Experimental Study On Evaporation Characteristics Of Binary Mixed Suspension Droplets Under Acoustic Fiel

Acoustic levitation technology has the advantage of high-precision manipulation of nano to millimeter-sized objects,various fluid media particles,large groups of particles,and individual particles,as well as translation and rotation of levitated objects in six degrees of freedom.Using mild acoustic waves,it interacts with microscopic objects and the environment in a non-contact,precise manipulation manner,and has applications in many chemical and biomedical fields.As the traditional method of solidified,suspended droplet evaporation research brings the droplet into direct contact with the substrate and hanging wire,which seriously affects the individual processes during droplet evaporation.Based on acoustic levitation technology,the droplets are manipulated with high precision and stability through experimental studies,aiming to investigate the influencing factors and the characteristics of their evaporation behaviors when the droplets are in a non-contact,suspended state evaporation process.An acoustic levitation device was fabricated,and the visualization of binary mixed droplets of three types(mono-volatile,bi-volatile and salt solution),six working substances(glycerol-water,glycerol-ethanol;ethanol-water,acetone-water;sodium chloride solution,potassium chloride solution)and different concentrations of evaporation experiments were completed by using high-speed photographic methods,infrared thermography and related processing software,and the visualization of different types of binary mixed droplets in The measurement of droplet morphology,evaporation rate,internal flow and temperature gradient inside the droplet during the evaporation process under acoustic suspension was achieved.The experimental results show that:The evaporation of single volatile binary droplet suspension is divided into two stages: the first stage is the evaporation of volatile components from the droplet surface,and the second stage is the evaporation of volatile components from the droplet interior across the glycerol to the droplet surface.Due to the high viscosity of glycerol,the droplet has a "long flat" shape;the evaporation rate is the largest at the beginning of the droplet evaporation,and then decreases gradually,the higher the concentration of glycerol,the lower the evaporation rate;the high viscosity of glycerol hinders the diffusion of water and ethanol components to the droplet surface;the temperature of the droplet surface rises slowly during the evaporation process,and the central The temperature at the surface of the droplet increased slowly during the evaporation process,and the temperature at the center decreased first and then increased.The evaporation of double volatile binary droplet suspension is divided into three stages: the first stage is the evaporation of high volatile components on the droplet surface,the second stage is the evaporation of high volatile components inside the droplet and low volatile components on the droplet surface,and the third stage is the evaporation of low volatile components.The initial shape of the droplet is ellipsoidal,the higher the concentration the closer the droplet is to a sphere;the evaporation rate of pure water droplet evaporation process remains basically constant,the addition of ethanol or acetone significantly affects the evaporation rate,the first stage of the evaporation rate is the largest,the evaporation rate gradually decreases during the evaporation process,the higher the concentration,the faster the average evaporation rate of the droplet;with the continuous evaporation of ethanol and acetone components on the droplet surface,the internal ethanol and acetone will continue to With the continuous evaporation of ethanol and acetone components on the surface of the droplet,the internal ethanol and acetone will continuously diffuse to the surface of the droplet;when the droplet is suspended and evaporated,there is a symmetrical temperature gradient inside the droplet,the surface temperature of the droplet is the highest and the center temperature is the lowest,the surface temperature remains unchanged during the evaporation of the droplet,and the internal temperature of the droplet gradually increases.The evaporation process of salt solution suspension droplets is in two stages:water evaporation and salt precipitation;the water evaporation stage keeps ellipsoidal shape;the salt precipitation stage precipitates crystals inside the droplet;the distribution of crystals is more dispersed in low concentration salt solution,and the distribution of crystals is more aggregated and more stable in high concentration salt solution;the higher the concentration,the shorter the evaporation time of the droplet;under the joint action of acoustic wave and gravity,the crystals generally precipitate and precipitate in the lower and axial position of the droplet;during the evaporation process,there is a more uniform and symmetric temperature distribution of the droplet as a whole,with the highest temperature at the surface of the droplet and the lowest temperature at the center of the droplet.The behavior of evaporation characteristics during the evaporation of binary mixed droplets is experimentally investigated using a novel acoustic suspension research method,which provides a strong basis for in-depth investigation of the evaporation mechanism of multi-component droplets and provides an important reference value for the field of non-contact droplet manipulation.