Tamil Nadu, India b Indian Institute of Information Technology, Design & Manufacturing-Kancheepuram Indian Institute of Technology-Madras, Chennai 600 036, Tamil Nadu, India c Fluid Mechanics, Thermal Engineering and Multiphase Flow (FUTURE), Dept. of Mechanical Engineering, King Mongkut’s University of Technology Thonburi, Bangmod, Bangkok 10140, Thailand Contents 1. Introduction ..................................................................................................... 630 2. Nanofluids ...................................................................................................... 630 3. Enhancement of thermal conductivity ................................................................................ 631 3.1. Dispersion of the suspended particles ........................................................................... 631 3.2. Intensification of turbulence .................................................................................. 631 3.3. Brownian motion ........................................................................................... 631 3.4. Thermophoresis ............................................................................................ 631 3.5. Diffusiophoresis ............................................................................................ 631 4. Experimental investigation ......................................................................................... 632 4.1. Forced convection heat transfer experiments with nanofluids ........................................................ 632 4.1.1. Experiments with metal oxide nanoparticles .............................................................. 632 4.1.2. Experiments with pure metal nanoparticles .............................................................. 633 4.1.3. Inferences from forced convection heat transfer experimental studies ......................................... 633 4.2. Natural convection heat transfer experiments with nanofluids ....................................................... 633 4.2.1. Inferences from natural convection heat transfer experimental studies ......................................... 634 4.3. Boiling heat transfer experiments with nanofluids ................................................................. 634 4.3.1. Inferences from boiling heat transfer experimental studies .................................................. 635 5. Mathematical modeling ............................................................................................ 635 5.1. Theoretical investigations for convective heat transfer of nanofluids .................................................. 635 5.2. Inferences from theoretical studies with nanofluids ................................................................ 637 6. Applications ..................................................................................................... 638 6.1. Micro-channels ............................................................................................. 638 6.2. Heat pipes ................................................................................................. 638 Renewable and Sustainable Energy Reviews 14 (2010) 629–641 ARTICLE INFO Article history: Received 26 June 2009 Accepted 6 September 2009 Keywords: Nanofluid Convective heat transfer Laminar flow Turbulent flow Nanoparticles Dispersion Thermal conductivity ABSTRACT A colloidal mixture of nano-sized particles in a base fluid, called nanofluids, tremendously enhances the heat transfer characteristics of the original fluid, and is ideally suited for practical applications due to its marvelous characteristics. This article addresses the unique features of nanofluids, such as enhancement of heat transfer, improvement in thermal conductivity, increase in surface volume ratio, Brownian motion, thermophoresis, etc. In addition, the article summarizes the recent research in experimental and theoretical studies on forced and free convective heat transfer in nanofluids, their thermo-physical properties and their applications, and identifies the challenges and opportunities for future research. ß 2009 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +91 99944 55741; fax: +91 44 22203261. E-mail addresses: godasir@yahoo.co.in (L. Godson), rajab@iiitdm.ac.in (B. Raja), mohanlal@annauniv.edu (D. Mohan Lal), somchai.won@kmutt.ac.th (S. Wongwises). 1 Tel.: +91 44 22578556; fax: +91 44 22574691. Contents lists available at ScienceDirect Renewable and Sustainable Energy Reviews journal homepage: www.elsevier.com/locate/rser 1364-0321/$ – see front matter ß 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.rser.2009.10.004