Document 5jE1Mp6EYyBD6xMJn6y3aag0

Heating Ventilating Air Conditioning Guide 1939 Table 3. Drying Time and Conditions for Representative Materials3__ C<on. Temperatube Deo F PSB CfINT Reutitb HUUIDZTT Drtiko This Tanin and other chemicals (spray dried)........ Terra Cotta (air drying in conditioned room).. Tobacco leaves____________________________ Tobacco sterna. Varnish refrigerator boxes.. Varnish steering wheels...... Veneer J4 in. 3-ply._______ 250-300 150-200 85-130 180-200 110 110-140 120-130 tJKe in. 5-ply.. 120-130 1% in. S-pIy----- 120-130 Vitreous Enamel sheets before firing........ ............... Wallboard pasted plywood___________________ Wallboard fiber insulating, roller type drier...... Wallboard fiber insulating, truck type drier..... Walnuts.____ !........................................................... Wheat, com, oats, rice, barley________________ Wire cloth Japan.................................................... Wool_____________________ ___________ _______ 170 300 300-385 300-385 100 180 200 105 35 25-35 35-40 35-40 35-10 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 2H-3 Hrs 24r-48 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. 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. .V = 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. 676 Chapter 35. Drying Systems I = air temperature. t< = stock temperature. t" = average stock temperature over short time interval, in a batch drier. *w = wet-bulb temperature, ji = specific heat of the stock. S = total radiation and conduction losses per unit time, ui = pounds of water per pound of dry stock. r = heat of evaporation of water. s = humid heat of air, heat necessary to raise 1 lb of dry air + II lb of steam 1 F. 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 (H, - Hi) = S(u>, - to,) (2) Table 4. Gas Combustion Constants3 Gas Carbon Hydrogen 4 ^ 53 si Ofc.. a s oS Sfc- Cu Ft peb Lb c 12.000 Heat op Combustion ' Btu per Lb Grom Net 14,140 14,140 Lbs peb Lb op Combustible Required for Combustion Oi Hi Air Flue Products COi HaO N, 2.667 8.873 11.540 3.667 -- 8.873 Hi 2.015 187.723 61.100 51,643 7.939 26.414 34353 8.939 26.414 Oxygen Oi 32.000 11.819 Nitrogen- Hi 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 8.54S cha 16.031 23.565 23,912 21,533 3.992 13.282 17.274 2.745 C,H, 30.046 12.455 22.215 20.312 3.728 12.404 16.132 2.929 C,Ha 44.062 8.365 21.564 19334 3.631 12.081 15.712 2.996 2.248 13382 . 1.799 12.404 1.635 12.081 Sulphur Dioxide SOt 64.060 5.770 Water Vapor HtQ 18.015 21.017 Air 28.900 13.063 All gas volumes corrected to 60 F and 30 in. mercury barometric pressure dry. 677