Nanofluids and its Applications

International Journal of Engineering, Management & Sciences (IJEMS) ISSN-2348 –3733, Volume-2, Issue-1, January 2015

Nanofluids and its Applications Deepak Kumar Bairwa , Khagendra Kumar Upman, Ganesh Kantak  Abstract— Recent advancements in nanotechnology have originated the new emerging heat transfer fluids. Nanofluids are potential heat transfer fluids with enhanced thermophysical properties and heat transfer performance. These fluids are obtained by suspending nanoparticles having sizes between 1 and 100 nm in regular fluids. In this paper, study of the applications and challenges of nanofluids have been compiled and reviewed. Substitution of conventional coolants by nanofluids appears promising. It can be applied in many devices for better performances (i.e. energy, heat transfer and other performances). At last challenges of nanofluids is discussed.

Index Terms— Nanotechnology, Nanofluids, Heat Transfer

I. INTRODUCTION The term "Nanotechnology" was first defined by Norio Taniguchi of the Tokyo Science University in 1974.

Nanotechnology shortened to "Nanotech", is the study of manipulating matter on an atomic and molecular scale.

Generally nanotechnology deals with structures sized between 1 to 100 nm and involve developing materials or devices within that size. For comparison, 10 nanometers is 1000 times smaller than the diameter of a human hair. The application of nanomaterials can be historically traced back to even before the generation of modern science and technology.

In 1857, Michael Faraday explained how metal nano particles affect the colour of church windows. In the past decades, sophisticated instruments for characterization and manipulation17-20 such as scanning electron microscopy, transmission electron microscopy and scanning probe microscopy became more available for researchers to approach the nanoworld. In the early 1990s Huffman and Kraetschmer, discovered how to synthesize and purify large quantities of fullerenes. This opened the door to their characterization and functionalization by hundreds of investigators in government and industrial laboratories.

Shortly after, at a meeting of the Materials Research Society in 1992, Ebbesen described to a spellbound audience his discovery and characterization of carbon nanotubes. This event sent those in attendance and others downwind of his presentation into their laboratories to reproduce and push Manuscript received January 20, 2015.

Deepak Kumar Bairwa , Jaipur Khagendra Kumar Upman, Jaipur Ganesh Kantak, Jaipur

those discoveries forward. Using the same or similar tools as those used by Huffman and Kratschmer, hundreds of researchers further developed the field of nanotechnology [2].

Nanofluids are a relatively new class of fluids which consist of a base fluid with nano-sized particles (1–100 nm) suspended within them. It is introduced by Choi on Argonne National Laboratory at 1995. ‘Nanofluid’ is a new class of heat transfer fluid that utilizes dispersion of fine scale metallic particles in a heat transport liquid in appropriate size and volume fraction to derive a significant enhancement in the effective heat transfer coefficient of the mixture. In comparison to dispersing micron-size ceramic particles, nanofluids consist of suspension of ultra-fine or nanometric metallic particles with much smaller size and volume fraction, and yet offer a remarkably higher efficiency of heat transport [1]. Nanofluids are two-phase systems with one phase (solid phase) in another (liquid phase). Nanofluids have been found to possess enhanced thermophysical properties such as thermal conductivity, thermal diffusivity, viscosity, and convective heat transfer coefficients compared to those of base fluids like oil or water. Nanofluids provide higher thermal conductivity compared to base fluids. Its value increases with particles concentration. Temperature, particles size, dispersion and stability do play important role in determining thermal conductivity of nanofluids. Figure 1 shows that the Comparison of the thermal conductivity of of common liquids, polymers and solids [10].

Figure 1: Comparison of the thermal conductivity of common liquids, polymers and solids [10]

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Nanofluids and its Applications

II. SYNTHESIS AND PREPARATION OF NANOFLUID Preparation of nanofluids is the first key step in experimental studies with nanofluids. Nanofluids are not just dispersion of solid particles in a fluid. The essential requirements that a nanofluid must fulfill are even and stable suspension, adequate durability, negligible agglomeration of particles, no chemical change of the particles or fluid, etc. Nanofluids are produced by dispersing nanometer scale solid particles into base liquids such as water, ethylene glycol, oil, etc. In the synthesis of nanofluids, agglomeration is a major problem.

There are mainly two techniques used to produce nanofluids: the single-step and the two-step method.

A. The Single-step Process The one-step process consists of simultaneously making and dispersing the particles in the fluid. In this method, the processes of drying, storage, transportation, and dispersion of nanoparticles are avoided, so the agglomeration of nanoparticles is minimized, and the stability of fluids is increased. The one-step processes can prepare uniformly dispersed nanoparticles, and the particles can be stably suspended in the base fluid. The vacuum submerged arc nanoparticle synthesis system is another efficient method to prepare nanofluids using different dielectric liquids . The different morphologies are mainly influenced and determined by various thermal conductivity properties of the dielectric liquids. The nanoparticles prepared exhibit needle-like, polygonal, square, and circular morphological shapes. The method avoids the undesired particle aggregation fairly well.

One-step physical method cannot synthesize nanofluids in large scale, and the cost is also high, so the one-step chemical method is developing rapidly. One-step chemical method is used for preparing copper nanofluids by reducing CuSO4 路 5H2O with NaH2PO2 路 H2O in ethylene glycol under microwave irradiation. Well-dispersed and stably suspended copper nanofluids were obtained. Mineral oil-based nanofluids containing silver nanoparticles with a narrow-size distribution were also prepared by this method . The particles could be stabilized by Korantin, which coordinated to the silver particle surfaces via two oxygen atoms forming a dense layer around the particles. The silver nanoparticle suspensions were stable for about 1 month. Stable ethanol-based nanofluids containing silver nanoparticles could be prepared by microwave-assisted one-step method .

In the method, polyvinylpyrrolidone was employed as the stabilizer of colloidal silver and reducing agent for silver in solution. The cationic surfactant octadecylamine (ODA) is also an efficient phase-transfer agent to synthesize silver colloids . The phase transfer of the silver nanoparticles arises due to coupling of the silver nanoparticles with the ODA molecules present in organic phase via either coordination bond formation or weak covalent interaction. Phase transfer method has been developed for preparing homogeneous and stable grapheme oxide colloids. Graphene oxide nanosheets were successfully transferred from water to n-octane after

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modification by oleylamine, and the schematic illustration of the phase transfer process is shown in Figure 2.

However, there are some disadvantages for one-step method.

The most important one is that the residual reactants are left in the nanofluids due to incomplete reaction or stabilization. It is difficult to elucidate the nanoparticle effect without eliminating this impurity effect [4].

Figure 2: Schematic illustration of the phase transfer process [4]

B. The Two Step Process Two-step method is the most widely used method for preparing nanofluids. Nanoparticles, nanofibers, nanotubes, or other nanomaterials used in this method are first produced as dry powders by chemical or physical methods. Then, the nanosized powder will be dispersed into a fluid in the second processing step with the help of intensive magnetic force agitation, ultrasonic agitation, high-shear mixing, homogenizing, and ball milling. Two-step method is the most economic method to produce nanofluids in large scale, because nanopowder synthesis techniques have already been scaled up to industrial production levels. Due to the high surface area and surface activity, nanoparticles have the tendency to aggregate. The important technique to enhance the stability of nanoparticles in fluids is the use of surfactants.

However, the functionality of the surfactants under high temperature is also a big concern, especially for high-temperature applications [4].

III. ADVANTAGES OF NANOFLUIDS 1. Compared to conventional solid-liquid suspensions for heat transfer intensifications, properly

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International Journal of Engineering, Management & Sciences (IJEMS) ISSN-2348 –3733, Volume-2, Issue-1, January 2015

2.

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engineered thermal nanofluids possess the following advantages: 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 [9].

liquid cooling of computer processors due to their high thermal conductivity.

2. Microscale Fluidic Applications: The manipulation of small volumes of liquid is necessary in fluidic digital display devices, optical devices, and microelectromechanical systems (MEMS) such as lab-on-chip analysis systems. This can be done by electrowetting, or reducing the contact angle by an applied voltage, the small volumes of liquid.

Electrowetting on dielectric (EWOD) actuation is one very useful method of microscale liquid manipulation. Nanofluids are effective in engineering the wettability of the surface and possibly of surface tension.

D. Biomedical Applications

IV. APPLICATION OF NANOFLUIDS Nanofluids can be used in various engineering applications.

These are following application of nanofluids.

A. Heat Transfer Applications 1. Industrial Cooling Applications: For the U.S. electric power industry, using nanofluids in closed loop cooling cycles could save about 10–30 trillion Btu per year (equivalent to the annual energy consumption of about 50,000–150,000 households).

2. Extraction of Geothermal Power and Other Energy Sources: When extracting energy from the earth’s crust that varies in length between 5 to 10 km and temperature between 5000C and 10000C, nanofluids can be employed to cool the pipes exposed to such high temperatures.

B. Automotive Applications 1. Nanofluid Coolant: The use of nanofluids as coolants would allow for smaller size and better positioning of the radiators. Owing to the fact that there would be less fluid due to the higher efficiency, coolant pumps could be shrunk and truck engines could be operated at higher temperatures allowing for more horsepower while still meeting stringent emission standards.

2. Lubricants: In automotive lubrication applications, surface-modified nanoparticles stably dispersed in mineral oils are effective in reducing wear and enhancing load-carrying capacity.

C. Electronic Applications 1. Cooling of Microchips: A principal limitation on developing smaller microchips is the rapid heat dissipation. However, nanofluids can be used for

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1. Cancer Theraupetics: Magnetic nanofluids are to be used to guide the particles up the bloodstream to a tumor with magnets. It will allow doctors to deliver high local doses of drugs or radiation without damaging nearby healthy tissue, which is a significant side effect of traditional cancer treatment methods.

2. Nanocryosurgery : Cryosurgery is a procedure that uses freezing to destroy undesired tissues Intentional loading of nanoparticles with high thermal conductivity into the target tissues can reduce the final temperature, increase the maximum freezing rate [3].

V. CHALLENGES OF NANOFLUIDS 1. Higher viscosity: The viscosity of nanoparticle–water suspensions increases in accordance with increasing particle concentration in the suspension. So, the particle mass fraction cannot be increased unlimitedly.

2. Lower specific heat: specific heat of nanofluids is lower than basefluid. CuO/ethylene glycol nanofluids, SiO2/ethylene glycol nanofluids and Al2O3/ethylene glycol nanofluids exhibit lower specific heat compared to basefluids. An ideal coolant should possess higher value of specific heat which enable the coolant to remove more heat.

3. Thermal conductivity: The existing models for predicting thermal conductivities of CNT nanofluids, including Hamilton–Crosser model, Yu–Choi model and Xue model, cannot predict the thermal conductivities of CNT nanorefrigerants within a mean deviation of less than 15%.

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Nanofluids and its Applications

4. High cost of nanofluids: Higher production cost of nanofluids is among the reasons that may hinder the application of nanofluids in industry. Nanofluids can be produced by either one step or two steps methods.

However both methods require advanced and sophisticated equipments.

5. Difficulties in production process: Nanoparticles are inherently produced from processes that involve reduction reactions or ion exchange. Furthermore, the base fluids contain other ions and reaction products that are difficult or impossible to separate from the fluids. Nanoparticles’ tendency to agglomerate into larger particles, which limits the benefits of the high surface area nanoparticles. To counter this tendency, particle dispersion additives are often added to the base fluid with the nanoparticles. Unfortunately, this practice can change the surface properties of the particles, and nanofluids prepared in this way may contain unacceptable levels of impurities [9].

[7] Harode, R.P., Deshmukh, M.S., (2011), “Nanofluids: Energy Efficient Heat Transfer Fluid”, International Journal of Fluids Engineering, 3(3), 301-309.

[8] Ranakoti, G., Dewangan, I.S., Kosti, S., Nemade, R., (2012), “Heat Transfer Enhancement by Nano Fluids”, Convective Heat and Mass Transfer, April 2012,1-9.

[9] Saidur, R., Leong, K.Y., Mohammad, H.A., (2011), “A Review on Applications and Challenges of Nanofluids”, Renewable and Sustainable Energy Reviews, 15, 1646-1668.

[10]Wen, D., Lin, G., Vafaei, S., Zhang, K., (2009), “Review of Nanofluids for Heat Transfer Applications”, Particuology, 7, 141-150.

VI. CONCLUSION Nanofluids are important because they can be used in numerous applications involving heat transfer, and other applications such as in biomedical, automotive etc. Colloids which are also nanofluids have been used in the biomedical field for a long time, and their use will continue to grow.

Colloids will see an increase in use in biomedical engineering and the biosciences.

Problems of nano particle agglomeration, higher viscosity, lower specific heat, difficulties in production process, all need to be examined in detail in the applications. Once the science and engineering of nanofluids are fully understood and their full potential researched, they can be reproduced on a large scale and used in many applications.

REFERENCES [1] Manna, I., (2009), “Synthesis, Characterization and Application of Nanofluid – An Overview”, Journal of the Indian Institute of Science, 89(1), 21-33.

[2] Arivalagan, K., Ravichandran, S., Rangasamy K., Karthikeyan E., (2011), “Nanomaterials and its Potential Applications”, International Journal of ChemTech Research, 3(2), 534-538 .

[3] Wong, K.V., Leon, O.D., (2010), “Applications of Nanofluids: Current and Future”, Advances in Mechanical Engineering, Volume 2010, doi:10.1155/2010/519659,1-11.

[4] Yu, W., Xie,H., (2012), “A Review on Nanofluids: Preparation, Stability Mechanisms, and Applications”, Journal of Nanomaterials, Volume 2012, doi:10.1155/2012/435873, 1-17.

[5] Ding, Y., Chen, H., Wang, L., Yang, C.Y., He, Y., Yang, W., Lee, W. P., Zhang L., Huo R., (2007)“Heat Transfer Intensification Using Nanofluids”, KONA Powder and Particle Journal,25, 23-38.

[6] Choi, S.U.S., (2008), “Nanofluids: A New Field of Scientific Research and Innovative Applications”, Heat Transfer Engineering, 29(5), 429–431.

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