Evaporation horizontal-tube evaporators

For short-tube vertical evaporators the heat-transfer coefficients can be estimated by using the same methods as for the long-tube vertical natural circulation evaporators. Horizontal-tube evaporators have heat-transfer coefficients of the same order of magnitude as the short-tube vertical evaporators. 

Fig. 1. Natural ckculation evaporators where C = condensate, E = entrainment return, F = feed, N = noncondensibles vent, P = product or concentrate, S = steam, V = vapor, and M = knitmesh separator (a) horizontal-tube, (b) short-tube vertical, (c) propeUer calandria, and (d) long-tube reckculating.

Fig. 3. Film-type evaporators (a) long-tube vertical, (b) falling film, and (c) horizontal tube. Terms are defined in Figure 1. M represents end view of (a).

Heat Transfer from Various Metal Surfaces In an early work, Pridgeon and Badger [Jnd. Eng. Chem., 16, 474 (1924)] pubhshed test results on copper and iron tubes in a horizontal-tube evaporator that indicated an extreme effect of surface cleanliness on heat-transfer coefficients. However, the high degree of cleanhness needed for high coefficients was difficult to achieve, and the tube layout and... 

FIG. 11-122 Evaporator types, a) Forced circulation, (h) Siibmerged-tiihe forced circulation, (c) Oslo-type crystallizer, (d) Short-tube vertical, (e) Propeller calandria. (f) Long-tube vertical, (g) Recirculating long-tube vertical, (h) Falling film, (ij) Horizontal-tube evaporators. G = condensate F = feed G = vent P = product S = steam V = vapor ENT T = separated entrainment outlet. 

Evaporators, Horizontal-Tube Type - The basic horizontal-tube evaporator is illustrated in Figure 12. The body of this evaporator is the liquor compartment and is in the form of a vertical cylinder. It is closed, top and bottom, with dished heads, although the bottom may be conical. The lower body ring is provided on opposite sides with steam compartments, closed on the outside by cover plates and on the inside by tube sheets. Between these tube sheets are fastened a number of horizontal tubes. The two steam chests with their connecting mbes form the steam compartment, and the tube wall heating surface. Steam is introduced into one steam chest and as it flows through the tubes it washes non-condensed gases and condensate ahead of it, so that these are withdrawn from the opposite steam chest. 

Figure 12. Horizontal tube evaporator (A) Steam inlet (B) Vent for non-condensed gas (C) Condensate outlet (D) Liquor inlet (E) Liquor outlet (F) Sight glass (G) Vapor outlet.

There are many modifications of the horizontal-tube evaporator, but these consist largely of changes in the shape of the body castings and not at all in the general arrangement or interrelationship of the parts. The horizontal-tube evaporator is best suited for non-viscous solutions that do not deposit scale or crystals on evaporation. Its first cost per square foot of heating surface is usually less than that of the other types of evaporators. 

Quiben and Thome (2007a,b) presented an experimental and analytical investigation of two-phase pressure drops during evaporation in horizontal tubes. Experiments were performed under diabatic conditions in tubes of d = S and 13 mm in the range of vapor quality x = 0—1, mass velocity G = 70—700kg/m s, heat flux q = 6.0—57.5 kW/m. The test fluids were R-134a, R-22 and R-410A. The results... 

Figure 14.17. Natural circulation evaporator with horizontal tubes...

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... 

Figure 8.16. Some types of evaporators, (a) Horizontal tube, (b) Calandria type, (c) Thermocompressor evaporator, (d) Long tube vertical, (e) Falling film, (f) Forced circulation evaporator-crystallizer, (g) Three types of Oslo/Krystal circulating liquid evaporator-crystallizers.

Tube evaporators may be designed as vertical tube evaporators (VTE) or horizontal tube evaporators (HTE). In the VTE. vapor produced in one effect is condensed in the next effect. The effect is an evaporator chamber receiving heat from an external source or from a higher effect and producing vapor and brine which may serve as a heat source for ihc next elfecl. To obtain high efficiency in the use of heal energy, the process is repeated in several evaporator effects arranged in series. Sec also Evaporation. 

Porous covering with micro heat pipe phenomena stimulates the evaporative heat transfer near 8-10 times to compare with pool boiling heat transfer on the smooth horizontal tube. 

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