This section is from the book "A Treatise On Architecture And Building Construction Vol4: Plumbing And Gas-Fitting, Heating And Ventilation, Painting And Decorating, Estimating And Calculating Quantities", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
The vaporization of the liquid may be accomplished by adding more heat to it, or by lessening or removing the atmospheric pressure upon it.
Air may be partially dried by cooling it to a low temperature. The vapor accompanying it will be condensed and thrown down as water, and when the air is afterwards warmed it will be correspondingly dry.
The efficiency of a drying apparatus which uses hot air as the drying medium will depend upon several factors, as follows:
1. The dryness of the air before it is heated.
2. The degree of heat that is given to the air.
3. The amount of surface of wet material from which evaporation can readily take place.
4. The volume of the air-current.
5. The thorough distribution of the fresh dry air over the evaporating surfaces.
G. The promptness with which the moistened air is removed.
If the air is compelled to travel a long distance over wet surfaces, it will evaporate moisture freely during the first part of its course, less in the middle, and almost none at the end of the course. It is, therefore, advisable that the air-currents be so arranged that none of them are obliged to travel over a course of undue length.
The drying rooms of laundries are usually deficient in circulation of air, although well supplied with heat. Heat alone cannot dry the clothes; the moist air must be removed as fast as it is moistened. The humidity of the outgoing air should not be allowed to approach saturation, but should be kept as low as practicable.