Review Paper Investigation on Enhancement of Heat Transfer Using Different Type of Nanofluids Review Authors 1 Ramesh Bhoi *, 2 Dinesh Dabhi, 3 Chetan Jaiswal Address for Correspondence: 1, 2 Mechanical Engineering Department, Gujarat Technological University, Gujarat, India 3 Assistant Professor, Mechanical Engineering Department, Parul Institute of Engineering & Technology, Gujarat Technological University, Gujarat, India Abstract: Nanofluids are new generation heat transfer fluid in which metallic or non-metallic nanoparticles are suspended in convectional fluid and this ultrafine particles change transport properties and heat transfer performance of the nanofluid. This paper presents an overall review of a number of researches on nanofluid heat transfer technologies and their applications for the energy efficiency improvement in various thermal systems in recent years. In this paper, the effect parameter such as nanoparticle diameter, nanoparticle concentration, types of nanoparticles and heat transfer comparison between nanofluid and pure fluid is studied. Introduction A reduction in energy consumption is possible by enhancing the performance of heat exchange systems. Heat transfer is one of the most important processes in industrial and consumer products. Heat transfer fluids such as water, mineral oil and ethylene glycol play a vital role in many industrial processes, including power generation, chemical processes, heating or cooling processes, and microelectronics. The poor heat transfer properties of these common fluids compared to most solids is a primary obstacle to the high compactness and effectiveness of heat exchangers. An innovative idea is to suspend ultrafine solid particles in the fluid which having thermal conductivities higher than conventional fluid for improving performance of heat exchange systems. Materials commonly used as nanoparticles include chemically stable metals (e.g. gold, copper), metal oxides (e.g., alumina, silica, zirconia, titania), oxide ceramics (e.g. Al2O3, CuO), metal carbides (e.g. SiC), metal nitrides (e.g. AIN, SiN), carbon in various forms (e.g., diamond, graphite, carbon nanotubes, fullerene) and functionalized nanoparticles. Solids have thermal conductivities which are orders of magnitude larger than those of conventional heat transfer fluids as shown in Table1. Table 1: Thermal conductivity of different type of material Material Carbon Metallic solids (pure) Non-metallic solids Metallic liquids Others Form Nanotubes Diamond Graphite Fullerenes film Silver Copper Nickel Thermal Conductivity (W/mK) 1800-6600 2300 110-190 0.4 429 401 237 Silicon 148 Aluminium Sodium at 644 K Water Ethylene Glycol Engine Oil R134a 40 72.3 0.613 0.253 0.145 0.0811 ijars/ Vol. II/ Issue I/Jan, 2013/295 1
Preparation of Nanofluids Preparation of nanofluids is important experimental studies with nanofluids because Nanofluids are not simply liquid-solid mixtures. Some special requirements are essential, e.g., even and stable suspension, durable suspension, negligible agglomeration of particles, no chemical change of the fluid, etc. Nanofluids are produced by dispersing nanometer-scale solid particles into base liquids such as water, ethylene glycol, oils, etc. There are mainly two techniques used to produce nanofluids: the single-step and the two-step method. oxide nanoparticles, while it is less successful with metallic particles. Thermo physical properties of nanofluid It is expected that the heat transfer coefficient of the nanofluid will depend on the thermal conductivity and the heat capacity of the base fluid and nanomaterials, flow pattern, Reynolds and Prandtl numbers, temperature, the volume fraction of the suspended particles, the dimensions and shape of the particles. So, some of the thermophysical properties used in this paper are defined as: The single-step direct evaporation approach was developed by Akoh et al. (1978) and is called the VEROS (Vacuum Evaporation onto a Running Oil Substrate) technique. The original idea of this method was to produce nanoparticles, but it is difficult to subsequently separate the particles from the fluids to produce dry nanoparticles. A modified VEROS process was proposed by Wagener et al. (1997). They employed high pressure magnetron sputtering for the preparation of suspensions with metal nanoparticles such as Ag and Fe. Eastman et al. (1997) developed a modified VEROS technique, in which Cu vapour is directly condensed into nanoparticles by contact with a flowing lowvapour-pressure liquid (EG). Zhu et al. (2004) presented a novel one-step chemical method for preparing copper nanofluids by reducing CuSO 4 5H 2 O with NaH 2 PO 2 H 2 O in ethylene glycol under microwave irradiation. Results showed that the addition of NaH 2 PO 2 H 2 O and the adoption of microwave irradiation are two significant factors which affect the reaction rate and the properties of Cu nanofluids.the two-step method is extensively used in the synthesis of nanofluids considering the available commercial nanopowders supplied by several companies. In this method, nanoparticles are first produced and then dispersed in the base fluids. Generally, ultrasonic equipment is used to intensively disperse the particles and reduce the agglomeration of particles. Eastman et al. (1997), Lee et al. (1999), and Wang et al. (1999) used this method to produce Al2O3 nanofluids. Also, Murshed et al. (2005) prepared TiO2 suspension in water using the twostep method. As compared to the single-step method, the two-step technique works well for Density ijars/ Vol. II/ Issue I/Jan, 2013/295 2 The nanofluid density ρnf is the average of the nano-particles and base fluid densities. ρ nf = ϕ ρ p + 1 ϕ ρ bf Specific heat The nanofluid specific heat is Viscosity Cp nf = ϕρ p Cp p + 1 ϕ ρ bf Cp bf ρ nf General and accurate models for prediction of viscosity of a nanofluid, μ, are not available at this time. However, the room temperature viscosity measured by Pak and Cho [8] can be correlated by means of the following equation. μ nf = μ bf 1 + 39.11ϕ + 533.9ϕ 2 Thermal conductivity Thermal conductivity of nanofluid for Al2O3+water is developed by [9] k nf k bf = Re nf.175 ϕ.05 k p k bf Experimental Approach.2324 Zeinali Heris et al (2012) investigate the effect of parameters such as nanoparticles concentration (ν), nanoparticle diameter (dp), and Reynolds number on the heat transfer in a triangular ducts using nanofluids. Fig. shows the average Nusselt number versus Re for pure water and water/ CuO nanofluid. They found enhancement of heat transfer by adding nanoparticles to the base fluid. For example, at
Re=2065, Nusselt number of water is increased from 3.79 to 5.38 by adding nanoparticles of CuO (.01 volume concentration, diameter of 10 nm). Figure 1: Comparison between nanofluid and pure fluid heat transfer Zeinali Heris et al investigate on average Nusselt number versus Reynolds at various concentration of CuO for 10nm-40nm nanoparticles. The effects of nanoparticle size and particle concentration on the thermal conductivity are shown in figure. It indicates that the average Nusselt number increases with nanoparticles concentration, and better enhancement is seen at lower particle diameters. They also compare the heat transfer enhancement using different kind of solid nano-additive; Fig. shows the Nusselt number versus Reynolds number of three nanofluids at various volume fraction for 10nm nanoparticles. So water/cu nanofluid with 0.04 volume concentrations of 10nm Cu nanoparticles has a maximum heat transfer in comparison with the two other types of nanofluid. Figure 2: Comparison of Nusselt number versus Reynolds number for three different nanofluids at 0.02, 0.04 volume fractions of 10nm nanoparticles. ijars/ Vol. II/ Issue I/Jan, 2013/295 3 Figure 3: The influence of CuO nanoparticles volume concentration on the Nusselt number over a range of Reynolds numbers with 10-40 nm diameter nanoparticles
Somaye NASR at al (2011) conducted experiments on concentric tube and plate heat exchanger and found out comparison of heat transfer rate at different nanoparticle concentration and mesh size of particle and different type of nanoparticle.. Figures 4 and 5 show the heat transfer rate and total heat transfer coefficients vs. hot fluid mass flow rate for various cold fluid flow rates. Also the comparison between the heat transfer of nanofluid and base fluid. Heat transfer rates increases with increasing in hot and cold liquid flow rates. Also for a given hot or cold flow rate, the heat transfer rate and total heat transfer coefficient of the nanofluid is higher than the distilled water. Increasing the hot fluid flow rate leads to an increase in the heat transfer rate and results in an increase in the heat transfer coefficient. Figure 5: Effect of hot and cold flow rate on overall heat transfer coefficient of nanofluids in concentric tube heat exchanger and plate heat exchanger Figure 4: Effect of hot and cold flow rate on heat transfer rate of nanofluids in concentric tube heat exchanger and plate heat exchanger ijars/ Vol. II/ Issue I/Jan, 2013/295 4 Figure 6: Comparison between heat transfer coefficient of distilled water and nanofluid in the concentric tube heat exchanger
Figure 9 shows overall heat transfer coefficient of nano-fluid and distilled water vs. hot fluid mass flow rate. From this figure it is clear that for a constant mass flow rate, heat transfer coefficients of nanofluid are much higher than distilled water. Figure 10 shows the comparison between heat transfer coefficients in the concentric tube and plate heat exchangers. It can be seen from this figure that the heat transfer coefficients for both distilled water and nanofluid in the plate heat exchanger is higher than double pipe heat exchanger. Because however the heat transfer areas are the same in the heat exchangers, but in the plate heat exchanger, the fluids spread out over the plates. This facilitates the transfer of heat, and greatly increases the speed of the temperature change. Figure 7: Comparison between heat transfer coefficient of distilled water and nanofluid in the plate heat exchanger Conclusion This paper presents an overview of the recent investigations in the study the thermophysical characteristics of nanofluids and their role in heat transfer enhancement from heat exchangers. Most of the experimental and numerical studies showed that nanofluids exhibit an enhanced heat transfer coefficient compared to its base fluid and it increases significantly with increasing concentration of nanoparticles as well as Reynolds number. Nomenclature C Cp h k m NTU Nu Q Re U ρ μ ε heat capacity rate, W/C specific heat J/kg C heat transfer coefficient, W/m 2 C thermal conductivity, W/m C mass flow rate, Kg/sec number of heat transfer units Nusselt number heat transfer rates, KW Reynolds number overall heat transfer coefficient W/ C density, kg/m3 dynamic viscosity, Kg/m s heat exchanger effectiveness Subscripts a air side c coolant side bf basefluid nf nanofluid p nano particle References 1. Akoh, H., Tsukasaki, Y., S.Yatsuya, and Tasaki, A. Magnetic properties of ferromagnetic ultrafine particles prepared by vacuum evaporation on running oil substrate. Journal of Crystal Growth,45, 495 500 (1978). Figure 8: Comparison between heat transfer coefficients in the plate heat exchanger and concentric tube heat exchanger 2. Wagener, M., Murty, B. S., and Gunther, B. Preparation of metal nanosuspensions by high pressure DC-sputtering on running liquids. In Komarnenl, S., Parker, J. C., and Wollenberger, H. J. (Editors), Nanocrystalline and Nanocomposite Materials II, volume 457, 149 154. Materials Research Society, Pittsburgh PA (1997). ijars/ Vol. II/ Issue I/Jan, 2013/295 5
3. Eastman, J. A., Choi, U. S., Li, S., Thompson, L. J., and Lee, S. Enhanced thermal conductivity through the development of nanofluids. Volume 457 of Materials Research Society Symposium - Proceedings, 3 11. Materials Research Society, Pittsburgh, PA, USA, Boston, MA, USA (1997). 4. Zhu, H., Lin, Y., and Yin, Y. A novel onestep chemical method for preparation of copper nanofluids. Journal of Colloid and Interface Science, 227, 100 103 (2004). 5. Lee, S., Choi, S. U. S., Li, S., and Eastman, J. A. Measuring thermal conductivity of fluids containing oxide nanoparticles. Journal of Heat Transfer, 121, 280 289 (1999). 6. Wang, X., Xu, X., and Choi, S. U. S. Thermal conductivity of nanoparticle-fluid mixture. Journal of Thermophysics and Heat Transfer, 13, no. 4, 474 480 (1999). 7. B.C.Pak and Y.Cho, 1998, Hydrodynamic and heat transfer study of dispersed fluids with submicron metallic oxide particles, J. of Experimental heat transfer, vol. 11, No. 2, pp 151-170. 8. Vasu, V., RamaKrishna, K., Kumar, A.C.S. 2007. Exploitation of Thermal properties of fluids embedded with nanostructured materials, International energy Journal 8: 181-190. 9. Haghshenas Fard, M.,A.A., et al Numerical and Experimental investigation of heat transfer of ZnO/water nanofluid in the concentric tube and plate heat exchangers THERMAL SCIENCE, Year 2011, Vol.15, No 1,pp.183-194. 10. S.Zeinali Heris et al, Cuo/Water Nanofluid Heat transfer Through traiangular Ducts, Iranian journal of Chemical Engineering (IAChE )Vol.9,No.1(Winter),2012. rhbhoi@gmail.com * Corresponding Author Email-Id ijars/ Vol. II/ Issue I/Jan, 2013/295 6