Nanofluids: A Review Preparation, Stability, Properties and Applications Atul Saini Department of Mechanical Engineering, Thapar University Patiala, India Harkirat Kaur Department of Chemical Engineering Thapar University Patiala, India Sumeet Sharma D. Gangacharyulu Department of Mechanical Engineering Department of Chemical Engineering Thapar university Thapar University Patiala, India Patiala, India Abstract—Nanofluids, suspension of nano sized particles having higher conductivity than base fluid, has reported many interesting properties which gains the attention of researchers and proved vital in many applications. This document is a review article on nanofluids. The article provides the basic information about nanofluids, their preparation methods, stability analyses, thermophysical properties and applications. Also discusses the future scope of nanofluids. Keywords—nanofluids; nanofluids preparation; stability; thermophsical properties; I. INTRODUCTION With the advancement in microelectronics industry, high heat flux devices has been started manufactured, but their heat dissipation is critical issue for their prominent use in industry and day to day life, since electronic chips slows down their functioning or even may damage completely due to heat accumulation. Hence the heat dissipation from these electronic chips and circuitry is most important and challenging task. However, the conventional coolants (water, oils and ethylene glycols) were proved futile because of their low thermal conductivity which leads to poor heat dissipation and slower performance of electronics chips. Therefore in 1873, J.C Maxwell proposed to add very small solid particles in the fluids (base fluids) to increase their thermal conductivity which further can increase the heat dissipation capacity. Small solid particles have higher thermal conductivity than base fluid hence an overall increase in heat dissipation capacity and thermal conductivity of base fluid [1]. It is known that micro and millimeter sized particles increases the thermal conductivity of base fluids, but when experiments were carried out it was found that in addition to increase in thermal conductivity some more problems like abrasive wear of pipeline, clogging of channels, sedimentation of particles and pressure drop, has been surfaced which restrict their use in micro industry. Later, to avoid these problem nano sized particles were introduced; with the development in nano scale industry and nanotechnology they gained the momentum for use in research area [2]. Nano particles are fine powdered particles which have size smaller than 100 nm. In 1993 Masuda et al [3] used the ultra-fine particles to enhance the thermal conductivity of liquid. Later in 1995, S.U.S Choi [4] proposed the use of nanoparticles in base fluids to increase the thermal conductivity. These particles may be metallic and non-metallic: Al2O3, CuO, SiO2, TiO2, Cu, Ni, Al, ZnO [5]. The fluid made by dispersing nanoparticles in them is known as nanofluids [5]. Nanofluids are the class of fluids which are formed by dispersing nano sized high conductivity materials (nanofibers, nanotubes, nanorods, nanowires, nanoparticles or nanosheets) into the base fluid, generally water, oils, ethylene glycol. The dilute suspensions of nanofluids are the advantage over colloidal solution for being having high heat transfer surface between fluid and particles. With these advantages nanofluids have applications in : transportation, heat transfer intensification, electronics applications, industrial cooling applications, heating buildings and reducing pollution, nuclear cooling, energy storage, solar absorption, friction reduction, magnetic sealing, biomedical application, nano drug delivery etc. [6]. There is two phase system in nanofluids one is solid and other liquid phase. Nanofluids possess better thermal properties (thermal conductivity, thermal diffusivity, convective heat transfer coefficient) than the base fluids. However with enhanced properties, in two phase system stability is the major challenge before the researchers. In this paper we will discuss preparation methods, some stability methods, thermophysical properties and applications of nanofluids. II. PREPARATION OF NANOFLUIDS A. Two- step method It is the most widely used method for preparing nanofluids, nanotubes, nanosheets and other nanomaterials. In this method nanoparticles are first made in dry powdered by different means of physical and chemical processes and then these nanoparticles are dispersed in base fluid with the help of ultrasonic agitation, ball milling, homogenizing, magnetic force agitation . This method is economic and easy way to produce nanofluids on large scale because nanotechnology industry has grown to these scales to produce these particles economically. However due to high surface activity nanoparticles made by this method has the tendency to agglomerate. The major steps in preparing nanofluids are given as. 1) Amount of nanoparticles required; calculated and weighed by using highly accurate and precise weighing machine. 2) After knowing the exact quantity of nanofluids, International Journal of Engineering Research & Technology (IJERT) ISSN: 2278-0181 http://www.ijert.org IJERTV5IS070044 (This work is licensed under a Creative Commons Attribution 4.0 International License.) Published by : Vol. 5 Issue 07, July-2016 www.ijert.org 11