Effect Of Roughness On Evaporation Process And Deposition Pattern Of Droplets With Mixed Nanoparticles

The occurrence of liquid evaporation is one of the most common phenomena in natural phenomena,and it is also an extremely important natural process.At present,researchers' research on droplet evaporation has been widely used in meteorological estimation,spray drying,aerospace,health care and fire safety and other fields.However,the existing research on droplet evaporation is in basic exploration,and some research results of scientific researchers are still divided.Therefore,it is urgent to deeply investigate the dynamic evolution of the characteristics of the droplet evaporation process and the deposition pattern left after the complete evaporation,as well as the force status of the particles during the evaporation process,so that the deposition pattern can be further controlled and the particle stress can be quantified get the theory law.In this paper,we use the experimental instrument DSA100 to observe that on three different surface roughness(0.1,0.15 and 0.2 ?m)optical glass surfaces,there are seven different particle size ratio particles(10nm: 30 nm = 1: 0,1: 9,2: 8,3: 7,4: 6,5: 5,and 0: 1)the evaporation process of aluminum oxide-deionized water nanofluid droplets with fixed concentration(1g/L),recording the changes in evaporation characteristics with time during droplet evaporation after the evaporation is completed,the deposition pattern attached to the solid surface is observed with a 3D digital video microscope and a 3D surface shape measuring instrument,and the basic characteristics of the deposition pattern are recorded.Combined with the droplet evaporation process,the effects of roughness and particle ratio on droplet evaporation process and deposition pattern formation were analyzed,and the following conclusions were obtained:(1)The experimental results show that the ratio of the fixed surface roughness to the various particle sizes of the particles in the solution is an important factor that affects the evaporation time during droplet evaporation,and the solid surface roughness is the factor that affects the initial contact angle and contact angle during droplet evaporation an important factor of speed.As the proportion of 10 nm particles in the solution increases,the evaporation time and growth rate of the droplets increase and as the solid surface roughness increases,the initial contact angle of the droplet and the contact angle during the evaporation of the droplet the reduction rate is reduced accordingly.(2)The deposition pattern after the droplets are completely evaporated is affected by the ratio of the multi-particle size and the roughness of the particles in the solution.During this experiment,two obvious deposition patterns were formed: three-ring structure(the solution contains two aluminum oxide nanoparticles of various particle sizes)and double ring structure(the liquid contains only aluminum oxide nanoparticles of one particle size).The roughness of the solid surface and the ratio of the multi-particle size of the particles contained in the solution are important factors affecting the droplet deposition pattern.Moreover,as the roughness and the proportion of 10 nm particles in the solution increase,the double ring structure embedded in the three ring structure gradually shrinks towards the center of the droplet,the outer ring pattern and particle gaps gradually disappeared,the area uniformly covering the nanoparticles gradually increased,and the particle aggregates gradually decreased.(3)The roughness of the solid surface and the ratio of multiple particles in the solution are important factors that affect the height parameter of the coffee circle in the droplet deposition pattern.As the surface roughness increases and the proportion of 10 nm particles in the solution increases,the capillary effect and the Marangoni effect generally show a decreasing trend,and as the surface roughness increases and the proportion of 10 nm particles in the solution increases,the height of the coffee circle in the deposition pattern slowly decreases,and the number of accumulated layers gradually decreases.When the height of the coffee circle is the smallest,its value is still far greater than the maximum particle diameter,so it is inferred that the coffee circle pattern is composed of multiple layers of particles.