Research On Preparation And Properties Of Silver Nanofluids

Nanofluids is a new type of heat exchanging medium with high thermal conductivity witch refers to the nanometer level metal, metal oxide, non metal, carbide, nitride or nano tube and other particles are added to the liquid medium(such as water, ethylene glycol, heat transfer oil, etc.) through a certain way(such as ultrasonic vibration, mechanical agitation,etc.) and the proportion. Nanofluids has great application prospect in the fields of heat energy,micro channel electron, chemical industry, vehicle, space and aviation, so it has become a hot research topic in many fields.In this paper, the preparation and characterization, thermal conductivity and rheological behavior of Ag-H2 O nanofluids with different morphologies are analyzed. The main research contents include the following aspects:1. The spherical(20~60nm) Ag-H2 O nanofluids with different mass fraction(0.0008~0.0032wt%) were prepared by one-step wet chemical method with sodium citrate(TSC) and ascorbic acid(AA) as reducing agent; The flake Ag-H2 O nanofluids with mass fraction(0.0016wt%) were prepared by one-step wet chemical method with sodium borate(NaBH4), sodium citrate(TSC) as reducing agent; the linear Ag-H2 O nanofluids with different mass fraction(0.0016~0.0124wt%) were prepared, the Ag nanowires were evenly dispersed into water through ultrasonic dispersion method.2. The effects of synthesis conditions on the morphology and size of the nanoparticles were studied through the analysis of UV/Vis, TEM, SEM and XRD. Research results show that:(1) The morphology of the prepared Ag nanoparticles were spherical, flake and linear structure;(2) We can control the size of spherical Ag nanoparticles and a brief analysis of its growth mechanism, the size of the reaction rate determines the size of the spherical silver nanoparticles, the faster the reaction rate is, the greater the nucleation density is, the smaller the particle size is;(3) The prepared nanofluids is uniform and has excellent stability.3. Using KD2 Pro thermal physical analyzer based on the principle of transient hot wire metho, the thermal conductivity of spherical and linear and flake Ag-H2 O nanofluids at different mass fractions(spherical 0.0008~0.0032wt%, linear for 0.0016~0.1024wt%, flake for 0.0016wt%) at different temperatures(20~60?) was determined respectively. On thebasis of this study, the effects of particle size, mass fraction, morphology and temperature on the thermal conductivity of silver water nano fluid were studied. The results showed that:(1)the thermal conductivity of 22 nm spherical Ag-H2 O nanofluids was about 6.19% higher than that of the 40 nm, which showed that the smaller the size of the silver nanoparticles, the higher the thermal conductivity of the nanofluids;(2) the mass fraction of the spherical Ag-H2 O nanofluids increased from 0.0008wt% to 0.0032wt% and its thermal conductivity increased from 9.67% to 14.43% at 30?;(3) the thermal conductivity of the linear Ag-H2 O nanofluids is improved by 7.57%~35.95% when the mass fraction was 0.0016wt% in the temperature range of 20~60?;(4) the thermal conductivity of the spherical, linear and flake Ag-H2 O nanofluids increased by 10.5%, 7.57% and 5.33% respectively when the mass fraction of was0.0016wt%. Comparing between experimental results and theoretical model, the heat transfer mechanism of nanofluid was studied.4. The viscosity of nanofluids with three kinds of morphologies was measured at different mass fractions by using DV2 T Brookfield Viscometer. The results show that the three morphologies of nanofluids are Newton fluid, and the viscosity increases with the increase of the mass fraction. The spherical Ag-H2 O nanofluids has the lowest viscosity and good fluidity. On the basis of the comparison of the calculated values of the experimental measurement and the viscosity theory model, the effect of various factors on the viscosity of nanofluids is further improved.