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 a millimetre).
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.
makes controlling the process much easier ( refer to remark
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
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 Cooling )
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 Protection )
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).