Pressure Change and Gas Mixing Induced by Oscillations in a Closed System

1985 ◽  
Vol 107 (1) ◽  
pp. 68-76 ◽  
Author(s):  
D. Isabey ◽  
A. Harf ◽  
H. K. Chang
Keyword(s):  
Pressure Change ◽  
Resonance Phenomenon ◽  
High Frequency Oscillation ◽  
Rigid Sphere ◽  
Straight Tube ◽  
Closed Volume ◽  
Pressure Amplitude ◽  
Convective Mixing ◽  
Gas Compression ◽  
Small Tube

In an attempt to delineate some mechanical behaviors found in branching airways, pressure transmission, gas motion, and mixing were studied during high-frequency oscillation (HFO) in an idealized system consisting of a large straight tube and a rigid sphere linked together by a small straight tube. Depending on the frequency f, and on the unsteadiness dimensionless parameter α, pressure amplitude in the large tube is either strongly attenuated or amplified in the sphere. This finding may provide a theoretical basis for the pressure resonance phenomenon observed in the lung by previous investigators. Gas compression in the closed volume causes convective mixing throughout the system. The measured dispersion was found to be proportional to f(VT/A)2, in agreement with a recent report. However, bulk convective mixing was sufficient to explain the dispersion for oscillatory volumes (VT) as small as 80 percent of the small tube volume, as has been previously suggested.

Gas Dispersion in a Model Pulmonary Bifurcation During Oscillatory Flow

1997 ◽  
Vol 119 (3) ◽  
pp. 309-316 ◽  
Author(s):  
M. Nishida ◽  
Y. Inaba ◽  
K. Tanishita
Keyword(s):  
Velocity Profile ◽  
Axial Velocity ◽  
Oscillatory Flow ◽  
Gas Transport ◽  
Main Bronchus ◽  
High Frequency Oscillation ◽  
Laser Doppler Velocimeter ◽  
Straight Tube ◽  
Gas Dispersion ◽  
Axial Velocity Profile

In order to clarify the gas transport process in high-frequency oscillation, we measured the axial velocity profile and the axial effective diffusivity in a single asymmetric bifurcating tube, based on the Horsfield airway model, with sinusoidally oscillatory flow. The axial velocity profiles were measured using a laser-Doppler velocimeter, and the effective diffusivities were evaluated using a simple bolus injection method. The axial velocity profile was found to be nonuniform, promoting axial gas dispersion by the spread of the concentration profile and lateral mixing. The geometric asymmetry of the bifurcation was responsible for the difference in gas transport between the main bronchi. The axial gas transport in the left main bronchus was 2.3 times as large as that of the straight tube, whereas the gas transport in the right main bronchus was slightly larger than that of the straight tube. Thus localized variation in gas transport characterized the heterogeneous respiratory function of the lung.

COMPARATIVE ANALYSIS OF NUMERICAL SIMULATION OF NATURAL CONVECTION

2016 ◽  
Vol 6 (2) ◽  
pp. 124-128
Author(s):  
Maksim N. NIKITIN
Keyword(s):  
Numerical Simulation ◽  
Comparative Analysis ◽  
Natural Convection ◽  
Turbulence Models ◽  
Computational Grid ◽  
Closed Volume ◽  
Central Section ◽  
Ansys Fluent ◽  
Wall Functions ◽  
Convective Mixing

It is studied numerical simulation conditions using software ANSYS Fluent, Code Saturne and OpenFOAM using the example of the problem of natural convection of air in the closed volume in the presence of the heating element. A comparative analysis of packets on the basis of three turbulence models (k-, k- SST и LES) is given, an assessment of the adequacy of the results is shown. As a benchmark experimental data on the temperature profi le in the central section are used. Assumptions about the destructive factors that reduce the accuracy of the decision, partly confi rms the results of a comparative analysis of the convective mixing intensity, are made. Combined turbulence model k- SST is used to determine the eff ectiveness of the implementation of the wall functions in packages Code Saturne and OpenFOAM to the computational grid with a variable dimensionless distance in the range of 1 y + 5 and 10 y + 50.

The Effect of Upstream Edge Geometry on the Acoustic Resonance Excitation in Shallow Rectangular Cavities

2014 ◽  
Author(s):  
Ahmed Omer ◽  
Nadim Arafa ◽  
Atef Mohany ◽  
Marwan Hassan
Keyword(s):  
Flow Instability ◽  
Acoustic Resonance ◽  
Resonance Mode ◽  
Resonance Phenomenon ◽  
Resonance Excitation ◽  
Base Case ◽  
Pressure Amplitude ◽  
Cavity Depth ◽  
Edge Geometry ◽  
Aspect Ratios

The flow-excited acoustic resonance phenomenon is created when the flow instability oscillations are coupled with one of the acoustic modes, which in turn generates acute noise problems and/or excessive vibrations. In this study, the effect of the upstream edge geometry on attenuating these undesirable effects is investigated experimentally for flows over shallow rectangular cavity with two different aspect ratios of L/D = 1 and 1.67, where L is the cavity length and D is the cavity depth, and for Mach number less than 0.5. The acoustic resonance modes of the cavity are self-excited. Twenty four different upstream cavity edges are investigated in this study; including round edges, chamfered edges, vortex generators and spoilers with different sizes and configurations. The acoustic pressure is measured with a flush-mounted microphone on the cavity floor and the velocity fluctuation of the separated shear layer before the onset of acoustic resonance is measured with a hot-wire probe. The results for each upstream cavity edge are compared with the base case when square cavity edge is used. It is observed that when chamfered edges are used, the amplitude of the first acoustic resonance mode is highly intensified with values reaching around 5000 Pa (compared to 2000 Pa for the base case) and a clear shift in its onset of resonance to higher flow velocities is observed. Similar trend is observed when round edges are used. The amplitude of the generated pressure of the first acoustic resonance mode is amplified with values exceeding 4000 Pa and a delay in its onset of acoustic resonance is observed as well. Most of the spoiler edges are found to be effective in suppressing the pressure amplitude of the excited acoustic resonance. However, the performance of each spoiler depends on its specific geometry (i.e. thickness, height, and angle) relative to the cavity aspect ratio. A summary of the results is presented in this paper.

scholarly journals Simulation of Infrasound Pistonphone

2020 ◽  
Vol 32 (5) ◽  
pp. 181-198
Author(s):  
Dmitrii Vital`Evich Golovin
Keyword(s):  
Fundamental Frequency ◽  
Sound Pressure ◽  
Control Point ◽  
Tuning Parameter ◽  
Polytropic Index ◽  
Heat Conducting ◽  
Closed Volume ◽  
Pressure Amplitude ◽  
The Stability ◽  
Semi Empirical

There are presented the results of numerical simulation of an applied acoustic problem – modeling of gas processes occurring in the measuring chamber of the infrasound pistonphone 3202 at different frequencies of piston oscillation (0.1 – 1000 Hz) and characterized by extremely small Mach numbers (9.1·10-7÷9.1·10-3). The simulation was performed using quasi-gas-dynamic (QGD) and quasi-hydrodynamic (QHD) equations of a viscous compressible heat-conducting gas with the use of a time-explicit difference scheme, all spatial derivatives was approximated by central differences. It is shown that QGD and QHD models can be used for a simulation of applied acoustics and, in particular, to the simulation of infrasonic pistonphone: the stability limits of the QGD and QHD algorithms in this problem were determined, the dependence of sound pressure on the tuning parameter α is investigated and it is shown that this dependence is quite small. The spectra of sound pressure at the control point calculated by QGD and QHD are given, their dependence on the tuning parameter α is shown, both models equally predict the value of the sound pressure amplitude at the fundamental frequency oscillations. At the end of the article, the sound pressure at the control point at the fundamental frequency oscillations obtained by using QGD and QHD is compared with the values calculated by using semi-empirical formula of sound pressure at closed volume for a case of small oscillations using the polytropic index obtained by Henry Gerber instead of the adiabatic coefficient.

Augmentation of Axial Dispersion by Intermittent Oscillatory Flow

1998 ◽  
Vol 120 (3) ◽  
pp. 405-415 ◽  
Author(s):  
G. Tanaka ◽  
Y. Ueda ◽  
K. Tanishita
Keyword(s):  
Stationary Phase ◽  
High Frequency ◽  
Oscillatory Flow ◽  
Effective Diffusivity ◽  
Axial Dispersion ◽  
High Frequency Oscillation ◽  
Gas Transfer ◽  
Straight Tube ◽  
Gas Dispersion ◽  
Molecular Diffusivity

The efficiency of axial gas dispersion during ventilation with high-frequency oscillation (HFO) is improved by manipulating the oscillatory flow waveform such that intermittent oscillatory flow occurs. We therefore measured the velocity profiles and effective axial gas diffusivity during intermittent oscillatory flow in a straight tube to verify the intermittency augmentation effect on axial gas transfer. The effective diffusivity was dependent on the flow patterns and significantly increased with an increase in the duration of the stationary phase. It was also found that the ratio of effective diffusivity to molecular diffusivity is two times greater than that in sinusoidal oscillatory flow. Moreover, turbulence during deceleration or at the beginning of the stationary phase further augments axial dispersion, with the effective diffusivity being over three times as large, thereby proving that the use of intermittent oscillatory flow effectively augments axial dispersion for ventilation with HFO.

Airway resistance due to alveolar gas compression measured by barometric plethysmography in mice

2005 ◽  
Vol 98 (6) ◽  
pp. 2204-2218 ◽  
Author(s):  
Stephen J. Lai-Fook ◽  
Yih-Loong Lai
Keyword(s):  
Body Temperature ◽  
Room Temperature ◽  
Airway Resistance ◽  
Pressure Amplitude ◽  
Sinusoidal Analysis ◽  
Time Curve ◽  
Gas Compression ◽  
Pressure Time ◽  
Residual Capacity ◽  
Compression Effects

We developed a method for measuring airway resistance (Raw) in mice that does not require a measurement of airway flow. An analysis of Raw induced by alveolar gas compression showed the following relationship for an animal breathing spontaneously in a closed box: Raw = AbtVb/[Vt (Ve + 0.5Vt)]. Here Abt is the area under the box pressure-time curve during inspiration or expiration, Vb is box volume, Vt is tidal volume, and Ve is functional residual capacity (FRC). In anesthetized and conscious unrestrained mice, from experiments with both room temperature box air and body temperature humidified box air, the contributions of gas compression to the box pressure amplitude were 15 and 31% of those due to the temperature-humidity difference between box and alveolar gas. We corrected the measured Abt and Vt for temperature-humidity and gas compression effects, respectively, using a sinusoidal analysis. In anesthetized mice, Raw averaged 4.3 cmH2O·ml−1·s, fourfold greater than pulmonary resistance measured by conventional methods. In conscious mice with an assumed FRC equal to that measured in the anesthetized mice, the corrected Raw at room temperature averaged 1.9 cmH2O·ml−1·s. In both conscious mice and anesthetized mice, exposure to aerosolized methacholine with room temperature box air significantly increased Raw by around eightfold. Here we assumed that in the conscious mice both Vt and FRC remained constant. In both conscious and anesthetized mice, body temperature humidified box air reduced the methacholine-induced increase in Raw observed at room temperature. The method using the increase in Abt with bronchoconstriction provides a conservative estimate for the increase in Raw in conscious mice.

Intrauterine pressure wave-form characteristics of spontaneous first stage labor

1975 ◽  
Vol 38 (3) ◽  
pp. 443-448 ◽  
Author(s):  
J. Seitchik ◽  
M. L. Chatkoff
Keyword(s):  
Pressure Wave ◽  
Total Duration ◽  
Pressure Change ◽  
Wave Form ◽  
Pressure Amplitude ◽  
Mean Values ◽  
Intrauterine Pressure ◽  
Start Up ◽  
Maximal Pressure ◽  
The Relationship

Intrauterine pressure wave-form parameters were measured in 827 contractions obtained from 26 patients in spontaneous labor. The coefficients of correlation between the maximal and minimal rates of pressure change and the maximal pressure amplitude were 0.78 and 0.63, respectively, and greater than or equal to 0.70 in 22/26 patients. Contractions partitioned into decile statistical groups of the pressure amplitude and both maximal and minimal rates. A linear relationship between these parameters has therefore been established. Contractions of greater amplitude tend to be longer, but the relationship between duration and amplitude is nonlinear with a limiting maximum contraction time. The duration of the midportion of the pressure wave appears invariate with respect to wave amplitude and only start-up and termination times increase with increasing amplitude. Mean values and standard deviations of the maximal amplitude (40.4 +/- 16.9mmHg). the maximal (2.4 +/- 0.9 mmHg/s) and minimal (-2.1+/- 0.9 mmHg/s)rates of pressure change, and the total duration of contractions (68.6 +/- 17.8s) were determined.

About nonlinear nonspherical oscillations of a gas bubble in an incompressible ideal liquid

2003 ◽  
Vol 3 ◽  
pp. 178-194
Author(s):  
M.A. Ilgamov ◽  
E.Sh. Nasibullaeva ◽  
D.V. Kondtratyev
Keyword(s):  
Parametric Analysis ◽  
Applied Pressure ◽  
Pressure Change ◽  
Ideal Liquid ◽  
System Of Equations ◽  
Pressure Amplitude ◽  
Gas Bubble ◽  
Initial Radius ◽  
Initial Deviation ◽  
Incompressible Ideal Fluid

A comparative parametric analysis of a system of equations describing the nonspherical oscillations of a gas bubble in an incompressible ideal fluid is performed. The terms up to a second order of smallness in the amplitude of the surface perturbation are taking into account. Numerical calculations of this system of equations for various parameters (initial deviation from the sphere, pressure amplitude, initial radius) and for various laws of the applied pressure change are carried out.

Aerosol bolus dispersion and convective mixing in human and dog lungs and physical models

1992 ◽  
Vol 73 (3) ◽  
pp. 862-873 ◽  
Author(s):  
F. S. Rosenthal ◽  
J. D. Blanchard ◽  
P. J. Anderson
Keyword(s):  
Flow Rate ◽  
Vital Capacity ◽  
Human Subjects ◽  
Packed Bed ◽  
Physical Models ◽  
Straight Tube ◽  
Particle Mobility ◽  
Convective Mixing ◽  
Artificial Larynx ◽  
Aerosol Dispersion

The dispersion of aerosol boluses in the lung is a probe for convective mixing and has been proposed as a marker for abnormal lung function. To better understand the factors underlying this phenomenon, aerosol dispersion was compared in human subjects, dogs, and various physical models. In all systems, dispersion increased with the volumetric penetration of the aerosol bolus. The rate of this increase was 83% greater in humans compared with dogs. Dispersion in dogs was close to that in a packed bed with beads of 2.5 mm. Aerosol dispersion decreased with increasing flow rate in human subjects. An artificial larynx inserted into the straight tube caused a 33% increase in dispersion. In humans, aerosol dispersion was significantly correlated with forced expired flow between 25 and 75% of vital capacity. A 2-s pause between inspiration and expiration increased dispersion 23–58% in three isolated dog lungs but did not affect dispersion in the packed bed. The data suggest that lung geometry, flow rate, particle mobility, and the larynx all significantly affect aerosol dispersion by influencing the reversibility of aerosol transport between inspiration and expiration.

Alveolar ventilation during high-frequency oscillation: core dead space concept

1984 ◽  
Vol 56 (3) ◽  
pp. 700-707 ◽  
Author(s):  
D. Isabey ◽  
A. Harf ◽  
H. K. Chang
Keyword(s):  
Tidal Volume ◽  
Dead Space ◽  
High Frequency ◽  
Alveolar Ventilation ◽  
High Frequency Oscillation ◽  
High Frequency Ventilation ◽  
Frequency Oscillation ◽  
Simple Physical Model ◽  
Small Tube ◽  
The Dead

To assess the role of direct alveolar ventilation during high-frequency ventilation, we studied convective gas mixing during high-frequency oscillation with tidal volumes close to the dead space volume in a simple physical model. A main conduit representing a large airway was connected with a rigid sphere (V = 77, 517, and 1,719 cm3) by a small circular tube (d = 0.3 and 0.5 cm; L = 5, 10, and 20 cm). The efficiency of sinusoidal oscillations (f = 5, 20, and 40 Hz) applied at one end of the main conduit was assessed from the washout of a CO2 mixture from the sphere; to flush CO2 from the main fluid line, a constant flow of air was used. The decay in CO2 concentration measured in the sphere was exponential and therefore characterized by a measured time constant (tau m). Taking the small tube volume as the ventilatory dead space (VD), an effective tidal volume (VT*) was computed from tau m and compared with the tidal volume (VT) obtained separately from the pressure variation in the sphere. The discrepancy between these two tidal volumes has been found to be uniquely dependent on the ratio VT/VD within the range of VT/VD studied (0.5–2.2). For VT/VD less than 1.2, VT* was larger than VT, indicating that the conventional concept of alveolar ventilation does not apply. From the partition of the oscillatory flow in the small tube into two regions, the core and the unsteady boundary layer, we theoretically computed the proportions of the sinusoidal flow (or tidal volume) and the dead space for each region.(ABSTRACT TRUNCATED AT 250 WORDS)

Sign in / Sign up

Export Citation Format

Share Document