Washers and scrubbers of various sorts are used extensively throughout industry, largely for the absorption of soluble gases. They are not very commonly used for cleansing the air of solid dust particles. The effectiveness of a washer in removing a dust depends on the ‘wettability’ of the dust by water. This is a function of the surface tension of the water when it is in contact with the solid involved. Different forces of surface tension are the rule for different materials. Thus, water finds it very difficult to wet greasy materials but fairly easy to wet non-greasy materials. Examples of greasy materials are atmospheric pollutants present in urban and industrial atmospheres; it follows that washing the air is not a very effective way of cleaning it of the dust normally present. Spray-type washers are not to be regarded as filters.
As was remarked above, air washers are an effective way of dealing with undesirable atmospheric gases such as sulphur dioxide, which may be taken into solution by the water. The washer water then becomes acidic and water treatment and a continuous blow down are essential.
Air washers are a potential source of the bacteria that cause legionnaires’ disease. It follows that they are a hygienic risk and are undesirable in air conditioning. See section 3.5.
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