Misting/Fogging systems
Misting system work by forcing water via a high pressure pump and tubing through a brass and stainless steel mist nozzle that has an orifice as size of about 5 micrometres producing a micro-fine mist. The water droplets that create the mist are so small, that it instantly flash evaporates. This flash evaporation can reduce the surrounding air as much as 35 °F in just seconds.
For static line systems, it is ideal to mount the mist line approximately 8 to 10 feet above the ground for optimum cooling.
Misting is used on for many different applications including athletics, orchids, pets, livestock, kennels, insect control, odor control, zoos, veterinary clinics, produce cooling, greenhouses, etc.
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Factors influencing rate of evaporation
Concentration of the substance evaporating in the air. If the air already has a high concentration of the substance evaporating, then the given substance will evaporate more slowly.
Concentration of other substances in the air. If the air is already saturated with other substances, it can have a lower capacity for the substance evaporating.
Temperature of the substance. If the substance is hotter, then evaporation will be faster.
Flow rate of air. This is in part related to the concentration points above. If fresh air is moving over the substance all the time, then the concentration of the substance in the air is less likely to go up with time, thus encouraging faster evaporation. In addition, molecules in motion have more energy than those at rest, and so the stronger the flow of air, the greater the evaporating power of the air molecules.
Inter-molecular forces. The stronger the forces keeping the molecules together in the liquid of solid state the more energy that must be input in order to evaporate them.
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The Science of evaporative coolers (Swamp coolers)
Understanding evaporative cooling performance requires an understanding of psychrometrics. Evaporative cooling performance is dynamic due to changes in external temperature and humidity level. Under typical operating conditions, an evaporative cooler will nearly always deliver air cooler than 80 °Fahrenheit (27 °Celsius). A typical residential swamp cooler in good working order should cool air to within 6°F - 8°F (3°C - 4°C) of the wet bulb temperature.
Some rough examples clarify this relationship.
At 90 °F (32 °C) and 15% relative humidity, air may be cooled to nearly 60 °F (16 °C).
At 90 °F (32 °C) and 50% relative humidity, air may be cooled to about 75 °F (24 °C).
At 105 °F (40 °C) and 15% relative humidity, air may be cooled to nearly 70 ° (21 °C).
Because swamp coolers perform best in dry conditions, they are prevalent and most effective in arid, desert regions like the southwestern USA and northern Mexico.
(cooling examples extracted from the June 25, 2000 University of Idaho publication, "Homewise (http://info.ag.uidaho.edu/homewise/homewise_062500.htm)").
