Contact dryer

Contact Dryers. Coatings on webs as well as sheets of newly formed paper can be dried by contacting the web around the surface of a heated dmm. Thus conduction is used to transfer the heat. Dmms can also be used to rapidly cool warm extmded films, to increase the viscosity, and soHdify the film. 

Contact dermatitis, from nickel, 17 119 Contact dryers, coatings, 7 29 Contact drying, 9 105-107 Contact icing, of food, 21 561 Contacting, differential, 10 760-762 Contact mechanics, 1 515-517 Contact mode atomic force microscopy, 3 320-325 17 63 Contact nucleation, 8 105 Contactors ozone, 17 801-802 selection of, 10 767-768... 

After a review of the customary calculation methods [97] for both essential classes of dryers (convective and contact dryers), the dimensioning methods for spray dryers [98, 99], fluidized and spouted bed dryers [100, 101, 102], cascading rotary dryers [103], pneumatic conveying dryers [104], conductive-heating agitated dryers [105] and layer dryers [106] were presented. They all confirmed the initially made conclusion that the scaling up of dryers is still made today without dimensional analysis and the model theory based thereupon. 

Another useful classification is whether or not a dryer is a direct or indirect dryer. A direct contact dryer is one in which the material is dried by exposure to a hot gas, whereas in an indirect contact dryer, the heat required for evaporation is transferred from a heating medium through a metal wall to the material. Generally, direct heat dryers are more efficient. Dryer efficiency is defined by the fraction of energy supplied to the drying equipment which actually causes the evaporation of the liquid. As we shall see later in the chapter, heating is not always necessary to achieve drying. 

For organic solvents, or solids which are highly flammable, are toxic, or decompose easily, contact dryers are often preferable to... 

Here Cg is the humid heat Cpc + YCpy. In convective dryers, the left-hand side is dominated by the sensible heat of the hot inlet gas GCsiTci in contact dryers, the heat input from the jacket pin is dominant. In both cases, the largest single term on the right-hand side is the latent heat of the vapor GXYq- Other terms are normally below 10 percent. This shows why the operating line of a convective dryer on a psychrometric chart is roughly parallel to a constant-enthalpy line. 

Continuous Contact Dryers The key parameter is the area of the heat-transfer surface As. In design mode, this can be found from the equation ... 

TABLE 12-25 Calculation of Key Dimensions for Various Batch Contact Dryers... 

Particles and powders below 1 mm are effectively dried in dispersion or contact dryers, but most through-circulation units are unsuitable. Conversely, for particles of several millimeters or above, through-circulation dryers, rotary dryers, and spouted beds are very suitable. 

A major division may be made between (1) dryers in which the solid is directly exposed to a hot gas (usually air) and (2) dryers in which heat is transferred to the solid from an external medium such as condensing steam, usually through a metal surface with which the solid is in contact. Dryers that expose the solids to a hot gas are called adiabatic or direct dryers , those in which heat is transferred from an external medium are known as nonadiabatic or indirect dryers. Dryers heated by dielectric, radiant, or microwave energy are also nonadiabatic. Some units combine adiabatic and nonadiabatic drying they are known as direct-indirect dryers. 

Contact dryer mobile product paddle dryer long... 

Comparing to their direct-contact counterparts indirect-contact dryers possess some advantages such as the reduced deterioration of the drying material due to an excessive exposure of the material to the high-temperature drying medium. In addition, adsorption of such toxic substances in the drying medium (in the case where direct combustion gases are used) as NO j is eliminated. 

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