What is fog really and which physical effects can be utilized with fog ?
Without discussing the various types of fog which are known to
meteorology we can say that fog consists of finest water droplets which are
so small that they are able to hover in air saturated with water vapour ( see also Relative Humidity
Natural fog occurs with droplets of some 0,12
mm (120 micron), for utilization in various areas of interest the diameter
of the droplets should not exceed a diameter of 30 micron (30 thousands of
The most frequent application of fog is simply humidification. The
central criterion for successful humidification is the "surface of
evaporation". This means that the smaller the droplets are the larger
their combined surface gets and therefore the fast the water is able to
evaporate into the surrounding air.
Fast evaporation makes controlling the process
much easier ( refer to remark 1 )
Fogging techniques are also used often to wet
surfaces - for instance to water plants by this means, for dust
binding, etc). This can be done with water alone
or using the water as a carrier medium for additives - like disinfectants,
pesticides, fungicide, ... In other cases simply a
fluid medium is atomized to aid some physical or chemical process - for
instance an acid.
Generally known and experienced is the physical process of
evaporative cooling. By means of evaporation of water in hot and dry air
heat energy is used up whereby this effect can be utilized for cooling
purposes (refer to Evaporative
The physical effect that water gives off heat when it freezes is not
as good known as evaporative cooling. The phenomenon can be used to protect
fruit orchards very efficiently from hoar-frost
( refer to Frost
In Architecture and Artwork the last years have shown that fog is
often used to create interesting visual effects; however depending on the
environment and the desired effect the used medium is not always water-fog,
but also frozen carbon dioxide (dry ice) and alcohol-fog (disco-fog).