Mass transfer rate experimental studies

Finally, a number of experimental studies have been conducted in a pressure range where the polymeric solution could boil. The vapor bubbles thus created would provide a much larger surface area for mass transfer than the surface area of the wiped film alone. And therefore, for fixed values of the diffusivity and the driving force, predicted values for mass transfer rates would be substantially lower than the measured values. Conversely, for a fixed mass transfer rate and driving force, use of the wiped film surface area alone would require unusually high values of the diffusivity in order to obtain agreement between theory and experiment. 

In a study in which styrene was stripped from polystyrene, Latinen (1962) concluded that his theory correctly described the dependence of mass transfer rates on screw speed and flow rate. This conclusion was based on the agreement obtained between the measured and predicted exit concentration of styrene over a broad range of screw speeds and flow rates (Fig. 8). But, agreement between the theoretical expression and the experimental data was obtained using a diffusion coefficient of the order of 3 X 10 m sec , at 2(X)°C a value which is unrealistically high for this system. If the system ethylbenzene-polystyrene—which has a diffusion... 

Dekker et al. [170] studied the extraction process of a-amylase in a TOMAC/isooctane reverse micellar system in terms of the distribution coefficients, mass transfer coefficient, inactivation rate constants, phase ratio, and residence time during the forward and backward extractions. They derived different equations for the concentration of active enzyme in all phases as a function of time. It was also shown that the inactivation took place predominantly in the first aqueous phase due to complex formation between enzyme and surfactant. In order to minimize the extent of enzyme inactivation, the steady state enzyme concentration should be kept as low as possible in the first aqueous phase. This can be achieved by a high mass transfer rate and a high distribution coefficient of the enzyme between reverse micellar and aqueous phases. The effect of mass transfer coefficient during forward extraction on the recovery of a-amylase was simulated for two values of the distribution coefficient. These model predictions were verified experimentally by changing the distribution coefficient (by adding... 

Mathematical models for mass transfer at the NAPL-water interface often adopt the assumption that thermodynamic equilibrium is instantaneously approached when mass transfer rates at the NAPL-water interface are much faster than the advective-dispersive transport of the dissolved NAPLs away from the interface [28,36]. Therefore, the solubility concentration is often employed as an appropriate concentration boundary condition specified at the interface. Several experimental column and field studies at typical groundwater velocities in homogeneous porous media justified the above equilibrium assumption for residual NAPL dissolution [9,37-39]. 

FR may vary considerably from face to face in the same crystal. Consequently, mean values of FR or F0 are of interest in the design of crystallization apparatus, whereas experimental studies with single crystals may measure mass transfer rates at specifically oriented surfaces. McCabe and Smith (M3) suggest a procedure for estimating the contribution of individual surface rate coefficients to mean values and a method for calculating the increase in linear crystal dimensions from the latter. 

The factor 0,808 arises from the oumerical compoution of a definite integral in the composition profile expression. The above ndutkm, which is valid only for short penetration distances where the velocity profile re me ms linear, predicts how the mass transfer rate is affected by the wall velocity gradient, Nnsselt07 provided a numerical solution of the above problem using the complete velocity profile expression, while Skelland" compares these results to experimental studies of mass transfer to laminar films. A number of similar problems am encountered when mass transfer in membrane systems is considered in Chapters 18-21. 

Since realistic wood feedstocks are heterogeneous, the uniform entity appropriate for fundamental studies to identify improved conditions for tar formation is the single particle. In it, the intraparticle conditions can be measured and related to process conditions that can be manipulated. In addition, the effect of heat and mass transfer rates on reaction products can be determined. The findings can be rationalized to all reactors in which the studied experimental conditions prevail. The investigation of reacting single particles has proven extremely successful in the development of catalytic reactors (2) and coal pyrolysis (3,4,5). 

Once adequate airflow rate, temperature, and moisture are defined to intensify the external exchange processes, drying operation usually becomes completely dependent on internal mass transfer rate. To calculate the effective diffusivity, Aff. one has to combine experimental results with Fick-type model. However, diffusion phenomenon has to be studied out the starting drying time (1 0). Hence, a starting accessibility is defined as the difference between the initial moistme content Wj and the value Wq calculated by extrapolating the diffusion model till f = 0. 

Lewis Pratt, in 1953, were the first to report that the observed Marangoni convection in their experimental ternary systems was beneficial to hquid-hquid extraction processes because it increased mass transfer rates. The effect of density gradients on interfacial convection was studied by several researchers including Berg Morig (1969), who investigated the interaction between buoyancy and interfacial tension driven effects in ternary systems. The combined interfacial convection was also seen to be beneficial to mass transfer processes. 

Cini et al. (1991b) proposed the use of a tubular Pd/AljOj mesoporous membrane for the hydrogenation of a-methylstyrene to cumene. A comparison between the tubular catalyst and a fully-wetted pellet revealed a rate increase by up to a factor of 20. From that study, several other theoretical (Torres et al, 1994) and experimental ones confirmed that a three-phase membrane reactor can improve the mass transfer rate of gas-liquid-solid systems. 

Xie W, Ji X, Peng X, et al Mass transfer rate enhancement for CO2 separation by ionic liquids experimental study on the effect of film thickness. IndEng Chem Res, Accepted. 

The traditional study of suspension crystallization has been carried out using the MSMPR crystallization model. It has been found that uniform mixing in a commercial-size crystallizer, as required by the MSMPR model, is impossible to achieve. Therefore, the understanding of industrial crystallization is hampered by the use of the MSMPR model. Also, it is difficult to experimentally study the effects of mixing on crystallization, as described earlier in Section 51.2.5. Therefore, the CFD presents the means for local simulation in the tank. Furthermore, CFD simulation enables the tank to be designed so that the shape and the positioning of the impellers and the liquid velocity create the optimal level of super-saturation and mass transfer rate in all locations. This is likely to result in a narrowing of the particle size distribution. 

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