BASED NANOFLUIDS AND ITS APPLICATION IN HEAT EXCHANGERS : A REVIEW

Nanofluids are potential heat transfer fluids with enhanced thermophysical properties and heat transfer performance. Nanofluids are prepared by suspending nanoparticles with average sizes below 100nm in heat transfer fluids such as water, oil, diesel, ethylene glycol. Due to their excellent characteristics, nanofluids find wide applications in various areas like heat transfer, automotive, electronic, biomedical, pharmaceutics and paints, etc. Heat exchangers are an integral part of any chemical industry and high performance during heat exchange is very important. However, low thermal conductivity is a primary limitation in developing energy-efficient heat transfer fluids, which can be overcome by use of nanofluids. The aim of this review is to summarize recent developments in research on the synthesis of nanofluids, enhancement of thermal conductivities, viscosity and heat transfer characteristics of alumina (Al2O3)-based nanofluids. The second section concentrates on application of alumina (Al2O3)-based nanofluids as a coolant in various types of heat exchangers: plate heat exchangers, shell and tube heat exchangers, air finned heat exchangers and double pipe heat exchangers. HOW TO CITE THIS ARTICLE: Manali D. Patil, SS. Barkade, Bankar VH, et al. Al2O3 Based nanofluids and its application in heat exchangers: A review. J. Technological Advances and Scientific Res. 2015; 1(4):377-385, DOI: 10.14260/jtasr/2015/53. INTRODUCTION: Nanofluids are a relatively new class of fluids, which consist of a base fluid with nano-sized particles (1–100nm) suspended within them. These particles generally a metal or metal oxide, increase conduction and convection coefficients, allowing for more heat transfer out of the coolant. Nanofluids have following Advantages over Conventional Fluids:  High specific surface area and therefore more heat transfer surface between particles and fluids.  High dispersion stability with predominant Brownian motion of particles.  Reduced pumping power as compared to pure liquid to achieve equivalent heat transfer intensification.  Reduced particle clogging as compared to conventional slurries, thus promoting system miniaturization.  Adjustable properties including thermal conductivity and surface wettability by varying particle concentrations to suit different applications. [1] Heat exchangers are widely used in many engineering applications, for example applications in chemical industry, power production, food industry, environment engineering, waste heat recovery, air conditioning and refrigeration. Suspensions of nano-sized particles in a fluid have been observed to significantly enhance the heat transfer properties Financial or Other, Competing Interest: None. Submission 18-12-2015, Peer Review 21-12-2015 Acceptance 28-12-2015, Published 30-12-2015. Corresponding Author: Dr. S. S. Barkade, Department of Chemical Engineering, SCOE, Pune. E-mail: shrikantbarkade09@gmail.com DOI: 10.14260/jtasr/2015/53. of the fluid, while being adept at neither clogging nor settling in a heat exchanger application, which a common problem associated with suspensions of larger particles. [2-3] Various researchers have studied Al2O3 based nanofluids. Al2O3 based nanofluids are more stable, easily available, cheap, corrosion resistant and shows good heat transfer property enhancement. [4] This article aims at an overview of the concept of “Alumina-based Nanofluids” and related research activities carried out. The review will focus mainly on engineering parameters such as synthesis, thermal conductivity and viscosity applications of alumina-based nanofluids in different types of heat exchangers. Synthesis of Nanofluids: Preparing a stable nanofluid without affecting the thermophysical properties of the nanofluid is a challenge. Therefore, selection of nanofluid synthesis method is very important. There are two different techniques available to prepare nanofluids namely single-step and two-step method. Two Steps Method: In two-step method initially dry nanoparticles/nanotubes are prepared using various physical and chemical processes and then these nanoparticles are dispersed into the base liquid. As the surface energy of nanoparticles is high, aggregation and cluster formations are unavoidable and will come into view easily. That results in the clogging of particles and ultimately results in the sedimentation of the particle. Thus, the main challenge for making nanofluids is the making of homogeneous dispersion. But there are some techniques available to minimize this problem, such as high shear and ultrasound. Generally, Nanofluids containing oxide particles and carbon nanotubes are produced efficiently and effectively by this method. [5-6] One-Step Method: One step mechanism is rarely used method for preparation of nanofluids. In this technique nanoparticle