Showing papers in "Chemical Engineering Communications in 1983"
TL;DR: In this article, a two-stage model of bubble formation accompanied by the pressure fluctuation in the gas chamber is presented and the results computed by this model are compared with the experimental results obtained for relatively wider range of gas chamber volume.
Abstract: The phenomena of the bubble formation from an orifice submerged in a liquid is classified according to their formation mechanisms and the estimation expressions of the bubble volume are reviewed The revised two-stage model of bubble formation accompanied by the pressure fluctuation in the gas chamber is presented and the results computed by this model are compared with the experimental results obtained for relatively wider range of gas chamber volume. Effects of some factors on the bubble volume, such as, gas chamber volume, orifice diameter, physical properties of gas and velocity of surrounding liquid are discussed
95 citations
TL;DR: In this article, the local and mean Nusselt number for free convection from an isothermal sphere as a function of the Rayleigh and Prandtl numbers are derived.
Abstract: Correlating equations are developed for the local and mean Nusselt number for free convection from an isothermal sphere as a function of the Rayleigh and Prandtl numbers. These expressions are based primarily on theoretical solutions for limiting cases, and hence are presumed to be more reliable than purely empirical correlations. The predictions of the proposed expressions are, however, validated by comparisons with prior experimental data. The expressions for the mean Nusselt number are shown to be applicable for all Ra and Pr. The expressions for the local Nusselt number are limited in applicability to the laminar boundary layer regime. The same equations are applicable to mass transfer and to combined heat and mass transfer in terms of the Sherwood, Schmidt and appropriately modified Rayleigh numbers.
84 citations
TL;DR: In this article, the results of Monte Carlo investigations of dispersion in one and two-phase flow through disordered porous media represented by square and simple cubic networks of pores of random radii are reported.
Abstract: We report results of Monte Carlo investigations of dispersion in one- and two-phase flow through disordered porous media represented by square and simple cubic networks of pores of random radii. Dispersion results from the different flow paths and consequent different transit limes available to tracer particles crossing from one plane to another in a porous medium. Dispersion is found to be diffusive for the process simulated, i.e., a concentration front of solute particles can be described macroscopically by a convective diffusion equation. Dispersivity in the direction of mean flow, i.e., longitudinal dispersivity, is found to be an order of magnitude larger than dispersivity transverse to the direction of mean flow. In two-phase flow, longitudinal dispersivity in a given phase increases greatly as the saturation of that phase approaches its percolation threshold; transverse dispersivity also increases, but more slowly. As the percolation threshold is neared, the backbone of the sublatlice occupied by t...
76 citations
TL;DR: In this article, the capacity of an adiabatic gas absorption column is limited through the formation of a temperature plateau, and the major heat effects are taken into account in the design of the column.
Abstract: In the design of adiabatic gas absorption, the temperature distribution within the column is an important consideration Temperature influences the degrees of heat and mass transfer through the thermodynamic phase equilibrium relationships and reaction rates The capacity of an absorber is limited through the formation of a temperature plateau Gas absorption in a chemically reactive solvent in an adiabatic packed column is modelled rationally for the first time taking into account the major heat effects An iterative computational method for computing packed bed height is presented The design procedure is illustrated by sample calculations for carbon dioxide (CO2) absorption in monoethanolamine (MEA)
64 citations
TL;DR: In this article, the dry reaction between SO2 and limestone has been investigated at low temperatures, and it has revealed that the relative humidity, the particle diameter and the limestone conversion have the most dramatic impacts on the reaction rate.
Abstract: The dry reaction between SO2 and limestone has been investigated at low temperatures. The study was focused on the wet-dry scrubbing application. Parameters investigated included: temperature: 313–353 K, SO2 concentration: 50–4000 ppm, oxygen concentration: 0–9 percent, carbon dioxide concentration: 0–10 percent, relative humidity 0–92 percent, limestone panicle diameter: 4–100 microns, and limestone conversion: 0–95 percent. The study has revealed that the relative humidity, the particle diameter and the limestone conversion have the most dramatic impacts on the reaction rate. A suggested reaction mechanism is outlined in great detail.
55 citations
TL;DR: In this article, the equations describing the retardation by surfactant of an essentially spherical droplet in creeping flow through an unbounded Newtonian liquid are developed in a general way, where the concentration distribution is determined by convection and coupled mass transfer processes of liquid-phase diffusion, adsorption kinetics, and surface diffusion.
Abstract: The equations describing the retardation by surfactant of an essentially spherical droplet in creeping flow through an unbounded Newtonian liquid are developed in a general way. The concentration distribution is determined by convection and the coupled mass transfer processes of liquid-phase diffusion, adsorption kinetics, and surface diffusion. Assuming that mass transfer occurs rapidly, an asymptotic solution is obtained showing uniform retardation, treating both phases and all mass transfer mechanisms simultaneously. For slow mass transfer, an asymptotic solution is obtained for stagnant cap behavior.
54 citations
TL;DR: In this article, the authors measured liquid velocity profiles in a bubble column with the aid of a hot-film anemometer, and two different types of profiles were detected that were characterized by the formation of a boundary layer at the column wall.
Abstract: Liquid velocity profiles in a bubble column were measured with the aid of a hot-film anemometer. Two different types of profiles were detected that were characterized by the formation of a boundary layer at the column wall. Under slow flow conditions, the boundary layer is large and controls the liquid velocity profile, but in turbulent flow the boundary layer is very small and has no significant effect on the velocity profile. Microscopic and macroscopic balances were used to predict both the liquid velocity profile and the average liquid velocity. The effect of the liquid velocity profile and average velocity on axial dispersion and gas-hold-up are analyzed and design procedures are recommended.
51 citations
TL;DR: In this article, power for agitation was measured under aerated and unaerated conditions in a 0.29 m vessel of Rushton dimensions at specific powers up to 18 W/kg.
Abstract: Power for agitation has been measured under aerated and unaerated conditions in a 0.29 m vessel of Rushton dimensions at specific powers up to 18 W/kg. The fluids studied were water. Newtonian solutions up to 19 m Pas and non-Newtonian shear thinning fluids some of which also exhibited a yield stress and some of which were viscoelastic. For the unaerated case, the power number-Reynolds number plot is in good agreement with the literature. For the aerated case, the result can conveniently be divided into three Reynolds number regions. At Re > ∼900, the data obtained for the solutions is not markedly different to that for water except that a higher impeller speed is required to achieve complete gas dispersion. For ∼ 10 < Re < ∼900. the power drawn is independent of gassing rate and greater levels of elasticity and the presence of a yield stress leads to the lowest power numbers. For Re < ∼10, the gassed and ungassed power numbers are equal.
48 citations
TL;DR: In this article, the authors developed a tentative cold bed hydrodynamic model for an idealized fluidized bed gasifier and showed that the model can predict bubbles forming in the fluidized beds.
Abstract: During the past three years we have developed a tentative cold bed hydrodynamic model for an idealized fluidized bed gasifier. The computer program calculates the pressure, the void fraction and the velocities for a single size solid and for a gas. The fluid bed never reaches a steady slate, but continually oscillates, as bubbles form, rise through the bed and collapse on top of the bed. In this paper we show that the hydrodynamic model can predict bubbles forming in the fluidized bed. Photographically determined bubble sizes agree with the predicted bubble sizes. They increase with height of bed and with jet velocity. The model produces bubble splitting which agrees with observations at higher jet velocities.
45 citations
TL;DR: In this paper, an experimental facility is described which enables the power drawn by each of two impellers to be determined separately by means of strain gauges using a flat-bottomed Perspex vess...
Abstract: An experimental facility is described which enables the power drawn by each of two impellers to be determined separately by means of strain gauges. In addition by using a flat-bottomed Perspex vess...
45 citations
TL;DR: In this article, a model for diffusional release of theophylline and albumin from ethylene-vinyl acetate based polymeric systems with dynamically changing porosity is presented.
Abstract: A model is presented for the diffusional release of theophylline and albumin from ethylene-vinyl acetate based polymeric systems with dynamically changing porosity. The model may be used to predict values of tortuosity of certain types of controlled drug delivery polymeric systems if drug dissolution limitations are negligible. The values of the tortuosity factor calculated indicate that small constrictions between large pores play an important role in the solute release behavior from these samples.
TL;DR: In this paper, the coupled fluid mechanics and mass transfer problems for the retardation by surfactant of an essentially spherical droplet in creeping flow are solved simultaneously by collocation methods with Newton iteration.
Abstract: The coupled fluid mechanics and mass transfer problems for the retardation by surfactant of an essentially spherical droplet in creeping flow are solved simultaneously. The mass transfer mechanisms of diffusion in the exterior liquid, surface diffusion, and adsorption kinetics are treated separately. No assumptions are made concerning the form of the velocity profile. The solutions are obtained by collocation methods with Newton iteration. The velocity profile and concentration distribution are improved simultaneously, not alternately. The numerical results reveal as limiting cases the uniformly retarded and stagnant cap interfacial velocity profiles considered previously.
TL;DR: In this paper, it was shown that the ratio of the microfluid/macrofluid volumes is roughly equal to that of the reaction/micromixing times.
Abstract: Micromixing is shown to proceed via three main mechanisms relying on the concept of “fluid aggregates”: (I) Laminar stretching (2) Turbulent erosion (3) Molecular diffusion, each with a characteristic time constant. Experiments are reported where chemical reactions are controlled by one or several of these processes. It is found that the ratio of the microfluid/macrofluid volumes is roughly equal to that of the reaction/ micromixing times. Tentative correlations are proposed to estimate the erosion and diffusion times and to calculate conversion and yield in micromixing controlled regime
TL;DR: For several polyoxyethylene alcohol nonionic surfactants, the effects of surfactant structure, temperature, electrolytes, and mechanical degradation on drag reduction near their coacervation temperatures were investigated in this article.
Abstract: For several polyoxyethylene alcohol nonionic surfactants not previously studied, the effects of surfactant structure, temperature, electrolytes, surfactant concentration, and mechanical degradation on drag reduction near their coacervation temperatures were investigated. Only linear alcohol derivatives were effective. Mechanically degraded solutions regain their drag reducing ability upon entering a low-shear region.
TL;DR: In this article, an extensive experimental investigation was conducted with activated carbons to establish the adsorption capacities of heavy metals (Cd2+, Ni2+, Cu2+, and Zn2+ ) in the presence of complexing agents (EDTA, triethylenetetramine (TRIEN), citrate, etc.).
Abstract: An extensive experimental investigation was conducted with activated carbons to establish the adsorption capacities of heavy metals (Cd2+, Ni2+, Cu2+, and Zn2+ ) in the presence of complexing agents (EDTA, triethylenetetramine (TRIEN), citrate, etc.). Adsorption equilibria are explained by species charges and carbon surface charge characteristics. In the pH range 7.5−8.0, the active sites are positively charged. The adsorption capacities of Cd2+ (and other heavy metals), free ligands, and cadmium-ligands are also a function of feed metal concentration, types of ligands, molar ratio of ligand/metal, and pH. Complete metal-ligand species distributions are calculated by computer solutions of multiple reaction equilibria. For an equilibrium cadmium concentration of 0.1 mM (pH 7.5−8.0), the sequence in adsorption capacity for cadmium chelates is Q Cd−EDTA > Q Cd−citrate > Q Cd−TRIEN > Q Cd−tartrate. A relationship between the adsorption capacity, surface charge of activated carbon, and the average species char...
TL;DR: In this paper, measurements have been made of the rate of deposition of magnetite particles from suspension in demincraliscd water pumped through vertical aluminium tubes of 19 mm bore over a range of temperatures I2-75°C and Reynolds number 7900 to 88500 under isothermal conditions.
Abstract: The deposition of magnetite from flowing water suspensions is a problem particularly important in boiler plant. Measurements have been made of the rate of deposition of magnetite particles from suspension in demincraliscd water pumped through vertical aluminium tubes of 19 mm bore over a range of temperatures I2-75°C and Reynolds number 7900 to 88500 under isothermal conditions. Bulk concentrations of magnetite particles (of the order of 2 μm diameter) were in the range 200-600 ppm. It would appear that deposition is mass transfer controlled. The initial deposilion rate for a given temperature and concentration varies as the suspension velocity to the power 0.73. The measured asymptotic deposition quantity varies as the suspension velocity to the power −0.66. The conclusions imply a sticking probability for the magnetite on to the aluminium lube walls as 1 for the experimental conditions.
TL;DR: In this article, the authors investigated theoretically the dynamics of a latent heat storage system consisting of a fixed bed operating close to thermal equilibrium with a percolating fluid, and the shape and propagation characteristics of the temperature profiles generated during loading and unloading of the bed were discussed, for various fusible materials, operating temperatures, initial and boundary conditions, and flow direction.
Abstract: This paper investigates theoretically the dynamics of a latent heat storage system consisting of a fixed bed operating close to thermal equilibrium with a percolating fluid. The model used is an idealized one, which emphasizes the role of the heat capacity factor, but neglects heat transfer resistances, losses, and hydrodynamic non-idealities. The approach is shown to resemble that used classicaly in non-linear adsorption, and analogous concepts, such as shock waves and dispersive waves are introduced. The shapes and propagation characteristics of the temperature profiles generated during loading and unloading of the bed are discussed, for various fusible materials, operating temperatures, initial and boundary conditions, and flow direction. The non-linear dependence of the enthalpy of the storage material on temperature is shown to play a central role in determining the qualitative features of these profiles. The aims of the article are mainly qualitative, conceptual and didactic.
TL;DR: In this article, the effect of coil pitch and the cross-sectional ellipticity on residence time distribution (RTD) for diffusion-free laminar flow in helically coiled tubes has been studied.
Abstract: The effect of coil pitch and the cross-sectional ellipticity on residence time distribution (RTD) for diffusion-free laminar flow in helically coiled tubes has been studied. The numerically computed RTDs reveal that the increase in the coil pitch broadens the RTD while the increase in the cross-sectional ellipticity narrows the RTD. The condition under which the effect of coil pitch on RTD can be ignored has been reported.
TL;DR: In this paper, the termination and propagation reactions in free radical homopolymerization are reviewed and some statements about limitations of the present models and recommendations will be made for future study.
Abstract: A deeper understanding of the dynamics of macromolecules in polymer melts (reptation theory—de Genne and others refer to PVC-Cleveland on long term aging of glassy polymers) has sparked a number of investigations on the modelling of the termination and propagation reactions in free radical homopolymerization. These recent contributions will be reviewed and some statements will be made about limitations of the present models and recommendations will be made for future study.
TL;DR: In this article, the coalescence behavior of bubble pairs formed on two adjacent capillary tubes was studied in aqueous solutions of n-alcohols and fatty acids at various concentrations.
Abstract: The coalescence behaviour of bubble pairs formed on two adjacent capillary tubes was studied in aqueous solutions of n-alcohols and fatty acids at various concentrations. Coalescence frequency and coalescence time were measured. The results show that coalescence time seems to be the best physical magnitude which can describe the coalescence process, because bubble coalesce only if the contact time of the bubbles is greater than the coalescence time. The coalescence time in solutions is proportional to the surface excess concentration of the solute. Coalescence time increases with the polarity of the hydrophylic group and its chain length and decreases with decreasing bubble size and increasing temperature.
TL;DR: In this article, the authors present a review of the SIMULATION of step growth polymerization in the context of the Chemical Engineering Communications: Vol. 20, No. 1-2, pp 1-52.
Abstract: (1983). INVITED REVIEW SIMULATION OF STEP GROWTH POLYMERIZATIONS. Chemical Engineering Communications: Vol. 20, No. 1-2, pp. 1-52.
TL;DR: In this article, the effects of solids and liquid surface tension on the gas holdup and the mass transfer parameters a and kL a were measured in two and three phase downflow bubble columns.
Abstract: Gas holdup, effective interfacial area and volumetric mass transfer coefficient were measured in two and three phase downflow bubble columns. The mass transfer data were obtained using the chemical method of sulfite oxidation, and the gas holdup was measured using the hydrostatic technique. Glass beads and Triton 114 were used to study the effects of solids and liquid surface tension on the gas holdup and the mass transfer parameters a and kL a . The gas holdup in three phase systems was measured for non-wettable (glass bead) and wettable (coal and shale particles) solids. The mass transfer data obtained in the downflow bubble column were compared with the values published for upflow bubble columns. The results indicate that in the range of superficial gas velocities (0.002-0.025) m/s investigated, the values of the mass transfer coefficient were of the same order of magnitude as those observed in upflow systems, but the values of interfacial area were at least two fold greater. Also, the results...
TL;DR: In this paper, the effective viscosity of elastic and inelastic liquids has been determined from the power consumption in stirred tanks, based on a power consumption of stirred tanks.
Abstract: The effective viscosity of elastic and inelastic liquids has been determined from the power consumption in stirred tanks
TL;DR: Steady-state and time-dependent non-Newtonian properties of structurally complex systems, such as suspensions and foodstuffs, are simulated by the extension of a recently developed fluid model that successfully describes pseudoplastic and thixotropic behavior, with or without yield stress.
Abstract: Steady-state and time-dependent non-Newtonian properties of structurally complex systems, such as suspensions and foodstuffs, are simulated by the extension of a recently developed fluid model. This model accommodates the concept of structure variation induced by flow via a kinetic approach similar to the treatment of reversible chemical reactions. Purely viscous and viscoelastic responses are considered, entailing different equations for the computation of their contribution to the overall stress sustained by the systems. The model successfully describes pseudoplastic and thixotropic behavior, with or without yield stress.
TL;DR: A theoretical expression based on the cell model has been developed to predict the dependence of the flow properties of a suspension in a wide range of solids concentration when the dispersing medium is a non-Newtonian liquid as mentioned in this paper.
Abstract: A theoretical expression based on the cell model has been developed to predict the dependence of the flow properties of a suspension in a wide range of solids concentration when the dispersing medium is a non-Newtonian liquid. Theoretical predictions show that the increase of the relative consistency coefficient of a suspension with increasing particle concentration is less dramatic when the flow index of the suspending medium is lower. Comparison with published data shows that the predictions of the present model for the relative consistency coefficient of a suspension in a non-Newtonian fluid are fairly accurate.
TL;DR: Porous media placed in the entrance of capillaries was found to reduce the pressure drop across the capillary by a factor of two or three for polystyrene as discussed by the authors. But no significant reduction was observed for a polymer melt such as polyethyleneterephthalate (PET) which is nearly devoid of memory.
Abstract: Porous media placed in the entrance of capillaries were found to reduce the pressure drop across the capillaries (▵Pc) by a factor of two or three for polystyrene. The reduction in ▵Pc was found to be a function of the distance of the porous media from the capillary entrance, the type of porous media, the length of the capillary, and the rheological properties of the polymer melt. No significant reduction in ▵Pc was observed for a polymer melt such as polyethyleneterephthalate (PET) which is nearly devoid of memory. The apparent shear rate for the onset of melt fracture was extended by a factor of three when polystyrene passed through the porous media before entering the capillary. No significant difference in die swell values was observed with the use of porous media in the entrance of the capillaries. The mechanism which accounts for these phenomena is believed to be associated with the break up of the entanglement network in the porous medium which temporarily changes the rheological propertie...
TL;DR: In this article, the elementary step model was used to simulate observed transients during forced periodic feed experiments and the model fit the observed behaviour well, in contrast to Langmuir-Hinshelwood models which only prove adequate for steady state behaviour.
Abstract: The periodic switching between two feed compositions to a gradientless reactor has been found to increase significantly the average reaction rate compared with steady stale operation. Another advantage of periodic feed switching, which has not been fully exploited in catalyst studies is in kinetic model discrimination where large variations can be forced into the predicted responses of several competitive models under consideralion. The elementary step model, with parameters determined from transient experiments, is used to simulate observed transients during forced periodic feed experiments. The model is found to fit the observed behaviour well, in contrast to Langmuir-Hinshelwood models which only prove adequate for steady state behaviour. Simulation studies coupled with experimental work help to clarify the role of adsorbed species during forced cycling.
TL;DR: A generalized bubble rise velocity correlation is developed to cover the range of conditions: liquid phase density = 45.1 to 74.7 lb/ft3, liquid phase viscosity = 0.233 to 59 cP, and interfacial tension = 15 to 72 dynes/cm.
Abstract: A generalized bubble rise velocity correlation is developed to cover the range of conditions: liquid-phase density = 45.1 to 74.7 lb/ft3, liquid-phase viscosity = 0.233 to 59 cP., and interfacial tension = 15 to 72 dynes/cm The gas-phase is air and the bubble size ranged from 1.2 to 15 mm. The developed correlation is based upon new dimensionless groups which contain the parameters affecting bubble rise velocity as well as their interaction, The correlation is independent of flow regimes and applicable for Reynolds numbers from 0.1 to 104. It is in good agreement with work appearing in the literature.
TL;DR: In this paper, a catalyst deactivation model is formulated which includes the combined effects of pore plugging and active site poisoning, and a computational algorithm is presented for solving the highly nonlinear system equations numerically.
Abstract: A catalyst deactivation model is formulated which includes the combined effects of pore plugging and active site poisoning. Intraparticle mass transfer is described by an equation which accounts for the configurational nature of diffusion, and poison deposition is assumed to be in accord with a parallel poisoning mechanism. A computational algorithm is presented for solving the highly nonlinear system equations numerically. The relative extent of deactivation by pore plugging and active site poisoning is determined by a dimensionless parameter, α, and several examples illustrate the effects that this parameter and other system parameters have upon the computed results. The model when combined with laboratory experiments should prove useful in optimizing catalyst pore size.
TL;DR: In this article, an expression for the coefficient of mass transfer from a solid particle suspended in a turbulent flow of liquid β = Q.261ScL -3/4 (EvL)1/4 has been obtained theoretically.
Abstract: On the basis of the model suggested in this paper an expression for the coefficient of mass transfer from a solid particle suspended in a turbulent flow of liquid β = Q.261ScL -3/4 (EvL)1/4 has been obtained theoretically. It is in good agreement with experimental data. The dissolution kinetics of particles is analytically described and a common procedure for calculating the dissolution of solids with arbitrary size distribution in stirred vessels has been developed on the basis of these results. The calculation results are compared with the experimental data obtained in vessels of different diameter with and without baffles.