SEMINAR(CH-510) On NANOFLUIDS BY: UMESH SHARMA ID:2011PCH5301 M.Tech (II Sem.)

NANOFLUIDS Nano fluids are the new class engineered fluid with high thermal conductivity obtained by suspending nanometer size (1-100nm) particles in a base fluid like water ,ethylene glycol, oil etc.

NANOPARTICLES AND BASE FLUIDS Aluminum oxide (Al2O3) Titanium dioxide (TiO2) Copper oxide (CuO) Base fluids Water Oil Ethylene glycol U.S. Choi and J.A. Eastman, “Enhanced heat transfer using nanofluids” U.S. Patent #6,221,275

Why Use Nanoparticles Studies of thermal conductivity of suspensions have been confined to mm- or μm-sized particles. The major challenge is the rapid settling of these particles in fluids. Nanoparticles stay suspended much longer than micro-particles and, if below a threshold level and/or enhanced with surfactants/stabilizers, remain in suspension almost indefinitely. Furthermore, the surface area per unit volume of nanoparticles is much larger (million times) than that of microparticles (the number of surface atoms per unit of interior atoms of nanoparticles, is very large). These properties can be utilized to develop stable suspensions with enhanced flow, heat-transfer, and other characteristics.

Methods for Producing Nanoparticles/Nanofluids Two nanofluid production methods has been developed in ANL to allow selection of the most appropriate nanoparticle material for a particular application. In two-step process for oxide nanoparticles (“Kool-Aid” method), nanoparticles are produced by evaporation and inert-gas condensation processing, and then dispersed (mixed, including mechanical agitation and sonification) in base fluid. In one-step process simultaneously makes and disperses nanoparticles directly into base fluid; best for metallic nanofluids.

-ZrO2 in water that produce with two - Cu Nanoparticles produced by Step method direct evaporation into ethylene glycol

Effect of Particle Clustering Some times nanofluids are in form of cluster when the concentration is high or when the time is increase. It is accepted that heat transfer is a surface phenomenon and the thermal energy interaction take places at the surface of nanoparticles. When the particles get agglomerated, the effective surface area to volume ratio decreases, thus reducing the effective area of thermal interaction of particles causing a decrease in the thermal conductivity of the fluid.

Mesh like structure observed, in water based CuO nanofluid of 0 Mesh like structure observed, in water based CuO nanofluid of 0.1 vol%after sonication for (a) 20min, (b) 60min and (c) 70 min. It can be seen the structure formation being only after 60 min from the sonication.

Stability of Nanofluid The agglomeration of nanoparticles results in not only the settlement and clogging of microchannels but also the decreasing of thermal conductivity of nanofluid. So stability evaluation methods for nanofluid are-: Sedimentation and Centrifugation Zeta potential analysis Spectral absorbency analysis

Ways to Enhance the Stability of Nanofluid 1) Use of various surfactants in Nanofluid Non ionic surfactant without charge groups in its head Anionic surfactant with negatively charged groups Cationic surfactant with positively charged groups Amphoteric surfactant with zwitterionic head groups 2) Surface Modification techniques 3) By dominating the repulsive force between the particles

Stability Mechanism of Nanofluid

Thermal Conductivity According to the report of Argonne National Laboratory, eight parameters effect the thermal conductivity of nanofluids, they got these results from about 124 researchers experiments, these effects are: Particle volume concentration Particle materials Particle size Particle shape Base fluid material Temperature Additive Acidity

Effect of Particle Volume Concentration: From the experimental results the general trend is clear: thermal conductivity enhancement increases with increase particle volume concentration. (Al in water) Al2O3. Effect of Particle Material: The thermal conductivity ratio is seen to increase faster for metal than oxide particles. (Particles in ethylene glycol)

Effect of Particle Size: Most of the researchers report that the larger particle diameters produce a large enhancement in thermal conductivity but in some cases the experiments show the different thing. A consistent trend appears where in the larger particle diameters produce a large enhancement in thermal conductivity. (Al in water) Al2O3 Effect of Particle Shape: All of the results indicate that elongated particles are superior to spherical for thermal conductivity enhancement. (SiC in water).

Effect of Base Fluid Material : The results show increased thermal conductivity enhancement for poorer (lower thermal conductivity) heat transfer fluid. The results show the least enhancement for water, which is the best heat transfer fluid with the highest thermal conductivity of the fluids compared. (Al in fluids) Al2O3 Effect of Temperature: The trend of all experimental shows increased thermal conductivity enhancement with increased temperature. (Al in water) Al2O3

Effect of Acidity (PH): Effect of Additives: Experiments have used fluid additives in an attempt to keep nanoparticles in suspension and to prevent them from agglomerating. The thermal conductivity enhancement improved by using the additive. (Cu in ethylene glycol) Effect of Acidity (PH): Limited studies have been published on the effect of fluid acidity on the thermal conductivity enhancement of nanofluids. But the general trend is that acidity increases the thermal conductivity enhancement. (Al in water) Al2O3

CONDUCTIVITY OF METALLIC NANOFLUIDS Three samples of CuO-ethylene glycol were taken first two stabilizer not added Labeled old- kept for 2 months Labeled new- 2 days old 1% Thioglycol acid added 40%increase in conductivity of acidic nanofluid for 3% Concentration. Thioglycol acid improves dispersion Metallic nanofluids greater conductivity compared to oxide nanofluids Effective conductivity of CuO-ethylene glycol nanofluid, Eastman et al. (2001)

THERMAL CONDUCTIVITY OF OXIDE NANOFLUIDS Measurement method 1)Linear relation between thermal conductivity and volume fraction. 2) Enhancement in water-Cuo nearly equals ethylene glycol-Al2O3 system 3) Ethylene glycol Cuo (24nm) system indicates maximum enhancement 4) Water-glycol Al2O3 (38nm) system least increment Enhanced thermal conductivity of oxide nanofluids (Lee et al., 1999)

Experimental Studies on Thermal Conductivity of Nanofluids Investigator Particles Size (nm) Fluids Observations Eastman et al (1997) Al2O3/CuO/Cu 33/36/ water,oil 60% improvement for 5 vol% CuO particles in water. Lee et al (1999) Al2O3/CuO 24.4,38.4/18.6,23.6 water,EG 20% improvement for 4 vol% Cuo/EG mixture. Das et al (2003) 38.4/28.6 water 2-4 fold increase over range of 21oC to 52oC. Hong et al (2005) Fe 10 EG 18% increase for 0.55 vol% Fe/EG nanofluids. Li and Peterson (2006) 36/29 enhancement with volume fraction and temperature Liu et al (2005) CNTs Ø20-30 μm EG,EO 12.4% for EG at 1 vol%, 30% for EO at 2 vol%.

ADVANTAGES OF NANOFLUIDS Reduced Pumping Power Minimal Clogging Miniaturized Systems Compared with suspended particles of millimeter-or-micrometer dimensions which were used in base fluids to enhance heat transfer of such fluids, nanofluids exhibit higher thermal conductivities. Many types of particles such as metallic and non-metallic, can be added into fluids to form nanofluids. Suspended particles of the order of millimeters or even micrometers may cause some severe problems such abrasive action of the particles causes erosion of pipelines which are not that severe in case of nanofluids.

DISADVANTAGES High Processing cost 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. Use of surfactants for stability which results in lowering of conductivity due to the formation of a thermal boundary layer around the particles.

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