Study On Microscopic Behavior Of Water Droplets In Oil And Demulsification Characteristics In Ultrasonic Standing Waves

Previous studies on ultrasonic demulsification are limited primarily to the law of the macro ultrasonic demulsification of crude oil.There have been not enough studies on the demulsification mechanism of ultrasonic standing wave field,neither a theoretical system Based on the self-designed ultrasonic standing wave&high-speed microscopy experimental system and macroscopical demulsification experimental system,this paper experimentally studies the suspension characteristics of single droplet,banding characteristics of droplet cluster,and demulsification characteristics of emulsion.The main contents and conclusions are as followsSuspension characteristics of single droplet in ultrasonic standing wave are studied.First of all,suspension mechanism of droplet is analyzed theoretically.Conditions that need to be satisfied for droplet suspension are analyzed.Suspension process of single droplet is recorded by the ultrasonic standing wave&high-speed microscopy experimental system,which includes two stages:transient motion and steady state.The suspension position of droplet is extracted as the key characteristic parameter.The effects of droplet radius,acoustic pressure amplitude and oil-water density ratio on the droplet suspension position are systematically studied.Results indicate that the droplet radius has no impact on suspension position of droplet at different frequencies.There is a critical acoustic pressure for droplet suspension.Droplets can't be suspended when the acoustic pressure is less than the critical pressure.Suspension position of the droplet gradually approaches to the position of pressure node with increasing acoustic pressure amplitude at different frequencies.Suspension position of droplet decreases linearly with increasing density ratio at different frequenciesBanding characteristics of droplet cluster in ultrasonic standing wave are studied.Banding interval and banding formation time are taken as the key characteristic parameters of the droplet banding.The banding interval is only related to the frequency,which closely corresponds to the half wavelength.The banding formation time under different conditions is calculated by using inhouse MATLAB codes.The effects of acoustic intensity,droplet diameter,oil viscosity and oil-water interfacial tension on the banding formation time are investigated.Results indicate that the range of acoustic intensity,within which the droplets banding can form,increases with the increase of frequency.Moreover,there exists a maximum allowable acoustic intensity for the banding formation,which also increases as the frequency increases.The oil-water interfacial tension has little impact on the banding formation timeDemulsification characteristics of emulsion are studied under the action of ultrasonic standing wave.Dehydration rate and relative dehydration rate are defined as the evaluation parameters of ultrasonic demulsification.The effects of acoustic intensity,frequency,irradiation time,surfactant concentration,oil viscosity,and water content on the dehydration effect of emulsion are studied detailly.There exists an optimal acoustic intensity to achieve maximum relative dehydration rate at different frequencies.The dehydration rate increases with the increase of irradiation time,and there exists an optimal irradiation time to achieve maximum relative dehydration.The dehydration rate decreases with the increase of surfactant concentration,and the relative dehydration rate is high with high concentration surfactant.The dehydration rate increases with the increase of oil viscosity,and there exists an optimal oil viscosity to achieve maximum relative dehydration.The dehydration rate increases and the relative dehydration rate decreases with the increase of water content.