Gas-liquid Interaction Research Articles

Determination of kinetic parameters of reactions in gas-liquid systems by electrical measurements

Diffusion is one of the processes that determines the physicochemical properties of gas—liquid systems and is accompanied by an increase in the conductivity of the liquid phase of the system. It is proposed that electrodynamic methods be used to determine the parameters of liquid—gas interaction.

Gas-liquid interaction in an apparatus with a disk mixer

Gas-liquid interaction in an apparatus with a disk mixer

Uptake of Haloacetyl and Carbonyl Halides by Water Surfaces

Gas-liquid uptake studies have been completed for the carbonyl halides CCl{sub 2}O and CF{sub 2}O and the haloacetyl halides CCl{sub 3}CCIO, CF{sub 3}CFO, and CF{sub 3}CCIO, which are intermediate products from gas phase oxidation of volatile halogen-containing species in the atmosphere. The fluorine-containing species result from the degradation of hydrochlorofluorocarbons (HCFCs) (proposed substitutes for chlorofluorocarbons, CFCs). The tropospheric lifetime of the halides depends on their dissolution in the aqueous phase, determined by Henry`s law solubility (H) and hydrolysis rate (k{sub hyd}). Using a bubble column apparatus, time-resolved gas-liquid interaction experiments measured the product Hk{sub hyd}{1/2}. Studies were performed at 278 K and pH = 1-13; for CCl{sub 3}CClO and CCl{sub 2}O, temperature was varied from 278 to 298 K. From this work and results from other laboratories, limits on values of the product Hk{sub hyd} were established and used to estimate a `global` cloud processing rate of these halides. A approximately 30-day upper limit to their tropospheric lifetime implies that tropospheric removal of the halide degradation products is fast enough not to contribute to the ozone depletion potential of the parent HCFCs. 39 refs., 6 figs., 1 tab.

Bubble Column Apparatus for Gas-Liquid Heterogeneous Chemistry Studies

A bubble column apparatus has been designed to conduct time-resolved gas-liquid interaction studies of interest in atmospheric chemistry. In the apparatus, a low pressure gas flow, carrying trace gas diluted in helium carrier gas, is `bubbled` through a flask containing 3.5 L of temperature-controlled liquid. The outlet gas flow is then sampled by a differentially pumped mass spectrometer. The position of the bubble injector, which determines the gas-liquid contact time, is computer controlled by means of a stepping motor. Modeling of the gas uptake and the validation of the apparatus performance are described. The apparatus in the present configuration can measure Henry`s law coefficients (H) for nonreactive species in the range 0.01-2.0 M/atm. For reactive species (reaction rate k) the apparatus measures Hk{sup $HLF} values in the range 0.08-100 (M/atm) s{sup -HLF}. 43 refs., 8 figs.

Investigation of Centrifugal Pump Performance Under Two-Phase Flow Conditions

A one-dimensional two-fluid model has been used to study the centrifugal pump head degradation phenomena and to analyze the gas-liquid interaction within the pump impeller under high pressure, steam-water two-phase flow conditions. The analytical model was used to predict the two-phase pump head data for the small-scale and full-scale nuclear reactor pumps and the predictions of the head degradation compared favorably with the test data for different suction void fractions. The physical mechanisms responsible for head degradation were also investigated.

Entry of gas molecules into liquids

Heterogeneous gas–liquid interactions play a fundamental role in many atmospheric processes. Pivotal for the understanding of such processes is the rate of gas uptake by the relevant liquid. Accurate experimental techniques have been developed to study uptake of gases by liquids. Gas–liquid interactions have already been investigated for more than thirty gas-phase species encompassing two classes of molecules: (1) those that do not react in the liquid but are readily solvated by it and (2) those that have low solubility in the liquid but react in the liquid rapidly to form highly soluble species. Uptake studies of non-reactive gas molecules in water have been explained by a model which treats the water surface as a narrow region of a dense gas-like state within which trace gas–solvent collisions occur. Gas accommodation occurs via nucleation of solvent molecules. Uptake studies for reactive gas molecules indicate that, for some species, reaction rates are much more rapid at the liquid interface than in the bulk liquid. The results of non-reactive and reactive uptake experiments are brought together here. The uptake model is briefly described, and the implication of the model for the kinetic nature of liquid surfaces is examined. Reaction-driven uptake studies which provide clear evidence for reactions at the gas/liquid interface are presented. The nature of interfacial reactions and their connection to the uptake model are examined.

The Physical and Mathematical Modelling of Gas Stirred Ladle Systems.

Considerable efforts have been made during the past two decades to investigate gas injection operations in steelmaking ladles. Towards these, numerous physical and mathematical model studies embodying aqueous as well as full scale systems have been reported. On the basis of an extensive literature search, a summary, discussion and analysis of these are now presented. For the sake of convenience and clarity of presentation, studies have been categorised into three major groups: (1) physical modelling studies, (2) combined physical and mathematical modelling studies and (3) mathematical modelling studies. In each of these categories, a great number of publications on various phenomena, such as gas-liquid interactions, turbulent fluid flow, mixing, solid-liquid mass transfer, etc. have been reported. Accordingly, and as discussed in the text, considerable improvements have resulted in our understanding of the various gas injection induced phenomena in ladle metallurgy operations. Coupled with these, extensive mathematical modelling studies have also lead to a reasonably accurate framework for carrying out engineering design and process calculations. Nonetheless, some obscurities and uncertainties still remain and these are pointed out, together with those areas where further work is needed.

Case study on the interaction of size dependent multiphase chemistry and detailed microphysics

It is widely accepted that clouds and precipitation systems are very important for the transformation and redistribution of chemical species in the atmosphere. Cloud droplets provide an alternate medium to the gas phase in which chemical reactions may proceed. The spectral composition of the droplets, on the one hand, is controlled by the drop formation via the activation of cloud condensation nuclei (CCN), the uptake of trace-gases and aqueous-phase chemical reactions. On the other hand, the chemical composition of the drops affects the dissolution of trace-gases and the rates and equilibria of the aqueous-phase reactions. A simple closed box model including explicitly spectral microphysics and a representative chemical mechanism is used to study the time evolution of the spectrally chemical composition of cloud droplets and to contrast the effects of dilution by condensation, of mixing by coagulation and break-up, of liquid phase reactions, and of interaction between the phases. The presented study suggest that cloud droplets of different sizes have different solute concentrations determined by the activation of size distributed aerosol particles and affected by condensation, coagulation, and break-up. If a chemically homogeneous aerosol distribution is assumed, the droplets of different sizes will have in this manner different dilutions and different pH but equal ratios between the aerosol related compounds. If also gas-liquid interactions and liquid-phase reactions are taken into account, the different pH and mass transfer coefficients in conjunction with microphysical processes will lead to quite different chemical composition over the drop spectrum and to a change of the spectral pH level.

EVIDENCE FOR DYNAMIC PHENOMENA IN RESIDUAL TRACHEAL TUBE BIOFILM

It has been proposed recently that a dynamic physical process occurring in the tracheal tube might account for the dissemination of bacteria and biofilm fragments into the lungs during mechanical ventilation, and the subsequent development of ventilator-associated pneumonia. In this study of tracheal tubes from consecutive adult intensive care patients, biofilms were detected radiographically in 45 of 50 tubes, and were found at the lower end of the tube more often than at the upper end (P < 0.005). In 37 of 50 tracheal tubes, the maximum biofilm thickness was equal to or greater than the 0.5 mm required for gas-liquid interaction in a tube with an i.d. of 8.5 mm. In 23 of 50 tubes, wave-like patterns were found. Five tubes had no biofilm inside the bevelled tip and another six showed evidence of biofilm loss for a greater distance from the tip. These observations suggest that the distribution of tracheal tube biofilm is caused at least in part by dynamic phenomena in the tracheal tube.

Gas Dynamics in the Central Cavity of the HYLIFE-II Reactortitle

In a HYLIFE-II ICF reactor, the microfusion of the D-T capsule in the center of the chamber produces X-rays that can ablate a thin layer off the liquid blanket which protects the first structural wall Thisablated material will implode toward the center line of the central cavity due to the initial vacuum and cylindrical geometry, and then rebound back to the liquid blanket vent through it and exert a pressure impulse'' onto the structural wall. The initial ablation occurs in a very short period with very small characteristic length and the implosion and rebounding processes feature very high pressures and temperatures. The proper design of the chamber relies on the reasonably accurate analysis of the gas dynamics in the central cavity and the gas-liquid interaction. In this paper, a second order Godunov numerical method is used to solve the compressible flow equations in the central cavity. The rarefaction and shock phenomena are very well captured by the numerical calculation. The equation of state for Flibe vapor is used in the calculation along with the parameters for the HYLIFE-II design. Since the radiation transport has not yet been included in the current calculations, the vapor possesses higher energy and therefore temperature.more » The total mass vaporized will also be underestimated in the later time of the calculation. The incorporation of a radiation calculation into this code is our next goal.« less

Physical Modalities of Therapy in Pediatric Rheumatic Diseases

The approach to rehabilitation management of childhood rheumatic disease differs in many ways from that of adult disease. Among the special considerations are the effects of chronic musculoskeletal inflammation in a growing and developing individual and the tendency of children to tighten their joints into positions of comfort, with fewer problems resulting from ligamentous laxity and instability. A comprehensive management approach includes much more than simply using medications--the tendency for the disease to exert deforming forces on the limbs must be constantly fought by a vigorous program of rehabilitation; education and psychologic support must be provided to the patient and family; potential problems must be discussed with the school; financial and vocational issues must be addressed.

Gas holdup in three-phase immobilized-cell bioreactors

A number of studies in the published literature deal with gas holdup in three-phase reactors. However, very few address the cases in which the solid density approaches that of the liquid phases and in which low gas velocities are involved. These conditions are commonly encountered in immobilized-cell bubble columns and in fluidized-bed bioreactors. This paper reports the effect of gas and liquid velocity upon gas holdup and bed expansion in fluidized-bed bioreactors. For liquid-fluidization of low-density alginate beads in the absence of gas, the terminal sedimentation velocity (vT) of the particles is a constant, and expansion of the bed follows Richardson and Zaki’s correlation. In the presence of gas, however, the apparent terminal sedimentation velocity value is affected by the velocity of the gas and liquid phases. For gas velocities above a minimum value, the calculated value of vT depends on liquid velocity only, and a constant bed expansion was observed for a range of gas and liquid flow rates. For the gas-liquid interactions, a modified drift-flux model was found to be valid. For superficial gas velocities between 5 and 17 cm/min, the modified drift-flux velocity was observed to be a function of gas velocity, suggesting the prevalence of a coalescence regime.

Mobilization of mucus by airway oscillations.

The effects of high frequency asymmetric airway oscillations on mucus clearance were evaluated in excised tracheas of sheep, in an animal model of excessive mucus production, and in patients with bronchiectasis. Asymmetric high frequency ventilation (15 Hz) with expiratory biased flow profiles (expiratory peak-flow greater than inspiratory peak-flow) could move mucus droplets towards the pharynx in rigid and flexible tracheas by gas-liquid interaction. In rigid tracheas the mucus was transported towards the periphery of the model lung if the oscillations were inspiratory biased. In very collapsible tracheas, however, even inspiratory biased oscillations moved the mucus cephalad. Parameters influencing direction and speed of mucus are airflow profile, peak-flow, airway compliance and lung resistance. Gamma-camera studies showed that in anesthetized dogs radiolabeled artificial mucus followed the direction of the bias during high frequency ventilation. In five human volunteers with bronchiectasis and excessive secretions the asymmetric airway oscillations were superimposed during spontaneous breathing using a mouthpiece. Airway wall vibrations following the pressure swings of the oscillator could be observed. During forced expiration inward bulging of the posterior membranes of trachea and bronchi occurred at the negative pressure phase of the oscillations. This event was associated with increased appearance of sputum in the central airways. We conclude that high frequency ventilation with asymmetric flow profiles applied via tube or mouthpiece might be an effective future treatment of mucostasis.

Fluid dynamics in bubble stirred ladles: Part II. Mathematical modeling

A mathematical model which describes the fluid flow in a bubble stirred ladle is presented. The model predicts mean flow, turbulent characteristics, bubble dispersion, and gas-liquid interaction from fundamental principles. Numerical predictions for a water model of a ladle show very satisfactory quantitative agreement with experimental results for all regions of the ladle. The model is applied to the study of refractory wear and yields results that are in qualitative agreement with practical experience.

Characterization, by inverse gas chromatography, of the surface properties of calcium carbonate before and after treatment with stearic acid

The interaction of n-alkanes with stearyl chains chemically fixed on the surface of calcite particles is investigated using inverse gas chromatography. Free enthalpy, enthalpy, entropy of adsorption and dispersive component of the surface free energy are determined. Untreated and stearic acid treated calcites have comparable affinities for the alkanes. However, the differences in adsorption entropies point to different interaction mechanisms: gas-solid adsorption for the untreated calcite and gasliquid interactions for the modified sample. Furthermore, for long chains probes, having more than 8 carbon atoms, the loss in entropy is smaller than for shorter chains. Possibly, long chains are only partially inserted in between the stearyl grafts, thus keeping a higher degree of freedom.

Mucus transport in the airways by two-phase gas-liquid flow mechanism: continuous flow model.

Mucus transport speed induced by two-phase gas-liquid interaction was measured in the continuous two-phase annular flow tube models, and factors influencing the transport speed were assessed in conjunction with rheological properties of mucus. The flow model was made with 1.0-cm-ID glass tubes and positioned either vertically or horizontally. During a continuous passage of airflow through the model tube, mucus stimulants were supplied into the tube at a rate of 0.5-2.0 ml/min. The advancing speed of the leading edge of the mucous layer and mean mucous layer thickness were then measured. The transport speed in the vertical tube model ranged from 1.1 to 3.1 cm/min with a mucus feed rate of 0.5 ml/min at airflow rates of 0.33-1.17 l/s and increased with increasing airflow rates but decreased rapidly with increasing viscosity of mucus. The transport speed increased almost proportionally with increasing mucus feed rate. Elasticity of mucus did not affect the transport speed itself. However, more elastic mucus caused lower flow resistance and thereby could be transported with a much reduced work load. The transport speed in the horizontal tube model was 5-60% faster than that in the vertical tube model. The mean mucous layer thickness in the vertical tube model was found to be in the range of 0.5-1.5 mm in the experimental conditions used, and decreased rapidly with increasing airflow rate and decreasing viscosity of mucus. From these data the transport speed could be functionally related to airway diameter, mucous layer thickness, and mucus production rate.

Preliminary results for a vortex induced, liquid handling and accountability procedure at zero gravity

Preliminary results are briefly summarized for a vortex induced, liquid handling and accountability process adapted to two phase fluids in zero gravity. The process, proposed by NASA Kennedy Space Center personnel and modelled at the National Bureau of Standards, for liquid transfer between two large rigid tanks in zero gravity, has been analysed for a selected range of fluid and flow parameters. This transfer process has been analysed in two stages. The initial ‘spin-up’ stage is modelled in the circular tank via tangential injection techniques. Vapour—liquid separation is predicted using an averaging process based on bubble and/or droplet drag characteristics, together with pertinent virtual mass considerations. The model produced permits the addition of other gas-liquid interactions. The subsequent liquid ‘pump-out’ stage is modelled using numerical computations of the conservative equations, applied to the annularized liquid layer that has been spun-up on the tank wall. Liquid pump-out is modelled for a range of parameters, such as Reynolds number and volume withdrawal rate. Examples are given to demonstrate both stages of the model. It is concluded that results are plausible and experimental vertification is now needed to validate the assumptions made, as well as the results predicted.

Gas‐Liquid Interactions in Oxygen Activated Sludge

A dynamic model has been developed for the gas-liquid interactions of a closed-tank oxygen system treating carbonaceous wastes. The model describes gas transfer between phases and accounts for equilibrium changes in the carbon dioxide-bicarbonate buffering system. The model was developed to provide a better understanding of process behavior and to provide a tool for gas phase control studies. Computer simulations of a four stage reactor were made to illustrate model predictions when using the conventional gas phase controls. Also, the effects of changing influent bicarbonate alkalinity, respiratory quotient, and gas-liquid volume ratio were examined. The dissolved oxygen concentration in the fourth stage was shown to vary widely and result in significant oxygen losses for the conventional control method. Influent bicarbonate alkalinity was shown to have a significant effect on pH, but changing the respiratory quotient had only a small effect on pH for moderate alkalinity wastewater. The gas-liquid volume ratio was found to have a significant influence on the response time for changing the fourth stage gas composition.

Influence of two-phase gas-liquid interaction on aerosol deposition in airways.

Many patients with chronic simple bronchitis, viz., chronic productive cough without major airway obstruction, frequently show enhanced aerosol deposition in the airways. We hypothesized that this phenomenon might relate in part to wave motion of an accumulated layer of mucus caused by dynamic, two-phase gas-liquid interactions. In the present investigation, two-phase gas-liquid interaction was demonstrated in vivo by observing wave motion during tidal breathing of radiopaque-labeled viscous and viscoelastic fluids that had been added to distal tracheas of conscious sheep. Total aerosol deposition in the lung and mean pulmonary resistance (RL) were measured after addition of 4 to 10 ml of viscoelastic or viscous fluids to the distal main bronchi of conscious sheep. Change in aerosol deposition over baseline after fluid addition was compared with change in RL. In 21 experiments, 5 for each of 3 viscoelastic fluids with varying characteristics and 6 for a viscous fluid, aerosol deposition was significantly enhanced in every experiment, irrespective of the type of fluid added. This increase in aerosol deposition ranged from 13 to 66% above baseline. The RL increased in 5 of the 6 experiments with viscous fluid and in 4 of the 15 experiments with viscoelastic fluids. There was less wavelike motion with viscous than with viscoelastic fluids. These results suggest that two-phase gas-liquid interaction in the airways can account for increased aerosol deposition with little alteration in airway resistance.

Modeling of wavy flow in inclined thin films in the presence of interfacial shear

A physical model is presented for predicting the various roll-waves characteristics in inclined thin films and in the presence of various distributions of interfacial shear and external pressure drop. The model is based on a periodical distortion of the hydrodynamic boundary layer in the wave front, followed by a recovery process in the wave trail. The solution is a closed form at the inception or at the well-developed regions, where the frequency is also predicted. For the developing region, one input (frequency) is required. A satisfactory agreement between predicted wave characteristics and experimental data is obtained, particularly at the low-intermediate interfacial shear range. With increasing the interfacial shear, both the wave frequency and wave velocity increase, while the wave amplitude decreases, independently with the mode of interfacial shear distribution. Applying the present model for various prescribed shear distributions, while comparing with available data of measurable wave characteristics, stimulates some thoughts on the unresolved gas-liquid interactions.