The steady axisymmetric flow in and around a deformable drop moving under the action of gravity along the axis of a vertical tube at intermediate Reynolds number is studied by solving the nonlinear free-boundary problem using a Galerkin finite-element method. For the case where the drop and suspending liquid have the same viscosity, the ratio of the densities is 6/5 or 5/6, and the radius of the tube is equal to twice the radius of a sphere having the drop volume, four significant results are apparent in the computations. First, we compute drops showing much more deformation, and in particular the development of considerably more non-convexity, than those found in previous calculations for non-zero Reynolds number. The degree of non-convexity typically grows with the Reynolds number. Secondly, external recirculation zones can be attached to or disjoint from the drop. We find when there is a single external recirculation zone, that is disjoint (as found by Dandy & Leal), it can attach to the drop as the Reynolds number is increased. As the Reynolds number further increases, this is immediately followed by division of the drop into two adjacent recirculating regions. Thirdly, we sometimes find two recirculation zones in the suspending liquid. Finally, the drag coefficient, axis ratio, and normalized interfacial and frontal areas of the drop can vary non-monotonically with the Weber number, exhibiting as many as four local extrema. The results are compared to previous theoretical and experimental work, and implications for drop motion and heat and mass transfer are discussed.

Axisymmetric steady flows driven by an electric field about a deformable fluid drop suspended in an immiscible fluid are studied within the framework of the leaky dielectric model. Deformations of the drop and the flow fields are determined by solving the nonlinear free-boundary problem composed of the Navier-Stokes system governing the flow field and Laplace's system governing the electric field. The solutions are obtained by using the Galerkin finite-element method with an elliptic mesh generation scheme. Under conditions of creeping flow and vanishingly small drop deformations, the results of finite-element computations recover the asymptotic results. When drop deformations become noticeable, the asymptotic results are often found to underestimate both the flow intensity and drop deformation. By tracking solution branches in parameter space with an arc-length continuation method, curves in parameter space of the drop deformation parameter D versus the square of the dimensionless field strength E usually exhibit a turning point when E reaches a critical value Ec. Along such a family of drop shapes, steady solutions do not exist for E > Ec. The nonlinear relationship revealed computationally between D and E2 appears to be capable of providing insight into discrepancies reported in the literature between experiments and predictions based on the asymptotic theory. In some special cases with fluid conductivities closely matched, however, drop deformations are found to grow with E2 indefinitely and no critical value Ec is encountered by the corresponding solution branches. For most cases with realistic values of physical properties, the overall electrohydrodynamic behaviour is relatively insensitive to effects of finite-Reynolds-number flow. However, under extreme conditions when fluids of very low viscosities are involved, computational results illustrate a remarkable shape turnaround phenomenon: a drop with oblate deformation at low field strength can evolve into a prolate-like drop shape as the field strength is increased.

Nomenclature: C, constant Eq. (5); C0'feed concentration, g/L; CO2' carbon dioxide flowrate g/h; d p' , particle diameter, cm; D c' column diameter, cm; D diffusion coefficient of dextrose, cm2/s; D z' dispersion coefficient, cm2/s; k l' , constant in pressure relationship, N in.-2/cm; L, bed length, cm; M, taper ratio, cm/cm; p product concentration, g/L; Pe z' peclet number; Q L' volumetric flow rate, L/h; r A (s), reaction rate, g/L/h; R bead radius, cm; R 0' diameter at bottom of tapered column, cm; s substrate concentrations, g /L; U g' superficial gas velocity, cm/ h; U l' , superficial liquid velocity, cm/h; x biomass concentration, g/L (dry-wt basis); γ co2/s' carbon dioxide yield coefficient, 0. 49 g/g; z, dimensionless axial position; ε g' gas-phase holdup; ε l' , liquid–phase holdup; ε s' solid-phase holdup; η effectiveness factor; µ l' , viscosity, g/cm/s; ρ s' solid density, g/L; ρ l' liquid density, g /L; ξ, dimensionless radial position in the bead; τ, constant, cm-0.59 mol1.03 g-1.03 s0.03 Eq. (7); ϕ, constant, N g /mol cm/s Eq. (7); φ, constant, N cm/mol Eq. (7); ψ, constant pressure at bottom of reactor, N/cm-1 Eq. (7); ω, constant, N g/mol/s Eq. (7).

An experimental apparatus has been assembled for the study of high-gradient magnetic separations of para- and dia-magnetic particles suspended in a liquid. The components of this system include a cryogenic magnet, equipment for light-intensity measurements, and a dynamic light-scattering technique for transient particle-size measurements. The flocculation of paramagnetic hematite particles of approximately 200-nm diameter under the influence of a uniform magnetic field is experimentally investigated. The effect of solution pH on particle growth as a result of flocculation is examined with and without the presence of the magnetic field. Results show that the flocculation rate of hematite particles increases with the intensity of the magnetic field.

Flocculation of paramagnetic particles under the influence of a strong magnetic field is reported in this article. Experimental information is obtained from fluctuation and intensity measurements of light passing through a particle suspension introduced in a uniform magnetic field. The magnetic field of strengths up to 6 T is generated by a cryogenic magnet operating at liquid helium temperatures. The phenomenon is analyzed by a Brownian flocculation model in which hydrodynamic, van der Waals, double-layer, and magnetic forces are incorporated for the estimation of the particle-flocculation rate. A population balance is employed in conjunction with the flocculation model to predict the evolution of the particle state with time. The effects of such important parameters as strength of the magnetic field, magnetic susceptibility of the particles, particle size, and zeta potential are investigated. Results show that particle size and magnetic susceptibility each play an important role in the selective flocculation of particles of different properties.

An alternative approach to the operation of bioprocessing systems within non-aqueous environments would require the development of reaction systems that would provide effective interfacial contact between the biocatalyst, contained within an aqueous phase, and the organic phase containing the substrate. A biphasic liquid-liquid (BLL) reactor that provides for intimate liquid-liquid contact would be the most probable approach for this application. For the BLL reactions considered in this work, the overall effectiveness of the system will depend on both compatibility of the biocatalyst with the chemical species present and intrinsic reaction and interfacial transport phenomena typically involved with liquid-liquid operations. The focus of this article is to investigate the removal and oxidation of p-cresol dissolved in toluene by aqueous-phase horseradish peroxidase. Contacting of the liquid-liquid biphasic enzyme system is carried out in an advanced solvent extraction contacting device, the electrically driven emulsion-phase contactor (EPC).

The discrete bivariate population-balance equation is formulated and solved to describe the kinetics of heterogeneous magnetic flocculation of colloidal paramagnetic particles in a uniform magnetic field. The particles are allowed to have various sizes and values of magnetic susceptibility. Computations show the importance of particle size and magnetic susceptibility on the flocculation rate and the transient bivariate (size/magnetic susceptibility) density function. The particle size distribution of certain magnetic-susceptibility particles and the magnetic-susceptibility distribution of certain size particles are calculated as functions of time and initial and operating conditions. The composition of a floc at any time depends on magnetic, van der Waals, double layer, and hydrodynamic forces among pairs of particles. The magnetic force is a function of the particle size, magnetic susceptibility, and strength of the magnetic field. Results are presented for various initial conditions of particles after ten minutes of flocculation. The results are of significance in understanding the forces among the particles and designing efficient magnetic separation processes.

The gram-negative cellulase-producing bacterium NCIMB 10462 has been previously namedPseudomonas fluorescens subsp. or var.cellulosa. Because of renewed interest in cellulose-degrading bacteria for use in the bioconversion of cellulose to chemical feed stocks and fuels, we re-examined the characteristics of this microorganism to determine its true metabolic potential. Metabolic and physical characterization of NCIMB 10462 revealed that this is an alkalophilic, nonfermentative, gram-negative, oxidase-positive, motile, cellulose-degrading bacterium. The aerobic substrate utilization profile of this bacterium has few characteristics consistent with a classification ofP. fluorescens and a very low probability match with the genusSphingomonas. However, total lipid analysis did not reveal that any sphingo-lipid bases are produced by this bacterium. NCIMB 10462 grows best aerobically, but also grows well in complex media under reducing conditions. NCIMB 10462 grows slowly under anaerobic conditions on complex media, but growth on cellulosic media occurred only under aerobic conditions. Total fatty acid analysis (MIDI) of NCIMB 10462 failed to group this bacterium with a known pseudomonas species. However, fatty acid analysis of the bacteria when grown at temperatures below 37°C suggest that the organism is a pseudomonad. Since a predominant characteristic of this bacterium is its ability to degrade cellulose, we suggest that it be calledPseudomonas cellulosa.

Chemical conversion processes are pervasive in the U.S. industry. Whether they are used to make intermediate or final products or to remove hazardous materials from process waste streams, they are critical elements in the processing industries. Because of the mild reaction conditions, unique specificity, and selectivity, advanced processing concepts utilizing biocatalytic conversions are now being considered for many industrial uses, including those directly related to energy production and efficiency. Almost all bioprocessing systems currently used by industry utilize the biocatalysts (microorganisms or extracted enzymes) in a {open_quotes}natural{close_quotes} aqueous environment. This has resulted in many important large-scale applications, particularly in the fermentation and pharmaceutical industries. An exciting new area of bioprocessing research is now evolving - the use of biocatalysts in contact with nonaqueous media such as organic liquids or gases, or supercritical fluids. Such approaches could result in additional bioprocessing concepts that would result in a much broader range of utility, especially in energy production and energy-efficient conversion processes in the chemical industry. In fact, a whole new industry may be evolving.

Three species of Sulfate-Reducing Bacteria (SRB) were able to grow using dibenzothiophene (DBT) as their sole source of sulfur and sole electron acceptor. Desulfotomaculum orientis and Desulfovibrio desulfuricans were grown at 30°C while Thermodesulfobacterium commune was grown at 60°C, in media containing lactate and citrate. Hydrogen sulfide was the product of dissimilatory sulfur reduction.

Biocatalysts allow the solubilization/liquefaction of coal at near-ambient temperatures. This research has focused on the chemical modification of enzymes to enhance their solubility and activity in organic media, and on optimal reactor design for a biocatalyst coal liquefaction process. Modification of hydrogenase and cytochrome c using dinitrofluorobenzene (DNFB) or methoxypolyethylene glycol p-nitrophenyl carbonate (PEG-n) has effected increased solubilities up to 20 g/L in organic solvents ranging from dioxane to toluene. Use of these modified enzymes in a small fluidized-bed reactor (with H-2 sparge) resulted in >40% conversion of bituminous coal in 24 h. Research using model compounds suggests that the conversion process may be in part owing to splitting at methyl or ethyl bridges, and perhaps saturation of ring structures. A new class of continuous columnar reactors will be necessary to achieve the high throughput and low inventory necessary for biocatalyst processes. The controlling mechanisms of particle transport in fluidized-bed systems using very small coal particulates are being studied. This has included the hydrodynamic modeling of coal segregation in fluidized-bed reactors, with direct microscopic visualization using fluorescence microscopy. A summary of our previously published work on enzyme modification and fluorescence visualization is presented.

This study analyzes the economic impact that a fluidized-bed reactor (FBR) using immobilizedZymomonas mobilis would have on a plant converting cornstarch into ethanol. The study addresses substituting this new technology into an existing plant or using it for a new plant. We have compared the processing steps required by the FBR with conventional technology, and developed process flow schematics, priced required equipment, and generated plant capital and operating cost estimates. This allowed a cost evaluation between the FBR and traditional technologies, such as well-mixed fed-batch fermentation. The study results indicate that the FBR technology can provide a significant reduction in the production costs of ethanol—a savings of >$0.02/gal if inserted into an existing plant, and a savings of >$0.06/gal if used at a new plant.