Document 3JDY3gEpgv1DvNpq67jaQ9N4a

7 Heating Ventilating Air Conditioning Guide 1938 Table 3. Drying Time and Conditions for Representative Materials3--Con. Material Temperature Deg F Per Cent Relative Huuiditt Drying Time Tanin and other chemicals (spray dried).............. - 250-300 Terra Cotta (air drying in conditioned room)........ 150-200 85-130 180-200 Varnish refrigerator boxes.............. ........................... . .110 110-140 120-130 120-130 . 120-130 Waliboard fiber insulating, roller type drier..... --. Wallboard fiber insulating, truck type drier...:--J \JVnnl ` .................................................. 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 2H-3 Hrs 24-48 Hrs 24 Hrs 20 Min oSee 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. 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. 658 Chapter 35. Drying Systems t = air temperature, f = stock temperature. --' ; t = average stock temperature over short time interval, in a batch drier. I?, = wet-bulb temperature, s' = specific heat of the stock: B = total radiation and conduction losses per unit time. v> = pounds of water per pound of dry stock. r = heat of evaporation of water. s = humid heat of air, IF. heat necessary to raise 1 lb of dry air + H lb of steam 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(u>i -- to,) (2) Table 4. Gas Combustion Constants3 Gas Carbon Hydrogen Oxygen Heat op Combustion las per La op Combustible a Cu Ft 3S | o per Lb Btu per Lb 5o 2u Gross Net Required for Combustion 0. Nt Air Flue Products COi BA Hi c 12.000 14.140 14,140 2.667 8.873 11.540 3.667 8.873 Hi 2.015 187.723 61.100 51.643 7.939 26.414 34.353 -- 8.939 26.414 0, 32.000 11.819 Nitrogen Nt 28.016 13.443 Carbon Monoxide CO 28.000 13.506 4,369 4.369 0.571 Carbon Dioxide COi 44.000 8.548 1.900 2.471 1.571 1.900 Methane Ethane Propane Sulphur Dioxide CHt 16.031 23.565 23.912 21,533 3.992 13.282 17.274 2.745 2.248 13.282 CtH, 30.046 12.455 22.215 20,312 3.728 12.404 16.132 2.929 1.799 12,404 CiHg 44.062 8.365 21,564 19,834 3.631 12.081 15.712: 2.996 ,1.635 : 12.081: 50i 64.060 ' 5.770 Water Vapor ff*0 18.015 21.017 Air -- 28.900 13.063 j - All gas volumes corrected to 60 E and 30 in.-mercury barometric pressure dry; 659 -