True liquid side mass transfer

Fig. 13. Interfacial areas (a) and true liquid-side mass-transfer coefficients (b) in countercurrent packed columns. (See tabulation on p. 71.)...

The true liquid-side mass-transfer coefficients /cl all lie between 4 X 10 and 2 x 10 cm/sec (Fig. 13) and may be considered independent of Mq. The most representative relationship for the liquid-side mass-transfer coefficient, accurate within a range of 20%, is probably the one contributed by Mohunta et al. (Ml7) ... 

The true liquid-side mass-transfer coefficient does not change significantly with agitator speed, depending only on the physicochemical properties of the gas-liquid system. For bubbles smaller than 2.5 mm in diameter (typical industrially with impeller tip speeds of 2.25 m/sec or more), the correlation of Calderbank and Moo-Young (C3) is valid for ki (in cm/sec) in pure liquids or solutions of nonionic solutes ... 

In regime 3, the reaction is sufficiently fast to completely consume the gaseous reactant in the liqnid film. Diffnsion and reaction are occurring simultaneously iu a parallel fashion in the liqnid film. The true liquid-side mass-transfer coefficient has no effect on the... 

Rate of inert (nitrogen) feed Fn(= Fgu of the previous section) O.I3mol/s Gas-liquid interfacial area ol = I2.0cm /cm of liquid True liquid side mass transfer coefficient ki = 2x I0 cm/s... 

Mass transfer is located in the liquid phase and the true liquid-side mass transfer coefficient only depends on the square root of the bubble diameter. 

The previous assumptions together with the classical relationships of the different specific absorption rates, depending on the chemical reaction regime used to determine interfacial parameters, lead to the theoretical mean reduced values of the gaseous reactant in the gas exit stream and to absorption efficiency for a gas-liquid dispersion, where a is the geometrical specific interfacial area and Rl is the mean true liquid-side mass transfer coefficient defined for a bubble of diameter dg. ... 

The true liquid side mass transfer coefficient kL all lie between 9.4 10 and 2X10-2 cm/s and are usually assumed independent of Uq. a representative relationship for kLa (in sec ) has been proposed by Mohunta et al. (42) (+ 20 %)... 

True liquid-side mass transfer coefficient (m/s)... 

The True Gas-Liquid Specific Contact Area (a) and the Liquid-Side Mass Transfer Coefficient (ki)... 

On a perforated plate the liquid side mass transfer coefficient kLa and gas side mass transfer coefficient k( a, based on the column volume, vary linearly with the dispersion height. The true liquid- and gas-side mass transfer coefficients and first increase with the dispersion height and then go through a maximum and decrease slightly (123). Sharma and Gupta (124) attribute this to different behavior of the density of dispersion and the average bubble size with increase in gas flowrate, which leads to a phase inversion point. These authors correlate their experimental data for 10 cm i.d. perforated plates without downcomers by the following expressions... 

Yadav,G.D. and M.M.Sharma. "feffect of diffusivity on true gas-side mass transfer coefficient in a model stirred contactor with a plane liquid interface". Chem.Engng.Sci. 34 (1979) 1423. 

The literature on measurement of mass transfer in vertical tubular reactors is very sparse. Kasturi and Stepanek (K3, K4) have presented data for a, ki a, and kca measured under identical conditions in the case of annular flow, annular spray flow, and slug flow. For the aqueous systems used (COj, air, NaOH) they have proposed the following correlation for the interfacial area fl = 0.23[(l - a)/QJ(AP/Z)i( whereQt is incm /sec and AP/Z is in N/m . Correlations for true liquid-side and gas-side mass-transfer coefficients by the same authors are difficult to generalize, as viscosity and surface tension were not varied. 

The mass transfer is completely dominated by the liquid-side resistance. This would also be true if we calculated the overall gas-side mass transfer coefficient, Kp. Gas absorption is commonly controlled by mass transfer in the liquid and is one reason that reactive liquids are effective. 

In cases where the major resistance is in the liquid phase, the ratio RL/ RT= 1 and the simplification can be made that the over-all coefficient is equal to the liquid film coefficient. Which resistance dominates has to be determined from the ratio kLa / (kGa Hc) (Table 3-3). For compounds with a low Hc such as semi-volatile organic compounds, both resistances can be important (Libra, 1993). In oxygen transfer the liquid-side resistance dominates and KLa = kLa. This is also true for most of the cases in ozone mass transfer, unless there is strong mass transfer enhancement by very fast or instantaneous reactions of... 

Emission of solvents depends on the evaporation rate of the solvent in the process. The evaporation rate from the surface depends on the concentration in the layer on the surface and the coefficient of mass transfer on the air-side. This relation is approximately true for degreasing operations using both liquid and vapors of organic solvents. 

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