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What is Fog?

A fog is a suspension of small liquid droplets in gas (generally air) characterized by its droplet size distribution (which can vary greatly). However, people tend to describe fogs qualitatively, using such descriptive terms as dry fog (10-15 micron volume mean diameter), wet fog (20-30 micron VMD), mist (30-60 micron), fine spray (above 60 micron), etc.

The stability of a fog may vary widely, depending on droplet size; relative humidity; liquid volatility, surface tension and density; air currents; particle size distribution; temperature; and condensation surfaces.
Fortunately, you don't have to predict fog behavior. Just thinking about your application usually will indicate what kind of fog would be best (and sometimes even the best equipment to use).

For example, a "dry" fog of small particles will be superior when droplets must diffuse widely, when wetting would be harmful or for gas contact applications such as odor control; smaller droplets have a greater surface to volume ratio, and they are more likely to travel with air currents. On the other hand, a “wet” fog of larger droplets would be better for particulate settling and for applications such as disinfection or mold control that specify wetting the surface.

In many applications, you’ll have to experiment to find the optimum droplet size. A humidification user must balance the advantages of a higher flow rate (shorter run time but larger droplets) against the possible disadvantages (poor distribution, droplet fallout, undesirable wetting).
For many liquids, it is often helpful to experiment first, applying water only (no chemical) to see what flow rate works best in your situation. [If you are using an oil-based liquid, substitute kerosene for water.]




How are Fogs Made?

There are three common fog generation techniques (a fourth combines two of these):

Thermal Foggers evaporate an oil-based liquid such as light kerosene on a hot surface. Upon exiting the nozzle, oil vapors condense into droplets to create a fine fog. Thermal foggers cannot dispense water-based products and are generally limited to outdoor use.

High Pressure Spray Nozzles can deliver a wide range of particle sizes, depending on liquid pressure and nozzle opening. For fog output, typical liquid pressures are 500 - 1,500 psi, and orifices 0.005 inch or smaller. Spray nozzles can handle both oil- and water-based liquids but require high grade filtration to protect against nozzle plugging. Over time, they are also susceptible to nozzle erosion resulting in larger droplet sizes.

Mechanical ("cold") Foggers produce small droplets by turbulent air shear in the fogging nozzle. The typical air source is a high velocity fan, usually integrated with the fogging nozzle as an integrated component. Liquid pressures are low, and since nozzles have no small orifices, plugging is usually not a problem. However, exit noise (about the same as a vacuum cleaner) may make a mechanical fogger inappropriate when a noiseless discharge is required.

The Air Atomizing Nozzle is a hybrid of the spray nozzle and the mechanical fogger. Liquid is first broken into coarse droplets with a low pressure nozzle, then further atomized with compressed air. The air atomizing nozzle therefore needs both a liquid pump and an air compressor. With larger liquid orifices, it is less vulnerable to plugging than the high pressure nozzle, but tends to produce larger droplets.

What is Fog?

Fogmaster began life as a division of the AFA Corporation, a pioneer in fogger and trigger sprayer technology, in the 1960's.

Fogmaster Corporation was formed in 1982 when AFA spun off its "cold" fogging manufacturing operations as a separate business. It expanded into its current Deerfield Beach facilities in 1986.


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