Document bBKoErOXgDyj9ddgozY93evG3

834 , CHAPTER 45 . .1946 Guide Controlled Air Supply for Supercharger, Carburetor and Engine Testing, by C. S. ` Leopold {Refrigerating, Engineering, August,'1943, p. 85). Air Conditioning Aids in Artillery'Optical Equipment {Heating and Ventilating, August, 1943, p. 46). Air Processing Needs of Plywood Plane Parts, by F. O. Jordan {Heating and Venti lating, April, 1944, p. 67). , ' Close Machine Tolerances Possible Through Temperature Control, by R. P. Dewey {Heating and Ventilating, April, 1944, p. 60). Design of Low Temperature Test Cabinets, by F. Crampton Frost and T. J. Lopiccolo , {Heating and Ventilating,July, 1944, p.57). Industrial Cooling as a Production Aid, by J. Partington, Jr. {Heating and Ventilating, April, 1944, p. 47). Penicillin, by Lester T. Avery {Heating and Ventilating, March, 1944, p. 45).. Penicillin Production Depends Upon Control of Air Conditions {Heating, Piping and Air Conditioning, April, 1944, p.,188). -, Heating, Air Conditioning and Insulation for Penicillin Production, by J. C. Siegesmund {Heating, Piping and Air, Conditioning, August, 1944, p. 475). 'Refrigeration Insures Quality of Clothing for the Army, by A. J. Mallinckrodt . {Heating and Ventilating, March, 1944, p. 79). iii ' ` ;`l CHAPTER 46 anACcconveying._S_uslems Classification of Systems, Hood Design Principles, Hood Suction and. Indraft Velocities, Duct System Design, Air Cleaning Equipment, Resistance of Systems, Air Flow Pro ducing Equipment, Protection Against Corrosion IN many industrial plants some type of exhaust system designed to collect and remove dusts, fumes, mists, vapors and gases is essential in order to promote efficiency, economy, and safety of operation. Defini tions of these various contaminants are included in Chapter 10, Air Contaminants. The theory of air flow in an exhaust system in the following paragraphs A to D will be found in a publication 1 of the American Foundrymen's Association. A. When the-air flow producing equipment of an exhaust system is properly operated it will produce a negative pressure (below atmospheric) in the exhaust side of the system sufficient to overcome all resistance and to sustain the desired air velocity; and, further, will overcome all resistances on the discharge or positive pressure side of the system so that the air drawn through exhaust inlets will be discharged against atmospheric pressure. B. An exhaust system is entirely.dependent on a sufficient volume of air flowing into the exhaust inlets to catch the matter to be exhausted before such matter has an oppor tunity to diffuse into the general atmosphere of the work place or room. C. The velocity of the air flowing into an exhaust inlet is usually of secondary im portance and' becomes an essential factor only when a certain velocity is required to overcome some force acting on the matter to be caught. The velocity within an exhaust ' system is only important to the extent that it shall be sufficient to convey the entrained matter and prevent it from settling or dropping out in the piping system. Velocity in' terms of velocity pressure is most essential in-designing a system because it is the basis upon which all calculations are made. In testing and checking a system the velocity as determined from the velocity pressure reading obtained by means of a Pitot tube is the only true indication of the exact air flow in a pipe or system. D. The total pressure within an exhaust system is only of importance in determining the power required to operate the system. Total pressure tests do not indicate the proper functioning of an exhaust system as related to the volume and velocity'of the air flowing into an exhaust inlet. , General design information is included in this chapter which is intended to relate primarily to industrial exhaust systems. CLASSIFICATION OF SYSTEMS In general there are two basic layouts of exhaust systems, the central and the multiple unit system. In. the central system a fan is located near the center of operations with a piping system radiating to the various machines to be served. In the multiple unit system, which is. sometimes employed where the machines to be served are widely scattered, or where the operations are apt to be independent or intermittent, small individual exhaust fans are located at the center, of the machine groups or at each machine. The unit arrangement has the advantage of flexibility. Exhaust systems may be classified with respect to the nature of the material to be handled by them as (a) those handling dust and (6) those handling fumes, mists, vapors and gases. There is'a marked difference in design details, of; systems serving dust producing operations and those exhausting the more vapor-like matter even though the same basic 835