Characterization Of Flow Patterns Research Articles

Characterization of fasting and postprandial flow patterns in the small intestine: Comparison of multichannel intraluminal impedance (MII) with manometry

Characterization of fasting and postprandial flow patterns in the small intestine: Comparison of multichannel intraluminal impedance (MII) with manometry

Effect of distraction osteogenesis of the mandible on upper airway volume and resistance in children with micrognathia.

Children with craniofacial anomalies often have compromise of the upper airway, a condition with potential for morbidity and mortality. In children with microretrognathia, the diminutive size and retruded position of the mandible reduces the size of the oropharynx, thereby predisposing to glossoptosis and airway obstruction. Although several authors have reported successful use of mandibular distraction osteogenesis to alleviate this type of upper airway obstruction, the physiologic relationship between changes in mandibular shape, size, and position and upper airway dynamics remains undefined. The purpose of this study was to develop methodologies to quantitatively evaluate upper airway dynamics in children with micrognathia both before and after mandibular distraction osteogenesis. The patient population consisted of four children with micrognathia who had successfully undergone upper airway stabilization by bilateral mandibular distraction osteogenesis. The data used were digitally archived computed tomographic scan data from high-resolution, thin-slice head computed tomographic scans obtained before and after mandibular distraction. Upper airway evaluation was performed in two ways: static and dynamic. Static analysis consisted of computer quantification of predistraction and postdistraction mandibular and upper airway volumes using Analyze imaging software. Dynamic analysis consisted of fabrication of rigid stereolithographic hollow cast models of the upper airway produced from computed tomographic scan data. Models were used for characterization of upper airway resistance and flow patterns as related to respiration. After distraction osteogenesis, mandibular total volume increased 32, 32, 18, and 25 percent (mean, 27 percent) and upper airway volume increased by 20, 31, 23, and 71 percent (mean, 37 percent). A significant decrease in flow resistance, both inspiratory and expiratory, was observed in the patient with the greatest upper airway volume increase (71 percent) after distraction. After distraction, the inspiratory resistance was diminished by 51 percent and the expiratory resistance diminished by 85 percent. However, the three patients with more modest upper airway volume increases of 20 to 31 percent demonstrated no statistically significant change in flow resistance after distraction. Results of this study support the conclusion that distraction osteogenesis of the micrognathic mandible increases the volume of the upper airway, roughly paralleling the increase in mandibular volume. In the biomechanical airway model studied, upper airway volume expansion has been shown to be able to decrease the flow resistance over the length of the airway, presumably secondary to an increase in the average cross-sectional area. The artificial rigidity of the stereolithographic "airway" compared with the elasticity of the human upper airway may account for the insensitivity of this model to smaller but clinically significant airway changes.

Stability of Fourier coefficients in relation to changes in respiratory air flow patterns

The characterization of respiratory air flow patterns is a subject of continuous interest. The pattern of the air flow curve is an individual characteristic which remains constant over long periods of time. Basically two different approaches have been proposed to determine the individual parameters of the respiratory flow, namely the graphical characterization, which originated from visual indices and subsequently led to harmonic analysis, and the optimal control modeling approach. It has been suggested that respiratory personality can be accurately characterized by the Fourier coefficients of the air flow curve. The first four Fourier sine components should reproduce the shape of the cycle and remain constant in different environmental conditions for one individual. This paper evaluates the possibilities of the Fourier approximation approach to characterize the respiratory personality. The Fourier sine coefficients which were assumed to be invariable were found to be very sensitive to changes in respiratory times. Both the amplitude and the angle of the Fourier sine transformation varied when duration of inspiration and expiration changed.

Characterization of two-phase flow patterns in small diameter round and rectangular tubes

The present study investigates the effect of tube diameter and shape on flow regime transitions for two-phase flow in tubes with small hydraulic diameters. Flow patterns for co-current flow of air–water mixtures in horizontal round and rectangular tubes are determined by high-speed video analysis to develop flow regime maps and the transitions between these flow regimes. Gas and liquid superficial velocities range from 0.1 to 100 m s −1, and 0.01 to 10.0 m s −1, respectively. Bubble, dispersed, elongated bubble, slug, stratified, wavy, annular–wavy, and annular flow patterns are observed. The effect of tube diameter and shape on the flow patterns for hydraulic diameters ranging from 5.5 to 1.3 mm is documented and compared with the literature.

Characterization of Oil-Water Flow Patterns in Vertical and Deviated Wells

SummaryAn oil-water flow pattern classification and characterization for wellbores is proposed based on the integrated analysis of experimental data, including frictional pressure drop, holdup, and spatial phase distribution, acquired in a transparent test section (2-in. i.d., 51-ft long) using a refined mineral oil and water (ρo / ρw = 0.85,μ o /μw 20.0, and σo-w = 33.5dyn/cm at 90°F). The tests covered inclination angles of 90°, 75°, 60°, and 45° from horizontal.The oil-water flow patterns have been classified into two major categories given by the status of the continuous phase, including water-dominated flow patterns and oil-dominated flow patterns. It was found that most water-dominated flow patterns show signifi- cant slippage but relatively low frictional pressure gradients. In contrast, all the oil-dominated flow patterns exhibit negligible slippage but significantly larger frictional pressure gradients. Six flow patterns have been characterized in upward vertical flow; three were water dominated and three were oil dominated. In upward inclined flow there were four water-dominated flow patterns, two oil-dominated flow patterns and a transitional flow pattern. Flow-pattern maps for each of the tested inclination angles are presented. A mechanistic model to predict flow-pattern transitions in vertical wells is proposed. The transitions to the very-fine- dispersed flow patterns were evaluated by combining the concepts of turbulent kinetic energy with the surface free energy of the droplets, while the transitions to the churn flow pattern and the phase inversion were predicted based on the concept of agglomeration. The model compares favorably with the measured data.

Characterization of hydraulic flow patterns in facultative aerated lagoons

A tracer study was conducted in the winter at the Sainte Julie (Quebec, Canada) lagoon facilities to ascertain the hydraulic flow characteristics. The lagoon system is a continuous discharge type consisting of three facultative aerated lagoons and a maturation pond operating in series. The first three are provided with bottom air diffusers, the number of which decreases from the first to the third lagoon. C-diagrams indicate significant short-circuiting for all lagoons. Long tails in the C-diagrams of lagoons 1, 2, and 3 suggest the presence of stagnant or dead regions within them reducing the effective volume of the lagoons and hence the treatment efficiency that could otherwise be achieved. Values of the dispersion number, d, were 0.392, 0.452, 0.283, and 0.487 for lagoons 1, 2, 3, and 4, respectively. The jacknife statistical technique is used to assess the impact of influent flow variations on the dispersion number. Fluid flow pattern in the lagoons does not follow the simple “flow-through” behaviour. Rather, circulatory patterns are superposed on this as indicated by the multiple-peaked C-diagrams. Also, the Polprasert and Bhattarai model gives good prediction of the dispersion number for aerated lagoons.

Characterization of hydraulic flow patterns in facultative aerated lagoons

A tracer study was conducted in the winter at the Sainte Julie (Quebec, Canada) lagoon facilities to ascertain the hydraulic flow characteristics. The lagoon system is a continuous discharge type consisting of three facultative aerated lagoons and a maturation pond operating in series. The first three are provided with bottom air diflusers, the number of which decreases from the first to the third lagoon. C-diagrams indicate significant short-circuiting for all lagoons. Long tails in the C-diagrams of lagoons 1, 2, and 3 suggest the presence of stagnant or dead regions within them reducing the effective volume of the lagoons and hence the treatment efficiency that could otherwise be achieved. Values of the dispersion number, d, were 0.392, 0.452, 0.283, and 0.487 for lagoons 1, 2, 3, and 4, respectively. The jacknife statistical technique is used to assess the impact of influent flow variations on the dispersion number. Fluid flow pattern in the lagoons does not follow the simple “flow-through” behaviour. Rather, circulatory patterns are superposed on this as indicated by the multiple-peaked C-diagrams. Also, the Polprasert and Bhattarai model gives good prediction of the dispersion number for aerated lagoons.

ON THE CAPABILITY OF THE FOURIER APPROXIMATION TO DESCRIBE BREATHING PATTERNS

The characterization of respiratory air flow patterns is a subject of continous interest. The graphical analysis of the air flow curves started with visual indices and subsequently lead to harmonic analysis. The research group of Dr. Benchetrit suggests that respiratory patterns can be accurately described by the Fourier approximation. It is suggested that the first four Fourier sine components satisfactorily reproduce the shape of the cycle. This paper evaluates the accuracy of the Fourier approximation approach in describing the breathing pattern. Our analysis shows that for smooth, nearly symmetric air flow curves even the first three components give a reasonable approximation. However, as the shape of the air flow curve differs from smooth, quite symmetric patterns and flattens, the accuracy of fit of the Fourier approximation deteriorates and becomes unsatisfactory.

Analysis of pulsed wave Doppler ultrasound spectra obtained from a model intracoronary catheter

Abnormal arterial blood flow patterns have been implicated in the evolution of various vascular disease processes. Intravascular ultrasound techniques using the pulsed wave Doppler catheter offer the opportunity to characterize these abnormal flow patterns. We have developed a mathematical model that predicts the first two moments of the Doppler spectrum obtained using a Doppler catheter based on the distribution of ultrasonic beam power and velocity profile of fluid flow with an arbitrary distribution of flow disturbances. A scaled-up, in vitro experimental arterial system was used to confirm the validity of the model. Comparison of the predicted first two moments of the Doppler spectrum to the experimental values in this system demonstrated that the distribution of beam power significantly affects the magnitude of the first two moments. Additionally, both velocity gradient and velocity fluctuation broadening effects play prominent roles in determining the magnitude of the second moment. These phenomena must therefore be considered when evaluating in vivo Doppler spectra used for the characterization of abnormal flow patterns.

Kinematic waves and flow patterns in bubble columns and three-phase fluidized beds

An electrical impedance technique was used for the obtention of the propagation speed of liquid volume fraction waves in bubble columns and in three-phase fluidized beds. This method also allowed an objective criterion for the characterization of several bubble flow patterns. Characterization was made by regarding the shape of the spectral density function in liquid volume fraction signals. This method is consistent with the one based on the slope of the superficial gas velocity vs. the volume fraction of liquid, which was also explored and extended to three-phase fluidized beds. Results of the flow pattern characterization obtained were compared with those already reported.

Characterization of mixing in reactor systems through analysis of regional tracer dilution data obtained with a gamma camera

AbstractA new approach to the characterization of flow patterns and mixing through analysis of regional tracer dilution data obtained with a gamma camera is presented. Studies performed in a small, two‐dimensional, multiple‐inlet vessel demonstrate the experimental technique and how data are analyzed to determine the intravessel spatial distribution of fluid deriving from the traced stream. Good agreement is shown between calculated values of the flow distribution and visually observed flow patterns.