Design and Atomization Experiments of an Ultrasonic Atomizer with a Levitation Mechanism

Abstract

<abstract> According to Lang equation, the diameter of droplet generated by an ultrasonic atomizer is inversely proportional to the ultrasonic drive frequency to the two-thirds power. In an ultrasonic aeroponic cultivation system, nutrient solution droplet sizes influence plant growth speed directly. If nutrient solution droplet sizes can be changed to meet a plant growth need during its different growth stages, the plant growth will <ext-link ext-link-type=uri xlink:href=app:ds:accelerate>accelerate</ext-link>. So, obtaining various sizes of droplets more efficiently and cheaply is expected in an ultrasonic aeroponic system. A new ultrasonic atomizer with an acoustic levitation <ext-link ext-link-type=uri xlink:href=javascript:void(0);>mechanism</ext-link> was developed to studythefeasibility of using only one ultrasonic atomizer to obtain various sizes of droplets. The atomizer‘s atomization surface was designed as a hemispheric shape, and a ball called Levitated ball was against this atomization surface. The atomization surface was mounting vertically upward when the atomizer was working. An acoustic radiation force was generated due to ultrasonic vibration of the atomization surface. The levitated ball would be levitated if its gravity force was less than or equal to the acoustic radiation force acting on it. Sizes of droplets generated by this atomizer were measured when a ceramic, steel, and glass ball were levitated using a spray laser particle size analyzer. Measurement results showed that values of NMD and D50 of droplets generated by this atomizer with a ceramic, glass, and steel ball levitated were respectively 4.78% and 5.83%, 22.06% and 22.04%, 34.76% and 32.30% less than those of droplets generated by this atomizer with no ball levitated. It was verified that using only one ultrasonic atomizer to obtain various sizes of droplets were feasible by changing the levitated ball‘s weight. Vertical displacements of those levitated balls were measured using a laser displacement sensor. Vertical displacement measurement results showed that a levitated ball‘s kinematic parameters would be changed along with its‘ weight. Furthermore, changes of a levitated ball‘s kinematic parameters would influence processes of collision between droplets and the levitated ball. This might be the reason why an ultrasonic atomizer with a levitating mechanism could generate various sizes of droplets.