In the present study, hydrodynamics of laboratory-scale asymmetric rotating impeller column (ARIC) and asymmetric rotating disk column (ARDC) have been studied. Effect of physical properties and operating parameters on drop size, dispersed phase holdup and axial mixing have been investigated. Correlations for prediction of mean drop size and holdup have been developed, in terms of power consumption per unit volume. The average absolute value of relative error (AARE) values in the prediction of drop size and holdup using these correlations are 18% and 14%, respectively. Furthermore, the hydrodynamic characteristics of ARIC have been compared with that of ARDC. Mass transfer performance of ARIC for the extraction of metal ions from phosphoric acid has been investigated. Effect of impeller speed on percentage extraction and continuous phase overall mass transfer coefficient has been examined. This work provides an insight into the performance of asymmetric rotary agitated extraction columns, useful in the design of such columns.

In the present work, a computational fluid dynamics (CFD) methodology has been applied to study the hydrodynamics of two phase flow in an asymmetric rotating disk contactor (ARDC) and asymmetric rotating impeller column (ARIC). The Euler–Euler model for multiphase flow and mixture k–ε model for turbulence have been used. The effect of different drag models on holdup of the dispersed phase has been investigated. The Kumar and Hartland (KH) drag model has been modified to predict the holdup accurately. The results of simulation have been validated with published experimental data. The average error in the prediction of holdup using a modified KH drag model is within ±11% of the experimental values. Hydrodynamics of ARDC and ARIC have been compared using simulations at different agitator speeds. The fraction of static holdup in ARDC and ARIC has been quantified. The developed CFD model has been used to predict the residence time distribution (RTD) of the dispersed phase.

Two different types of CTC (Crush, Tear and Curl) teas were used for infusion kinetics study. Infusion kinetics for these and their ground and sieved fractions were studied over a 15-min period at 60°C and 80°C. Samples were analyzed using UV-Vis spectroscopy. Results of infusion have been interpreted in terms of gallic acid equivalence (GAE). Fractions with smaller particle size show faster infusion. First-order rate constants for largest and smallest fractions were 0.257–0.685 min−1, respectively, at 60°C. A quasi-steady-state model was developed, which determines initial dissolution rate, diffusion rate from actual infusion rate and hence rate controlling step. At 80°C, the infusion rate of the 0.33 mm granules was found to be 98% of the dissolution rate as compared to 68% in case of 1.99 mm granules. The diffusivity values were found to be 2.23×10−10 m2/s and 4.34×10−10 m2/s at 60°C and 80°C, respectively.

In this study, the swelling kinetics of individual tea particles as well as bed of tea granules were investigated for different types of teas. The swelling experiments involved image analysis and volume measurements of tea particles. Each individual particle shows different swelling characteristics. Separating funnels and cylindrical columns of varying sizes were used to study the changes in volume of tea bed. Swelling in separating funnel was observed to be more than that in column. The effect of temperature, particle size, bed height and vessel diameter were investigated. The extent as well as the rate of swelling is found to increase with rise in temperature (60 to 80 °C) and reduction in particle size. A decrease in swelling is observed with increase in bed height as well as decrease in vessel diameter and vice a versa. About 70 to 75 % swelling occurs in the first 40 to 45 s. Two empirical models viz. Weibull and Peleg were used to fit the experimental data. The rate parameters obtained for a sample T5 at different temperatures were in the range of 0.012 to 0.016. The volume changes of all the teas were compared with their elution behavior, by measuring the absorbance of a diluted sample of brew at 272 nm. The activation energies for the process of tea swelling calculated for T1 (1.2 mm), T5 (2.2 mm) and T5 (0.72 mm) were 14.156, 8.37 and 13.42 kJ/mol respectively.

Mathematical model to predict tea infusion kinetics which accounts for swelling kinetics of tea granules is presented. Swelling kinetics of tea granules has never been taken into account for models developed so far. Differential equations (DEs) for concentration of tea constituents inside tea granule with respect to radius and time were derived. Solution methodology for these DEs is developed based on Crank-Nicholson scheme. Tea infusion profile is obtained using this model by knowing the swelling kinetics, partition constant and initial contents in tea granules. Diffusivity and product of interfacial area (As) and backward rate constant (k−1) are the fitting parameters. Model prediction is fitted to the experimental data published previously (R2 = 0.90–0.98). The fitted diffusivity (3.33 × 10−10 m2/s) and Ask−1 (2 m3/(kg.s)) predicted the infusion profile of other sized tea granules very well. This model predicts the infusion during initial stage very accurately without any empirical parameter.