International Conference on Ideas, Impact and Innovation in Mechanical Engineering (ICIIIME 2017) ISSN: 2321-8169 Volume: 5 Issue: 6 882 -– 886 ______

Title: Nanofluids

1 2 3 Bharambe Kushal S. , Bhide Harshad S. , Prof. Anilkumar Sathe

1Student, Mechanical Engineering, Smt. Kashibai Navale College of Engineering, Pune, [email protected] 2Student, Mechanical Engineering, Smt. Kashibai Navale College of Engineering, Pune, [email protected] 3Professor, Mechanical Engineering, Smt. Kashibai Navale College of Engineering, Pune, [email protected]

ABSTRACT

Graphene flakes have been investigated worldwide as an additive for and lubricants due to their excellent thermo-physical and tribological properties. As a result, we have highlighted various synthesis methods, properties, measurement procedures that have been experimented and developed. Moreover, factors affecting the stability, , electrical conductivity have been delineated in detail. Although very few mechanisms have been proposed to explain the enhancement of thermal conductivity, stability some key concerns have been presented. This exhaustive review along with the critical comments and recommendations provided could be useful for future directions in this research field. It is expected that it could be a quick reference guide to have an overview of the different phenomena in graphene nanofluids and the most essential parameters that influence the expected thermal performance of graphene nanofluids.

Keywords: Graphene, Nanofluids, Synthesis, Density, Thermal conductivity, etc.

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1. INTRODUCTION

Heat removal and management is a major concern for any technology that deals with high power and small size. Growing energy demands, precision manufacturing, miniaturization, nuclear regulations and critical economies demand high efficient coolants and lubricants. Use of nanofluids to address these issues has been subject of interest by the many scientists around the world. In many cases, a nanofluid can be custom made to fit a particular need and can act as a flexible cooling method, adapting to the requirements of a specific system. In essence, nanofluids have the potential to become the world’s first smart/adaptable . The heat transfer applications directly or indirectly affect people’s daily life and require an additional research in order to improve their efficiencies. Along with an advancement in manufacturing techniques, the products that have small size, high heat flux and non-uniform heat flux have occupied a significant portion in many industries. Also, with low thermal conductivity and high of common heat transfer liquids including water, ammonia, and mineral oil are the major issues in heat transfer applications. The convective thermal performance was often inefficient and created barriers. in designing small heat rejecting devices. Therefore, an innovative coolant like nanofluid with improved heat transfer properties is desired.

2. CARBON-BASED NANOFLUIDS

Carbon-based nanofluids can be defined as the nanofluids which contain carbon-based as the suspended in the base fluids. They are synthesized by using following materials as nanoparticles:

1. Graphene 2. Nano-diamonds 3. Fullerenes

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International Conference on Ideas, Impact and Innovation in Mechanical Engineering (ICIIIME 2017) ISSN: 2321-8169 Volume: 5 Issue: 6 882 -– 886 ______4. Carbon Nano-tubes

3. GRAPHENE

Graphene is an allotrope of carbon in the form of a two-dimensional, atomic-scale, hexagonal lattice in which one atom forms each vertex. It is the basic structural element of other allotropes, including graphite, charcoal, carbon nanotubes and fullerenes. Graphene is a 2D building material for carbon materials of all other dimensionalities. It can be wrapped up into 0D Bucky balls, rolled into 1D nanotubes or stacked into 3D graphite [1].

Fig.1-Different forms of Graphene

4. METHODS & MECHANISMS OF GRAPHENE SYNTHSIS

In 1958, Hummers’ method was developed to produce graphene oxide as faster, safer and more efficient method. Before development of Hummers’ method, the production of graphene oxide was hazardous and slow due to the usage of concentrated nitric and sulphuric acid.

Oxygen Carbon Water Ash Carbon-to-oxygen Method (%) (%) (%) (%) atomic ration

Hummers 47.06 27.97 22.99 1.98 2.25

Staudenmaier 52.112 23.99 22.2 1.90 2.89

Table-1: A comparison of Hummers method to the Staudenmaier method.

The Staudenmaier, Hofmann and Hummers methods introduced the addition of potassium chlorate. Hummers and Offerman created a method as an alternative to the above methods at the National Lead Company after noting the hazards wastes. Their approach was involved adding graphite powder to a solution of concentrated acid. However, they simplified it to just graphite, concentrated sodium nitrate, sulphuric acid and potassium nitrate [2].

883 IJRITCC | June 2017, Available @ http://www.ijritcc.org (Special Issue) ______

International Conference on Ideas, Impact and Innovation in Mechanical Engineering (ICIIIME 2017) ISSN: 2321- 8169 Volume: 5 Issue: 6 882 -– 886 ______

Fig-2: Hummers’ method to obtain Graphene & Graphene oxide

Different mechanisms for graphene synthesis are as follows [3]:

Synthesis Method Size of Graphene Graphene produced Mechanism

Thermal decomposition of Epitaxial growth >50 μm Pristine hydrocarbons

Peeling off layers using Mechanical exfoliation 10 μm Pristine scotch tape

Chemical vapour Carbon segregation or >100 μm Pristine deposition precipitation

Chemically modified Decomposition, reduction and Chemical exfoliation >100 nm graphene subsequent exfoliation

Liquid phase Exposing graphite to solvents exfoliation <20 μm Pristine and sonication

Un-zipping carbon Chemically modified Longitudinal unzipping of <10 nm Nanotubes graphene CNT

Table-2: Different mechanisms & their yields

884 IJRITCC | June 2017, Available @ http://www.ijritcc.org (Special Issue) ______

International Conference on Ideas, Impact and Innovation in Mechanical Engineering (ICIIIME 2017) ISSN: 2321-8169 Volume: 5 Issue: 6 882 -– 886 ______5. PROPERTIES OF GRAPHENE NANOFLUIDS

5.1 THERMAL CONDUCTIVITY

Based on literature study it has been found that thermal conductivity of nanofluids is influenced by size, temperature, concentration, particle motions and so on. In this section, some of these parameters have been reviewed. The following diagram shows all the parameters on which the thermal conductivity of graphene nanofluids depends [4]:

Morphology

Clustering Temperature

Parameters

Thermal Concentration conductivity

Motion

Fig-3: Parameters that affect the thermal conductivity of nanofluids

5.2 DENSITY OF GRAPHENE NANOFLUIDS

Density of Nano fluid is one of the main parameters for assessing the heat transfer characteristics. Density of the nanofluids can be calculated experimentally as well as theoretically [5].

The density of nanofluids can be calculated by using the following formula:

��풏�� =����풏�� + (ퟏ − ��)��풃풇

where 휑 - volume fraction of sample

푛�� - nanofluid

푛��-nanoparticle

푏�� – base fluid

885 IJRITCC | June 2017, Available @ http://www.ijritcc.org (Special Issue) ______

International Conference on Ideas, Impact and Innovation in Mechanical Engineering (ICIIIME 2017) ISSN: 2321-8169 Volume: 5 Issue: 6 882 -– 886 ______6. ADVANTAGES OF GRAPHENE NANOFLUIDS

Advantages of graphene nanofluids over other nanofluids are as follows:

1. Easy to synthesis and longer suspension time (More stable) 2. Larger surface area/volume ratio (1000 times larger) 3. Higher thermal conductivity 4. Lower erosion, corrosion and clogging 5. Lower demand for pumping power 6. Reduction in inventory of heat transfer fluid 7. Significant energy saving

7. DISADVANTAGES OF GRAPHENE NANOFLUIDS

Disadvantages of graphene nanofluids with respect to other nanofluids are as follows:

1. High Processing cost

2. Agglomeration at higher pH value and also at high temperatures because of the ability of the particle to overcome thermal energy barrier leading to an increase in Van der Waals forces and

hence resulting in decrease of conductivity. 3. Use of surfactants for stability which results in lowering of conductivity due to the formation of a thermal boundary layer around the particles.

8. APPLICATIONS OF GRAPHENE NANOFLUIDS

The different applications of graphene nanofluids are as follows:

Nuclear System Cooling Space and Defense Solar Absorption Mechanical Application Magnetic Sealing Biomedical Application Heat transfer Intensification Electronic Application Transportation Industrial Cooling Application Heating Building and Reducing Pollution References

(1) Geim AK, Novoselov KS. The rise of graphene. Nat Mater 2007;6(3): pp.183–91. (2) Hummers Jr WS, Offeman RE. Preparation of graphitic oxide. J Am Chem Soc 1958; 80:1339. (3) Li P, Zheng Y, Wu Y, Qu P, Yang R, Zhang A. Nanoscale ionic graphene material with liquid-like behavior in the absence of solvent. Appl Surf Sci 2014;314: pp. 983–90 (4) Mehrali M, Sadeghinezhad E, Latibari S Tahan, Mehrali M, Togun H, Zubir MNM, et al. Preparation, characterization, viscosity, and thermal conductivity of nitrogen-doped graphene aqueous nanofluids. J Mater Sci 2014;49: 7156–71. (5) Ahammed N, Asirvatham L, Wongwises S. Effect of volume concentration and temperature on viscosity and surface tension of graphene–water nanofluid for heat transfer applications. J Therm Anal Calorim 2015:1– 11. 886 IJRITCC | June 2017, Available @ http://www.ijritcc.org (Special Issue) ______