Enhancing thermal conductivity of fluids with nanoparticles Prepared by: Smith R Kashid T.E. Mech. Roll no:344
Introduction: • Modern nanotechnology provides new opportunities to process and produce • materials with average crystallite sizes below 50 nm. Fluids with nanoparticles • suspended in them are called nanofluids.Aterm proposed by Choi in 1995 of • the Argonne National Laboratory, U.S.A.
Synthesis of nanofluids: • There are mainly two techniques used to produce nanofluids: • i) The single-step method. • ii) The two-step method. • Some special requirements are essential e.g. even and stable • suspension, durable suspension, negligibleagglomerationof • 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 (EG), • oils, etc.
The single-step method: • The single-step direct evaporation approach was developed • by Akohet al. and is called the VEROS (Vacuum • Evaporation onto a Running Oil Substrate) technique. • A modified VEROS process was proposed by Wagener et al. • Eastman et al. also developed a another modified VEROS • technique • Zhu et al. presented a novel one-step chemical method • A vacuum-SANSS (submerged arc nanoparticle synthesis • system) method has been employed by Lo et al. • Recently, a Ni nanomagnetic fluid was also produced by Lo • et al. using the SANSS method.
The two-step method:. • In this method, nanoparticles was first produced and • then dispersed in the base fluids. Generally, • ultrasonicequipment is used to intensively disperse • the particles and reduce the agglomeration of • particles. • For example, • Eastman et al. , Lee et al. , and Wang et al used this • method to produce Al2O3 nanofluids. Also, Murshed • et al. Prepared TiO2 suspension in water using the • two-step method.
Aadvantage: • one-step technique :- nanoparticle agglomeration is minimized. • the two-step technique works well for oxide nanoparticles. • Disadvantage: • One-step techniqe :- only low vapor pressure fluids are compatible with such a process. • Two step tehnique:- less successful with metallic particles.
Potential benefits of nanofluids: • enhancement of heat transfer due to increased pumping • power can be estimated from the following • equation: • h/h0 = (P/P0)^0.29 • For a nanofluid flowing in the same heat transfer • equipment at a fixed velocity, enhancement of heat • transfer due to increased thermal conductivity can be • estimated from the equation: • hnf/h0 = (knf/k0)2/3
In heat exchangers that use conventional fluids, heat transfer can only be improved by significantly increasing flow rates.
Liu et al. (1988) have studied the influence of particle • loading and size on the pressure drop of slurry. • the potential benefits of nanofluids could provide • tremendous performance,size/weight, and cost • advantages.
Future challenges : • The use of nanofluids in a wide variety of applications • appears promising, but the development of the field is • hindered by: • (i) the lack of agreement between results obtained in • different laboratories • (ii) the often poor characterization of the suspensions • (iii) the lack of theoretical understanding of the • mechanisms responsible for the observed changes in properties.
FUTURE RESEARCH PLANS: • The research effort to produce and characterize the heat • transfer behavior of nanofluids will consist of following main tasks. • 1. Nanophase metal powders will be produced in existing • state-of-the-art gas-condensation preparation systems at ANL. The particle size and agglomeration behavior of nanophase powders in liquids will be studied. • 2. Technology for production of nanoparticle suspensions will be developed and the stability, dispersion, and rheological/transport properties of these nanofluids will be investigated. • 3. Practical applications of nanofluids will be Investigated.
Conclusion: • The concept of nanofluids is an innovative idea. One of the benefits of nanofluids will be dramatic reductions in heat exchanger pumping power. • The use of nanofluids in a wide range of applications appears promising, but the development of the field faces several challenges • A critical review of the state-of-the-art nanofluids research • for heat transfer application was conducted in this work, which • showed that our current understanding on nanofluids is still quite • limited.