Gas absorption into non-newtonian fluids in rotating disc contactors

Mass transfer characteristics (k_Ia and a) for rotating disc contactor where a number of discs are mounted on a horizontal shaft and are partially submerged in a pool of liquid, are determined experimentally for Newtonian and non-Newtonian fluids. A simple model based on wetted area is developed which correlates the data within 10%.     

Gas absorption with photochemical reaction

Gas-liquid reactions can be activated by high energy radiations (photons). When gas absorption is accompanied by pseudo-first order reaction further enhancement in the specific rate of absorption can be realised for situations where either the reactive species in the liquid phase is activated or the dissolved solute gas is activated.     

Simultaneous absorption with reversible instantaneous chemical reaction

The approach presented recently [1] for analyzing absorption and desorption mass transfer problems with instantaneous chemical reaction is extended to the case of simultaneous absorption of two gases, A and A′. The analysis is developed for arbitrary stoichiometry. The following simple case is discussed in detail:A + B₁?B₂A′ + B₁?B₃ where B₁ is the liquid phase reactant and B₂, B₃ the reaction products. The analysis takes into account the “shift” reaction, which for the simple case above is:A + B₃?A′ + B₂This reaction takes place in the region near the interface. The analysis differs from previous work which, with one exception, ignored the “shift” reaction and restricted attention to zero values of the concentrations of B₂ and B₃ in the bulk liquid.The analysis shows that the conditions where the physical driving forces (a_i-a_o) for absorption of both gases are large and positive does not imply that the chemical driving forces (α_i-α_o) are both positive. In fact, it is shown that cases arise where one component may desorb even though its physical driving force is positive.A simplified thermodynamic model useful for extrapolation of mixed CO₂ and H₂S equilibrium data in amine solutions to very low values of acid gas loading in solution is developed. Tower profiles for simultaneous absorption of CO₂ and H₂S in monoethanolmine solution are considered in light of the new analysis. The good kinetic selectivity measured for H₂S at the absorber lean end is due to the fact that carbon dioxide is not absorbed in the instantaneous reaction regime. At the absorber rich end, where a temperature bulge develops, CO₂ is absorbed in the instantaneous regime, causing H₂S to be desorbed even though its physical driving force favors absorption.     

Gas phase solid-catalysed chemical reaction in spouted beds

Previously reported experimental work on the decomposition of ozone in a 0.15 m diameter spouted bed of angular iron oxide catalyst particles has been extended to spherical catalyst particles in both 0.15 m and 0.22 m dia. columns. Other variables, aside from column diameter, included catalyst particle size, bed depth, spouting velocity, and reaction rate constant (varied by adjusting the bed temperature). The use of a photometric analyser allowed analysis of concentrations at the inlet and exit from the bed, at different radial positions at the bed surface, and at several positions within the bed itself. Very little effect of particle size was found over the range studied (2.58 to 4.38 mm). Contrary to previous expectations, the conversion was found to decrease as the bed diameter was increased.The concentration gradients observed in the annulus indicate that the streamtube model is superior to the one-dimensional model, despite the fact that overall conversions predicted by these previously derived models are again similar. The observed gradients were not, however, as pronounced as those predicted by the streamtube model, and this suggests that radial dispersion in the annulus cannot be entirely neglected.     

Enhancement of absorption of a gas into a stagnant liquid in which a heterogeneously catalysed chemical reaction occurs

The CBS method[1, 2] is applied to measure the enhancement factor for the absorption of pure hydrogen from a gas bubble of constant size into a sta     

The effect of chemical reaction on the breakup of liquid jets

Linear stability analysis predicts that a chemical reaction occurring at or near a liquid jet interface may strongly influence its breakup into droplets. Jet length is shown to depend primarily on the site of the reaction (at the interface or in one of the bulk phases), the transfer rates of the various species, and the interfacial tension dependence on composition and secondarily on a number of other factors. Experiments with silicone oil jets (containing various carboxylic acids) in water (containing a range of concentrations of sodium hydroxide) confirm qualitatively the principal predictions of the analysis.     

Mass transfer in laminar liquid jets: Measurement of diffusion coefficients

Laminar liquid jets used in mass transfer studies have been generally discharged from convergent nozzles or orifices. The use of long straight capillary tubes to discharge the liquid jet is studied in this work and numerical values of the jet diameter and surface velocity are obtained. These computed values are applied to predict the actual absorption rates in the laminar jet for different values of N_J= N_Re/N_Fr, N_we and the axial coordinate. The effect of N_we is slight and can be disregarded in analysing experimental data. Experimental values of absorption of CO₂ in water and water-glycerol solutions are obtained using a laminar liquid jet discharged from capillary tube and good agreement is found between the computed values and the measured absorption rates. The results are applied to the determination of diffusion coefficient for the CO₂ in water glycerol solutions.     

Mass transfer with chemical reaction in a foam bed contactor

On the basis of dodecahedral structure of a foam bed, a model to predict conversion in a foam bed contactor with mass transfer with chemical reaction has been developed. To verify the proposed model, experiments have been carried out in a semi-batch apparatus for the absorption of lean CO₂ gas in a foam of sodium hydroxide solution. The proposed model predicts fairly well the experimentally found absorption values.     

Steady state multiplicity depending on coalescence in liquid—liquid continuous stirred reactors with reaction in the dispersed phase

The influence of drop coalescence and breakup on the existence of multiple steady states is studied for a two-phase stirred isothermal reactor where the chemical reaction in the d?ispersed phase obeys the rate expression ? r = kC/(1 + KC)². The random coalescence model developed by Curl was simulated using a modified Spielman and Levenspiel Monte Carlo technique.For certain range of the coalescence rate, Damköhler number, and dimensionless feed concentration, multiple steady states have been investigated.A special case has also been considered wherein the existence of multiple steady states for finite values of the coalescence rate is contrasted to the unique steady state solution for an infinite coalescence rate.     

Mass transfer with mth order chemical reaction for multi-particle systems

The steady-state diffusion equation with convective term and mth order chemical reaction term was numerically solved by the finite difference method. The penetration theory agreed only with the numerical solution around single spheres in an infinite potential flow field. The enhancement factor varies with the values of the Reynolds number, void fraction and contamination factor.     

Mixing and fast chemical reaction—VI: Extension of the reaction zone

Work reported earlier[1, 3] as well as here indicates that mixing at the molecular scale (micromixing) takes place by molecular diffusion in fluid elements, which are simultaneously undergoing laminar deformations. Whereas simple shear was considered before, the present analysis describes diffusion and reaction in regions deformed by extensional flow. After outlining various simple types of extension, results in the literature[4,7] are quoted, which were obtained from observations on the diffusion of heat spots in turbulent air. These indicated stretching motions in two directions with a corresponding shrinkage in the third. Direct application of these findings to diffusion in the direction of shrinkage leads to predictions of th product distribution from competitive, consecutive reactions. Without fitting any parameters, these predictions agree quite well with the distributions of two dyestuffs produced by two diazo coupling reactions. Insufficient fluid mechanical information is available to enablea more accurate comparison; matters requiring further study are listed.     

Period doubling and complex dynamics in an isothermal chemical reaction system

Stability and bifurcation theory have been used to organize a computational study of the dynamics of a three-variable isothermal reaction system with quadratic kinetics. This system exhibits a cascade of period-doubling bifurcations over decreasing intervals of parameter changes. This simple example illustrates a wide variety of complicated dynamics and shows that the qualitative dynamic features of isothermal reaction systems may be extremely sensitive to parameter values.     

Mixing and fast chemical reaction—VII Deforming reaction zone model for the CSTR

Earlier work on batch reactors indicated that the final stage of homogenisation to the molecular scale (micromixing) occurs by molecular diffusion in deforming fluid elements. The product distribution of, for example, consecutive, competitive reactions is sensitive to concentration gradients at the molecular scale (segregation). Such reactions may be used as reactive tracers to throw light on the behaviour of small fluid elements. Moreover an understanding of micromixing allows the selectivity of fast, multiple reactions to be better controlled. This paper describes two ways of applying the unsteady-state equations for diffusion and reaction within a shrinking fluid element to determine the steady-state concentrations in a CSTR. The iterative model is more economical in computer time than the dynamic model and applies to fast reactions (i.e. when the time for diffusion and reaction is a small fraction of the mean residence time). It described well the measured effects on the product distribution of varying the volumetric feed rati the stoichiometric ratio and of changing the operating mode from semicontinuous to continuous. When the initial size of the deformable fluid element is identified with the Kolmogoroff microscale and a reasonable estimate of shear rate is introduced, a highly satisfactory prediction of experimental resu knowing the kinematic viscosity and the power consumption of the stirrer, becomes possible.