The Chemical Engineering Journal and the Biochemical Engineering Journal最新文献

A model for the dynamics of hydrodynamically controlled spherical bubble growth in quiescent viscous newtonian and non-newtonian liquids is presented. Two constitutive equations were used to describe the behavior of the liquid medium: (1) a simple power law relation and (2) a truncated power law. Application of the truncated power law resulted in four differen cases: (a) at all times the liquid acts as a newtonian liquid; (b) at all times the liquid behaves as a simple power law liquid; (c) at all times the liquid close to the growing bubble obeys a power law relation and the liquid far away from the bubble behaves as a newtonian liquid; (d) all the liquid initially behaves as a newtonian liquid and at some time transforms to a two-region liquid. Analytical expressions were derived for bubble growth as a function of dimensionless system parameters. The relevance of this work to the process of polymer devolatilization is discussed.

A multi-branch/multi-cell model has been developed and used to evaluate the tray efficiency of examples of distillation trays with different layouts of the downcomer areas. The multi-branch/multi-cell model predicts that the trays with different downcomer area distribution patterns to have a different tray efficiency. Hence, it can help in the identification of the most efficient downcomer layout pattern and in the quantification of the expected efficiency differences.

Experiments were performed in liquid—solid loop reactor with a loop length of 14.45 m and an inner diameter of 90 mm under high velocity conditions. The variations in pressure gradient along the downflow, upflow and bend sections of the loop were investigated respectively. Pressure gradient in the downflow and upflow sections can be predicted with the model developed. The axial phase holdups are uniformly distributed along the loop. The liquid and solids velocities in the reactor are almost the same in the operating range tested. The axial dispersion coefficients of the liquid and solid phases were measured with the tracer injection response method and the dispersion coefficients of the solid and liquid phases are nearly the same. These characteristics make the liquid—solid system behave as a pseudo-homogeneous sytem and make the high velocity loop reactor easy to scale up. A commonly used correlation for axial dispersion substantially underestimated the axial dispersion coefficients.

The purpose of the present investigation is to establish a relation between acid equivalents and the atomic [O]/[C] ratio of regenerated humic acids. A linear relationship is found to exist between acid equivalents and atomic [O]/[C] ratio of regenerated humic acids. Correlation coefficients for equations relating acid equivalent produced by various methods (namely titration, ion-exchange and formulation of copper salt) with the atomic [O]/[C] ratio ranged between 0.91–1.00 on a dry-ash-free basis and 0.94–0.97 on a dry-mineral matter-free basis.

In this study the rheological data obtained for various differently concentrated oil-in-water emulsions from viscometers of different design and geometry are analysed and compared. The two types of viscometers used are a Fann coaxial cyclinder viscometer with different rotor-bob combinations and a Bohlin constant-stress rheometer with a cone-and-plate geometry. The results obtained from the two instruments for the same emulsions show large discrepancies. For example, the cone-and-plate measurements show strong shear-thickening (dilatant) behaviour in emulsions although no such effect is seen in the coaxial cylinder viscometer. The observed discrepancies in the measurements are explained in terms of the “creaming effect” in emulsions. While a small amount of creaming has little or no effect on the viscosity measurements in a coaxial cylinder geometry, it can have a large effect on the measurements in a cone-and-plate geometry.

We report experimental measurements on air—water mass transfer characteristics in two pulsed baffled reactors in a scale-up format. The experiments have, for the first time, investigated the scale-up parameters involved in such reactors and identified the optimal baffle spacing and the optimal superficial gas velocity for enhanced mass transfer performance. The experimental results indicate that the mass transfer rate strongly depends on the combination of the baffle spacing, aeration rate and oscillation frequency and amplitude. The mass transfer data, corrected for temperature effect and oxygen probe responses, are correlated in terms of power density and superficial gas velocities to show the scale-up correlation for the pulsed baffled reactors where the mass transfer performance is better in a large diameter reactor than in a small diameter reactor.

The influence of the slurry density on the fine wet grinding performances of a batch ball mill was examined for an alumina hydrate feed. Irrespective of the operating conditions, the size reduction process proceeds fast in the first period of grinding (20 min); then its rate progressively reduces and after 1–2 h the size of the product approches a final asymptotic value. The initial grinding rate is higher and the final mean diameter smaller using quite diluted feeds (water content 50%–80%), which represent the optimal operating conditions. When the slurries are dense (20% water), the rate of the grinding process can be enhanced by adding a small amount (2–10 kg m⁻³) of a grinding aid (sodium metaphosphate), which improves the flowability of the suspension. The product size distributions can be adequately described using the Rosin—Rammler expression: an attempt was made to relate the characteristic size of the distribution to the time and to the water content.

The present work focuses on the flow characteristics and mixing induced by Sulzer SMRX static mixers. It is observed both experimentally and numerically that pressure drop increases linearly with velocity for this mixer type and that, as expected, this effect is amplified when multiple mixers are placed in the flow field. It is further shown numerically that the slope of the pressure drop versus velocity curve increases for increasing internal mixer tube crossing angles. Moreover, it is found that mixing efficiency is a strong function of the internal tube crossing angle. Finally, analysis of the pressure drop results, particle patterns at the reactor outlet, streamlines, and the intensity of segregation suggests that the optimum configuration of an SMRX mixer is one with a 90° internal tube crossing angle. It also shows to what extent the use of two static mixers provide enhanced mixing compared to one.