Evaporators calculations

Atomization. Droplet heatup and evaporation calculations can be done for any droplet size, but are most often carried out to reflect the behavior of a mean-sized droplet. The finer the droplet, the less time required for the various steps in the destmction of the waste. 

Dusek (1), Shy (2 and Bauer (3) give examples of modelling the structure-property relation of several networks (Tg, gel point, etc.). Examples are described of models on solvent evaporation, calculation of functionalities, molecular weight of resins (4), etc. 

Because the number of evaporators represents an integer-valued variable, and because many engineers use tables and graphs as well as equations for evaporator calculations, some of the methods outlined in Chapters 9 and 10 can be applied for the optimization of multi-effect evaporator cascades. 

The rates of evaporation of water through unimolecular fi has been examined by Hedestrom and by the writer. It is foi that the rate of evaporation of water through unimolecular fi of fatty acids on the surface of water is relatively slow in compari to the high rate of evaporation calculated with the aid of Herz-Knudsen equation. The rate is approximately inveri proportional to the surface film pressure F as is indicated fi the following figures. 

Remove the organic solvent at 40°C under reduced pressure using a rotary evaporator. Calculate the weight of the lipid ... 

Langmuir2 has used the reciprocal of the rate of evaporation as a measure of the resistance to evaporation, and considers the total resistance as the sum of the several partial resistances due to the water itself (a nearly negligible resistance), the film, and the vapour above. That of the water itself was taken as the reciprocal of the theoretical rate of evaporation, calculated from the vapour pressure as in Chap. I, 6. 

Thermocompression Evaporators Thermocompression-evaporator calculations [Pridgeon, Chem. Metall. Eng., 28, 1109 (1923) Peter, Chimia (Switzerland), 3,114 (1949) Petzold, Chem. Ing. Tech., 22, 147 (1950) and Weimer, Dolf, and Austin, Chem. Eng. Prog., 76(11), 78 (1980)] are much the same as single-effect calculations with the added complication that the heat supplied to the evaporator from compressed vapor and other sources must exactly balance the heat requirements. Some knowledge of compressor efficiency is also required. Large axial-flow machines on the order of 236-mVs (500,000-ftVmin) capacity may have efficiencies of 80 to 85 percent. Efficiency drops to about 75 percent for a 14-mVs (30,000-ft /min) centrifugal compressor. Steam-jet compressors have thermodynamic efficiencies on the order of only 25 to 30 percent. 

The separative capacity is analogous to the heat duty of an evaporator or other process equipment. The separation potential is analogous to the enthalpy per mole of the streams entering or leaving an evaporator. Calculations of material balances and separative capacity in an isotope separation plant are made in similar fashion to conventional material and heat balances. A form for such calculations is illustrated in Table 12.8, which illustrates the calculation of the separative capacity of an isotope separation cascade producing 1 mol/day of at 0.80 mole... 

As shown in Chap. 11 [Eq. (11.35)], the overall resistance to heat transfer between the steam and the boiling liquid is the sum of five individual resistances the steam-film resistance the two scale resistances, inside and outside the tubes the tube-wall resistance and the resistance from the boiling liquid. The overall coefficient is the reciprocal of the overall resistance. In most evaporators the fouling factor of the condensing steam and the resistance of the tube wall are very small, and they are usually neglected in evaporator calculations. In an agitated-film evaporator the tube wall is fairly thick, so that its resistance may be a significant part of the total. 

The vapour pressure of V2O5 has been determined between 973 and 1473 K, and the enthalpy of evaporation calculated as ca. 143 kJ mol . The electrical conductivity of liquid V2O3 has been measured as a function of both temperature and partial pressure of oxygen. Raman and i.r. spectra or oriented single-crystals of V2O5 have been recorded and the absorption frequencies compared with those calculated using a simple transferred force-field. 2... 

In evaporator calculations, three relations must be satisfied material balance required rates of heat transfer and heat balance. These relations must be applied to each effect in a multiple-effect system as well as to the total system. The equations describing evaporator systems can be solved algebraically but the process is tedious and time consuming. Trial-and-error procedures are generally used as follows ... 

The Dow Chemical Company has a solvent related computer program, Chemcomp, which simulates evaporation profiles for solvent blends. Other features include the ability to measure the effects of humidity on evaporation, calculation of the Hansen solubility parameters for the solvent blend, and inclusion of data on the relative rate of evaporation of the blend at 90% as compared to a standard n-butyl acetate being equal to 1.0. More information on Chemcomp and related solvent modeling computer programs can be obtained from Dow at 1-800-258-2436... 

EVAPORATION CALCULATION GROSS HEAT INPUT FROM GAS ... 

The cooling effect of alcohol on the skin is due to its evaporation. Calculate the heat of vaporization of ethanol (ethyl alcohol), C2H5OH. 

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