Investigation On The Stability And The Convective Heat Transfer Characteristics Of Nanofluids

With the rapid development of MEMS, Nanofluids have become today's research focus for the predominant thermophysical properties. Nanofluids are the stable suspensions prepared by dispersing nanometer-sized particles (<100nm) in the conventional fluid such as water, alcohol or glycol. In the present study, the preparation methods,stability,viscosity,flow characteristics in micro-channels and convective heat transfer characteristics have been studied.Firstly, the two-step method was adopted to prepare the Cu-Water nano-fluid with different mass faction of particles. In this article, the effect of SDBS dispersant concentrations on the stability of nanofluids has been investigated. The result shows that nanofluid has better stability when the mass faction of Cu particles is the same as SDBS dispersant concentrations. At the same time, the viscosity of Cu-Water nano-fluid has been studied. We found that the viscosity of nanofluids increases with an increase in the mass faction of Cu particles.Secondly, both numerical simulations and experimental study have been performed on the flow characteristics of Cu-water nanofluids including 1% mass faction of Cu nanoparticles. The results show that the mass flow of nanofluids is in line with the driven pressure, and the mass flow of nanofluids increases with increasing the driven pressure, and we found that single-phase hypothesis can be successfully applied to nanofluids. However, the numerical results are different from the experimental date, which is due to the cluster of nanoparticles in based fluids,changes in viscosity of nanofluids,the size effect,the concentrations of SDBS and the boundary slip.Finally, the effects of the Reynolds number,volume fraction and type of based fluid and nanoparticles on the convective heat transfer characteristics of nanofluids under the laminar flow conditions have been numerical studied by using single phase model. The computed results show that the convective heat transfer coefficient of nanofluids is higher than that of the based liquid, however, which is closely related to properties of the based liquid, nanoparticles, and its volume fraction. The heat transfer coefficient of nanofluids increases with increasing the thermal conductivity of nanoparticles and base fluid, and increases with an increase in the volume fraction of nanoparticles. The heat transfer coefficient of nanofluids almost keeps constant for Cu-water nanofluids with a fixed volume fraction, which has nothing to do with the Reynolds number.