Materials Science and Engineering B 139 (2007) 141–148 Development and characterization of Al 2 Cu and Ag 2 Al nanoparticle dispersed water and ethylene glycol based nanofluid M. Chopkar a , S. Kumar b , D.R. Bhandari c , P.K. Das d , I. Manna a,∗ a Department of Metallurgical and Materials Engineering, Indian Institute of Technology, Kharagpur, WB 721302, India b School of Materials Engineering, Purdue University, Indiana 47907, USA c Thermal Group, ISRO Satellite Center, Vimanapura, Bangalore 560017, India d Department of Mechanical Engineering, Indian Institute of Technology, Kharagpur, WB 721302, India Received 25 September 2006; received in revised form 25 January 2007; accepted 27 January 2007 Abstract Nanofluids offer excellent scope of enhancing thermal conductivity of common heat transfer fluids. In the present study, we have synthesized Al 2 Cu and Ag 2 Al nanoparticles by mechanical alloying, prepared nanofluids by dispersing about 0.2–1.5 vol.% these nanoparticles in water and ethylene glycol, characterized the size/microstructure of nanoparticles by X-ray diffraction and transmission electron microscopy, and measured the thermal conductivity of nanofluid using a modified thermal comparator. The results indicate that the present nanofluids records 50–150% improvement in thermal conductivity. Both experimental results and analytical study indicate that the degree of enhancement strongly depends on identity/composition, size, volume fraction and shape (aspect ratio) of the dispersed nanoparticles. © 2007 Elsevier B.V. All rights reserved. Keywords: Nanofluid; Thermal conductivity; Al-based nanoparticles; Water; Ethylene glycol; Thermal comparator 1. Introduction Heat transfer over a finite distance using a fluid medium (liq- uid/gas) is essential in several engineering practices like heat exchanger, refrigerators, automobiles, power plants, etc. The ability to transfer heat across a given thermal gradient enhances the efficiency of energy conversion and improves the design and performance of automobile engine, heat transfer devices and microelectro-mechanical systems. Heat transfer through fluid is essentially convection dominated. However, the coefficient of convective heat transfer strongly depends on thermal conduc- tivity of the fluid. Since thermal conductivity of solids is orders of magnitude greater than that of liquids, dispersion of solid particles in a given fluid is bound to increase its thermal con- ductivity. However, dispersion of milli- and micrometer-sized particles is prone to sedimentation, clogging and erosion of pipes and channels. In contrast, nanofluid is a stable colloidal suspension of low (<1%) volume fraction of ultra-fine solid par- ticles in nanometric dimension dispersed in conventional heat ∗ Corresponding author. Tel.: +91 3222 283266; fax: +91 3222 282280. E-mail address: imanna@metal.iitkgp.ernet.in (I. Manna). transfer fluid to offer a dramatic enhancement in conductivity of the fluid without the above-mentioned problems encountered in dispersing coarse particles [1–6]. Despite several attempts, the precise mechanism for this significant enhancement is not yet established. Hence, continued efforts are warranted to syn- thesize different types of nanofluid and study its heat transfer characteristics. In the past, nanofluid was synthesized by col- lecting nanometric alumina (Al 2 O 3 ) and copper oxide (CuO) particles (prepared by chemical vapor deposition) or dispers- ing nanostructured copper, gold or carbon nanotube in common heat transfer fluids like water, transformer oil or ethylene glycol [1,4]. It has recently been shown that a two stage approach of synthesizing nanometric powders by mechanical alloying and subsequently dispersing the same in a given fluid could be a more flexible method of producing nanofluid with greater scope of scaling up the process of synthesis [7,8]. The performance of nanofluid critically depends upon the size and distribution of dispersoids and their ability to remain suspended and chemically un-reacted in the fluid. It is suggested that the uniformity and stability of suspension can be ensured by maintaining appro- priate pH, using surface activators or surfactant and employing ultrasonic vibration [3,6]. Though temperature dependence of thermo-physical properties of the solid particles and fluid can 0921-5107/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.mseb.2007.01.048