Document wrQox3MXy703zwzRwoOJ9L2J6

HEATINC VENTILATING AIR CONDITIONING CUIDE .1941 Table 3. Drying Time and Conditions for Representative Materials3--Con. Material Temperature Deo F Peb Cent Relative Humidnr Drtxng Time Tanin and other chemicals (spray dried)................. Terra Cotta (air drying in conditioned room)...... Tobacco leaves............ .................. ........... Tobacco stems........................................... Varnish refrigerator boxes Varnish steering wheels.......................................... Veneer ]/i in. 3-ply....:........................................... 250-300 150-200 85-130 180-200 110 110-140 120-130 % in. 5-ply. ............................................ 120-130 1)4 in. 5-ply. ....................... ............................. 120-130 Vitreous Enamel sheets before firing.................. Wallboard pasted plywood....................^.............. Wallboard fiber insulating, roller type drier--......... Wallboard fiber insulating, truck type drier Walnuts............. ............ ..... Wheat, corn, oats, rice, barley.............................. Wire cloth Japan.....................1.............. Wool....._.................................................... 170 300 300-385 300-385 100 180 200 105 35 25-35 35-40 35-40. 35-40 Instantaneous 12-96 Hrs 12 Hrs 12 Hrs 5-7 Hrs Overnight 6-8 Hrs + 2 Hrs acclima tion 16-18 Hrs + 4 Hrs acclima tion ' 20-24 Hrs + 4 Hrs acclima tion 15-20 Min 2)4-3 Hrs 24r48 Hrs 24 Hrs 20 Min See references at end of chapter. the common constituents of fuel are shown in Table 4. The heating values of oils are shown in Fig. 7. The sensible heat in Btu contained in the products of combustion of an average fuel oil and various gases is given in Fig. 8. The problem of securing complete combustion in a heater is important, in order to secure efficiency and the absence of soot formation, but unlike the ordinary power or heating boiler, excess air need not be maintained at a minimum in most cases. Excess air is generally admitted either in the heater or before the products go into the drier. DESIGN In all drying problems, data regarding temperatures, time, and hu midity must be obtained by experiment or previous experience. Experi ments are best performed at the temperatures, humidities, and velocities to be actually used in the full sized drier, and with full size samples, j The following nomenclature and explanation of terms will be used in the discussion of drying calculations: H -- humidity of air, pounds of water vapor per pound of dry air. G = pounds of dry air supplied to the drier per unit of time. 5 = pounds of stock dried per unit of time in a continuous drier. 5' -- pounds of stock charged per batch to a discontinuous drier. 0 = time. Q = total heat'supplied to the drier 708 CHAPTER 40. DRYING SYSTEMS t = air temperature. I' = stock temperature. tn = average stock temperature over short time interval, in a batch drier. tv, = wet-bulb temperature. r1 = specific heat of the stock. B = total radiation and conduction losses per unit time, to = pounds of water per pound of dry stock. r = heat of evaporation of water. s - humid heat of air, i.e., heat necessary to raise 1 lb of dry air + H lb of steam IF. Subscript (1) designates conditions at the point where the material in question (air or stock) enters and (2) where it leaves the drier. Air driers may be divided into two classes, those in which all moisture evaporated from the stock leaves the drier as vapor in the effluent air, and those in which part or all of the moisture is condensed from the air in the drying equipment itself. In any continuously operating drier of the first type the relation between moisture content of the stock and quantity of air required for the drying operation is given by the equation: G (Ht - Hi) = S(wi - to,) (2) Table 4. Gas Combustion Constants3 Chemical F ormula Gas e j< Cu Ft per Lb Heat or Combustion Btu per Lb Lam per Lb or Combustible Required for Combustion Flue Products si 0s Gross Net 0, N, Air COi BtO Mi Carbon Hydrogen C 12.000 14.140 14,140 2.667 8.873 11.540 3.667 -- 8.873 H, 2.015 187.723 61.100 51,643 7.939 26.414 34.353 -- 8.939 26.414 Oxygen 0, 32:000 11.819 Nitrogen N, 28.016 13.443 --:------- Carbon Monoxide CO 28.000 13.506 . 4.369 4.369 0.571 1.900 2.471 1.571 -- 1.900 Carbon Dioxide Methane Ethane Propane COi 44.000 8.548 r CHa 16.031 23.565 23.912 21.533 3.992 13.282 17.274 2.745 cyffa 30.046 12.455 22,215 20,312 3.728 12.404 16.132 2.929 C,BS 44.062 8.365 21.564 19334 3.631 12.081 15.712 2.996 2.248 13.282 1.799 12.404 1.635 12.081 Sulphur Dioxide S02 64.060 5.770 Water Vapor 11,0 18.015 21.017 Air 28300 13:063 All gas volumes corrected to 60 F and 30 in.'mercury barometric pressure dry. 709