Thin-film evaporators Application

Another common device used in the rubber industry is the thin film evaporator. This device is very often used in the manufacture of ultra-low molecular weight elastomers that are used in sealant applications or specialty coatings, and as processing aids in conventional rubber compounding processes. The thin film evaporator described earlier, has found a multitude of other industry applications, including food processing operations. 

Fischer, R. Agitated Thin Film Evaporators—Process Applications, Chemical Engineering, Sept. 13,1965, p.186. 

FISCHER, R. Chem Eng., Albany 72, No. 19 (13 Sept. 1965) 186-90. Agitated thin film evaporators. Part 3. Process applications. 

T iquid films, whether in the form of natural falling films or in the more advanced form of mechanically agitated films in thin-film apparatus, offer convenient conditions for the solution of many difficult processing problems because of the films favorable surface-to-volume ratio and good heat transfer. This is especially so with an agitated film between heating wall and film. The agitated-film principle has previously found its broadest application in thin-film evaporators. 

The favorable working conditions of the thin-film evaporator enabled the equally successful application of the thin-film principle for fractionation (5), absorption, chemical reactions (6), and drying (7, 8). In these processes and applications, the thin-film apparatus is used mainly to treat heat sensitive and lower-viscosity products that flow on the influence of gravity alone. This particular type of apparatus in a special design can also be used to process highly viscous products to... 

The difference in processing behavior between rotors provided with straight blades and those with pitched blades is shown in Figure 6 by an application referring to solvent recovery from a polymer solution of low initial viscosity. The evaporation capacity of a thin-film evaporator equipped with straight blades decreases considerably as soon as the concentrated polymer reaches a viscosity between 1000 and 2000 P. The greatly increased mean film thickness that characterizes this vis-... 

ULTRA - THIN FILM EVAPORATION (UTF) - APPLICATION TO EMERGING TECHNOLOGIES IN COOLING OF MICROELECTRONICS... 

Moghaddam, S. and Ohadi, M., 2002, Thin Film Evaporator with Splayed Eleetrodes , U.S. patent pending, Application number 60/419,690, October... 

Ultra-Thin Film Evaporation(UTF)-Application to Emerging Technologies in Cooling of Microelectronics 321... 

Product recovety is some combination of rote methods of using processing tools and inspired application of new and conventional separation tools. For example, if aldehydes make distillation infeasible because of polymerization products and/or vacuum distillation costs, then one can consider utilizing the Cannizzaro reaction to make organic acid salts and ketones from the aldehydes before proceeding. Many bench-scale processing techniques such as thin-film evaporation have been scaled up to handle larger quantities of temperature sensitive materials. Assistance in utilization of these techniques can usually be obtained from the equipment vendors. 

In agitated thin-film evaporators, a thin layer of solution is spread on the heating surface by mechanical means. Wiped-film evaporators are used for very viscous materials and for producing solid products (see Figure 10.34). The design and applications of this type of evaporator are discussed by Mutzenburg (1965), Parker (1965), and Fischer (1965). 

In large-scale applications, waste streams of BTFs may be safely reclaimed by distillation in an explosion-proof distillation unit or still. Most stills available today have reclaim efficiencies of 90 to 99%. Using a high efficiency, thin-film evaporation still, 95% or more of the BTF maybe recovered from the spent solvent sludge. To further increase the amount of reclaimed solvent and to reduce the volume of waste that must be disposed of, stills can be equipped to employ steam stripping. 

Mechanically agitated thin-film evaporators are used for four general types of applications ... 

Volatility and non-fogging are other properties that have to be developed by a proper method of production or composition. A plasticizer having a low volatility is obtained by passing a mixture of reacted products through a thin film evaporator at temperature in the range of 200-250 under pressme lower than 5 kPa and evaporation of 5 to 30% of the composition. In automotive applications, where fogging is the major concern, plasticizers based on organic diphosphates are used (n=l) ... 

Application for Thin-Film Evaporators Thermal separation in an evaporator may be conveniently characterized by the viscosity of the nonvolatile stream—the concentrate. Figure 11-27 illustrates various evaporator types and typical viscosity ranges for their useful applications. Unless other considerations are important (thermal stability, fouling tendencies), the terminal viscosity frequently dictates the type of evaporator selected. By far, most evaporation... 

Viscous Liquids. Fluids with viscosities up to 50.000 centipoise can be processed in a standard thin-layer evaporator. "Zero-clearance" rotors do not exhibit the range of viscosity application that "fixed-clearance" rotors exhibit. Some firms manufacture "thin-film" vertical extruders" for the 50,000 to 20,000,000 centipoise range where fluids cease to flow under the influence of gravity alone. Thin-film evaporators, inherently low-pressure-drop devices, have mechanical turbulence and therefore relatively good heat transfer properties over a wide range of viscosities. 

Miscellaneous Applications. A variety of special evaporation problems have been solved in thin-film evaporators evaporation and chemical reaction two-phase flow (immiscible fluids, slurries, suspensions) cocurrent evaporation high overhead splits multiple-effect evaporation end others. 

Most industrial thin-film evaporators are used in complex chemical processes where several evaporators are employed to perform the required separation a preconcentrator which may be a relatively inexpensive evaporator or perhaps some other separation device, and a thin-film evaporator as a "finisher" to reach the final concentration or degree of volatile recovery. In other applications a feed preheater is used and the feed ntaterial is flashed into the thin-film evaporator. In any case, all thin-film evaporator suppliers make discrete, standard sizes ranging up to about 450 square feet. It is important to properly utilize thin-film evaporator surface because of Its relatively higher cost (20 to 30 times more expensive than tubular evaporators). 

While mathematical models have been developed for predicting performance of thin-film evaporators, suppliers of thin-film machinery maintain extensive pilot plant testing laboratories for obtaining development and process data with small evaporators. Data obtained from one or two days of testing on several drums of feed material are sufficient for predicting and scaling performance to large evaporator applications. 

For the vast majority of applications, the extreme accuracy of SPRTs cannot justify their high cost, large size, and fragile construction. Instead, manufacturers offer a wide selection of industrial platinum resistance thermometers (IPRTs), which are smaller, far more robust, and only slightly less aceurate than SPRTs. They can be either wire-wound or made of thin films evaporated on a substrate, and are most commonly provided with 100 resistance at... 

The number of oxides is large since most metallic elements form stable compounds with oxygen, either as single or mixed oxides. However, the CVD of many of these materials has yet to be investigated and generally this area of CVD has lagged behind the CVD of other ceramic materials, such as metals, carbides, or nitrides. The CVD of oxides has been slower to develop than other thin-film processes, particularly in optical applications where evaporation. 

Another evaporation technique is molecular beam epitaxy (MBE). MBE produces extremely pure and very thin films with abrupt composition changes and is being considered for extremely exacting electronic and optoelectronic applications. PI However, the deposition rate is very slow and the process is still considered experimental. 

Soft metals such as In, Ag, Sn, Pb, and Au can lead to reasonably low friction coefficients, when used as solid lubricants, due to their low shear strength. The metals were generally applied as thin films prepared by the vacuum deposition process. Especially, in applications to the high temperature conditions where liquid lubricants fail due to the evaporation, the thin films of soft metals can provide effective protection to the surfaces in sliding. 

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