Mass transfer in agitated vessels

Skelland, A. H. P. and J. M. Lee, "Drop Size and Continuous Phase Mass Transfer in Agitated Vessels," AlChE J. 27 (1981) 99-111. 

Skelland AHP and Lee JM. Drop size and continuous-phase mass transfer in agitated vessels. AIChE J 1981 27 99-111. 

Levins, D.M. Glastonbury, J. Application of Kolmogoroffs theory to particle-liquid mass transfer in agitated vessels. Chem. Eng. Sci. 1972, 27, 537-542. 

Crystallization and dissolution data obtained from agitated vessel studies may be analysed by the methods discussed above, but a survey of the literature related to the subject of solid-liquid mass transfer in agitated vessels shows that there is an extremely wide divergence of results, correlations and theories. The difficulty is the extremely large number of variables that can affect transfer rates, the physical properties and geometry of the system and the complex liquid-solid-agitator interactions. 

The Kolmogoroff theory can account for the increase in mass transfer rate with increasing system turbulence and power input, but it does not take into consideration the important effects of the system physical properties. The weakness of the slip velocity theory is the fact that the relationship between terminal velocity and the actual slip velocity in a turbulent system is really unknown. Nevertheless, on balance, the slip velocity theory appears to be the more successful for solid-liquid mass transfer in agitated vessels. 

Stenberg, O., and Andersson, B. (1988a), Gas-liquid mass transfer in agitated vessels-I. Evaluation of the gas-liquid mass transfer coefficient from transient-response measurements, Chemical Engineering Science, 43(3) 719-724. 

Lakkonen M, MoUanen P, Alopaeus V, Aittamaa J. (2007) Modeling local gas-liquid mass transfer in agitated vessels. Trans. IChemE, Part A, Chem. Eng. Res. Des., 85(A5) 665-675. 

Warmoeskerken MMCG, Smith JM. (1981) Hydrodynamics and mass transfer in agitated vessels. In Proceedings of Seventh International Congress of Chemical Engineers, Prague, 1981. Paper B 3.4. 

Regarding mass transfer between fluid and particle, many correlations have been proposed for both gaseous and liquid phase mass transfer. Usually the contribution of molecular diffusion and that of fluid flow are considered to be additive as in the case of mass transfer in agitated vessels. 

The gas-liquid volumetric mass-transfer coefficient for the agitation of power-law fluid in an aerated vessel can be expressed in the form kLaL = f PJV, ug) (Hocker et al, 1981). For the mass transfer in a vessel with an unbroken interface, the relationship Sh = /(Re, Sc) given by Eq. (7.4) is recommended. 

Mathematical simulation of heat, mass, or momentum transfer in agitated vessels is often untenable, due to the three-dimensional components of the material and energy balances, and the large number of material and process variables. In such cases, dimensional analyses are the preferred method of correlation. Numerous references are available for a review of dimensional analysis in engineering applications [30-32],... 

Mass Transfer Mass transfer in plate and packed gas-liquid contactors has been covered earHer in this subsection. Attention nere will be limited to deep-bed contactors (bubble columns and agitated vessels). Theory underlying mass transfer between phases is discussed in Sec. 5 of this handbook. 

Interfacial Area This consideration in agitated vessels has been reviewed and summarized by Tatterson (op. cit.). Predictive methods for interfacial area are not presented here because correlations are given for the overall volumetric mass transfer coefficient liquid phase controlhng mass transfer. 

The mass transfer coefficient is expected to relate gas power per unit volume and gas terminal velocity. Measurement of gas bubble velocity is troublesome in the experimental stage of aeration. Extensive research has been conducted for an explanation of the above correlation. Gas-liquid mass transfer in low viscosity fluids in agitated vessels has been reviewed and summarised as stated in (3.5.1.7)—(3.6.2) 3... 

Gal-Or and Resnick (G2, G6, G8) recently proposed a theoretical model, based on the gas residence time, for total mass transfer in a gas-liquid agitated contactor. They assumed that the number of bubbles in the vessel... 

The double lines in Figure 3.44 represent the Sh number based on the mass transfer coefficient, in the case of a single-particle fall in water, for three different particle densities (Harriot, 1962). This value is considered to be the minimum mass-transfer coefficient in liquid-solid films in agitated vessels. Taking into account the fact that the actual Sh value in an agitated vessel is 1.5 -8 times its minimum value, it is apparent that the mass transfer coefficients are much higher in the case of agitated vessels. 

Davies, J. T. (1986). Particle suspension and mass transfer rates in agitated vessels. Chem. Eng. Progress. 8 175-181. 

Zlokarnik (1978) examined the effect of coalescence on the volumetric mass-transfer coefficient in agitated vessels. 

Mechanical agitation and gas-liquid mass transfer are very important in viscous fermentation media. Most recently, Lim and Yoo (1989) and Lee and Wang (1989) have examined mixing effects in the fermentation of Xanthan gum. Aunins-cf al. (1989) evaluated the effects of paddle geometry on power input and mass transfer in small-scale animal cell culture, 500 mL Corning spinner vessels. The results indicate that power dissipation dependency differs from literature correlations and may compromise scale-up at constant power input from these vessels. 

The temperature had a major effect on the rate of reaction/decomposition, observed by the rate of condensation in the main collection vessel. If this figure is compared with the results in the absence of agitation (Figure 21.4), the same shaped curves are found and the same order of magnitude in the rate of degradation can be noticed. Nevertheless the apparent shorter reaction time demonstrates the effect of improved heat and mass transfer in the semi-batch equipment due to the agitation system. 

To integrate d with t, we must relate the mass transfer coefficient (k) to the independent parameters of the system. Levins and Glastonbury (1972) have developed an accurate correlation to predict mass transfer coefficients for suspended particles in agitated vessels. 

Boon-Long S, Laguerie C, and Couderc JP. Mass transfer from suspended solids to a liquid in agitated vessels. Chem Eng Sci 1978 33 813-819. 

Asai, S., Konishi, Y., and Sasaki, Y. Mass Transfer Between Fine Particles and Liquids in Agitated Vessels, J. Chem. Eng. Jpn. 21, 107-112 (1988). 

Coalescence frequencies can have a pronounced effect on the rate of mass transfer or chemical reaction in a liquid-liquid dispersion. Various investigators have attempted to model and measure coalescence frequencies in agitated vessels. A review of the experimental techniques is given by Rietema (R12) and Shah et al. (S16). 

A variety of models are employed to predict extent of reaction and selectivity for complex reactions which occur in liquid-liquid dispersions in agitated vessels. The nature of the models depends on which phases the reaction occurs in, the relative magnitude of the time scales of the mass transfer and reaction processes compared to the mixing processes, com-... 

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