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894 CHAPTER 45 : 1949 Guide Air Conditioning in the Bakery, by W. L. Fleiaher (A.S.H.V.E. Transactions, Vol. 37, 1931, p. 141). Proper Air Conditions for the Manufacturing of Confections, by A. E. Stacey, Jr. (A.S.H.V.E. Journal Section, Heating, Piping and Air Conditioning, October, 1937, p. 640). Air Condition the Bakery Throughout, by W. W. Reece (Heating, Piping and Air Conditioning, August, 1936, p. 149). Bureau of Standards Studies Determine Press Room Conditioning Requirements, by C. G. Weber (Heating, Piping and Air Conditioning, March, 1936, p. 137). Silica Gel Air Conditioning System Serves Rotogravure Printing Plant, by H. E. Ryerson (Heating, Piping and Air Conditioning, August, 1937, p. 497). Moisture Control by Liquid Absorption Offers a Useful Air Conditioning Tool, by F. M. Johnson (Heating, Piping and Air Conditioning', December, 1938, p. 782). Humidity in the Pressroom (Heating and Ventilating, May, 1932, p.35)/ Dehumidifying with Gas in a Printing Plant (Heating and Ventilating, May, 1935, P*. 31)* Air Conditioning in the Paper Industry (Heating and Ventilating, October, 1935, p. 23). Air Conditioning the Newspaper Plant, by R. T. Williams (Heating and Ventilat ing, September, 1937, p. 63). Air Conditioning Requirements of Multicolor Offset Printing, by C. G. Weber (Refrigerating Engineering, December, 1936, p. 6). Reactions of Lithographic Papers to Variations in Humidity and Temperature, by C. G. Weber and L. W. Snyder (U.S. Bureau of Standards Journal of Research, January, 1934). The Treatment of Offset Papers for Optimum Register, by C. G. Weber and M. N. V: Geib (If. S. Bureau of Standards Joumal of Research, February, 1936). Effect of Air Conditioning Upon Munitions, by J. I. Lyle (A.S.H.V.E. Transac tions, Vol. 23, 1917, p. 383). Air Conditioning of Blackout Plants, by W. A. Grant (A.S.H.V.E. Transactions, Vol. 48,1942, p.459). The Engineering Control of Some Solvent Hazards in War Industries, by S. C. Rothman (A.S.H.V.E. Transactions, Vol. 50, 1944, p. 319). Air Conditioning as Applied in Theatres and Film Laboratories, by D. C. Lindsay (Transactions Society of Motion Picture Engineers, April, 1927, Vol. XI, No. 30 p. 335-365). Air Conditioning for Textile Plants Making aiid Using Synthetic Yarns, by'L. L. Lewis (Rayon Textile Monthly, July, August, September, 1930). Air Conditioning for Clothing Research Laboratory (Heeding and Ventilating, July, 1943, p. 69). Refrigeration Insures Quality of Clothing, for the Army, by A. J. Mallinckrodt (Heating and Ventilating, March, 1944, p. 79). . Refrigeration for Textile Mill Air Conditioning, by P. h. Davidson (Heating and Ventilating, May, 1947, p. 57). Relation of Air Conditions to Tobacco Curing, by *J.; Johnson and W. B. Ogden (Wisconsin Agricultural Research BureauWO: 1-48,1931). \ , ... Air Processing Needs of Plywood Plane Parts, by F. O. Jordan (Heating and Ven tilating, April, 1944, p. 67). Heating, Air Conditioning, and Insulation for Penicillin Production, by J. C. Siegesmund (Heating, Piping and Air Conditioning, August, 1944, p. 475). Controlled Air Supply for Supercharger, Carburetor and Engine Testing, by C. S. Leopold (Refrigerating Engineering, August, 1943, p. 85). . Close Machine Tolerances Possible Through Temperature Control, by R/P. Dewey (Heating and Ventilating, April, 1944, p. 60). ' Operating and Maintenance Charges for Air Conditioning Machine Shops, by H. B. Lammers (Heating, Piping and Air Conditioning, February, 1946, p. 93). Ventilation of Long Tunnels During Construction, by W. B. Harris (Heating and Ventilating, July, p. 63 and August, 95,1947). Foundry Ventilation, by Jim Black and Lester Avery (Heating, Piping and Air Conditionxng, March, p. 71, April, p. 78, and May, p. 89, 1947). .. . > Smoke and Dust Control, Heating'and Ventilating in the Sorel Plant (Industrial Heating, February, p..236. and March, p. 422, 1947). ` CHAPTER 46 INDUSTRIAL EXHAUST SYSTEMS Classification of Systems, Hood Design Principles, Capture Velocity and Hood Suction, Duct System Design, Resistance of System, Efficiency of System, Air Flow Producing Equipment, Protection Against Corrosion and Abrasion 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 Con taminants. The theory of air flow in an exhaust system in the following paragraphs A to D will be found in a publication1 of the American Foundrymen's Association. A. When the air flow producing equipment of an exhaust system is properly oper ated 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 iDlets 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 op portunity 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 importance 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 sys tem. 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 deter mining the power required to operate the system. Total pressure tests do not in dicate 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 dusts and certain fumes and mists of large particle size, and (b) those handling vapors, gases and certain fumes and mists of small particle size. Design details differ in systems serving dust producing operations and those exhausting the 895