Numerical Modeling of Steady Inspiratory Airflow Through a Three-Generation Model of the Human Central Airways

1997 ◽  
Vol 119 (1) ◽  
pp. 59-65 ◽  
Author(s):  
F. Wilquem ◽  
G. Degrez
Keyword(s):  
Flow Behavior ◽  
Flow Distribution ◽  
Reynolds Numbers ◽  
Experimental Investigations ◽  
Generation Model ◽  
Kirchhoff’S Laws ◽  
Flow Configurations ◽  
Lateral Branches ◽  
Moody Diagram ◽  
Good Agreement

Two-dimensional steady inspiratory airflow through a three-generation model of the human central airways is numerically investigated, with dimensions corresponding to those encountered in the fifth to seventh generations of the Weibel’s model. Wall curvatures are added at the outer walls of the junctions for physiological purposes. Computations are carried out for Reynolds numbers in the mother branch ranging from 200 to 1200, which correspond to mouth air breathing at flow rates ranging from 0.27 to 1.63 liters per second. The difficulty of generating grids in a so complex configuration is overcome using a nonoverlapping multiblock technique. Simulations demonstrate the existence of separation regions whose number, location, and size strongly depend on the Reynolds number. Consequently, four different flow configurations are detected. Velocity profiles downstream of the bifurcations are shown to be highly skewed, thus leading to an important unbalance in the flow distribution between the medial and lateral branches of the model. These results confirm the observations of Snyder et al. and Tsuda et al. and suggest that a resistance model of flow partitioning based on Kirchhoff’s laws is inadequate to simulate the flow behavior accurately within the airways. When plotted in a Moody diagram, airway resistance throughout the model is shown to fit with a linear relation of slope −0.61. This is qualitatively in good agreement with the experimental investigations of Pedley et al. and Slutsky et al.

Effect of Manifold Design on Flow Distribution in Parallel Micro-Channels

2003 ◽  
Author(s):  
Ralph L. Webb
Keyword(s):  
Flow Distribution ◽  
Reynolds Numbers ◽  
Published Data ◽  
Micro Electro Mechanical Systems ◽  
Micro Channels ◽  
Significant Disagreement ◽  
Manufacturing Tolerances ◽  
Header Design ◽  
Laminar And Turbulent Regimes ◽  
Good Agreement

Gas or liquid flow in multiple, parallel micro-channels is of interest for Micro-Electro-Mechanical Systems (MEMS) cooling applications. The published data for friction in 10-to-400μm hydraulic diameter, single micro-channels show good agreement with the conventional equations in the laminar and turbulent regimes. However, investigators of flow in multiple, parallel micro-channels in the same range of channel sizes report significantly different results. They report significant disagreement with the conventional equations and argue that transition occurs at Reynolds numbers as small as 200, dependent on the channel shape. This paper proposes that the apparent discrepancies of friction in multiple micro-channels can be attributed to flow mal-distribution. Flow mal-distribution is expected in multi-channels, because of manufacturing tolerances and poor manifold design. It can be minimized by proper header design and better manufacturing tolerances.

scholarly journals Influence of wall waviness on friction and pressure drop in channels

1981 ◽  
Vol 4 (4) ◽  
pp. 805-818 ◽  
Author(s):  
K. Vajravelu ◽  
Ali H. Nayfeh
Keyword(s):  
Pressure Drop ◽  
Flow Behavior ◽  
Reynolds Numbers ◽  
Wavy Wall ◽  
Governing Equations ◽  
Short Waves ◽  
Gradient Parameter ◽  
Arbitrary Amplitude ◽  
Wavy Channels ◽  
Good Agreement

An attention has been given to investigate the flow behavior of an incompressible viscous fluid confined in horizontal wavy channels and set in motion due to the movement of the upper wall and the pressure differences. The governing equations have been solved analytically as well as numerically subject to the relevant boundary conditions by assuming that the solution consists of two parts: a mean part and a disturbance or perturbed part. For small and moderate Reynolds numbers, the analytical solution for the perturbed part has been found to be in good agreement with the numerical one. The effects of Reynolds number, the pressure gradient parameter, and the undulation wavenumber on friction and pressure drop are found to be quite significant. In addition to the flow behavior for both long and short waves and for large Reynolds numbers, the effect of the wall waviness on friction and pressure drop has been examined for any arbitrary amplitude of the wavy wall.

scholarly journals EXPERIMENTAL AND NUMERICAL RESEARCH ON FLOW IN THE LAST STAGE OF 1090MW STEAM TURBINE

2018 ◽  
Vol 20 ◽  
pp. 43-50
Author(s):  
Michal Hoznedl ◽  
Kamil Sedlák
Keyword(s):  
Steam Turbine ◽  
Nuclear Power ◽  
Flow Behavior ◽  
Reynolds Numbers ◽  
Exhaust Hood ◽  
Cfd Simulations ◽  
Flow Parameters ◽  
Numerical Research ◽  
Last Stage ◽  
Good Agreement

The paper deals with experimental and numerical research in the last stage of real 1090MW steam turbine with the last steel blade length 1220mm placed in nuclear power station. The last stage was equipped with twelve static pressure taps. It was also possible to probe in two planes - before and behind the last stage using pneumatic or optical probes. A number of last stage flow parameters were determined at the root and tip wall for nominal turbine output. Among those parameters are static pressures, Mach and Reynolds numbers, last stage reactions and steam wetness. All the directly measured and evaluated flow parameters are taken from locally measured points and that is why even 3D CFD calculation of the whole system - last stage, diffuser and exhaust hood was implemented. Measured and calculated parameters are compared. Especially static pressures are in very good agreement; the only steam wetness has bigger difference due to different measurement position. Locally measured values are enough to estimate the flow behavior of the last stage. On the other hand, the CFD simulations with well determined boundary conditions, meshes and geometry and is effective tool to simulate even very complicated flow structures in the last stage and exhaust hood.

Flow Distribution Manifolds

1976 ◽  
Vol 98 (4) ◽  
pp. 654-665 ◽  
Author(s):  
R. A. Bajura ◽  
E. H. Jones
Keyword(s):  
Flow Rate ◽  
Distribution Systems ◽  
Flow Distribution ◽  
Nonlinear Ordinary Differential Equation ◽  
Flow Equation ◽  
Experimental Results ◽  
General Application ◽  
Lateral Branches ◽  
Flow Resistances ◽  
Good Agreement

Flow distribution in the lateral branches of dividing, combining, reverse, and parallel flow manifold systems is studied both analytically and experimentally. Predictions for the flow rates and pressures in the headers of any of the above four basic manifold configurations are obtained from the solution of two first order differential equations involving the flow rate and the pressure difference across headers (pressure-flow equation set), or by the solution of a second order, nonlinear ordinary differential equation involving the flow rate alone (flow distribution equation). Experimental results are presented for various manifold designs having different lateral/header area ratios, lateral flow resistances, and length/diameter ratios. Good agreement is obtained between the analytical and experimental results. Dimensionless parameters which affect flow distribution are identified and discussed with respect to the generalized coefficients of the analytical model. The present method of analysis is proposed for general application in evaluating the performance of flow distribution systems.

Steady flow in a model of human central airways

1980 ◽  
Vol 49 (3) ◽  
pp. 417-423 ◽  
Author(s):  
A. S. Slutsky ◽  
G. G. Berdine ◽  
J. M. Drazen
Keyword(s):  
Reynolds Number ◽  
Steady Flow ◽  
Coefficient Of Friction ◽  
Flow Distribution ◽  
Reynolds Numbers ◽  
Total Flow ◽  
Pressure Flow ◽  
Moody Diagram ◽  
Distribution Of Flow

We studied the pressure-flow relationships and flow distribution under steady conditions in a model of human central airways, over a range of tracheal Reynolds' numbers (350-30,000) by using air or helium. We found that the Moody diagram [log coefficient of friction CF = delta P/[1/2 rho (V2/A2)] vs. log Reynolds' number (Re)] had a slope of -1 for Re less than 500, a slope 0 for Re greater than 10,000, and slopes between -1 and 0 for 500 less than or equal to Re less than or equal to 10,000. The distribution of flow among branches was dependent on tracheal Reynolds' number so that, as tracheal Reynolds' number increased, the upper lobes received proportionally less of the total flow than the lower lobes. Because the airways in the upper lobes generally had greater branching angles than those in the lower lobes, this result was consistent with the hypothesis that the effective resistances introduced by branching angles was flow dependent, increasing proportionally more the greater the angle.

Experimental investigations of the stability of channel flows. Part 1. Flow of a single liquid in a rectangular channel

1970 ◽  
Vol 43 (1) ◽  
pp. 145-164 ◽  
Author(s):  
Timothy W. Kao ◽  
C. Park
Keyword(s):  
Rectangular Channel ◽  
Stability Boundary ◽  
Reynolds Numbers ◽  
Experimental Investigations ◽  
Neutral Stability ◽  
Wave Speeds ◽  
Low Reynolds Numbers ◽  
The Stability ◽  
Ultimate Fate ◽  
Good Agreement

The stability of the laminar flow in a rectangular channel with aspect ratio 1:8 was investigated experimentally, with and without artificial excitation. The critical Reynolds number based on the hydraulic diameter and the average velocity was found to be 2600. Behaviour of damped and growing waves, using artificial excitation, was examined in detail. In particular the progress of growing disturbances was followed. Breaking was found to be the ultimate fate of a growing wave. Spectra of growing and damped waves were also obtained. Measurements were made for wavelengths, wave speeds and amplification or damping rates. The neutral stability boundary in the αr, R plane was determined. In the damped region, comparison of several aspects of the behaviour of the measured disturbances with the plane Poiseuille theory for spatial decay yielded good agreement.Three-dimensionality and non-linear subcritical instability were briefly examined. Neutral subcritical waves at low Reynolds numbers appeared possible when the exciter amplitude was quadrupled.The possible bearings of the present study on the stability of plane Poiseuille flow are suggested.

Simulation of Unsteady Flow Around a Cylinder

2015 ◽  
Vol 3 (2) ◽  
pp. 28-49
Author(s):  
Ridha Alwan Ahmed
Keyword(s):  
Stokes Equations ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Mean Value ◽  
Navier Stokes ◽  
Cylinder Surface ◽  
Navier Stokes Equations ◽  
Flow Around A Cylinder ◽  
Numerical Grid ◽  
Good Agreement

       In this paper, the phenomena of vortex shedding from the circular cylinder surface has been studied at several Reynolds Numbers (40≤Re≤ 300).The 2D, unsteady, incompressible, Laminar flow, continuity and Navier Stokes equations have been solved numerically by using CFD Package FLUENT. In this package PISO algorithm is used in the pressure-velocity coupling.        The numerical grid is generated by using Gambit program. The velocity and pressure fields are obtained upstream and downstream of the cylinder at each time and it is also calculated the mean value of drag coefficient and value of lift coefficient .The results showed that the flow is strongly unsteady and unsymmetrical at Re>60. The results have been compared with the available experiments and a good agreement has been found between them

Packing Effect on the Transfer Integrals and Mobility in α,α′-bis(dithieno[3,2-b:2′,3′-d]thiophene) (BDT) and its Heteroatom-Substituted Analogues

2011 ◽  
Vol 64 (12) ◽  
pp. 1587 ◽  
Author(s):  
Ahmad Irfan ◽  
Abdullah G. Al-Sehemi ◽  
Shabbir Muhammad ◽  
Jingping Zhang
Keyword(s):  
Electron Transfer ◽  
Electron Mobility ◽  
Hole Mobility ◽  
Experimental Investigations ◽  
Hole Transfer ◽  
Space Group ◽  
Space Groups ◽  
Transfer Integrals ◽  
Packing Effect ◽  
Good Agreement

Theoretically calculated mobility has revealed that BDT is a hole transfer material, which is in good agreement with experimental investigations. The BDT, NHBDT, and OBDT are predicted to be hole transfer materials in the C2/c space group. Comparatively, hole mobility of BHBDT is 7 times while electron mobility is 20 times higher than the BDT. The packing effect for BDT and designed crystals was investigated by various space groups. Generally, mobility increases in BDT and its analogues by changing the packing from space group C2/c to space groups P1 or . In the designed ambipolar material, BHBDT hole mobility has been predicted 0.774 and 3.460 cm2 Vs–1 in space groups P1 and , which is 10 times and 48 times higher than BDT (0.075 and 0.072 cm2 Vs–1 in space groups P1 and ), respectively. Moreover, the BDT behaves as an electron transfer material by changing the packing from the C2/c space group to P1 and .

scholarly journals Validation of MATLAB algorithm to implement a two-step parallel pyrolysis model for the prediction of maximum %char yield

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Ibiba Taiwo Horsfall ◽  
Macmanus Chinenye Ndukwu ◽  
Fidelis Ibiang Abam ◽  
Ololade Moses Olatunji ◽  
Ojong Elias Ojong ◽  
...  
Keyword(s):  
Experimental Data ◽  
Isothermal Condition ◽  
Char Yield ◽  
Experimental Investigations ◽  
Time Saving ◽  
Pyrolysis Products ◽  
Pyrolysis Model ◽  
Experimental Yield ◽  
By Products ◽  
Good Agreement

AbstractNumerical modeling of biomass pyrolysis is becoming a cost and time-saving alternative for experimental investigations, also to predict the yield of the by-products of the entire process. In the present study, a two-step parallel kinetic model was used to predict char yield under isothermal condition. MATLAB ODE45 function codes were employed to solve a set of differential equations that predicts the %char at varying residence times and temperatures. The code shows how the various kinetic parameters and mass of pyrolysis products were determined. Nevertheless, the algorithm used for the prediction was validated with experimental data and results from past works. At 673.15 K, the numerical simulation using ODE45 function gives a char yield of 27.84%. From 573.15 K to 673.15 K, char yield ranges from 31.7 to 33.72% to 27.84% while experimental yield decreases from 44 to 22%. Hence, the error between algorithm prediction and experimental data from literature is − 0.26 and 0.22. Again, comparing the result of the present work with the analytical method from the literature showed a good agreement.

Upward Vertical Two-Phase Flow Through an Annulus—Part II: Modeling Bubble, Slug, and Annular Flow

1992 ◽  
Vol 114 (1) ◽  
pp. 14-30 ◽  
Author(s):  
E. F. Caetano ◽  
O. Shoham ◽  
J. P. Brill
Keyword(s):  
Flow Pattern ◽  
Annular Flow ◽  
Two Phase Flow ◽  
Flow Behavior ◽  
Bubble Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Through ◽  
Physical Phenomena ◽  
Good Agreement

Mechanistic models have been developed for each of the existing two-phase flow patterns in an annulus, namely bubble flow, dispersed bubble flow, slug flow, and annular flow. These models are based on two-phase flow physical phenomena and incorporate annulus characteristics such as casing and tubing diameters and degree of eccentricity. The models also apply the new predictive means for friction factor and Taylor bubble rise velocity presented in Part I. Given a set of flow conditions, the existing flow pattern in the system can be predicted. The developed models are applied next for predicting the flow behavior, including the average volumetric liquid holdup and the average total pressure gradient for the existing flow pattern. In general, good agreement was observed between the experimental data and model predictions.

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