Drying nonadiabatic

Single-pass, jacketed tube for increases in heat input, faster drying (nonadiabatic)... 

In indirect or nonadiabatic drying, the heat is transferred by conduction from a hot surface, first to the material surface and then into the bulk. This chapter discusses only indirect drying. 

Evaporative cooling—when drying a solid with free or bound moisture, the effect of a phase change from the liquid state to the vapor state removes energy from the liquid-solid mass. This results in a reduction of temperature in a nonadiabatic operation, whereas in an... 

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. 

As far as the drying operation itself is concerned, adiabatic dryers are generally less expensive than nonadiabatic dryers, in spite of the lower thermal efficiency of adiabatic units. Unfortunately there is usuaUy a lot of dust carryover from adiabatic dryers, and these entrained particles must be removed almost quantitatively from the drying gas. Elaborate particle-removal equipment may be needed, equipment that may cost as much as the dryer itself. This often makes adiabatic dryers less economical than a buttoned-up nonadiabatic system in which little or no gas is used. Rotary dryers are an example they were once the... 

Indirect dryers, also called nonadiabatic units, separate the heat transfer medium from the product to be dried by a metal wall. These dryers are subdivided on the basis of heat applied by radiation or through heat transfer surface and also by the method in which volatile vapors are removed. 

Jonassen O, Kramer K, Strpmmen I, Vagle E. Nonadiabatic two-stage counter-current fluidized bed dryer with heat pump. In Rudolph V, Keey RB, eds. Drying 94. Proc. 9 Inti. Drying Symposium (IDS 94), Gold Coast, Australia, 1994, pp 511-517. 

Drying methods have been evolved aroimd every product s specific requirement. The process takes many forms and uses many different kinds of equipment. In general, drying is performed by two basic methods (a) adiabatic processes and (b) nonadiabatic processes. In adiabatic processes, the heat of vaporization is supplied by the sensible heat of air in contact with the material to be dried. In nonadiabatic processes, the heat of evaporation is supplied by radiant heat or by heat transferred through walls in contact with the material to be dried. Dehydration may also be accomplished by mechanical dewatering. However, in this chapter, dehydration due only to adiabatic or nonadiabatic as defined above will be described. 

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