Document e1MgJY2rKEd2QEZaeeabDo1nG

910 CHAPTER 44 1950 Guide involved that a detailed treatment is beyond the scope of this chapter. It is possible to cover only a few salient points of the general subject. CLASSIFICATION OF PROBLEMS In general, any industrial air conditioning problem in processing may be classified under one or more of the following: 1. Control of regain. 2. Control of rate of chemical reactions. 3. Control of rate of biochemical reactions. 4. Control of rate of crystallisation. 5. Control of temperature for close tolerance machining and grinding. 6. Control of dew-point for protection of highly polished surfaces. 7. Control of humidity for static electricity elimination: 8. Control of conditions for material test laboratories. Moisture Content and Regain In the manufacture or processing of hygroscopic materials such as tex tiles, paper, wood, leather, tobacco and foodstuffs, the temperature and relative humidity of the air have a marked influence upon the rate of pro duction and upon the weight, strength, appearance and general quality of the product. The moisture content of materials having a vegetable or animal origin, and to a lesser extent minerals in certain forms, comes to equilibrium with the moisture of the surrounding air. This moisture con tent is known as regain. Standards of regain are fixed in the trade and are the fundamental basis for the control of certain physical qualities of the material during manufacture. Manufacturing economy requires that the moisture content be main tained at a level favorable to rapid and satisfactory manipulation, and to a minimmn loss of material through breakage. A uniform condition is desirable in order that high speed machinery may be adjusted permanently for the desired production with a minimum loss from delays, wastage of raw material and defective product. Moisture content refers to free mois ture (as in a sponge) and to hygroscopic moisture (which varies with at; mospheric conditions). It is usually expressed as a percentage of the total weight of material. Regain is more specific and refers only to hy groscopic moisture. It is expressed as a percentage of the bone-dry'weight of material. For example, if a sample of cloth weighing 100.0 g is dried to a bone-dry weight of 93.0 g, the loss in weight, or 7.0 g, represents the weight of moisture originally contained. This expressed as a per centage of the total weight (100.0 g) gives the moisture content of 7 per cent. The regain, which is expressed as a percentage of the bone-dry weight, . 7.0 ' . . 18 93~0 or ` per cent' The use of the term regain does not imply that the material as a whole has been completely dried out and has re-absorbed moisture. A basis for calculating the regain of textiles is obtained by drying, under standard conditions, a sample from the lot; and the dry weight thus ob tained is.used in the calculations to determine the regain. Table 2 shows the regain or hygroscopic moisture content of several organic and inorganic materials when in equilibrium at a dry-bulb temper ature of 75 F and various relative humidities. The effect of temperature as compared to the relative humidity is comparatively unimportant, al though sudden changes in temperature cause a slight change in regain even when the relative humidity remains stationary. Changes in tem perature do, however, affect the rate of absorption or drying, although Industrial Air Conditioning 911 Table 2. Regain or Hygroscopic Materials Moisture Content Expressed in Per Cent of Dry Weight of the Substance, at Various Relative Humidities--Temperature, 76 F Classi fication Material Description Relative Humidnr--Per Cent 10 20 30 40 50 60 70 80 90 Cotton Sea island--roving 2_5 3.7 4.6 5.5 6.6 7.9 9.5 IL5 14.1 Hartsharne Cotton American--cloth 2.6 3.7 4.4 5.2 5.9 6.8 8.1 10-0 14.3 Schloesing' ` Cotton " Absorbent M 9.0 12.5 15.7 18.5 20.8 218 24.3 25.8 Fawa Natural Textile Fibers Wool Silk Linen Australian merino--skein 4.7 7.0 8.9 10.8 12.8 14.9 17.2 19.9 23.4 Hartahorne . Raw cbevennes--skein 5.2 5.5 6.9 8.0 8.9 10.2 11.9 14J I8J Schloesing Table cloth 1.9 2.9 3.6 4J S.l 6.1 7.0 8.4 10.2 Atkinson ' i Linen Dry spun--yarn 3.6 5.4 6.5 7.3 8.1 8.9 9.8 11.2 13.8 Sommer Jute Average of several grades 3.1 5.2 6,9 8.5 10.2 112 14.4 17.1 20.2 Storch Hemp Manila and sisal--rope 17 4.7 6.0 7.2 8.5 9.9 11.6 13.6 1S.7 Fuwa Rayons Viscose Nitrocellu lose Cupramontum Average skein Cellulose Acetate Fiber 4.0 5.7 6.8 7.9 9J 10.8 114 14J 16.0 Robertson 0.8 1.1. 1.4 1.9 2.4 3.0 3.6 4J 5.3 Robertson M. F. Newsprint Wood pulp--24% ash 11 3.2 4.0 4.7 5.3 6.1 7.2 8.7 10.6 U.aB.ofS. H. M. F. Writing Wood pulp--3% ash 3.0 4.2 5.2 6.2 7.2 8.3 9.9 119 14.2 U.S.B.ofS. Paper White Bond Rag--1% ash 14 3.7 4.7 5.5 6.5 7J 8.8 10.3 13.2 U.KB.ofa Com. Ledger 75% rag--1% ash 3.2 4.2 5.0 5.6 6.2 6.9 8.1 10.3 13.9' u.aB.ofa Kraft Wrapping Coniferous 3.2 4.6 5.7 6.6 7.6 8.9 10.5 12.6 14.9 u.aB.ofa Leather Sole oak--tanned 5.0 8.5 11.2 13.6 16.0 18.3 20.6 24.0 29.2 Phelps Catgut Racquet strings 4.6 72 8.6 10.2 110 14.3 17.3 19.8 21.7 Fewa Misc. Organic Materials Glue Rubber Wood Hide Solid tires Timber (average) 3.4 4.8 5.8 6.6 7.6 9.0 10.7 11.8 12.5 Fuwa 0.11 0.21 0.32 0.44 0.54 0.66 0.76 0.88 0.99 Fuwa 3.0 4.4 5.9 7.6 9.3 1U 14 0 17.5 22.0 Forest P. Lab. Soap White- 1.9 3.8 5.7 7.6 10.0 119 16.1 19.8 23.8 Fuwa .. Tobacco Cigarette 5.4 8.6 11.0 13.3 16.0 19.5 25.0 33.5 500 Ford White Bread 0.5 1.7 3.1 4.5 6.2 8.5 11.1 14.5 19.0 Atkineon Crackers 11 2.8 3.3 3.9 5.0 6.S 8.3 10.9 14.9 Atkinson Foodstuffs Macaroni Flour 5.1 7.4 8.8 10.2 117 13.7 16.2 19.0 22.1 Atkinson 16 4.1 5.3 6.5 8.0 9.9 12.4 15.4 19.1 Bailey , ` Starch 12 3.8. 5.2 6.4 7.4 8-3 9.2 10.6 12.7 Atkinson Gelatin 0.7 1.6 2.8 3.8 4.9 6.1 7.6 9.3 11.4 Atkinson * Asbestos Fiber Finely divided 0.16 0.24 0.26 0.32 0.41 0.51 0.62 0.73 0.84 Fuwa . Silica Gel Inorganic Domestic Coke 5.7 9.8 117 13.2 17.2 18.8 20.2 21.5 22.6 Fuwa 0.20 0.40 0.61 0.81 1.03 1.24 1.46 1.67 1.89 Sdvig Activated Charcoal Steam activated 7.1 4.3 218 26.2 23.3 29.2 30.0 31.1 32.7 Fuwa Sulfuric Acid HtSO* 33.0 11.0 17:5 52.5 57.0 51.S 67.0 73.5 32.5 Mason this property generally varies with the nature of the material, its thickness and density. .. When hygroscopic materials. absorb moisture from the surrounding air they deliver to. the air sensible, heat equivalent to the latent heat released py the moisture to the material. This amount of heat should be included m the load estimate.