Mass-transfer coefficient, determination

Table 12.2 summarizes the more useful correlations for jD and jH that have been proposed by various investigators. The indicated correlations are quite consistent with one another in the regions where they overlap. Although the mass transfer coefficients determined from these correlations are not particularly large, they lead to high mass transfer rates when they are multiplied by the external surface area of the bed. For more detailed treatments of mass transfer... 

K is the mass transfer coefficient, determined using Equation 3-18,... 

A mass transfer coefficient determined from some subsurface soil column elution studies was inverse log-linearly related to the octanol-water partition coefficient (i.e., K0Vf) for closely related compounds, and polarity in the molecule caused an additional decline in the mass transfer coefficient. 

Table 2.2 gives examples of mass transfer coefficients determined from both the single particle and fixed bed models for the evaporation of water from particles of the same diameter and density as in Table 2.1, assuming the diffusivity of water in air to be 3 x 10 m s h Once... 

Many parameters affect the mass transfer between two phases. As we discussed above, the concentration gradient between the two phases is the driving force for the transfer and this, together with the over-all mass transfer coefficient, determines the mass transfer rate. The influence of process parameters (e. g. flow rates, energy input) and physical parameters (e. g. density, viscosity, surface tension) as well as reactor geometry are summed up in the mass transfer coefficient. The important parameters for Kta in stirred tank reactors are ... 

The composition of the mobile phase also has an influence on the partition coefficients of inorganic substances and the separation efficiency. Concentrations of the mobile-phase constituents should provide partition coefficient values needed for the enrichment or separation of components under investigation. If a step-elution mode is used, partition coefficients higher than 10 and less than 0.1 are favorable for the enrichment of components into the stationary phase and their recovery into the mobile phase, respectively. Chemical kinetics factors may also play an important role in the separation of inorganic species by CCC [9]. It has been shown that the values of mass-transfer coefficients determine the... 

The mean annual flux of CO2 between the atmosphere and ocean, based on measurements of fccb in the ocean and atmosphere, and the gas exchange mass transfer coefficient determined from wind speed. From Takahashi eta/. (2002). (See Plate 8.)... 

The multicomponent mass transfer coefficients may be evaluated with the help of Eqs. 8.3.30 and 8.3.31 using the binary mass transfer coefficients determined above and the bulk gas-vapor composition. The result of the calculation is the following matrix ... 

It must be stressed that the individual mass-transfer coefficients, determined using Eqs (21)-(23), include both the diffusive and the osmotic transport components. Qf, and Qf, i, Qe, and Qe, i, Qr, and Qr,, represent the changes in the quantities of the solute, that is, in the concentrations and volumes between sampling time i, and i, i. Therefore, experimental determination of the osmotic pressure gradients. An, and calculation of osmotic mass-transfer coefficients, FQ, may be excluded. Overall mass-transfer coefficients of solute species through the BAHLM system are calculated using Eqs (8) and (9). 

After obtaining the original data it is necessary to correct the effect of the concentration polarization. In the mixed solutions it is not certain whether it is possible to use the mass transfer coefficient determined in a single solution. Here this value are used since no other correct method is known. Values of rejection, R, thus obtained are shown in Fig. 10 for vitamin Bi2 only and for the case with ovalbvimin gel layer. In this figure it is shown the rejection of different membrane are same due to the gel layer formation of ovalbumin. 

Table 2 summarizes the mass transfer coefficients determined for this model for batch tubes, stirred batch, and flowthrough reactor coi gurations and shows that the diffusive mass transfer coefficient kd increases in this order of reactor type. However, one would expect the mass transfer coefficient to follow such a pattern as flow is increased. On the other hand, although the rate constants for conventional models based on only chemical reaction can also be fit to data from these three reactor types, rate constants for these models should only depend on temperature, and these variations would not be expect. Thus, coupling mass transfer to reaction appears to provide a more meaningful explanation for the effects of flow on performance, but further work is needed to Mly develop and evaluate this approach. 

Mass transfer coefficient determined from liquid water evaporation data in chamber. 

The practical response to these difficulties has been to lump the interfacial area with the intrinsic rate constant for the mass transfer process. The lumped parameter is known as the effective mass transfer coefficient. This approach permits useful analysis of data such as effluent concentration histories from laboratory columns or wells in the field, and it permits the construction of tractable mathematical models of macroscopic transport (1-5). However, an effective mass transfer coefficient determined in this way for one set of conditions may not apply in a different soil, for a different volume fraction of NAPL, at a different flow rate, etc. 

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