Film-type evaporators

Pig. 4. Batch process for producing phosphatidylcholine fractions. 1, Ethanol storage tank 2, deoiled lecithin 3, solubiHzer 4, blender 5, film-type evaporator 6, ethanol-insoluble fraction 7, ethanol-soluble fraction 8, aluminum oxide 9, mixer 10, decanter 11, dryer 12, aluminum oxide removal 13, phosphatidylcholine solution 14, circulating evaporator 15, cooler 16, dryer and 17, phosphatidylcholine. 

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).

Evaporators in commercial use include circulatory systems, shell and tube heat exchangers and falling film-type evaporators. The falling film evaporator has the advantages of a small working volume and a short residence time. All evaporators produce steam that must be purified, and some of the techniques mentioned above can also be applied to this steam103. 

It has been shown that the actual amount of heat transmitted will depend on a great many factors and will vary considerably with the type of apparatus and the kind of liquor. Outside of water distillation, the extreme limits in actual practice are probably 8 lb. per hour per square foot for electrolytic caustic liquor from 25 to 48° in a vertical-tube evaporator and 62 lb. evaporation per hour per square foot for malt extract from 5 to 30°Bd. in a rapid circulation film type evaporator with steam at 5 lb. and a vacuum of 28 in. Practical results of various liquids are given in later paragraphs, p. 375 et seq. 

The wet deck or surface, is the heart of most cooling towers. Generally, it takes the form of PVC (polyvinyl chloride) plastic film type surface. Water is made to spread out on this surface maximizing it s contact area with air to encourage evaporation. It consists of individual vacuum formed sheets with proprietary patterns of ridges. 

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. 

The fill illustrated in Figures 9-1 lOA and B is typical of many cooling tower heat transfer evaporative cooling surfaces. The wooden splash type is the oldest in terms of length of usage, while the film types (some fabricated of plastic) have been in service about 40 years [148]. 

On the other hand, Tennakone and co-workers utilized a p-type semiconductor material, such as Cul (band gap,-3.1 eV), as a hole conductor and produced a solid-state DSSC [141,145,146]. Acetonitrile solution of Cul was dropped onto the surface of a dye-coated Ti02 film, which was heated up to approximately 60°C and then the solution penetrated into the film. After evaporation of the acetonitrile, Cul was deposited into a nanoporous Ti02 film. The Au-coated TCO substrate as the counterelectrode was pressed onto the surface of the Ti02/dye/ Cul film. In the system using the santalin dye photosensitizer, an efficiency of 1.8% was obtained under irradiation of 80 mW/cm2 [141] and the efficiency reached 4.5% for the Ti02/N3 dye/CuI/Au system. These results suggested that a highly efficient solid-state DSSC could be produced [145]. In these systems,... 

A knowledge of the thicknesses of flowing liquid films is of importance in a wide range of practical problems involving film flow. Such problems include the calculation of heat transfer in evaporators and condensers, mass transfer in film-type equipment, the design of overflows and downcomers, etc. 

Low-temperature evaporators of the falling-film type were heavily utilized in the citrus industry through the 1950 s and... 

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