Document 4Qyn3DGjqNad99zwBvODmj5aV

Table 1. Driers for Evaporation of Water Where headroom is available Drying is almost instantaneous Where heating of metal from in1Jside out is important Where one side cannot come in contact with supports until dry Where material comes in sheets or rolls, and will stand direct contact with heating surface Hygroscopic materials dried with vacuum, and packed immediately Where material will stand rough handling and is not subject to balling up 100 Steam Coils, Air, to Electricity, Products For high production 350 of Combustion Cost of operation high, for expensive materials Water, Steam ' Jacketed, may have Where dust must be saved Vacuum on top When production does not war rant continuous drier HEATING VENTILATING AIR CONDITIONING CUIDE 1941 a 3 <3 g -* 125 to Air, 250 Steam Coils 120 to Air, Products of 350 Combustion Electricity / 80 to Steam Coils, Air, 180 Electricity 0I3 1 . ace, See Hrtco e2 l & 80 to Water, 300 Steam O On Air, Steam, . Products of Combustion to 310 Steam, may have Vacuum on Top to Steam inside 350 of Drum Air, v? . Steam Coils si Si' Flowed on Drum, Dry Material Scraped off Continuous Sheets, Endless Chain Belt Continuous Sheets, Suspended on Metal Screens Falls through by Gravity Sprayed into Chamber Placed in' High Frequency Field Cascades through Truck, T ray, Belt Liquids, Slurries Paper, Textiles, Chemicals Paper, Chemicals Grains,. . . Sand Solutions over 30% Solids Metals, for removal of traces of Water Chemicals, Explosives, Phar Tray. Basket, maceuticals, Food Products Tumbling Drum Shoveled into Drum or Pan Suspended, Truck, Ceramics, Chemicals, Lumber, Food Products Chemicals too sticky for Rotary Drier Yarns, Lumber, Foodstuffs Tray Paper, Leather, Bulk Festoon . Tower or Column. Spray Induction Continuous Cylinder Drum Rotary Tunnel Vacuum Agitated Com partment I Id -g W ' ' gb* * 698 In te rm itte n t Batch: , or CHAPTER 40. DRYINC SYSTEMS Conduction or Direct Contact Drying This method of drying is advantageous where the material can be flowed on to the drying surface and the dried material scraped off, or where the material to be dried can be handled in a sheet, and where there is no danger of subjecting the product to the full temperature of the heating medium. The source of heat for this method may be steam, electricity, hot oil or hot water. Convection The circulation of heated air or. other- gases about the material to be dried is generally termed convection drying. The convection may be either natural or forced. With forced circulation, the temperature of the AM* undercun* and above oven temperature represents useful heat Area between wren end room temperature represents heat in vented r ei l 1 s Example Wftien air is suppbed to oven M temperature CO CM Vented heat equals reea BCDf BCH J ABEF A 8 J K Lb *n circulated Fig. 1. Relation Between Useful and Total Heat Supplied Whiting Slab drier is more uniform and the rate of drying is much higher than with natural circulation. Where humidity is used, the control is much easier, and more accurate. The source of heat for a convection drier may be steam, electricity, hot water, oil-fired heater, gas-fired heater, or coal furnace. Where either oil, gas or coal is used, the type of heater may be direct or indirect; i.e., the products of combustion may be used (direct), or the circulated air may be heated through an interchanger (indirect). . Where the direct type is used, there is naturally a higher thermal efficiency, but it can only be used where the odor, soot, or the chemical elements of the products of combustion do not affect the material -being dried. When heat economy is an important consideration this method (Fig. 1) may be used, permitting a small amount of air to be circulated, if a sacrifice of accurate control of temperature and humidity can Jje justified. DRIERS The term adiabatic drier is applied to a drier in which all the heat is supplied by air externally heated. The temperature of the air in the 699