Fog Droplets And Their Size In Mist And Fog Systems

Manufacturer of fog machines and fog nozzles refer to the droplet size and their number, when it comes to quality. This is often decisive for the efficiency of a fog system. But what is the meaning of that?

Fogging systems atomize water under high pressure and form a fine fog consisting of small water droplets. Their size determines, inter alia, their floating properties and the ability to saturate the air or to bind other substances.

A fog nozzle never produces always the same droplet size. Furthermore the droplet size is different depending on the ambient temperature, relative humidity, air speed, nozzle type, pressure and measuring point. Manufacturers of nozzles should therefore include details of these parameters. A direct comparison would only be meaningful if different nozzle types are examinated under the same conditions with a standard measurement device.

But to understand the meaning of quantities and proportions of water droplets in fog and mist systems, you should get an idea of some numerical examples.

It is not possible here to enter into all the specific parameters, so the following calculations are simplified and purely theoretical.

A water droplet produced by an authentic Fog System, has an average diameter of about five microns. This is five millionths of a meter or five thousandths of a millimeter. From this you can calculate volume and surface of a single droplet. Therefore a fog system produces with one liter of water 15’000’000’000’000 water droplets, with a total surface of 1200 m2. The area of a football field could be produced accordingly with about six liters of water.

If a fog nozzle produces larger water droplets the exchange surface decrease is linear to the droplet diameter. However, the number of droplets decreases in a logarithmic relationship.

Fog systems used for industrial purposes, have 300 – 1000 nozzles depending on the application. A fog nozzle uses in continuous operation 7-8 liters of water per hour. There is no other comparable medium being able to produce such a large exchange surface.

Another very important advantage resides in the huge cooling potential, which is produced by the fog systems. This is known as evaporative cooling or adiabatic cooling. From an energetic point of view, traditional cooling systems can hardly keep up with fog systems. But this kind of cooling is essentially limited to the warm and dry season, because the cooling efficiency depends on climatic conditions. Therefore, the number of water droplets formed and their size are important.

An average droplet size of about five microns can be achieved only with impaction pin nozzles and pressures of more than 80 bars. This sets high standards to the material, the quality of the nozzle, the water quality and on the observance of safety standards. Only a few manufacturers are able to take into account these normative requirements.

But many fog system sellers do not even work in this segment: on the one hand, as already mentioned, because of the requirements and on the other, by reason of the large price differences.
A high pressure fog system that produces with special impaction pin nozzles particles of an average size of five microns, involves higher investments. Cost-effective flat nozzle without impaction pin nozzle and plastic piping can withstand only limited pressure and are physically unable to produce so small water droplets. However, they may be highly advantageous when it comes to producing low cost mist in the garden and leisure sector. You will notice a difference visually, but only if two different systems (fog and misting) are operated in parallel.

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