Document aBjdjxm7prn7gLJ4GBrV6d7e

American Society of Heating and Ventilating Engineers GuideT 1935 Table 1. Regain of Hygroscopic Materials Moisture Content Expressed in Per Cent of Dry Weight of the Substance at Various Relative Humidities--Temperature, 75 F ^ l Classi* Material Description Relative Homom--Per Cent 10 20 30 40 50 60 70 80 90 Avrao&rn Cotton Cotton Sea island--roving American- cloth 2.5 3.7 4.6 5.5 6.6 7.9 93 113 14.1 Hartahorne 2.6 3.7 4.4 5.2 5.9 6.8 8.1 10.0 143 Schloesing Cotton Absorbent 4.8 9.0 12.5 15.7 18.5 20.8 22.8 24.3 25.8 Fuwa Textile Fibres Wool______ ___ Australian,merino--skein -4.7- -7.0 8.9 10.8- 12.8- 14.9 17.2 19.9 23.4- Hartahorne' ~" Silk Raw chevennee--skein 3.2 5.5 6.9 8.0 8.9 10.2 11.9 14.3 18.8 Schloesing linen Table cloth 1.9 2.9 3.6 4.3 5.1 6.1 7.0 8.4 10.2 Atkinson linen Dry spun--yarn ' 3.6 5.4 6.5 73 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 12.2' 14.4 17.1 20.2 Storch Hemp Manila and sisal--rope 2.7 4.7 6.0 7.2 8.5 9.9 11.6 13.6 15.7 Fuwa , Rayons Viscose Nitrocellu lose Cupramonium Average skein 4.0 5.7 6.8 7.9 9.2 10.8 12.4 14.2 16.0 Robertson ^ Cellulose Acetate Fibre 0.8 1.1 1.4 1.9 2.4 3.0 3.6 4.3 5.3 Robertson M. F. Newsprint Wood pulp--24% ash 2.1 3.2 4.0 4.7 5.3 6.1 7.2 8.7 10.6 u. s. b. of a Paper H. M. F. Writing White Bond Wood pulp--3% ash Rag--1% asb 3.0 4.2 S.2 6.2 7.2 8.3 9.9 11.9 14.2 u. a b. of a 2.4 3.7 4.7 5.5 6.5 7.5 83 10.8 13.2 o.s. B.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 0. S. B. of S. Kraft Wrapping Coniferous 3.2 4.6 5.7 6.6 7.6 8.9 10.5 12.6 14.9 o. a b. of a 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 7.2 8.6 10.2 12.0 14.3 17.3 19.8 21.7 Fuwa Glue Organic Rubber Materials Wood Hide Solid tire Timber (average) 3.4 4.8 5.8 6.6 7.6 9.0 10.7 11.8 123 Fuwa 0.11 0.21 0.32 -0.44 0.54 0.66 0.76 0.33 0.99 POWB 3.0 4.4 5.9 7.6 ,9.3 11.3 14.0 173 22.0 Forest P. Lab. Soap White 1.9 3.8 5.7 7.6 10.0 12.9 16.1 19.8 233 Fuwa Tobacco Cigarette 5.4 8.6 11.0 13.3 16.0 19.5 25.0 333 50.0 Ford White Bread 0.5 1.7 3.1 4.5 6.2 8.5 11.1 143 19.0 Atkinson Crackers 2.1 2.8 3.3 3.9 5.0 6.5 8.3 10.9 14.9 Atkinson Food stuffs Macaroni Flour 5.1 7.4 8.8 10.2 11.7 13.7 16.2 19.0 22.1 Atkinson 2.6 4.1 53 6.5 8.0 9.9 12.4 15.4 19.1 3ai)ey Starch 2.2 3.8 5.2 6.4 7.4 8.3 9.2 10.6 12.7 ttkinson Gelatin 0.7 1.6 2.8 3.8 4.9 6.1 7.6 9.3 11.4 itkinson Asbestos Fibre finely divided 0.16 0.24 0.26 0.32 0.41 0.51 0.62 0.73 0.84 ''uwa Silica Gel 5.7 9.8 12.7 15.2 17.2 18.8 20.2 213 22.6 iHiwa Inorganic domestic Coke 0.20 0.40 0.61 0.81 1.03 1.24 1.46 1.67 139 Selvig Activated Charcoal Steam activated . . lulphuric Acid VtSOi 7.1 4.3 22.8 16.2 28.3 29.2 50.0 31.1 3X7 i'UWR *3.0 11.0 17.5 52.5 57.0 51.5 57:0 73.5 323 fiason 66 Chapter 3--Industrial Air Conditioning HYGROSCOPIC MATERIALS Air conditioning is extensively used in the manufacture or processing of hygroscopic materials such as textiles, paper, wood, leather, tobacco, and foodstuffs. Where the physical properties of the product affect value, the question of moisture is of special importance. With increase in moisture content, hygroscopic materials ordinarily become softer and more pliable. Economy of manufacturing, therefore, requires that the moisture content be maintained at a percentage most favorable to rapid and satisfactory manipulation and to a minimum loss of material through breakage. A constant 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.______ ____ In the processing of hygroscopic materials, it is usually necessary to secure a final moisture content suitable for the goods as shipped. Where the goods are sold by weight it is proper that they contain a normal or standard moisture content. Air conditioning is important in certain branches of the chemical industry in controlling the temperature of reaction and facilitating or retarding evaporation. The control of moisture content of air supplied to blast furnaces in the manufacture of pig iron also has proved advantageous. The moisture content of a hygroscopic material at any time depends upon the nature of the material and upon the temperature and especially the relative humidity of the air to which it has been exposed. Not only do different materials acquire different percentages of moisture after prolonged exposure to a given atmosphere, but the rate of absorption or drying out varies with the nature of the material, its thickness and density. Table 1 shows the regain or hygroscopic moisture content of several organic and inorganic materials when in equilibrium at a dry-bulb tem perature of 75 F and various relative humidities. The effect of relative humidity on regain of hygroscopic substances is clearly indicated. The effect of temperature is comparatively unimportant. In the case of cotton, for instance, an increase in temperature of 10 deg has the same effect on regain as a decrease in relative humidity of one per cent. Changes in temperature do, however, affect the rate of absorption or drying. Sudden changes in temperature cause temporary fluctuations in regain Conditioning and Drying Exposure of hygroscopic materials to an atmosphere of controlled humidity and temperature for the purpose of establishing a specified moisture condition in the material is called conditioning. Where the desired final moisture content is relatively low, the term drying is usually used. In any case, control of relative humidity, temperature, air velocity and length of exposure are all of more or less importance. The conditioning treatment may be undertaken in a special enclosure (conditioning room) or it may be accomplished in the same room and at the same time as some regular manufacturing process. For instance; in the weaving of textiles a high relative humidity is commonly employed to keep the yarn strong and pliable, thus assisting in the weaving process and 67