Research On Evaporation Flow Process Of Nanoparticle-containing Droplets And Particle Deposition Characteristics

The droplets containing nanoparticles will form a certain deposition pattern after evaporation on the solid surface.The pattern can be controlled by changing the shape of nanoparticles,substrate temperature,substrate dip angle,initial particle concentration,adding surfactant and increasing electric field,and these control technologies play an important role in inkjet printing,coating technology and other fields.Further study on the internal mechanism of the effect of these factors on droplet evaporation is helpful to better control the deposition pattern.Therefore,in this paper,numerical simulation method is used to deeply analyze the evaporation and particle deposition characteristics of droplets containing nanoparticles on the heated substrate:(1)Aiming at the evaporation deposition process of droplets containing nanoparticles on a uniformly heated horizontal solid substrate,the evolution equation of droplet thickness and nanoparticle concentration was established based on the lubrication theory.The viscosity model suitable for different shapes of nanoparticles was introduced into the equation,and the evaporation deposition process of droplets containing anisotropic nanoparticles was analyzed.The results show that the increase of initial concentration will lead to the uniform deposition of droplets,and the decrease of interfacial thermal resistance and the increase of superheat will thicken the particle deposition at the edge of droplet,the deposition range of nanoparticles with different shapes is: spherical > rod > ellipsoid,and the deposition thickness is:ellipsoid > rod > spherical.(2)On the basis of(1),a new viscosity model considering the influence of temperature and the volume fraction of nanoparticles on the viscosity was derived based on the existing viscosity data.The effect of substrate temperature on the characteristics of droplet deposition was studied by using this model.And the model was used to study the effect of substrate temperature on droplet deposition characteristics.The calculation results show that as the temperature of the substrate increases,the spreading range of droplets becomes larger,the deposition thickness of particles at the edge of droplets becomes thinner.(3)The process of evaporation and particle deposition of droplets containing spherical nanoparticles on a uniformly heated inclined solid substrate was analyzed,the evolution equation of droplet thickness and nanoparticle concentration was established based on the lubrication theory,and the evaporation deposition process of the droplet was theoretically studied.The results show that the droplet evaporation process on the inclined substrate can be divided into three stages according to the movement of the contact lines on both sides: the droplets are moved and spread,the spreading range is continuously enlarged;the droplets move and shrink,the spreading range is reduced;the droplets are pinned and contracted,the front contact line is pinned on the substrate,and the rear contact line is continuously moved downward.In addition,with the increase of the dip angle of the substrate,the deposition height first increases and then decreases.With the increase of the initial nanoparticle concentration,the droplet deposition gradually changes from annular deposition to uniform deposition.