Vertical evaporators

FIG. 11-28 Effect of viscosity on heat transfer in short-tiihe vertical evaporator, To convert centipoises to pascal-seconds, multiply by 10 to convert British thermal units per hoiir-sqiiare foot-degrees Fahrenheit to joules per square meter-second-kelvins, multiply hy 5.6783,... 

Circffiation in the standard short-tube vertical evaporator is dependent entirely on boiling, and when boihng stops, any sohds present settle out of suspension. Consequently, this type is seldom used as a ciystaUizing evaporator. By instalhng a propeller in the downtake, this objection can be overcome. Such an evaporator, usually called a pro-... 

Best applications of short-tiihe vertical evaporators ... 

FIG. 11-123 Temperature variations in a long-tube vertical evaporator. 

Major evaporator designs include forced-circulation, long-tube vertical (both rising and falling film), and calandria-type evaporators. The economics of a particular process will dictate the evaporator style and model best suited to a particular application. Forced-circulation and calandria evaporators are required for processes where crystals are formed. These evaporators are designed to keep crystals suspended in solution to prevent scaling of the equipment. Long-tube vertical evaporators are used to concentrate a liquid that does not have solids present. 

Falling-film vertical evaporators, direct expansion systems, and vacuum freezing techniques may also be used. 

Sinek, J. R. and E. H. Young, Heat Transfer in Palling-Pilm Lonai-Tube Vertical Evaporators, Chem. Ens. Pros., V. 58, No. 12, p. 74 (1962). 

Long tube vertical evaporators with either natural or forced circulation are most popular. Tubes are 19-63 mm dia and 12-30 ft long. 

A forward-feed double-effect standard vertical evaporator with equal heating areas in each effect is fed with 5 kg/s of a liquor of specific heat capacity of 4.18 kJ/kgK, and with no boiling-point rise, so that 50 per cent of the feed liquor is evaporated. The overall heat transfer coefficient in the second effect is 75 per cent of that in the first effect. Steam is fed at 395 K and the boiling-point in the second effect is 373 K. The feed is heated to its boiling point by an external heater in the first effect. 

Flow regimes in a vertical evaporator or boiler tube... 

The use of vertical tubes is associated with Robert, and this type is sometimes known as the Robert or Standard Evaporator. A typical form of vertical evaporator is illustrated in Figure 14.18, in which a vertical cylindrical body is used, with the tubes held between two horizontal tube plates which extend right across the body. The lower portion of the evaporator is frequently spoken of as the calandria section shown in Figure 14.19. Tubes... 

Stroebe, G. W., Baker, E. M., and Badger, W. L. Trans. Am. Inst. Chem. Eng. 35 (1939) 17. Boiling film heat transfer coefficients in a long-tube vertical evaporator. 

This is a process mainly used in power plants for separation of dissolved matters by evaporation of the water. Multistage flash distillation, multiple-effect vertical long-tube vertical evaporation, submerged tube evaporation, and vapor compression are effective process equipment. It may require pH adjustment. The process removal efficiency is about 100%. 

Evaporation of Sea Water in Long-Tube Vertical Evaporators... 

STANDIFORD AND BJORK—EVAPORATION IN LONG-TUBE VERTICAL EVAPORATORS... 

As soon as the electrophoretic chamber is saturated with water vapor and under good working conditions, the horizontal evaporation flow practically disappears and only the vertical evaporation flow remains to compensate for condensation of water on the walls of the chamber. 

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