Document O33Bx4r9gJogomxgVvnaRmRwM

656 CHAPTER 37 1948 Guide. Spnty Apparatus *7. 657 introduces moistened air; and (2) direct-, which sprays moisture into the room or introduces moisture by means of steam jets. As in the cases of humidification by use of an air washer, the heat necessary for the vaporization of the moisture added to the air by direct, humidification is secured either from heat stored in the spray water or by a transformation of sensible to latent heat in the air humidified. In the latter case the enthalpy of the air remains constant but the dry-bulb, temperature of the.air is reduced. Direct humidification is usually preferable where high relative humidi-. ties must be maintained, but where there is little cooling or ventilation required. In comfort air conditioning, where both humidification and ventilation are required, the indirect humidifier is preferable: In indus trial applications, where the cooling or ventilation load is large and where very high relative humidities must be maintained, a combined system employing both direct and indirect humidifiers is sometimes .used. Fig. 3! Approximate Well Water emperaturesT at D epths of 30 to 60 Ft Spray Generation Spray generation is obtained:by (1) atomization, (2) impact, (3) hydraulic separation, and (4) mechanical separation. Atomization involves the use of a compressed air jet'to reduce the water' particles to a fine spray. - With the impact method, a jet of water under pressure impinges directly on the end of a small round wire. Where hydraulic separation is employed, a jet of water enters a cylindrical chamber and escapes' through an axial port with a rapid rotation Which causes .it immediately to separate in a fine Cone-shaped spray. In the ' mechanical separation process, water is thrown by centrifugal force from the surface of a rapidly revolving disc and separates into particles suf ficiently small to be: utilized in .certain types of mechanical .humidifiers. Spray Distribution . , Spray distribution-is obtained by (1) air jet, (2) induction, and (3) fan ' propulsion. .- -- The air jet which generates the spray in atomizers also carries the spray through a space sufficient for its distribution and evaporation, anti this method of distribution is termed air jet. Where distribution is obtained by induction, the aspirating effect of an impact or centrifugal Spray jet is utilized to induce a current of air to flow through a duct or casing, and this air current distributes the spray. Fan propulsion obviously consists ' of the utilization of fans to entrain and distribute the spray. Industrial type direct humidifiers are commonly classified as (1) atomizing, (2) high-duty, (3) spray and (4) self-contained or centrifugal. Atomizing Humidifiers There are several types of atomizing humidifiers which employ nozzles placed within the room and rely upon compressed air to effect complete atomization of the water so that it can be converted to vapor by the heat ' of the room air. Some of these nozzles depend upon an aspirating effect to draw the water into the nozzle and atomize it, others operate on a combined air and water pressure. It is usual for nozzles of the water pressure type to be controlled by a diaphragm valve actuated by the pressure of the atomizing air. High-Duty Humidifiers Water is supplied to high-duty humidifiers under high pressure (usually about 150 lb per square inch) through pipe lines from a centrally-located