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274 CHAPTER 22 1962 Guide And Data Book N -- disk speed, revolutions per hour. A* " p -- p. = vapor-pressure difference, atmospheres. pk "* partial pressure of water vapor in air, atmospheres, p. "* vapor pressure of water at t* atmospheres. Q *= average volumetric gas rate, cubic feet per second, r =* disk radius, feet. S weight of solids in feed, pounds per pound of feed, t, air or gas temperature, Fahrenheit. A inlet temperature, Fahrenheit U = outlet temperature, Fahrenheit. U " temperature of particle, solid, or surface of evaporation, Fahrenheit. I* " wet-bulb temperature of drying air, Fahrenheit. <i = make-up air temperature, Fahrenheit. ft " temperature of air entering stock, Fahrenheit. It -* exhaust air temperature, Fahrenheit. fmi -- entering stock temperature, Fahrenheit. Imt ** leaving stock temperature, Fahrenheit. At "(! -- <)" temperature difference between air and sur face of evaporation, Fahrenheit. Ala> * logarithmic mean between air temperature entering and leaving the bed, and the wet-bulb temperature, Fahren heit. V -- volume of chamber, cubic feet. e average specific volume of gas, cubic feet per pound. Wi TM humidity ratio of entering air, pounds of water vapor per pound of dry air. Wt humidity ratio of leaving air, pounds of water vapor per pound of dry air. to moisture content on dry basis at any time 8, pounds of - water per pound. toc * critical moisture content, pounds water per pound dry material. to* water content, dry basis, of the drop as it enters the drying chamber, pounds per pound of dry solid, to. moisture content at equilibrium with external condi tions, pounds per pound dry material. tCf weight of water in feed, pounds per pound of feed, to. " moisture content at start of diffusions! period, pounds per pound dry material. " - drying rate, pounds of water per (hour) (pound dry material). (dtpj -- constant drying rate, pounds per (hour) (pound dry d8 material). ^ falling rate, pounds water per (hour) (pound of dry stock). 8 time, hours, fi, = residence time, seconds. pl - density of feed,, pounds per cubic foot, p, -- bulk density of dry granular bed, density of dry - particle, pounds per cubic foot. REFERENCES 1 W. R. Marshall, Jr. and S. J. Friedman: Drying (Perry's Chemical Engineer*' Handbook, McGraw-Hill Co., New York, 1950, 3rd ed.). Indicated material supplied by W. R. Marshall, Jr. and S. J. Friedman, authors of the Section on Drying in the Third Edition of the Chemical Engineers' Handbook. Permis sion to use this material has been kindly granted to The Guide by the Editor,-John H. Perry, and by McGraw-Hill Book Company, publishers of the Chemical Engineers' Hand book. * W. R. Marshall, Jr: The drying of foods (Heating, Piping and Air Conditioning, September to December 1942, also No vember and December 1943). * C. B. Shepherd, C. Hadloek, and R. C. Brewer: Drying materials in trays (Industrial and Engineering Chemistre April 1938). 4 B. W. Gamson, G. Thodos, and O. A. Hougen: Heat, mass and momentum transfer in the Sow of gases through granular sjaolmids (American Institute of Chemical Engineers Transactions 1 W. M. Grosvenor: Calculations for dryer design (American Institute of Chemical Engineer* Transactions, Vol. 1, 1908 d jbsa K' * S. J. Friedman: Steps in the selection of drying equipment (Healing and Ventilating, February 1951, p. 95). ' What the air conditioning engineer should know about drying (Heating and Ventilating, December 1942). S. J. Friedman, R. A. Gluckert, and W. E_ Marshall: Cen trifugal disk atomisation (Chemical Engineering Progress, Vol 48. 1952, p. 181). ^ * J. H. Perry (ed.): Chemical Engineers' Handbook (McGrawHill Book Co., New York, 1950, 3rd ed., p. 806). " G. G. Brown and Associates: Unit Operations (John Wilev A Sons, New York, 1950, p. 564). 11 Tobacco Curing (Virginia Agricultural Experimental Station Technical Bulletin 116, January 1951). Agricultural Index (H. W. Wilson Co., New York). BIBLIOGRAPHY C. F. Prutton and C. 0. Miller: Factors influencing the per formance of rotary dryers (American Institute of Chemical Engineers Transactions, February, August 1942). W. R. Marshall and O. A. Hougen: Drying of solids by through circulation (American Institute of Chemical Engineers Transactions, 1942). A. WeisseJberg: Factors that influence dryer performance (Chemical and metallurgical Engineering, August 1932). O. A. Hougen: Typical dryer calculations (Chemical and Metallurgical Engineering, January, March 1940). S. J. Friedman and W. R. Marshall, Jr.: Studies in rotary drying, I and II (Chemical Engineering Progress, 1949). ^^Symposiurn on drying (/ndustrial and Engineering Chemistry, T. K. Sherwood: The Drying of Solids (Massachusetts Insti tute of Technology Bulletin Noe. 237, 247,258). T. P. Brown: Radiant energy drying with heat lamps (Metal Industry, December 1939, p. 607). E. W. Flosdorf: Drying by sublimation (Pood Industry, January 1945, p. 607). F. H. Slade: Evaporative drying system (Food Manufactur ing, March 1943, p. 70). D. W. Biocheno: The spray dryer--its possibilities in indus try (Pood Manufacturing, June 1944, p. 195). L. E. Stout, K. J. Caplan, and W. G. Baird: Mechanism and rate of drying by near-tofra-red radiation (American Institute of Chemical Engineers Transactions, Vol. 41, 1945, p. 283). O. A. Hougen, H. J. McCauley, and W. R. Marshall: Limita tions of diffusion equations in drying (American Institute of Chemical Engineers Transactions, vol. 1, 1940, p. 183). V. P. Victor: An introduction to convection drying and dry ing calculations (Heating and Ventilating, December 1944, p. 67). Irvin Lavine and O. D. Sutherland: Revised psychrometric chart assists high temperature design (Chemical and Metal lurgical Engineering, April 1928, p. 226). C. R. Wilkie and O. A. Hougen: Mass transfer in the flow of gases through granular solids extended to low modified Rey nolds numbers (American Institute of Chemical Engineers Transactions, Vol. 41, 945, p. 445). W. R. Marshall: Current Status of the Theory and Practice of Drying (University of Wisconsin, Engineering Experiment Station Reprint No. 265). CHAPTER 23 PROCESS AND PRODUCT AIR CONDITIONING Genera/ Requirements for Manufacture, Processing, and Preservation; Design Conditions and Application Data; Cfassffrcofion of Problems; Moisture Content and Regain; Conditioning and Drying,- Chemical and Biochemical Reactions,- Crystallization; Control for Machining, Polishing, and for Static Electricity Elimination; Laboratory Conditions; Calculations ROCESS and product air conditioning is concerned gfamHing of the processing problems involved. Since indi Pwith the design and application of equipment for ob vidual processes and machines are changing rapidly, air con taining proper conditions for the manufacturing, processing, ditions must be revised constantly to meet sew requirements. aod preserving of material, equipment, and commodities. Table 1 lists the temperatures and relative humidities This chapter includes a general discussion of these condi required for storage of certain commodities, and for man tions and also a comprehensive list of specific requirements ufacturing and processing of others. In some cases the for various types of products and processes which are not temperatures and relative humidities listed in Table 1 discussed in Chapters 24 to 30. Storage requirements for vari have no direct influence upon the product itself, but do ous commodities are discussed in Chapters 46 to 50. affect the efficiency of employees and, in turn, the work manship, uniformity, and cost of production. Sometimes a GENERAL REQUIREMENTS FOR MANUFACTURE, PROCESSING, AND PRESERVATION In order to apply air conditioning to industrial processes, :: compromise between the known, optimum condition for processing and that required for worker comfort is unavoid able. Air conditioning for industrial processes is so extensive the air-conditioning engineer must have a thorough under- . (Text continued on p. 78) Table 1 ....Temperatures and Humidities Applicable ,to Industrial Air Conditioning APPLES--See Chapter 47 BAKERIES--See Chapter 34 BANANAS--See Chapter 47 BREWING--See Chapter 35 CANDY--See Chapters 33 . (Manufacturing) and 50 (Storage) fMOft Tmp. f | AH.% CERAMICS Refractory............................................. Molding room....................................... Clay storage.......................................... Dacalcomaoia production.................... Decorating room................................... 80 60 to 80 75 to 80 75 to 80 50 to 90 60 to 70 35 to 65 48 ' 48 * Schedule drying, depending upon the cl&y. Temperature and humidity must be controlled in the dec orating shop in the whiteware plants, and the decalcomania production room. Dust control is essential, and the dust count must be held down to four million particles per cubic foot due to the danger of wlicosia, CEREAL Packaging. 75 to 80 45 to 50 - CITRUS FRUIT--See Chapter 48 Storage: DISTILLING 35 to 40 65 to 72 SO to 60 Mashing done at 150 to 155 F, then cooled to 64 to 68 F. Mash heated to 165 F and then cooled to 80 F, then pitched with yeast and fermented at mritnm temperature of 85 F. Cooling for various distilling processes normally accom plished by use of river or well water depending on tempera tures and availability. Low humidity and dust control important where grains are ground. Viscous filters preferred as mold spores and bacteria are trapped in the viscous film, preventing propagation. fracas* loop. F tm.% aeCTRICAl PRODUCTS Electronics and X-ray: Coil and transformer winding......... Electrical instruments: Thermostat assembly and calibra^ Humidistat assembly and calibra- Sxnall mechanisms: Switchgear: , Thermal circuit breakers assembly Water wheel generators: Rectifiers: *' Processing selenium and copper ox- Dust control is essentia) in these processes * Hold constant temperature. 72 68 70 76 76 72* 76 73 73 73 75 68 76 70 74 15 40 50 to 55 50 to 55 50 to 55 40 to 45 60 to 63 50 50 50 65 to 70 20 to 40 30'th 60 30 to 50 30 to 40 275