The Steady Expiratory Pressure-Flow Relation in a Model Pulmonary Bifurcation

1993 ◽  
Vol 115 (3) ◽  
pp. 299-305 ◽  
Author(s):  
J. M. Collins ◽  
A. H. Shapiro ◽  
E. Kimmel ◽  
R. D. Kamm
Keyword(s):  
Pressure Drop ◽  
Reynolds Numbers ◽  
Generation Model ◽  
Cross Sectional ◽  
Pressure Flow ◽  
Frictional Pressure Drop ◽  
Curved Tube ◽  
Equivalent Length ◽  
Dye Visualization ◽  
Sectional Shape

Experiments were conducted over a range of Reynolds numbers from 50 to 8000 to study the pressure-flow relationship for a single bifurcation in a multi-generation model during steady expiratory flow. Using the energy equation, the measured static pressure drop was decomposed into separate components due to fluid acceleration and viscous energy dissipation. The frictional pressure drop was found to closely approximate that for an equivalent length of curved tube with the same curvature ratio as in the model bifurcation. The sensitivity of these results to changes in airway cross-sectional shape, non-planar configuration, and flow regime (laminar-turbulent) was investigated. In separate experiments using dye visualization and hot-wire anemometry, a transition to turbulent flow was observed at Reynolds numbers between 1000 and 1500. Transition had very little effect on the pressure-flow relation.

Experiments on the pressure drop created by a sphere settling in a viscous liquid. Part 2. Reynolds numbers from 0·2 to 21,000

1968 ◽  
Vol 32 (4) ◽  
pp. 705-720 ◽  
Author(s):  
Guili A. Feldman ◽  
Howard Brenner
Keyword(s):  
Pressure Drop ◽  
Large Diameter ◽  
Reynolds Numbers ◽  
Cross Sectional ◽  
Number Range ◽  
Liquid Part ◽  
Small Spherical Particle ◽  
Quiescent Liquid ◽  
Limiting Value ◽  
Unbounded Fluid

The pressure drop ΔP created by the motion of a ‘small’ spherical particle settling along the axis of a large-diameter circular cylinder filled with a quiescent liquid was measured in the particle Reynolds number range (based on diameter) from Re = 0·2 to 21,000. For Re < 125 it was found that ΔPA/D = 2·0 (A = cylinder cross-sectional area; D = particle drag), in agreement with existing theory in the Stokes and Oseen regimes. Beyond Re = 125 a fairly abrupt transition occurs, the ΔPA/D ratio decreasing asymptotically towards 1·0, the limiting value predicted by elementary momentum principles for an ‘unbounded’ fluid, with increasing Re. At Re ≈ 6000 the transition is essentially complete.

Pressure Drop for Fully Developed Turbulent Flow in Circular and Noncircular Ducts

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Zhipeng Duan ◽  
M. M. Yovanovich ◽  
Y. S. Muzychka
Keyword(s):  
Fluid Flow ◽  
Pressure Drop ◽  
Turbulent Flow ◽  
Square Root ◽  
Sectional Area ◽  
Cross Sectional ◽  
Physical Behavior ◽  
Frictional Pressure Drop ◽  
Fully Developed Turbulent Flow ◽  
The Cross

The objective of this paper is to furnish the engineer with a simple and convenient means of estimating frictional pressure drop in ducts and the original physical behavior can be clearly reflected. Fully developed turbulent flow frictional pressure drop in noncircular ducts is examined. Simple models are proposed to predict the frictional pressure drop in smooth and rough noncircular channels. Through the selection of a novel characteristic length scale, the square root of the cross-sectional area, the effect of duct shape has been minimized. The proposed models have an accuracy of 6% for most common duct shapes of engineering practice and can be used to predict pressure drop of fully developed turbulent flow in noncircular ducts. It is found that the hydraulic diameter is not the appropriate length scale to use in defining the Reynolds number to ensure similarity between the circular and noncircular ducts. By using the Reynolds number based on the square root of the cross-sectional area, it is demonstrated that the circular tube relations may be applied to noncircular ducts eliminating large errors in estimation of pressure drop. The square root of the cross-sectional area is an appropriate characteristic dimension applicable to most duct geometries. The dimensionless mean wall shear stress is a desirable dimensionless parameter to describe fluid flow physical behavior so that fluid flow problems can be solved in the simple and direct manner. The dimensionless mean wall shear stress is presented graphically and appears more general and reasonable to reflect the fluid flow physical behavior than the traditional Moody diagram.

Mixed Convective Low Flow Pressure Drop in Vertical Rod Assemblies: I—Predictive Model and Design Correlation

1989 ◽  
Vol 111 (4) ◽  
pp. 956-965 ◽  
Author(s):  
K. Y. Suh ◽  
N. E. Todreas ◽  
W. M. Rohsenow
Keyword(s):  
Pressure Drop ◽  
Mixed Convection ◽  
Wide Spectrum ◽  
Natural Circulation ◽  
Reynolds Numbers ◽  
Low Flow ◽  
Spatial Average ◽  
Frictional Pressure Drop ◽  
Friction Factors ◽  
Geometric Arrangements

A predictive theory has been developed for rod bundle frictional pressure drop characteristics under laminar and transitional mixed convection conditions on the basis of the intraassembly and intrasubchannel flow redistributions due to buoyancy for a wide spectrum of radial power profiles and for the geometric arrangements of practical design interest. Both the individual subchannel correlations and overall bundle design correlations have been formulated as multipliers applied to the isothermal friction factors at the same Reynolds numbers. Standard and modified subchannel friction factors have been obtained to be used with spatial-average and bulk-mean densities, respectively. A correlating procedure has been proposed to assess the effects of interacting subchannel flows, developing mixed convective flow, wire wrapping, power skew, rod number, and transition from laminar flow. In contrast to forced convection behavior, a strong rod number effect is present under mixed convection conditions in bundle geometries. The results of this study are of design importance in natural circulation conditions because the mixed convection frictional pressure losses exceed the corresponding isothermal values at the same Reynolds numbers.

Thermal Transport in a Microchannel Exhibiting Ultrahydrophobic Microribs Maintained at Constant Temperature

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
D. Maynes ◽  
B. W. Webb ◽  
J. Davies
Keyword(s):  
Nusselt Number ◽  
Pressure Drop ◽  
Laminar Flow ◽  
Constant Temperature ◽  
Thermal Transport ◽  
Flow Direction ◽  
Relative Size ◽  
Reynolds Numbers ◽  
Frictional Pressure Drop ◽  
Smooth Channel

This paper presents numerical results exploring the periodically repeating laminar flow thermal transport in a parallel-plate microchannel with ultrahydrophobic walls maintained at constant temperature. The walls considered here exhibit alternating microribs and cavities positioned perpendicular to the flow direction. Results describing the thermally periodically repeating dynamics far from the inlet of the channel have been obtained over a range of laminar flow Reynolds numbers and relative microrib/cavity module lengths and depths in the laminar flow regime. Previously, it has been shown that significant reductions in the overall frictional pressure drop can be achieved relative to the classical smooth channel laminar flow. The present predictions reveal that the overall thermal transport is also reduced as the relative size of the cavity region is increased. The overall Nusselt number behavior is presented and discussed in conjunction with the frictional pressure drop behavior for the parameter range explored. The following conclusions can be made regarding thermal transport for a constant temperature channel exhibiting ultrahydrophobic surfaces: (1) Increases in the relative cavity length yield decreases in the Nusselt number, (2) increasing the relative rib/cavity module length yields a decrease in the Nusselt number, and (3) decreases in the Reynolds number result in smaller values of the Nusselt number.

Effect of Header Design on Pressure Drop in Microchannel Heat Sink for MEMS Applications

2014 ◽  
Vol 984-985 ◽  
pp. 1184-1189
Author(s):  
Chelliah Anbumeenakshi ◽  
M.R. Thansekhar ◽  
M. Radhakrishnan
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Heat Sink ◽  
Deionized Water ◽  
Microchannel Heat Sink ◽  
Micro Channel ◽  
Cross Sectional ◽  
Parallel Microchannels ◽  
Sectional Shape ◽  
Header Design

Experiments have been performed to investigate the pressure drop in the microchannel heat sink by varying the cross sectional shape of the header at the inlet and at the outlet for two types of arrangement U type and Z type. The experiments are performed by using deionized water as a coolant for a mass flow rate of 50 – 120 kg/hr and Reynolds number of range 100 - 600 in an Al microchannel rectangular heat sink with 25 numbers of parallel microchannels. Experiment was carried out to find the suitable inlet and outlet header combination for both U type heat sink and Z type heat sink. The various cross sectional shapes used in this micro channel are triangular, trapezoidal and rectangular.

Soft-ANN based correlation for air-water two-phase flow pressure drop estimation in a vertical mini-channel

2021 ◽  
pp. 095440622110203
Author(s):  
Barroso-Maldonado Juan Manuel ◽  
Riesco-Ávila José Manuel ◽  
Picón-Núñez Martín ◽  
Belman-Flores Juan Manuel
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Two Phase Flow ◽  
Reynolds Numbers ◽  
Phase Flow ◽  
Inertial Forces ◽  
Two Phase ◽  
Soft Matrix ◽  
Frictional Pressure Drop ◽  
Matrix Correlation

In this paper, an Artificial Neural Network soft matrix correlation to estimate the pressure drop of air-water two-phase flow is developed. The applicability of the model is extended by using dimensionless physical numbers as inputs (Air-Reynolds number, Water-Reynolds number, and the ratio of Air Inertial Forces to Water Inertial Forces), so the model can be implemented for vertical pipes with the proper combination of diameter-velocity-density-viscosity allowing estimations of dimensional numbers within the range of: Air-Reynolds numbers (430–6100), Water-Reynolds number (2400–7200), and Air-Water-Inertial forces ratio (1.6–1834), including the diameter range from 3 to 28 mm. Experimental measurements of frictional pressure drop of water-air mixtures are determined at different conditions. A search of the most suitable density, viscosity, and friction models was conducted and used in the model. The performance of the proposed ANN correlation is compared against published expressions showing good approximation to experimental data; results indicate that the most used correlations are within a mean relative error ( mre) of 23.9–30.7%, while the proposed ANN has a mre = 0.9%. Two additional features are discussed: i) the applicability and generality of the ANN using untrained data, ii) the applicability in laminar, transitional, and turbulent flow regimen. To take the approach beyond a robust performance mapping, the methodology to translate the ANN into a programmable equation is presented.

Numerical Simulations of Misalignment Effects in Microfluidic Interconnects

2010 ◽  
Vol 1272 ◽  
Author(s):  
Sudheer Rani ◽  
Taehyun Park ◽  
Byoung Hee You ◽  
Steven Soper ◽  
Michael C Murphy ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Area Ratio ◽  
Straight Pipe ◽  
Flow Area ◽  
Cross Sectional ◽  
Area Reduction ◽  
Equivalent Length ◽  
End To End

AbstractNumerical simulations were performed to see the effect of geometrical misalignment in pressure driven flows. Geometric misalignment effects on flow characteristics arising in three types of interconnection methods a) end-to-end interconnection, b) channel overlap when chips are stacked on top of each other, and c) the misalignment occurring due to the offset between the external tubing and the reservoir were investigated. For the case of end-to-end interconnection, the effect of misalignment was investigated for 0, 13, 50, 58, and 75% reduction in the available flow area at the location of geometrical misalignment. In the interconnection through channel overlap, various possible misalignment configurations were simulated by maintaining the same amount of misalignment (75% flow area reduction) for all the configurations. The effect of misalignment in a Tube-in-Reservoir interconnection was investigated by positioning the tube at an offset of 164μm from the reservoir center. All the results were evaluated in terms of the equivalent length of a straight pipe. The effect of reynolds number (Re) was also taken into account by performing additional simulations of aforementioned cases at reynolds numbers ranging from 0.075 to 75. The results are interpreted in terms of equivalent length (Le) as a function of Re and misalignment area ratio (A1:A2), where A1 is the original cross-sectional area of the channel and A2 is the available flow area at mismatch location. Equivalent length calculations revealed that the effect of misalignment in tube-in-reservoir interconnection method was the most insignificant when compared to the other two methods of interconnection

Experiments on the pressure drop created by a sphere settling in a viscous liquid

1963 ◽  
Vol 17 (1) ◽  
pp. 89-96 ◽  
Author(s):  
Irwin Pliskin ◽  
Howard Brenner
Keyword(s):  
Pressure Drop ◽  
Viscous Liquid ◽  
Pressure Difference ◽  
Circular Tube ◽  
Reynolds Numbers ◽  
Experimental Measurements ◽  
Sectional Area ◽  
Small Sphere ◽  
Cross Sectional ◽  
The Difference

Experimental measurements were made of the difference in pressure at large distances on either side of a spherical particle settling slowly along the axis of a long circular tube filled with viscous liquid. At low particle Reynolds numbers and for small sphere-cylinder diameter ratios, it was found that the product of the pressure difference and the cross-sectional area of the tube is equal to twice the drag on the particle, in accord with theory.

On the cross-sectional shape of the cellulose crystallites in the tunicate Halocynthia papillosa

1990 ◽  
Vol 48 (3) ◽  
pp. 566-567
Author(s):  
J.-F. Revol ◽  
Y. Van Daele ◽  
F. Gaill
Keyword(s):  
Contrast Imaging ◽  
Animal Kingdom ◽  
Bright Field ◽  
Field Mode ◽  
Cross Sectional ◽  
Ultrathin Sections ◽  
The Cross ◽  
Sectional Shape ◽  
Valonia Ventricosa ◽  
C Nmr

The only form of cellulose which could unequivocally be ascribed to the animal kingdom is the tunicin that occurs in the tests of the tunicates. Recently, high-resolution solid-state l3C NMR revealed that tunicin belongs to the Iβ form of cellulose as opposed to the Iα form found in Valonia and bacterial celluloses. The high perfection of the tunicin crystallites led us to study its crosssectional shape and to compare it with the shape of those in Valonia ventricosa (V.v.), the goal being to relate the cross-section of cellulose crystallites with the two allomorphs Iα and Iβ.In the present work the source of tunicin was the test of the ascidian Halocvnthia papillosa (H.p.). Diffraction contrast imaging in the bright field mode was applied on ultrathin sections of the V.v. cell wall and H.p. test with cellulose crystallites perpendicular to the plane of the sections. The electron microscope, a Philips 400T, was operated at 120 kV in a low intensity beam condition.

Sign in / Sign up

Export Citation Format

Share Document