Atomization Process

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 Atomizer

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.

Ultrasonic Spray Nozzles

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.

eNozzle drive system

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.

  • It uses proprietary Microcontroller based “Digital phase lock loop” technology, which automatically locks to the natural frequency of the nozzle.
  • The equipment operates on AC power. It can tolerate wide variation in the AC voltage, i.e. it operates on universal AC voltage range in the range viz. 90 volts to 270volts so as operate on any continent. (DC power of 24 driven equipment can be availed on demand if desired)
  • The atomization process can be controlled by programmable controllers using RS232 COM port to achieve (Available on demand if desired)
    • Atomization On-Off control
    • Nozzle power drive level control
  • Operating frequency range: 20 KHz to 200 KHz.
  • Displays messages in the event of misuse or malfunctioning along with alarm viz. powering drive without connecting nozzle to drive.
  • Display of power consumed by nozzle.
  • Available in a table top model.

Solvent characteristics for successful Atomization

Liquids that are used for atomization can be classified as follows:

  • Pure, single component liquids (water, alcohol, bromine, etc.)
  • True solutions (salt water, polymer solutions, etc.)
  • Mixtures with un-dissolved solids (coal slurries, polymer beads/water, silica/alcohol, suspensions, etc.)

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.

  • particle size,
  • concentration of solids,
  • Viscosity of the solvent

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

  • Syringe pumps for metered volume applications where precise dispensing is required
  • Gravity systems for research and laboratory environments