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708 CHAPTER 33 1950 Guide ,The Mathematical Theory of the Cottrell Electric Precipitator, by A. W. Simon (Iron and Steel Engineering, 8 1929, p, 143-6). Progress in the Art of Electrical Precipitation Since 1900, by P. E. Landolt (Trans actions, American Electrochem. Society, 61,1927). Some Factors and Principles Involved in the Separation and Collection of Dust, Mist and Fume from Gases, by Evald Anderson (Transactions, American Institute of Chemical Engineers, 16,1924, Pt. 1, p. 69-86). Electrical Precipitation of Solids from Smelter Gases, by Ross B. Rathbun (Trans actions, American Institute of Electrical Engineers, 41,1922, p. 815).' . Electrical Engineering Features of the Electrical Precipitation Process, by G. H. Horne (Transactions, American. Institute of Electrical Engineers, 41,1922, p. 808). Characteristics of Unit Dust Collectors, by Arthur C. Stern, Jack BalifT, Arthur E. Perina, Robert Crowley, Benjamin Feiner.and Arthur A. Urbano (A.S.H.V.E. Journal Section, Heating, Piping and Air Conditioning, May, 1946, p. 117). CHAPTER 34 I SPRAY APPARATUS Air Washers, Humidification with Air Washer, Dehumidification and Cooling with Air Washers, Well and Water Main Temperatures, Apparatus for Direct Humidification, Unit Humidifiers, Water-Cooling Towers, Water Use and Conservation, Rivers and Lakes, Spray Cooling' Ponds, Atmos- pheric and Mechanical Draft Cooling Towers, Mechanics of At mospheric Water-Cooling, Design Conditions, Water-Cooling" Tower Design, Selection of Water-Cooling Towers, Operation and Maintenance AIR humidification is effected by the vaporization of water, and always requires heat from some source. This heat may be added to the water prior to the time vaporization occurs, or it may be secured by a transformation of sensible heat of the air being humidified to latent heat ' as the vapor is added to the air. The thermodynamics of the process are discussed in Chapter 3. The removal of moisture from air may, or may not, involve the removal of heat from the air-vapor mixture. With spray equipment, dehumidification of air always necessitates the removal of heat. AIR WASHERS An air washer consists essentially of a chamber or casing in which is provided a. spray nozzle system> a tank at the bottom of the chamber for collecting the spray water .as it falls, and an eliminator section at the leaving end of the chamber for removal of drops of entrained moisture from the delivered air. Air is drawn through the casing of the washer, where it comes into intimate contact with the spray water. A heat transfer takes place between the air and water, resulting in either humi dification or dehumidification of the air, depending, upon the method of operation and the relative temperatures of air and spray water. ' - To prevent backlash of spray ahead of the washer chamber, and to aid in. more uniform air distribution, inlet diffusion plates or eliminator baffles, where necessary, are provided in the air entrance end of the air washer. Inlet diffusion plates are used when the air flow and water spray are in the same direction; eliminator baffles;of- special design are used where one or. more of the water sprays opposes, the air flow. At the outlet end of the washer suitable flooded'eliminator plates are used.' These: plates, for the removal of entrained moisture, usually cause four to six changes in direction of the air flow. Figs^ 1 and 2 show the essential construction features of conventional, air washers. Intimate contact between the air and the water is secured (1) by breaking the water into fine drops, (2)'by passing the air over sur faces continuously wetted by water, or (3) by a combination of the two. The' wetted surfaces in an air washer may be . of fiber glass, metal or scrubber plate construction." Scrubber plate types of washers are generally used to wash reclaimable products from the air, and are composed of several baffle type plates located across' the air stream. Water is supplied at the top of the washer to spray over these plates. In the case of the fiber glass or metal surfaces, the water spray is usually rather coarse and at , 709