On the use of approximate velocity profiles for modeling multiphase reactors

The use of an approximate axial gas velocity profile in a two-phase reactor model has been studied. The approximate velocity was assumed to vary linearly with conversion, which reduces the number of differential equations to be solved. The approximate model was studied in systems with one or two reactions. In most cases, the approximate and rigorous solutions were in good agreement. However, when mass transfer strongly influenced the velocity profile, errors in conversion became significant (～ 15%). Reactions with no change in the number of moles are also subject to errors if the rigorous velocity profile is not accounted for.     

Vapour—liquid equilibria of the systems acetone—benzene,benzene—cyclohexane and acetone—cyclohexane at 25°C

Vapour—liquid equilibrium data for the binary systems acetone—benzene, benzene—cyclohexane and acetone—cyclohexane have been determined experimentally at 25°C. The reduction producers based on P - x - y as well as on P - x isothermal data sets, which incorporate usual thermodynamically consistent models expressing the dependence of activity coefficients of liquid composition, have been examined for representing the reported results. Nonideal behaviour of the both phases has been taken into account. Thermodynamic consistency of the data has been shown by comparing of the experimentally obtained vapour compositions with those calculated from P - x data using the best of the examined models for activity coefficients.     

The counter-current backmixing model for fluid bed reactors — computational aspects and model modifications

Numerical solution of differential equations describing the counter-current backmixing model of Fryer and Potter is very difficult due to the boundary value nature of the problem. Several numerical methods (shooting, superposition and finite difference) have been described and tested on a problem with a single first-order reaction in an isothermal fluid bed reactor. It was found that the finite difference method is the most stable method and provides accurate solution over the entire range of parameters that were investigated, while the shooting and the superposition methods could not produce accurate solutions for some parameter values. Also, some modifications of the Fryer and Potter model such as: compartment models and conversion to an initial value type of problem (Jayraman-Kulkarni-Doraiswamy model), have been described. Results obtained from compartment models are in close agreement with predictions obtained from the original Fryer and Potter model. This paper is dedicated to Dr L K Doraiswamy on his sixtieth birthday. Computations reported in this paper were carried out by N Nasif, J G Daly and S H Lane.     

X-ray microanalysis of intestinal chloride transport in vitro and in vivo

Chloride secretion from crypt cells in mouse duodenum or jejunum was investigated in in vivo and in vitro models by electron probe X-ray microanalysis. IBMX-induced chloride secretion could not be demonstrated in vivo, presumably because of competing systemic effects. However, chloride secretion could be induced by 300 microM IBMX in vitro. The best results were obtained under the following conditions: a long preincubation of the tissue slices in high potassium or saline buffer (preferably in high potassium buffer), oxygenated with 95% O(2) and 5% CO(2), at low temperature (4 degrees C), followed by IBMX stimulation in saline buffer at 37 degrees C. Chloride efflux was accompanied by efflux of Na and K.     

Hydrodynamic studies with foaming and non-newtonian solutions in bubble columns

Experiments were conducted in 0.05 m ID and 0.23 m ID by 3 m tall bubble columns to study the effect of surfactants and viscosity of liquid medium on gas hold-up and Sauter mean bubble diameter. The addition of n-butanol (0.5 and 1 wt.%) to water leads to the formation of foam and consequently produces higher gas hold-ups. The foam could be eliminated completely with the addition of a sufficient quantity (0.5 wt.%) of carboxymethyl cellulose to the aqueous alcohol solution. In the absence of foam, gas hold-ups were similar to those obtained with pure liquids. Sauter mean bubble diameters, obtained using the dynamic gas disengagement technique, increase with viscosity of liquid medium.