Volumetric overall mass-transfer coefficients

Overall mass-transfer coefficient, m/s or ft/s Volumetric overall mass-transfer coefficient, s" ... 

Use experimental breakthrough data to estimate the volumetric overall mass-transfer coefficient for fixed-bed adsorption. 

Calculate volumetric overall mass-transfer coefficients in fixed-bed adsorption from correlations for the individual coefficients, and use them for breakthrough predictions. 

A bed of ion-exchange beads 1.5 mm in diameter is used to deionize water at 293 K with a superficial velocity of 0.6 cm/s. The feed concentration is 0.02 M NaCl, and the resin has an equilibrium capacity of 2.4 eq/L of resin bed. The porosity of the 2-m-depth bed is 0.35. For monovalent ions, the effective diffusivity in the pores of the resin is about one-tenth of the normal liquid diffusivity (McCabe et al., 2005). Calculate the volumetric overall mass-transfer coefficient, Kca, and the number of mass-transfer units, N. Use equation (1-133) to calculate the diffusivity of NaCl in water. 

In the present work, the mass transfer performance characteristics of MEA-CO2 and DETA-CO2 systems in terms of the volumetric overall mass transfer coefficient (AgOv) were investigated. By means of determination of KqO, it is simple and effective to describe the mass transfer behavior of any solvent in the packed column. (Aroonwilas and Tontiwachwuthikul, 1998) [1] and Maneeintr et al, 2010 [6]) have successfully adopted this method to study the mass transfer performance for CO2 absorption into 2-amino-2-methyl-l-propanol (AMP) using Sulzer EX structured packing and into 4-diethylamino-2-butanol (DEAB) using Sulzer DX structured packing, respectively. Lastly, the predictive correlations of Kqu, for CO2 absorption into aqueous solutions of MEA and DETA were developed. The predicted Ag v results were then compared with the experimental results in terms of absolute average deviation (AAD). 

It is necessary to allow for changes in the interfacial area between the gas and the liquid. This interfacial area not only is a function of the type and size of tower packing chosen, but also it may vary with flow rates. The interfacial area is accounted for by the use of a volumetric overall mass transfer coefficient (K a or Kj a). Note that this interfacial area is the same for the gas film as for the liquid film as applied to Equations 3-6 and 3-7. 

Overall Mass-Transfer Coefficient In systems with relatively sparing soluble gases, where the gas-phase resistance is negligible, the mass-transfer rate can be determined by using the concept of an overall volumetric mass-transfer coefficient kLa as follows ... 

The reported study on gas-liquid interphase mass transfer for upward cocurrent gas-liquid flow is fairly extensive. Mashelkar and Sharma19 examined the gas-liquid mass-transfer coefficient (both gas side and liquid side) and effective interfacial area for cocurrent upflow through 6.6-, 10-, and 20-cm columns packed with a variety of packings. The absorption of carbon dioxide in a variety of electrolytic and ronelectrolytic solutions was measured. The results showed that the introduction of gas at high nozzle velocities (>20,000 cm s ) resulted in a substantial increase in the overall mass-transfer coefficient. Packed bubble-columns gave some improvement in the mass-transfer characteristics over those in an unpacked bubble-column, particularly at lower superficial gas velocities. The value of the effective interfacial area decreased very significantly when there was a substantial decrease in the superficial gas velocity as the gas traversed the column. The volumetric gas-liquid mass-transfer coefficient increased with the superficial gas velocity. 

The second component in Eq. (3), 2<,cCs( A7t), represents the solute volumetric flux, driven by osmotic pressure gradient. Osmotic mass-transfer coefficient corresponds to the osmotic overall mass-transfer coefficients fCrtF on the feed side and on the strip side of the BAHLM system which... 

The interfacial area for mass transfer is from equation (2-88), a - 600 m l. The overall mass-transfer coefficient is from (9-55), K - 0.042 m/s the volumetric... 

Table 5.3 presents capacities of different modules. The AFR can be used over temperature and pressure ranges of -60 to 200 °C and 0-18 bar, respectively. The glass and ceramic construction eliminates contamination and corrosion in most cases. These are in a way similar to plate heat exchangers. The volumetric heat transfer coefficient is about 1.5 MW/m -K, which is about 1000 times higher than that in the jacketed vessels. Likewise the estimated overall mass-transfer coefficient between the phases for liquid-liquid systems is about 2 0 s which is more than 100 times those in a jacked vessel [29]. The... 

The overall mass transfer coefficients (Llu) were also determined for the three different types of TBP/IL mixtures (30 %, v/v) as a function of residence time at constant nitric acid concentration (3 M) and are shown in Fig. 6.13. As it can be seen, the mass transfer coefficients in general were quite similar in the first 10 s. The extraction efficiency (Eeff) in this time period was below 70 %. The decrease of the volumetric mass transfer coefficient as a function of the residence time can be... 

With known overall mass transfer coefficients kd and /tg, specific volumetric interface area Og and axial dispersion coefficient, the solution gives the actual concentration profile of the key component in the column. In [6.26], methods to measure the longitudinal mixing in countercurrent extraction columns are described and approaches to calculate the Bodenstein number and the axial dispersion coefficient for common extractor designs are given. 

Film and overall mass-transfer coefficients in packed towers. As discussed in Section 10.5 it is very difficult to measure experimentally the interfacial area A m between phases L and V. Also, it is difficult to measure the film coefficients k and ky and the overall coefficients K and Kf Usually, experimental measurements in a packed tower yield a volumetric mass-transfer coefficient that combines the interfacial area and mass-transfer coefficient. 

Seibert et al. reported that the overall volumetric mass transfer coefficient varied directly with flow rates however, it was much more affected by the dispersed phase rate compared to the continuous phase rate [21]. These investigators also observed that the overall mass transfer coefficient initially increased rapidly with an increase in continuous-phase velocity however, above a continuous-phase velocity of 40 ft/h, the mass transfer coefficient approached a fixed value. The overall mass transfer coefficient increased almost linearly with the dispersed-phase velocity. Their data for 15 IMTP packing is shown in Figure 11-9 with the aqueous-phase being continuous. 

Ky- overall mass transfer coefficient for the gas phase, kg/(s.m ) or kmoI/(s.m ) KqO = KQXig- volumetric mass transfer coefficient for the gas phase, 1/s ... 

K a Overall volumetric liquid-pbase mass-transfer coefficient kmoP[(s-m )(mole-fraction (lbmol)/[(h-tt )(mole-traction... 

Volumetric Mass-Transfer Coefficients and Kia Experimental determinations of the individual mass-transfer coefficients /cg and /cl and of the effective interfacial area a involve the use of extremely difficult techniques, and therefore such data are not plentiful. More often, column experimental data are reported in terms of overall volumetric coefficients, which normally are defined as follows ... 

Extrapolation of KgO data for absorption and stripping to conditions other than those for which the origin measurements were made can be extremely risky, especially in systems involving chemical reactions in the liquid phase. One therefore would be wise to restrict the use of overall volumetric mass-transfer-coefficient data to conditions not too far removed from those employed in the actual tests. The most reh-able data for this purpose would be those obtained from an operating commercial unit of similar design. 

Traditional Design Method The traditionally employed conventional procedure for designing packed-tower gas-absorption systems involving chemical reactions makes use of overall volumetric mass-transfer coefficients as defined by the equation... 

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. 

Measurements simply of the extent of extrac tion in an agitated vessel lead to the overall Volumetric mass-transfer coefficients, Kca, or... 

The plot of the rate of disappearance of CO per volume of liquid in the serum bottles versus partial pressure of CO in the gas phase based on (3.14.4.14) could give the constant slope value of KLa/H. Henry s constant is independent of the acetate concentration but it is only dependent on temperature. The overall volumetric mass transfer coefficient can be calculated based on the above assumption. The data for various acetate concentrations and different parameters were plotted to calculate the mass transfer coefficient. 

In most types of mass-transfer equipment, the interfacial area, a, that is effective for mass transfer cannot be determined accurately. For this reason, it is customary to report experimentally observed rates of transfer in terms of mass-transfer coefficients based on a unit volume of the apparatus, rather than on a unit of interfacial area. Calculation of the overall coefficients from the individual volumetric coefficients is made practically, for example, by means of the equations ... 

Heat removal is accomplished by internal cooling coils or wall jacket exchangers. Hydrodynamic regimes are complex, because of complicated flow patterns, prone to quick and dramatic changes. Usually a few overall parameters are considered, such as gas residence time and holdup, solid suspension, energy input, volumetric mass transfer coefficient (sec 3.2. 

The overall volumetric mass transfer coefficients measured by pure oxygen absorption were expressed as a function of the total specific power dissipated in the liquid as follows ... 

In many practical applications, gas-liquid mass transfer plays a significant role in the overall chemical reaction rate. It is, therefore, necessary to know the values of effective interfacial area (aL) and the volumetric or intrinsic gas-liquid mass transfer coefficients such as kLah, kL, ktaL, kg, etc. As shown in Section IX, the effective interfacial area is measured by either physical e.g., photography, light reflection, or light scattering) or chemical methods. The liquid-side or gas-side mass-transfer coefficients are also measured by either physical (e.g., absorption or desorption of gas under unsteady-state conditions) or chemical methods. A summary of some of the experimental details and the correlations for aL and kLaL reported in the literature are given by Joshi et al. (1982). In most practical situations, kgaL does not play an important role. 

Gas-liquid mass transfer can have a strong effect on TBR overall performance therefore its accurate evaluation is essential for achieving successful design and scale-up. In spite of the vast information available on gas-liquid mass transfer characteristics of atmospheric TBRs [1,2] only a few researchers have studied how interfacial areas, a, and volumetric liquid-side mass transfer coefficients, kLa, evolve at elevated pressures. For example, it has been reported that both a and kLa increase as gas density is rised while the gas superficial velocity is kept constant [3-5], Similar observations regarding gas hold-up and two-phase pressure drop, as well as the delay in the onset of pulsing have also been reported [6],... 

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