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Phases—Mass Transfer

This chapter sets out to provide a means of handling these types of interphase mass transfer problems taking into consideration their fundamental characterizing variables, the conservation of mass, and appropriate constitutive relationships. [Pg.205]


The relationship of the overall gas-phase mass transfer coefficient to the individual film coefficients maybe found from equations 4 and 5, assuming a straight equiHbrium line ... [Pg.20]

Height of one overall gas-phase mass-transfer unit m ft... [Pg.589]

Gas-phase mass-transfer coefficient for dilute systems kmoP[(s-m )(kPa solute partial pressure)] lbmol/[(h-fF)lbf/in solute partial pressure)]... [Pg.589]

Transfer of material between phases is important in most separation processes in which two phases are involved. When one phase is pure, mass transfer in the pure phase is not involved. For example, when a pure liqmd is being evaporated into a gas, only the gas-phase mass transfer need be calculated. Occasionally, mass transfer in one of the two phases may be neglec ted even though pure components are not involved. This will be the case when the resistance to mass transfer is much larger in one phase than in the other. Understanding the nature and magnitudes of these resistances is one of the keys to performing reliable mass transfer. In this section, mass transfer between gas and liquid phases will be discussed. The principles are easily applied to the other phases. [Pg.600]

The overall gas-phase and hquid-phase mass-transfer coefficients for concentrated systems are computed according to the following equations ... [Pg.603]

When it is known that Hqg varies appreciably within the tower, this term must be placed inside the integr in Eqs. (5-277) and (5-278) for accurate calculations of hf. For example, the packed-tower design equation in terms of the overall gas-phase mass-transfer coefficient for absorption would be expressed as follows ... [Pg.603]

In a similar way, hquid-phase mass-transfer rates may be defined by the relations... [Pg.603]

The Shei wood-number relation for gas-phase mass-transfer coefficients as represented by the film diffusion model in Eq. (5-286) can be rearrangecTas follows ... [Pg.604]

The important point to note here is that the gas-phase mass-transfer coefficient fcc depends principally upon the transport properties of the fluid (Nsc) 3nd the hydrodynamics of the particular system involved (Nrc). It also is important to recognize that specific mass-transfer correlations can be derived only in conjunction with the investigator s particular assumptions concerning the numerical values of the effective interfacial area a of the packing. [Pg.604]

For the liquid-phase mass-transfer coefficient /cl, the effects of total system pressure can be ignored for all practical purposes. Thus, when using Kq and /cl for the design of gas absorbers or strippers, the primary pressure effects to consider will be those which affect the equilibrium curves and the values of m. If the pressure changes affect the hydrodynamics, then Icq, and a can all change significantly. [Pg.610]

Effects of Temperature on tiQ and tii The Stanton-number relationship for gas-phase mass transfer in packed beds,... [Pg.610]

With regard to the liqiiid-phase mass-transfer coefficient, Whitney and Vivian found that the effect of temperature upon coiild be explained entirely by variations in the liquid-phase viscosity and diffusion coefficient with temperature. Similarly, the oxygen-desorption data of Sherwood and Holloway [Trans. Am. Jnst. Chem. Eng., 36, 39 (1940)] show that the influence of temperature upon Hl can be explained by the effects of temperature upon the liquid-phase viscosity and diffusion coefficients. [Pg.610]

It should be noted that the highest possible absorption rates will occur under conditions in which the hquid-phase resistance is negligible and the equilibrium back pressure of the gas over the solvent is zero. Such situations would exist, for instance, for NH3 absorption into an acid solution, for SO9 absorption into an alkali solution, for vaporization of water into air, and for H9S absorption from a dilute-gas stream into a strong alkali solution, provided there is a large excess of reagent in solution to consume all the dissolved gas. This is known as the gas-phase mass-transfer limited condition, wrien both the hquid-phase resistance and the back pressure of the gas equal zero. Even when the reaction is sufficiently reversible to allow a small back pres-... [Pg.617]

FIG. 14-5 Nnmher of overall gas-phase mass-transfer units in a packed absorption tower for constant mGf /LM solution of Eq. (14-23). (From Sherwood and Pigford, Absorption and Extraction, McGraw-Hill, New York, 1952. )... [Pg.1356]

The HETP of a packed-tower section, valid for either distillation or dilute-gas absorption and stripping svstems in which constant molal overflow can be assumed and in which no chemical reactions occur, is related to the height of one overall gas-phase mass-transfer unit Hqc by the equation... [Pg.1356]

The flnid properties are represented by the Schmidt numbers of the gas and liqnid phases. For gases, the Schmidt unmbers normally are close to nuity and are independent of temperatnre and pressnre. Thns, the gas-phase mass-transfer coefficients are relatively independent of the system. [Pg.1358]

By contrast, the hqnid-phase Schmidt unmbers range from about 10" to lO and depeua strongly on the temperature. The effect of temperature on the liquid-phase mass-transfer coefficient is related primarily to changes in the hquid viscosity with temperature, and this derives primarily from the strong dependency of the hqnid-phase Schmidt number upon viscosity. [Pg.1358]

If the liqmd-phase reaction is extremely fast and irreversible, the rate of absorption may in some cases be completely governed by the gas-phase resistance. For practical design purposes one may assume (for example) that this gas-phase mass-transfer limited condition will exist when the ratio yj/y is less than 0.05 everywhere in the apparatus. [Pg.1363]

Figure 14-10 illustrates the gas-film and liquid-film concentration profiles one might find in an extremely fast (gas-phase mass-transfer limited) second-order irreversible reaction system. The solid curve for reagent B represents the case in which there is a large excess of bulk-liquid reagent B. The dashed curve in Fig. 14-10 represents the case in which the bulk concentration B is not sufficiently large to prevent the depletion of B near the liquid interface and for which the equation ( ) = I -t- B /vCj is applicable. [Pg.1363]

Whenever these conditions on the ratio yjy apply, the design can be based upon the physical rate coefficient /cg or upon the height of one gas-phase mass-transfer unit He- The gas-phase mass-transtor hmited condition is approximately vahd, for instance, in the following systems absorption oi NH3 into water or acidic solutions, vaporization of water into air, absorption of H9O into concentrated sulfuric acid solutions, absorption of SO9 into alkali solutions, absorption of H9S from a dllute-... [Pg.1363]

Table 14-3 presents a typical range of values for chemically reacting systems. The first two entries in the table represent systems that can be designed by the use of purely physical design methods, for they are completely gas-phase mass-transfer limited. To ensure a negligible liquid-phase resistance in these two tests, the HCl was absorbed into a solution maintained at less than 8 percent weight HCl and the NH3 was absorbed into a water solution maintained below pH 7 by the addition of acid. The last two entries in Table 14-3 represent liquid-phase mass-transfer hmited systems. [Pg.1365]

Danckwerts and Gillham did not investigate the influence of the gas-phase resistance in their study (for some processes gas-phase resistance may be neglected). However, in 1975 Danckwerts and Alper [Trans. Tn.st. Chem. Eng., 53, 34 (1975)] showed that by placing a stirrer in the gas space of the stirred-cell laboratoiy absorber, the gas-phase mass-transfer coefficient fcc in the laboratoiy unit could be made identical to that in a packed-tower absorber. When this was done, laboratoiy data obtained for chemically reacting systems having a significant gas-side resistance coiild successfully be sc ed up to predict the performance of a commercial packed-tower absorber. [Pg.1366]


See other pages where Phases—Mass Transfer is mentioned: [Pg.20]    [Pg.37]    [Pg.44]    [Pg.63]    [Pg.42]    [Pg.501]    [Pg.106]    [Pg.589]    [Pg.589]    [Pg.589]    [Pg.589]    [Pg.589]    [Pg.589]    [Pg.600]    [Pg.602]    [Pg.603]    [Pg.603]    [Pg.604]    [Pg.604]    [Pg.624]    [Pg.1349]    [Pg.1349]    [Pg.1349]    [Pg.1364]    [Pg.1365]   


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Convective heat and mass transfer. Flows with phase change

Convective heat and mass transfer. Single phase flow

Dense-phase fluidized beds mass transfer

Disperse Phase to Wall Mass Transfer

Dispersed-phase mass-transfer coefficient

Extraction continuous-phase mass transfer coefficients

Gas phase mass transfer

Gas-phase mass transfer, rate

General case for gas-phase mass transfer

Immiscible phases, mass-transfer operations

Interphase mass transfers diffusion between phases

Liquid phase mass transfer problems

Liquid-Phase Mass Transfer with Chemical Reactions

Liquid-phase chemical reaction rates, mass transfer effects

Mass Transfer Between Two Phases

Mass Transfer Mediated by a Vapour Phase

Mass Transfer in One Phase

Mass transfer across a phase boundary

Mass transfer between phases

Mass transfer between phases concentration profiles

Mass transfer between phases film coefficients

Mass transfer between phases overall coefficients

Mass transfer bulk phase

Mass transfer coefficient gas-phase

Mass transfer coefficient liquid phase

Mass transfer coefficient liquid phase diffusivity effect

Mass transfer coefficients in two phase

Mass transfer coefficients three-phase slurry reactors

Mass transfer disperse-phase volume

Mass transfer fluid-phase momentum

Mass transfer heavy phase

Mass transfer in dense-phase fluidized beds

Mass transfer in two-phase flow

Mass transfer light phase

Mass transfer mobile phase

Mass transfer stagnant mobile phase

Mass transfer with stagnant continuous phase

Multiple Phases-Mass Transfer

Phase Mass Transfer with Chemical Reactions

Phase boundary, mass transfer across

Phase dispersion mass transfer

Phase equilibrium and mass transfer

Phase-space advection mass and heat transfer

Polymeric stationary phase, mass transfer

Principles of mass transfer between two phases

Resistance to Mass Transfer in the Mobile Phase

Resistance to Mass Transfer in the Mobile and Stationary Phases

Resistance to Mass Transfer in the Stationary Phase

Single-Phase Mass Transfer Inside or Outside Tubes

Single-Phase Mass Transfer in Packed Beds

Solid-phase mass transfer coefficient

Stationary phase mass transfer

Two-Directional Mass Transfer Between Phases

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