Study On Spreading Dynamic Characteristics Of Nanofluids Droplet Impinging On Solid Surface

The process of droplet impacting on the solid surface is widely used in the industry.Especially with the increasing demand for integration and miniaturization of electronics,incremental heat transfer and cooling technology based on nanofluids droplet deposition has become a frontier problem in microelectronics engineering.Studying the dynamic behavior of nanofluid droplets impacting on the solid surface would provide theoretical support for this technology.In this study,the impacting process of nanofluid droplets on solid wall was studied by visual measurement.This study revealed the influence of rheological properties of nanofluids on the droplets spreading process,and proposed a prediction model for the spreading behavior of droplets impinging on the solid walls.The main contents of this study are as follows:Firstly,three kinds of nanoparticles(cylindrical carbon nanotubes,flake graphene and spherical graphite powder)with different microstructures were dispersed into high viscosity base solution(epoxy resin)to prepare uniform and stable epoxy resin-based nanofluids without surfactant.Secondly,water-based nanofluids with good dispersion were prepared by dispersing carbon nanotubes in deionized water with SDS surfactant.The results of SEM and electron microscopy showed that the nanofluids prepared in this study had good dispersion.Then,we measured the shear viscosity and related physical properties of the prepared nanofluids,and it was found that three different nano-dispersed phases made the epoxy resin solution show different shear thinning degree.The shear thinning behavior of nanofluids was analyzed by power-law rheological model.The surface tension of water-based nanofluids is weakened obviously due to the addition of SDS surfactant,and the solution also shows shear thinning characteristics.High-speed digital camera and microscope were implied to visualize the impact of epoxy resin-based nanofluid droplets on solid surface.By studying the dynamic contact angle(DCA),spreading factor(D*)and dimensionless height(H*)during droplet impacting process,the influence of the shear thinning characteristics of nanofluids,the impact surface wettability and inertia force on droplet spreading process was analyzed.It is found that the rheological properties of nanofluids affect the impacting behavior of droplets,and the shear viscosity plays a major role in the impact process.The effect of surface wettability on droplet impacting behaviors is more significant for the fluid(larger n)with higher shear viscosity and less shear.Based on the analysis of a large number of experimental data,a prediction model for the maximum spreading factor of droplets in nanofluids is proposed,which is in good agreement with the experimental data.Finally,through the visual analysis of the process of water-based nanofluids droplets impacting on the solid surface,it is found that the rebounding process of deionized water is inhibited by the addition of SDS surfactant,and the rebounding of deionized water droplets with SDS and carbon nanotubes are further inhibited.