Effects of surface tension and viscosity on airway reopening

1990 ◽  
Vol 69 (1) ◽  
pp. 74-85 ◽  
Author(s):  
D. P. Gaver ◽  
R. W. Samsel ◽  
J. Solway
Keyword(s):  
Surface Tension ◽  
Fluid Viscosity ◽  
Opening Pressure ◽  
Viscous Forces ◽  
Considerable Portion ◽  
Airway Opening ◽  
Wall Compliance ◽  
Large Opening ◽  
Surface Tension Forces ◽  
The Relationship

We studied airway opening in a benchtop model intended to mimic bronchial walls held in apposition by airway lining fluid. We measured the relationship between the airway opening velocity (U) and the applied airway opening pressure in thin-walled polyethylene tubes of different radii (R) using lining fluids of different surface tensions (gamma) and viscosities (mu). Axial wall tension (T) was applied to modify the apparent wall compliance characteristics, and the lining film thickness (H) was varied. Increasing mu or gamma or decreasing R or T led to an increase in the airway opening pressures. The effect of H depended on T: when T was small, opening pressures increased slightly as H was decreased; when T was large, opening pressure was independent of H. Using dimensional analysis, we found that the relative importance of viscous and surface tension forces depends on the capillary number (Ca = microU/gamma). When Ca is small, the opening pressure is approximately 8 gamma/R and acts as an apparent “yield pressure” that must be exceeded before airway opening can begin. When Ca is large (Ca greater than 0.5), viscous forces add appreciably to the overall opening pressures. Based on these results, predictions of airway opening times suggest that airway closure can persist through a considerable portion of inspiration when lining fluid viscosity or surface tension are elevated.

Measurement of pleural pressure at low and high frequencies in normal rabbits

1987 ◽  
Vol 63 (3) ◽  
pp. 1142-1146 ◽  
Author(s):  
D. A. Chartrand ◽  
T. H. Ye ◽  
J. M. Maarek ◽  
H. K. Chang
Keyword(s):  
Body Surface ◽  
Pressure Transducer ◽  
Esophageal Pressure ◽  
Pleural Pressure ◽  
Opening Pressure ◽  
High Frequencies ◽  
Occlusion Test ◽  
Airway Opening ◽  
Catheter Tip ◽  
The Relationship

In eight tracheotomized adult rabbits placed in the supine position, we employed a catheter-tip piezoresistive pressure transducer to measure esophageal pressure (Pes) and assessed the validity of taking the changes in Pes to be the changes in pleural pressure (Ppl). We applied an occlusion test in which the tracheal cannula was occluded during either spontaneous inspiratory efforts or body surface oscillations ranging from 3 to 50 Hz. The relationship between Pes and airway opening pressure (Pao) was recorded. In all instances, the changes in Pes and Pao were virtually identical in both amplitude and phase. We conclude that, as evaluated by the occlusion test, a catheter-tip pressure transducer placed in the esophagus of rabbits can give adequate estimation of local pleural changes up to at least 50 Hz.

Stokes flow past bubbles and drops partially coated with thin films. Part 2. Thin films with internal circulation – a perturbation solution

1983 ◽  
Vol 132 ◽  
pp. 295-318 ◽  
Author(s):  
Robert E. Johnson ◽  
S. S. Sadhal
Keyword(s):  
Thin Films ◽  
Fluid Layer ◽  
Cell Structure ◽  
Creeping Flow ◽  
Immiscible Fluid ◽  
Fluid Viscosity ◽  
Perturbation Scheme ◽  
Bulk Fluid ◽  
Viscous Forces ◽  
Surface Tension Forces

In the present study we examine the steady axisymmetric creeping flow due to the motion of a liquid drop or a bubble which is partially covered by a thin immiscible fluid layer or film. The analysis is based on the assumption that surface-tension forces are large compared with viscous forces which deform the drop, and that the circulation in the film is weak. The latter assumption is satisfied provided that the film-fluid viscosity is not too small. A perturbation scheme based on the thinness of the fluid layer is used to construct the solution.One of the principal results is an expression for the drag force on the complex drop. We also find that the extent to which the drop or bubble is covered the film has a maximum value depending on the magnitude of the driving force on the film. In addition, we find the rather interesting result that when the ratio of the primary drop viscosity and bulk fluid viscosity is greater than ½, the circulation within the film may have a double-cell structure.

Stokes flow past a sphere coated with a thin fluid film

1981 ◽  
Vol 110 ◽  
pp. 217-238 ◽  
Author(s):  
Robert Edward Johnson
Keyword(s):  
Surface Tension ◽  
Contact Angle ◽  
Stokes Flow ◽  
Fluid Layer ◽  
Fluid Film ◽  
Fluid Viscosity ◽  
Flow Past ◽  
Surface Tension Forces ◽  
Force Equilibrium ◽  
Flow Past A Sphere

The present study examines the steady, axisymmetric Stokes flow past a sphere coated with a thin, immiscible fluid layer. Inertial effects are neglected for both the outer fluid and the fluid film, and surface tension forces are assumed large compared with the viscous forces which deform the fluid film. Furthermore, the present analysis assumes that the mechanism driving the fluid circulation within the film is not too large. From force equilibrium on the film we find that a steady fluid film can only partially cover the sphere, i.e. the film must be held to the sphere by surface tension forces at the contact line. The extent of the sphere covered by the film is specified, in terms of the solid–fluid contact angle, by the condition of global force equilibrium on the fluid film.Using a perturbation scheme based on the thinness of the fluid layer the solution to the flow field is obtained analytically, except for the fluid-film profile (i.e. the fluid–fluid interface) which requires numerical calculations. One of the principal results is an expression for the drag force on the fluid-coated particle. In particular, we find that the drag on a sphere is reduced by the presence of a fluid coating when the ratio of the film fluid viscosity to the surrounding fluid viscosity is less than ¼. Detailed numerical computations are conducted for a few typical cases. The calculations show that a film of prescribed areal extent, i.e. specified contact angle, is only possible when the magnitude of the driving force on the film is below some maximum value. A simple experiment was also performed, and photographs, which qualitatively illustrate the fundamental fluid-film configurations predicted by the theory, are presented.

Mean airway opening pressure as an index of inspiratory muscle task intensity

1986 ◽  
Vol 60 (1) ◽  
pp. 304-306 ◽  
Author(s):  
F. D. McCool ◽  
D. E. Leith
Keyword(s):  
Endotracheal Tube ◽  
Inspiratory Muscle ◽  
Muscle Training ◽  
Opening Pressure ◽  
Mean Values ◽  
Time Integral ◽  
Pressure Time ◽  
Airway Opening ◽  
Inspiratory Resistance ◽  
The Relationship

The relationship between mean values of pressure (pressure-time integral including both inspiration and expiration) measured at the airway opening (Pao) and in the esophagus (Pes) is described for ventilation on a variety of external inspiratory resistances. Pao/Pes was 0.85 or greater when the external inspiratory resistance was a 4.0-mm or smaller endotracheal tube adaptor. Additionally, Pao can be easily and accurately measured by a slowly responding mechanical manometer. This device is simple in design, unpowered, inexpensive, and can be used outside the laboratory as part of an inspiratory muscle training program.

Pulmonary Airway Reopening: Effects of Non-Newtonian Fluid Viscosity

1997 ◽  
Vol 119 (3) ◽  
pp. 298-308 ◽  
Author(s):  
H. T. Low ◽  
Y. T. Chew ◽  
C. W. Zhou
Keyword(s):  
Surface Tension ◽  
Film Thickness ◽  
Yield Stress ◽  
Newtonian Fluid ◽  
Shear Thinning ◽  
Fluid Viscosity ◽  
Polyethylene Tube ◽  
Airway Reopening ◽  
Airway Opening ◽  
Fluid Film Thickness

This paper considers the effects of non-Newtonian lining-fluid viscosity, particularly shear thinning and yield stress, on the reopening of the airways. The airway was simulated by a very thin, circular polyethylene tube, which collapsed into a ribbonlike configuration. The non-Newtonian fluid viscosity was described by the powerlaw and Herschel-Buckley models. The speed of airway opening was determined under various opening pressures. These results were collapsed into dimensionless pressure-velocity relationships, based on an assumed shear rate γ˙ = U/(0.5 H), where U and H are the opening velocity and fluid film thickness, respectively. It was found that yield stress, like surface tension, increases the yield pressure and opening time. However, shear thinning reduces the opening time. An increased film thickness of the non-Newtonian lining fluid generally impedes airway reopening; a higher pressure is needed to initiate the airway reopening and a longer time is required to complete the opening process.

Airway resistance measured in liquid-trapped guinea pig lungs by micropuncture

1988 ◽  
Vol 65 (6) ◽  
pp. 2446-2452
Author(s):  
Y. L. Lai ◽  
S. Ganesan ◽  
S. J. Lai-Fook
Keyword(s):  
Guinea Pig ◽  
Airway Resistance ◽  
Close Association ◽  
Maximum Volume ◽  
Liquid Pressure ◽  
Opening Pressure ◽  
Airway Narrowing ◽  
Airway Opening ◽  
Liquid Trapping ◽  
The Relationship

We studied the relationship between bronchoconstriction and the degree of trapping in saline-filled lungs isolated from guinea pigs postmortem after rapid exsanguination. Airway resistance was measured in nine lungs, and in five lungs the site of airway narrowing was located radiographically. Animals were anesthetized with pentobarbital sodium, degassed by O2 absorption, then rapidly exsanguinated when O2 absorption was almost complete. Liquid trapping was assessed from the pressure-volume behaviour measured in saline-filled lungs. During a slow deflation from maximum volume, alveolar liquid pressure (Palv) was measured by the micropipette-servonulling method, airway opening pressure (Pao) by a strain gauge, and flow rate (Q) by weighing a reservoir connected to the airway. Airway resistance (Raw) was calculated at different lung volumes from the relationship: Raw = (Palv-Pao)/Q. In untreated lungs, Raw and fluid trapping were relatively high, and severe bronchoconstriction occurred at the level of the main stem and lobar bronchi. Nifedipine infusion reduced Raw 40-fold and decreased trapping. Raw was further reduced 10-fold and fluid trapping was minimal in lungs pretreated with nifedipine before exsanguination. Results suggest a close association between bronchoconstriction and fluid trapping in guinea pig lungs.

On convection cells induced by surface tension

1958 ◽  
Vol 4 (5) ◽  
pp. 489-500 ◽  
Author(s):  
J. R. A. Pearson
Keyword(s):  
Surface Tension ◽  
Convective Motion ◽  
Critical Value ◽  
Dimensionless Number ◽  
Temperature Variations ◽  
Viscous Forces ◽  
Buoyancy Forces ◽  
Disturbance Analysis ◽  
Paint Films ◽  
Surface Tension Forces

A mechanism is proposed by which cellular convective motion of the type observed by H. Bénard, which hitherto has been attributed to the action of buoyancy forces, can also be induced by surface tension forces. Thus when a thin layer of fluid is heated from below, the temperature gradient is such that small variations in the surface temperature lead to surface tractions which cause the fluid to flow and thereby tend to maintain the original temperature variations. A small disturbance analysis, analogous to that carried out by Rayleigh and others for unstable density gradients, leads to a dimensionless number B which expresses the ratio of surface tension to viscous forces, and which must attain a certain minimum critical value for instability to occur. The results obtained are then applied to the original cells described by Bénard, and to the case of drying paint films. It is concluded that surface tension forces are responsible for cellular motion in many such cases where the criteria given in terms of buoyancy forces would not allow of instability.

Analysis of the Opening Characteristic of Hydraulic Control One-Way Valve in Vertical Hydraulic Cylinder Balance Circuits

2013 ◽  
Vol 318 ◽  
pp. 15-20 ◽  
Author(s):  
Pei Qun Su ◽  
Zhi Hui Deng
Keyword(s):  
Structural Parameters ◽  
Hydraulic Cylinder ◽  
Necessary Condition ◽  
Speed Ratio ◽  
Hydraulic Control ◽  
Opening Pressure ◽  
Large Opening ◽  
The One ◽  
Relationship Of ◽  
The Relationship

Hydraulic control one-way valve as the retaining element of vertical hydraulic cylinder, often is due to improper application to produce large opening pressure, not unlocking, vibration, noise etc.fault. This paper analyses two vertical hydraulic balance circuit, one makes use of the one-way throttle valve and another is not,calculates the necessary condition and opening pressure of hydraulic control one-way valve reverse opening, obtains the opening characteristic of hydraulic control one-way valve in vertical balancing circuit, acquires the relationship of the reverse opening pressure with hydraulic cylinder balance pressure, hydraulic cylinder speed ratio, hydraulic control one-way valve structural parameters. Lastly, how to correctly use the hydraulic control one-way valve is discussed in the vertical hydraulic cylinder balanced circuit.

INFLUENCE OF SURFACE TENSION FORCES ON FILMWISE CONDENSATION INTENSITY

2016 ◽  
Vol 7 (1-2) ◽  
pp. 93-102
Author(s):  
Vasily Buz ◽  
Konstantin Goncharov ◽  
Henry F. Smirnov
Keyword(s):  
Surface Tension ◽  
Surface Tension Forces

scholarly journals Influence of Eccentricity and Angular Velocity on Force Effects on Rotor of Magnetorheological Damper

2018 ◽  
Vol 180 ◽  
pp. 02091
Author(s):  
Dominik Šedivý ◽  
Petr Ferfecki ◽  
Simona Fialová
Keyword(s):  
Magnetic Induction ◽  
Magnetorheological Damper ◽  
Squeeze Film ◽  
Fluid Viscosity ◽  
Squeeze Film Damper ◽  
Viscous Forces ◽  
Angular Velocities ◽  
Volume Method ◽  
Gap Width ◽  
Made In

This article presents the evaluation of force effects on squeeze film damper rotor. The rotor is placed eccentrically and its motion is translate-circular. The amplitude of rotor motion is smaller than its initial eccentricity. The force effects are calculated from pressure and viscous forces which were measured by using computational modeling. Damper was filled with magnetorheological fluid. Viscosity of this non-Newtonian fluid is given using Bingham rheology model. Yield stress is not constant and it is a function of magnetic induction which is described by many variables. The most important variables of magnetic induction are electric current and gap width between rotor and stator. The simulations were made in finite volume method based solver. The motion of the inner ring of squeeze film damper was carried out by dynamic mesh. Numerical solution was solved for five different initial eccentricities and angular velocities of rotor motion.

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