scholarly journals Viscoelastic liquid curtains: experimental results on the flow of a falling sheet of polymer solution

2019 ◽  
Vol 873 ◽  
pp. 358-409 ◽  
Author(s):  
A. Gaillard ◽  
M. Roché ◽  
S. Lerouge ◽  
C. Gay ◽  
L. Lebon ◽  
...  
Keyword(s):  
Velocity Field ◽  
Flow Rate ◽  
Extensional Flow ◽  
Free Fall ◽  
Viscoelastic Liquid ◽  
Mean Velocity ◽  
Constant Flow Rate ◽  
Polymer Addition ◽  
Continuous Sheet ◽  
Newtonian Liquids

We experimentally investigate the extensional flow of a sheet – or curtain – of viscoelastic liquid falling freely from a slot at constant flow rate under gravity. Extruded liquids are aqueous solutions of flexible polyethylene oxide (PEO) and of semi-rigid partially hydrolysed polyacrylamide (HPAM) with low shear viscosities. Velocimetry measurements reveal that the mean velocity field $U(z)$ (where $z$ is the distance from the slot exit) does not reduce to a free fall. More precisely, we show that the liquid falls initially with sub-gravitational accelerations up to a distance from the slot which scales as $g\unicode[STIX]{x1D70F}_{fil}^{2}$ (where $g$ is gravity and $\unicode[STIX]{x1D70F}_{fil}$ is the extensional relaxation time of the liquid) due to the stretching of polymer molecules. Beyond this elastic length, inertia dominates and the local acceleration reaches the asymptotic free-fall value $g$. The length of the sub-gravitational part of the curtain is shown to be much larger than the equivalent viscous length $((4\unicode[STIX]{x1D702}/\unicode[STIX]{x1D70C})^{2}/g)^{1/3}$ for Newtonian liquids of density $\unicode[STIX]{x1D70C}$ and dynamic viscosity $\unicode[STIX]{x1D702}$ which is usually small compared to the curtain length. By analogy with Newtonian curtains, we show that the velocity field $U(z)$ rescales on a master curve. Besides, the flow is shown to be only weakly affected by the history of polymer deformations in the die upstream of the curtain. Furthermore, investigations on the curtain stability reveal that polymer addition reduces the minimum flow rate required to maintain a continuous sheet of liquid.

Simulation of mechanically stirred two-phase liquid-gas flow

1986 ◽  
Vol 51 (5) ◽  
pp. 1001-1015 ◽  
Author(s):  
Ivan Fořt ◽  
Vladimír Rogalewicz ◽  
Miroslav Richter
Keyword(s):  
Spatial Distribution ◽  
Velocity Field ◽  
Gas Flow ◽  
Liquid Velocity ◽  
Model Parameters ◽  
Two Phase ◽  
Mean Velocity ◽  
Rushton Turbine ◽  
Low Viscosity ◽  
Volumetric Gas Flow Rate

The study describes simulation of the motion of bubbles in gas, dispersed by a mechanical impeller in a turbulent low-viscosity liquid flow. The model employs the Monte Carlo method and it is based both on the knowledge of the mean velocity field of mixed liquid (mean motion) and of the spatial distribution of turbulence intensity ( fluctuating motion) in the investigated system - a cylindrical tank with radial baffles at the wall and with a standard (Rushton) turbine impeller in the vessel axis. Motion of the liquid is then superimposed with that of the bubbles in a still environment (ascending motion). The computation of the simulation includes determination of the spatial distribution of the gas holds-up (volumetric concentrations) in the agitated charge as well as of the total gas hold-up system depending on the impeller size and its frequency of revolutions, on the volumetric gas flow rate and the physical properties of gas and liquid. As model parameters, both liquid velocity field and normal gas bubbles distribution characteristics are considered, assuming that the bubbles in the system do not coalesce.

Absorption of oxygen into solutions of polymers

1986 ◽  
Vol 51 (10) ◽  
pp. 2127-2134 ◽  
Author(s):  
František Potůček ◽  
Jiří Stejskal
Keyword(s):  
Mass Transfer ◽  
Aqueous Solutions ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Flow Rate ◽  
Liquid Flow ◽  
Flow Curve ◽  
Liquid Flow Rate ◽  
Polymer Concentration ◽  
Newtonian Liquids

Absorption of oxygen into water and aqueous solutions of poly(acrylamides) was studied in an absorber with a wetted sphere. The effects of changes in the liquid flow rate and the polymer concentration on the liquid side mass transfer coefficient were examined. The results are expressed by correlations between dimensionless criteria modified for non-Newtonian liquids whose flow curve can be described by the Ostwald-de Waele model.

scholarly journals EFFECT OF TUBE PITCH ON HEAR TRANSFER IN SPRINKLED TUBE BUNDLE

2015 ◽  
Vol 55 (5) ◽  
pp. 329 ◽  
Author(s):  
Petr Kracík ◽  
Jiří Pospíšil
Keyword(s):  
Flow Rate ◽  
Tube Bundle ◽  
Thin Liquid Film ◽  
Thermal Conditions ◽  
Tube Length ◽  
Falling Film ◽  
Constant Flow Rate ◽  
Physical Conditions ◽  
The Individual ◽  
Tube Pitch

Water flowing on a sprinkled tube bundle forms three basic modes: the Droplet mode (the liquid drips from one tube to another), the Jet mode (with an increasing flow rate, the droplets merge into a column) and the Membrane (Sheet) mode (with a further increase in the flow rate of the falling film liquid, the columns merge and create sheets between the tubes. With a sufficient flow rate, the sheets merge at this stage, and the tube bundle is completely covered by a thin liquid film). There are several factors influencing both the individual modes and the heat transfer. Beside the above-mentioned falling film liquid flow rate, these are for instance the tube diameters, the tube pitches in the tube bundle, or the physical conditions of the falling film liquid. This paper presents a summary of data measured at atmospheric pressure, with a tube bundle consisting of copper tubes of 12 millimetres in diameter, and with a studied tube length of one meter. The tubes are situated horizontally one above another at a pitch of 15 to 30 mm, and there is a distribution tube placed above them with water flowing through apertures of 1.0mm in diameter at a 9.2mm span. Two thermal conditions have been tested with all pitches: 15 °C to 40 °C and 15 °C to 45 °C. The temperature of the falling film liquid, which was heated during the flow through the exchanger, was 15 °C at the distribution tube input. The temperature of the heating liquid at the exchanger input, which had a constant flow rate of approx. 7.2. litres per minute, was 40 °C, or alternatively 45 °C.

scholarly journals Quantitative Monitoring of Dynamic Blood Flows Using Coflowing Laminar Streams in a Sensorless Approach

2021 ◽  
Vol 11 (16) ◽  
pp. 7260
Author(s):  
Yang Jun Kang
Keyword(s):  
Blood Flow ◽  
Flow Rate ◽  
Blood Viscosity ◽  
Measurement Errors ◽  
Present Method ◽  
Test Fluid ◽  
Constant Flow Rate ◽  
Rbc Aggregation ◽  
Sinusoidal Flow ◽  
Analytical Expressions

Determination of blood viscosity requires consistent measurement of blood flow rates, which leads to measurement errors and presents several issues when there are continuous changes in hematocrit changes. Instead of blood viscosity, a coflowing channel as a pressure sensor is adopted to quantify the dynamic flow of blood. Information on blood (i.e., hematocrit, flow rate, and viscosity) is not provided in advance. Using a discrete circuit model for the coflowing streams, the analytical expressions for four properties (i.e., pressure, shear stress, and two types of work) are then derived to quantify the flow of the test fluid. The analytical expressions are validated through numerical simulations. To demonstrate the method, the four properties are obtained using the present method by varying the flow patterns (i.e., constant flow rate or sinusoidal flow rate) as well as test fluids (i.e., glycerin solutions and blood). Thereafter, the present method is applied to quantify the dynamic flows of RBC aggregation-enhanced blood with a peristaltic pump, where any information regarding the blood is not specific. The experimental results indicate that the present method can quantify dynamic blood flow consistently, where hematocrit changes continuously over time.

scholarly journals New velocity map and mass-balance estimate of Mertz Glacier, East Antarctica, derived from Landsat sequential imagery

2003 ◽  
Vol 49 (167) ◽  
pp. 503-511 ◽  
Author(s):  
Etienne Berthier ◽  
Bruce Raup ◽  
Ted Scambos
Keyword(s):  
Velocity Field ◽  
Drainage Basin ◽  
Flow Speed ◽  
East Antarctica ◽  
Landsat Images ◽  
Mean Velocity ◽  
Speed Increase ◽  
Glacier System ◽  
Show Evidence ◽  
Basal Melting

AbstractAutomatic feature tracking on two Landsat images (acquired inJanuary 2000 and December 2001) generates a complete and accurate velocity field of Mertz Glacier, East Antarctica. This velocity field shows two main tributaries to the ice stream. Between the tributaries, a likely obstruction feature in the bedrock results in a slow-down of the flow. A third Landsat image, acquired in 1989 and combined with the 2000 image, permits the determination of the glacier mean velocity during the 1990s. Although some parts of the Mertz Glacier system show evidence of slight speed increase, we conclude that the Mertz flow speed is constant within our uncertainty (35 m a−1). Using this complete velocity field, new estimates of the ice discharge flux, 17.8 km3 a−1 (16.4 Gt a−1), and of the basal melting of the tongue, 11 m a−1 of ice, are given. Our results lead to an apparent imbalance of the drainage basin (ice discharge 3.5 km3 a−1 lower than the accumulation). Considering previous studies in the Mertz Glacier area, we then discuss the uncertainty of this imbalance and the problems with accumulation mapping for this region.

Оdrеđivаnjе brzinе struјаnjа vаzduhа u prаvоugаоnоm zаtvоrеnоm cevovodu korišćenjem metoda polja brzina

2021 ◽  
Vol 23 (2) ◽  
pp. 57-63
Author(s):  
Marija Lazarevikj ◽  
◽  
Valentino Stojkovski ◽  
Viktor Iliev
Keyword(s):  
Velocity Profile ◽  
Flow Rate ◽  
Air Flow ◽  
Displacement Transducer ◽  
Linear Displacement ◽  
Local Velocity ◽  
Air Flow Rate ◽  
Mean Velocity ◽  
Measured Velocity ◽  
Integration Techniques

In the technical practice, it is often necessary to measure or control the fluid flow rate in pipelines and channels. The velocity-area method requires a number of meters located at specified points in a suitable cross-section of closed conduits. Simultaneous measurements of local mean velocity with the meters are integrated over the gauging section to provide the discharge. In this paper, three approaches of this method are applied on a rectangular closed conduit to determine the air flow rate with integration techniques used to compute the discharge assume velocity distributions that closely approximate known laws, especially in the neighborhood of solid boundaries. For this purpose, meters for velocity were 7 Pitot tubes placed vertically in predefined measurement points covering the conduit height, and moved horizontally along the conduit width. The position of the Pitot tubes along the conduit width was monitored and controlled by a linear displacement transducer. Pressure is measured using digital sensors. The first technique for determination of air flow rate is on basis of fixed (stopping) measuring points across the conduit width as averaged values of local velocity, the second one is semi continual measurement of velocity profile by applying interpolation between the average local velocity on fixed (stopping) points and measured velocity in the movement between two positions, and the third is by continuously moving the Pitot tubes without stopping. The results of the three techniques are calculated and presented using different types of software. Considering the last technique, comparison of results is made applying different movement speeds of the Pitot tubes in order to examine their influence on the velocity profile.

scholarly journals Effect of the Flame Dome Depth and Improvement of the Pressure Loss in the Dump Diffuser

1998 ◽  
Author(s):  
Shinji Honami ◽  
Wataru Tsuboi ◽  
Takaaki Shizawa
Keyword(s):  
Velocity Profile ◽  
Reynolds Stress ◽  
Flow Rate ◽  
Pressure Loss ◽  
Total Pressure ◽  
Flow Behavior ◽  
Sudden Expansion ◽  
Mean Velocity ◽  
The Mean ◽  
Stress Profiles

This paper presents the effect of flame dome depth on the total pressure performance and flow behavior in a sudden expansion region of the combustor diffuser without flow entering the dome head. The mean velocity and turbulent Reynolds stress profiles in the sudden expansion region were measured by a Laser Doppler Velocitmetry (LDV) system. The experiments show that total pressure loss is increased, when flame dome depth is increased. Installation of an inclined combuster wall in the sudden expansion region is suggested from the viewpoint of a control of the reattaching flow. The inclined combustor wall is found to be effective in improvement of the diffuser performance. Better characteristics of the flow rate distribution into the branched channels are obtained in the inclined wall configuration, even if the distorted velocity profile is provided at the diffuser inlet.

scholarly journals Effect of gravity on aerosol dispersion and deposition in the human lung after periods of breath holding

2000 ◽  
Vol 89 (5) ◽  
pp. 1787-1792 ◽  
Author(s):  
Chantal Darquenne ◽  
Manuel Paiva ◽  
G. Kim Prisk
Keyword(s):  
Flow Rate ◽  
Turbulent Mixing ◽  
Direct Evidence ◽  
Human Lung ◽  
Hold Time ◽  
Aerosol Deposition ◽  
Breath Holding ◽  
Breath Hold ◽  
Constant Flow Rate ◽  
Aerosol Dispersion

To determine the extent of the role that gravity plays in dispersion and deposition during breath holds, we performed aerosol bolus inhalations of 1-μm-diameter particles followed by breath holds of various lengths on four subjects on the ground (1G) and during short periods of microgravity (μG). Boluses of ∼70 ml were inhaled to penetration volumes (Vp) of 150 and 500 ml, at a constant flow rate of ∼0.45 l/s. Aerosol concentration and flow rate were continuously measured at the mouth. Aerosol deposition and dispersion were calculated from these data. Deposition was independent of breath-hold time at both Vp in μG, whereas, in 1G, deposition increased with increasing breath hold time. At Vp = 150 ml, dispersion was similar at both gravity levels and increased with breath hold time. At Vp = 500 ml, dispersion in 1G was always significantly higher than in μG. The data provide direct evidence that gravitational sedimentation is the main mechanism of deposition and dispersion during breath holds. The data also suggest that cardiogenic mixing and turbulent mixing contribute to deposition and dispersion at shallow Vp.

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