Larry A. Glasgow

BUBBLE BREAKUP AND COALESCENCE IN TURBULENT GAS-LIQUID DISPERSIONS

Theoretical models are proposed to describe bubble breakup and coalescence in a turbulent gas-liquid dispersion. The first model, which is mainly based on probablistic theory, gives reasonable prediction of bubble breakage frequency in terms of the liquid density, interfacial tension, bubble diameter, and the turbulent energy dissipation rate. The second model predicts the binary bubble coalescence frequency as a function of the liquid viscosity, interfacial tension, bubble diameter, turbulent energy dissipation rate, and the surface immobility parameter. Favorable agreement between the breakage and coalescence models and the experimental evidence indicates that these models could be used to predict dispersion properties such as bubble size distributions and interfacial areas.

A Review of the Effects of Shear and Interfacial Phenomena on Cell Viability

The shear sensitivity of animal and plant cells is a problem often encountered in large-scale cell culture. Such sensitivity varies with different cell lines and the severity of cellular damage may depend on both the magnitude and the duration of the shear stress. In a bioreactor, the shear susceptibility of cells depends on their response to hydrodynamic forces arising from fluid motions of particular scale. Cell damage may be induced by forces in the bulk liquid phase, but fluid motions associated with the gas-liquid interface are especially energetic. The detrimental effects of hydrodynamic forces are abated by the addition of some polymers, such as Pluronic F-68, methylcellulose, or serum; the exact mechanisms of protection are the subject of current research.

DYNAMICS OF BUBBLE SIZE DISTRIBUTION IN TURBULENT GAS-LIQUID DISPERSIONS

The population balance equation coupled with the proposed breakage kernel and the previously developed breakage model is applied to the analysts of bubble size distribution for non-coalescing systems in a bench-scale airlift column. Good agreement obtained between the theoretical results and the experimental data is encouraging and indicates that the model is suitable for predicting dispersion properties such as bubble size and interfacial area in turbulent gas-liquid dispersions.

Wall pressure fluctuations and bubble size distributions at several positions in an airlift fermentor

Measurements of bubble size distribution using direct photographic methods and image analysis have been made on a cylindrical split-column airlift fermentor. Wall pressure fluctuation measurements have also been collected at several vertical positions for a number of systems with different viscosities operated over a range of air flow rates. Tap water, salt water, and CMC in water solutions have been used in the investigation.

FLOC CHARACTERISTICS IN WATER AND WASTEWATER TREATMENT

ABSTRACT The behavior of an aggregate of colloidal particles, or floc, in a water treatment process is dependent upon its physical characteristics, including size, strength, density, and permeability. It is no exaggeration to say that the success of a water treatment operation can be gauged by the properties of the aggregates produced. Size and density are particularly important in sedimentation processes where the rate of solids subsidence constrains plant operation. Strength and permeability are indicators of the ease with which sludge may be dewatered for ultimate disposal. An experimental study of how floc characteristics are interrelated has been completed. In the case of kaolin-polyacrylamide aggregates, physical properties are largely determined by the conformation of the macromolecular bridges. Measurements of the viscosity of the dilute polymer solution under varied pH and ionic strength conditions have shown that macroion extension is greatest at a pH of about 6.5 for minimal counter-ion concent...

FLOC SIZE REDUCTION IN THE TURBULENT ENVIRONMENT

ABSTRACT The dynamic behavior of the particle size distribution (PSD) in wastewater treatment processes results from the interaction of a random growth process with nonlinear, stochastic hydrodynamics. Successful modeling of the PSD response to high dissipation conditions depends upon accurate quantification of the breakage mode, the local dissipation rate, transition probability, and the daughter particle size distribution; the inferential determination of these quantities from PSD data is difficult, at best. Direct photographic observation of floc breakup in a turbulent jet apparatus and in the Impeller stream of a baffled, agitated tank has provided opportunities to measure both the breakage mode and the daughter particle size distribution for individual parent floes. These data have been used in successful PSD modeling in lean, batch systems characterized by irreversible breakage.

AGGREGATE DISINTEGRATION IN TURBULENT JETS

A state-of-the-art, high-speed video system has been used to observe floc disintegration occurring in the thin shear layer of a turbulent jet. The macrovideographic images have provided details of the breakage process that were heretofore unavailable. This information has been used to validate and quantify a force balance model that establishes a more rational framework for the description of floc breakage. It also has provided a much more detailed picture of the threshold levels of stress required for the breakage of specific floc structural types. The ultimate objective of this line of research is to use this framework to successfully describe the response of floc structures to hydrodynamic stress in coagulation processes and to provide a means by which substantial improvements can be made in solid-liquid separation processes.

CHARACTERIZATION OF THE DOWNFLOW SECTION OF AN AIRLIFT COLUMN USING BUBBLE SIZE DISTRIBUTION MEASUREMENTS

Bubble size distributions in an airlift column were investigated with an emphasis on the downflow section. Measurements have been made using direct photographic techniques in conjunction with image analysis in a split cylinder airlift column. Information extracted from these measurements includes local gas hold-up, variation of Sauter mean bubble diameter with column length, and liquid circulation velocity. An air-tap water system was studied for purposes of comparison, while effects of electrolyte concentration and viscosity were studied using salt water, and two carboxymethyl cellulose (CMC) concentrations in water, respectively. The effect of energy input was studied by varying air flow rate to produce superficial velocities ranging from 2·59 cm/s to 10·36 cm/s.

Acoustic studies of interfacial effects in airlift reactors

Abstract Rational design of airlift reactors for the culture of plant and animal cells is impeded by a lack of understanding of the causes of loss of viability. Some recent speculations in the literature suggest that gas-liquid interfacial phenomena have played prominent roles in observed instances of loss of viability in both insect and animal cell cultures. The important interfacial events may include bubble formation and detachment at the sparger, bubble coalescence and breakage, and bubble disengagement at the free surface-entailing film thinning, film rupture, and film droplet ejection. We have carried out an experimental investigation of interfacial phenomena using macrovideography and acoustic signals recorded at both the sparger and the free surface. Data have been collected for several liquid media including distilled water, distilled water with electrolyte (NaCl), and aqueous solutions of glycerol (μ = 3 to 9.5 cP). The studies were conducted in a 3-liter, acrylic plastic, split-column airlift r...

Effective gas flow arrangements in soil venting

Soil venting is a remediation technology specifically designed to extract contaminant vapors from vadose-zone soils through application of vacuum at one or more recovery wells installed below the surface. In the present work, screening models are developed which can contribute to the design and optimization of soil venting processes by providing means for comparative evaluation of different extraction strategies. The development of a steady-state gas flow model and a vapor-phase mass transport model permits vacuum extraction performance and venting gas flow patterns to be evaluated for desired combinations of well placement, operating pressure(s), surface capping, air injection, and soil characteristics. Additionally, the performance of the gas-flow model was assessed by comparison with laboratory and field data.