Atomization refers to the process of breaking up bulk liquids into droplets. A spray is a collection of moving droplets that usually are the result of atomization. They are moving in a controlled fashion. A droplet is a small particle of liquid having a more or less spherical shape.
The particles are round due to the liquid’s surface tension. Surface tension is the property of a liquid that causes droplets to pull together in a spherical form and resist spreading out. This property causes sheets or thin ligaments of liquid to be unstable; that is, they break up into droplets, or atomize.
Ultrasonic atomization relies on an electromechanical device that vibrates at a very high frequency. On the vibrating surface capillary waves developed in the liquid are released. A capillary wave is a wave traveling along the phase boundary of a fluid, whose dynamics are dominated by the effects of surface tension. The fluid passes over the vibrating surface of the nozzle and the vibration causes the fluid to break into droplets.
The amount of liquid atomized is decided by the rate at which the liquid is introduced. Low spray velocity of this technology avoid the phenomenon of material bounce back which is a drawback of pressure atomizer.
iMinds technologies Ultrasonic spray nozzles system supersede pressure nozzles on various accounts, precisely in application areas where wastages of costly solvents due to over spray is not permissible. This system reduces overspray by 80 percent and control air pollution. The atomization of solvents produces spray of low velocity droplets. The velocity of the spray is in the range of 21cm/sec to 36cm/ sec. and is function of applied power. The size of droplet is controllable in the range of 10 to 100 micron. The orifice of ultrasonic nozzle is above 0.8 mm. This avoids clogging of nozzle.
The nozzles are made up of titanium and stainless steel. This avoids rusting of nozzles. Ultrasonic nozzle gives better service for longer time. These nozzles operate with low flow rates. It gives controllable continuous or intermittent, reliable, soft, low velocity spray. The applications demand droplet size in the range of 10 micron to 100 micron. The droplet size is decided by nozzle operating frequency, property of liquid: typically surface tension and viscosity. The solvents flow rate is governed by orifice size, atomization surface area, operating frequency and liquid characteristics.
This equipment drives the ultrasonic nozzle with high frequency electrical energy and regulated output power. Following are the important features which makes it a rugged power source with PC programmability.
Solvent characteristics for successful Atomization
Liquids that are used for atomization can be classified as follows:
For successful atomization of the pure liquids, the viscosity should be of less than 50 cps.
True solutions; behave the same as pure liquids. However if solution contains very long-chained polymer molecules their length interfere with the atomization process due to long length. Such molecules will span the region of the bulk liquid and stop formation of two or more drops.
For mixtures with undissolved solids, following factors influence ability to atomize.
If the particle size is more than one-tenth the median drop diameter, the mixture may not atomize properly. If above mentioned condition is not met there is a high probability that a majority of the drops will form without entrapping the particle. A practical upper limit on solids concentration is about forty percent. The ability to atomize is affected by the viscosity of the solvent and the ability of the solid component to remain suspended.
Liquid delivery systems for Ultrasonic Spray Nozzles