Steady expiratory flow in dog lungs: an isovolume preparation

1981 ◽  
Vol 51 (5) ◽  
pp. 1331-1337 ◽  
Author(s):  
S. L. Sneddon ◽  
J. D. Brain
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Laminar Flow ◽  
Flow Region ◽  
Flow Limitation ◽  
Opening Pressure ◽  
Pressure Flow ◽  
Pleural Surface ◽  
Airway Opening ◽  
Expiratory Flow

By supplying air and other gases through discs glued to the pleural surface, we studied steady expiratory flow at constant volume. Dog lungs were studied at constant PA - Ppl (alveolar minus pleural pressure) of 7 to 10 cmH2O, as increasing flow was achieved by increasing driving pressure [Ppl - Pao (airway opening pressure)]. Flow became limited (independent of further increases in Ppl - Pao) at between 3.5 and 5.5 l/s. Isovolume-pressure-flow (IVPF) curves constructed from forced expirations at graded efforts yielded similar maximal flows. When the airways were made rigid by drying, flow limitation was abolished. When various gases were passed through the dried lung Moody plots of normalized pressure drop (CD) vs. Reynolds number (Re) showed that all of the data could be plotted on a single curve. Although variable among animals, all Moody plots showed a laminar flow region at Re below 100 and an inertial region at Re above 10,000, with a distinct transition.

scholarly journals Airway Closure and Expiratory Flow Limitation in Acute Respiratory Distress Syndrome

2022 ◽  
Vol 12 ◽  
Author(s):  
Claude Guérin ◽  
Martin Cour ◽  
Laurent Argaud
Keyword(s):  
Acute Respiratory Distress Syndrome ◽  
Respiratory Distress Syndrome ◽  
Respiratory Distress ◽  
Distress Syndrome ◽  
Flow Limitation ◽  
Airway Closure ◽  
Opening Pressure ◽  
Expiratory Flow Limitation ◽  
Airway Opening ◽  
Expiratory Flow

Acute respiratory distress syndrome (ARDS) is mostly characterized by the loss of aerated lung volume associated with an increase in lung tissue and intense and complex lung inflammation. ARDS has long been associated with the histological pattern of diffuse alveolar damage (DAD). However, DAD is not the unique pathological figure in ARDS and it can also be observed in settings other than ARDS. In the coronavirus disease 2019 (COVID-19) related ARDS, the impairment of lung microvasculature has been pointed out. The airways, and of notice the small peripheral airways, may contribute to the loss of aeration observed in ARDS. High-resolution lung imaging techniques found that in specific experimental conditions small airway closure was a reality. Furthermore, low-volume ventilator-induced lung injury, also called as atelectrauma, should involve the airways. Atelectrauma is one of the basic tenet subtending the use of positive end-expiratory pressure (PEEP) set at the ventilator in ARDS. Recent data revisited the role of airways in humans with ARDS and provided findings consistent with the expiratory flow limitation and airway closure in a substantial number of patients with ARDS. We discussed the pattern of airway opening pressure disclosed in the inspiratory volume-pressure curves in COVID-19 and in non-COVID-19 related ARDS. In addition, we discussed the functional interplay between airway opening pressure and expiratory flow limitation displayed in the flow-volume curves. We discussed the individualization of the PEEP setting based on these findings.

scholarly journals Predicting the Pressure Drop of Corrugated Sheet Structured Packings in Deep Vacuum Applications

2019 ◽  
Vol 33 (3) ◽  
pp. 303-323
Author(s):  
Žarko Olujić
Keyword(s):  
Pressure Drop ◽  
Laminar Flow ◽  
Flow Region ◽  
Packed Bed ◽  
Internal Diameter ◽  
Flow Conditions ◽  
Natural Choice ◽  
Total Reflux ◽  
Wire Gauze ◽  
Structured Packings

Advanced corrugated sheet structured packings are considered a natural choice for<br /> deep vacuum distillation. In many of these applications that occur at absolute pressures<br /> below 0.01 bar at the top of the column, the low density gas/vapor driven by pressure<br /> ascends through an irrigated packed bed under laminar flow conditions. This implies that the packing geometry features aiming to reduce the form drag of advanced packing may not be as effective, if at all, as experienced in common applications where turbulent flow prevails. To consider this appropriately, a theoretically founded expression for laminar flow friction factor has been incorporated into Delft model (DM). With this extension, the predicted pressure drop within laminar flow region approaches closely that estimated using well-established empirical model available in software package SULCOL. In absence of adequate experimental evidence, extended DM was validated using newest data obtained at FRI with an advanced wire gauze structured packing in total reflux experiments carried out with paraxylene/orthoxylene system at 0.02 and 0.1 bar top pressure in a column with internal diameter of 1.22 m.

The Effect of Twisted-Tape Width on Heat Transfer and Pressure Drop for Fully Developed Laminar Flow

1996 ◽  
Vol 118 (3) ◽  
pp. 584-589 ◽  
Author(s):  
W. M. Chakroun ◽  
S. F. Al-Fahed
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Laminar Flow ◽  
Friction Factor ◽  
Twisted Tape ◽  
Constant Wall Temperature ◽  
Low Reynolds Number Flows ◽  
Temperature Boundary ◽  
Series Of Experiments

A series of experiments was conducted to study the effect of twisted-tape width on the heat transfer and pressure drop with laminar flow in tubes. Data for three twisted-tape wavelengths, each with five different widths, have been collected with constant wall temperature boundary condition. Correlations for the friction factor and Nusselt number are also available. The correlations predict the experimental data to within 10 to 15 percent for the heat transfer and friction factor, respectively. The presence of the twisted tape has caused the friction factor to increase by a factor of 3 to 7 depending on Reynolds number and the twisted-tape geometry. Heat transfer results have shown an increase of 1.5 to 3 times that of plain tubes depending on the flow conditions and the twisted-tape geometry. The width shows no effect on friction factor and heat transfer in the low range of Reynolds number but has a more pronounced effect on heat transfer at the higher range of Reynolds number. It is recommended to use loose-fit tapes for low Reynolds number flows instead of tight-fit in the design of heat exchangers because they are easier to install and remove for cleaning purposes.

Design and Analysis of Passive Y-Type Micromixers for Enhanced Mixing Performance for Biomedical and Microreactor Application

2016 ◽  
Vol 15 (03) ◽  
pp. 161-172 ◽  
Author(s):  
Pranjal Sarma ◽  
P. K. Patowari
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Flow Behavior ◽  
Flow Region ◽  
Entrance Angle ◽  
Packing Factor ◽  
Flow Parameters ◽  
Lower Reynolds Number ◽  
Staggered Arrangement ◽  
Obstacle Geometry

In this paper, endeavor has been made to design and analyze different Y-type micromixers by characterizing the mixing and flow behavior in ultra-low Reynolds number region. The effects of different geometric and flow parameters on the mixing and pressure drop are studied through computational fluid dynamics (CFD) simulations using COMSOL Multiphysics software. The parameters investigated are obstacle geometry, obstacle arrangement, obstacle depth, aspect ratio (AR), entrance angle ([Formula: see text], Reynolds number (Re) and obstacle packing factor (OPF). The simulation results reveal that rectangular shaped obstacles in staggered arrangement gives the best mixing. Increasing obstacle depth and OPF increases both mixing and pressure drop whereas increasing entrance angle enhances mixing but has negligible effect on pressure drop. Also both the mixing and pressure drop performance enhances with decreasing AR and lower Reynolds number gives better mixing in the lower laminar flow region.

Mixing Analysis of Laminar Flow in Static Mixers with Circle Grid Fractal Perforated Plate Elements

2014 ◽  
Vol 607 ◽  
pp. 417-421
Author(s):  
Bukhari Manshoor ◽  
Izzuddin Zaman ◽  
Azwan Sapit ◽  
Amir Khalid
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Laminar Flow ◽  
Flow Pattern ◽  
Coefficient Of Variation ◽  
Fluid Dynamic ◽  
Perforated Plate ◽  
Static Mixers ◽  
Plate Elements ◽  
Flow Splitting

The static mixers are widely used in many industries to obtain the desired type of mixing. In the context of mixing process, two different fluids and have a different properties will mix in a single equipment to produce an another fluid with a new property. In this research, a new approach of static mixers was proposed for pipeline mixing. The flow pattern, pressure drop and mixing characteristics (coefficient of variation) were carried out by means of computer simulations. The static mixers introduced here consists of a series of perforated plate with circle grids fractal pattern elements. The simulations work were carried out by using a commercial package of Computational Fluid Dynamic (CFD), ANSYS CFX 14.0 software. Three levels of laminar flow with Reynolds numbers (Re) of 100, 200 and 400 respectively had been used to investigate the performance of the static mixers introduced here. The effectiveness of circle grid perforated plate static mixer had been evaluated by comparing the homogeneity level of mixing fluids for each flow simulated. The simulations gave a new insights in the flow pattern in circle grids fractal perforated plate elements. The pressure drop predictions compare favorably with literature data and the coefficient of variation (COV) value for circle grid perforated plate with 50% porosity at Reynolds number 100 was 0.0744 which is out of the range meanwhile at Reynolds number 200 and 400 was 0.0483 and 0.0247 respectively which are in the range of reasonable target for many applications. Mixing in the elements occurs through a combination of flow splitting and shearing at the junctions of successive elements. Besides that, simple installation and manufacturing of this type of static mixers makes the fractal perforated plate’s element an excellent static mixing device.

Experimental Study on Thermal-Hydraulic Performance of Single-Phase Water Flow in Narrow Rectangular Channel

2009 ◽  
Author(s):  
Mei Wang ◽  
Yan Wen ◽  
Suizheng Qiu ◽  
Guanghui Su ◽  
Weifeng Ni
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Laminar Flow ◽  
Friction Factor ◽  
Water Flow ◽  
Single Phase ◽  
Rectangular Channel ◽  
Flow Region ◽  
Phase Water

The purpose of this study is to discover the differences of pressure drop and heat transfer of single-phase water flow between conventional channels and narrow rectangular channels. Furthermore, the differences between the level and the vertical channel have been studied. The gap of the test channel is 1.8mm. Compared with conventional channels, the narrow rectangular channel showed differences in both flow and heat transfer characteristics. The critical Reynolds number of transition from laminar flow to turbulent flow is 900∼1300, which is smaller compared with conventional channels. The friction factor is larger than that of the conventional channels and the correlation of friction factor with Reynolds number was given by experimental results. From the relation graph of Nusselt number and Reynolds number, the demarcation of the laminar flow region and turbulence flow region is obvious. In laminar region, Nusselt number almost remained constant and approximately consistent with numerical simulation results. While in turbulent region, Nusselt number increased significantly with increasing Reynolds number. A new Nusselt number correlation was obtained based on Dittus-Boelter equation, and the coefficients were less about 13% than that of Dittus-Boelter equation.

Multiple Capillary Pressure Drop Standards

1975 ◽  
Vol 8 (2) ◽  
Author(s):  
C. H. Keith ◽  
J. A. Corbin
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Turbulent Flow ◽  
Capillary Tube ◽  
Small Diameter ◽  
Flow Region ◽  
Glass Capillary ◽  
Pressure Drops ◽  
Laminar And Turbulent Flow ◽  
Glass Drawing

AbstractThis paper describes a simple device, consisting of a collection of glass capillary tubes, which can be used as a stable, pressure insensitive standard for calibrating pressure drop machines. For air flowing through a single capillary tube of the proper dimensions to give a pressure drop similar to that of a filter rod, the Reynolds number is about 2000, the boundary between laminar and turbulent flow. Since turbulent flow gives pressure drops which vary with atmospheric pressure, it is desirable to reduce this quantity to a level where laminar flow is always present. This can be accomplished by distributing the flow among 10 parallel capillaries of very small diameter. The capillaries were formed by drawing pyrex tubing on a Hupe glass drawing machine to a finished internaI diameter of .44 mm. Ten Iengths of this capillary were mounted in 8 mm tubing and were encased in a clear resin. After polymerization of the resin, the composite rod was sawed into appropriate lengths and cleaned in an ultrasonic bath. Microscopic examination of the finished tubes showed that each capillary was a clean, smooth-walled tube with a sharp entrance and exit. Calculation of the Reynolds number for the composite capillary gave a value of 314, which is well within the Iaminar flow region. The agreement between measured pressure drops of these standards and those calculated using Poiseuille's Iaw with an entry and exit correction is excellent. Daily measurements of the pressure drop of these standard tubes for a period of a month were conducted, and the random variability was found to be 1 % or Iess. Measurements of the pressure drop of these tubes at various pressures and temperatures covering the range of normaI laboratory conditions also demonstrated a lack of significant variability. Fouling of the tubes from atmospheric dust was not found to be a significant factor

Characterization of Surface Roughness Effects on Laminar Flow in Microchannels by Using Fractal Cantor Structures

2009 ◽  
Author(s):  
Chengbin Zhang ◽  
Yongping Chen ◽  
Panpan Fu ◽  
Mingheng Shi
Keyword(s):  
Surface Roughness ◽  
Reynolds Number ◽  
Fractal Dimension ◽  
Pressure Drop ◽  
Laminar Flow ◽  
Flow Direction ◽  
Roughness Effects ◽  
Relative Roughness ◽  
Smooth Channel

The fractal characterization of the topography of rough surfaces by using Cantor set structures is introduced in this paper. Based on the fractal Cantor surface, a model of laminar flow in rough microchannels is developed and numerically analyzed to study the characterization of surface roughness effects on laminar flow. The effects of Reynolds number, relative roughness, and fractal dimension on laminar flow are all discussed. The results indicate that the presence of roughness leads to the form of the detachment, and eddy generation is observed at the shadow of the roughness elements. The pressure drop in the rough channel along the flow direction is no longer in a linear fashion and larger than that in the smooth channel. The fluctuation characteristic of pressure drop along the stream, which is due to the vortex formation at the wall, is found. Differing from the smooth channel, the Poiseuille number for laminar flow in rough microchannels is no longer only dependent on the cross-sectional shape of the channel, but also strongly influenced by the Reynolds number, relative roughness and fractal dimension of the surface.

Flow Boiling Heat Transfer and Two-Phase Flow Pressure Drop in Thin-Rectangular Channels

2008 ◽  
Author(s):  
Yasuo Koizumi ◽  
Tomonari Yamada ◽  
Hiroyasu Ohtake
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Laminar Flow ◽  
Flow Boiling ◽  
Flow Region ◽  
Flow Channel ◽  
Phase Flow ◽  
Two Phase ◽  
Rectangular Channels ◽  
Boiling Flow

Heat transfer and pressure drop of single- and two-phase flow in thin-rectangular channels of the width of 10 mm have been examined. The gap clearance δ of the flow channel covered a range from 0.6 mm to 0.1 mm. In the water single-phase flow condition, the narrowness effect came out around δ = 0.37 ∼ 0.35 mm. Below that value, the friction factor became lower than the value of the usual size in the laminar flow region and the transition from the laminar flow to the turbulent flow was delayed. The Nusselt number also showed dependency on the Reynolds number even in the laminar flow region and became lower than the value for the usual size over the whole Reynolds number region. Bubbly flow, slug flow, semi annular flow and annular flow were observed in boiling flow. The flow pattern transition agreed well with the Baker flow pattern map for the usual size. The Martinelli and Nelson method for the two-phase pressure drop of the boiling flow predicted well present experimental results. Boiling was dominant during the forced flow boiling. The heat transfer coefficient of the boiling flow was larger than the value of the usual sized flow channel. The critical heat flux was lower than the value of the usual sized flow channel. The Koizumi and Ueda method predicted well the trend of the critical heat flux of the present experiments.

Approximate Calculation of Pressure Drop in Laminar Flow of Generalized Newtonian Fluid Through Channels with Insert

1995 ◽  
Vol 60 (9) ◽  
pp. 1476-1491
Author(s):  
Václav Dolejš ◽  
Petr Doleček ◽  
Ivan Machač ◽  
Bedřich Šiška
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Laminar Flow ◽  
Numerical Solution ◽  
Newtonian Fluid ◽  
Calculation Method ◽  
Approximate Calculation ◽  
Creeping Flow ◽  
Experimental Results ◽  
Generalized Newtonian Fluid

An equation of Rabinowitsch-Mooney type has been suggested for approximate calculation of pressure drop in flow of generalized Newtonian fluid through channels with insert both in the region of creeping flow and at higher values of the Reynolds number, and this calculation method has been verified for four types of insert using own numerical solution and experimental results as well as literature data.

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