scholarly journals Estimation of inspiratory pressure drop in neonatal and pediatric endotracheal tubes

1999 ◽  
Vol 87 (1) ◽  
pp. 36-46 ◽  
Author(s):  
Pierre-Henri Jarreau ◽  
Bruno Louis ◽  
Gilles Dassieu ◽  
Luc Desfrere ◽  
Perre W. Blanchard ◽  
...  
Keyword(s):  
Pressure Drop ◽  
Laminar Flow ◽  
Flow Regime ◽  
Internal Diameter ◽  
Empirical Equations ◽  
Itô Formula ◽  
Ito Formula ◽  
Endotracheal Tubes ◽  
Curved Tube ◽  
Measured Pressure

Endotracheal tubes (ETTs) constitute a resistive extra load for intubated patients. The ETT pressure drop (ΔPETT) is usually described by empirical equations that are specific to one ETT only. Our laboratory previously showed that, in adult ETTs, ΔPETT is given by the Blasius formula (F. Lofaso, B. Louis, L. Brochard, A. Harf, and D. Isabey. Am. Rev. Respir. Dis. 146: 974–979, 1992). Here, we also propose a general formulation for neonatal and pediatric ETTs on the basis of adimensional analysis of the pressure-flow relationship. Pressure and flow were directly measured in seven ETTs (internal diameter: 2.5–7.0 mm). The measured pressure drop was compared with the predicted drop given by general laws for a curved tube. In neonatal ETTs (2.5–3.5 mm) the flow regime is laminar. The ΔPETT can be estimated by the Ito formula, which replaces Poiseuille’s law for curved tubes. For pediatric ETTs (4.0–7.0 mm), ΔPETT depends on the following flow regime: for laminar flow, it must be calculated by the Ito formula, and for turbulent flow, by the Blasius formula. Both formulas allow for ETT geometry and gas properties.

scholarly journals Numerical Prediction of Heat Transfer Characteristics of Nanofluids in a Minichannel Flow

2014 ◽  
Vol 2014 ◽  
pp. 1-7 ◽  
Author(s):  
Arjumand Adil ◽  
Sonam Gupta ◽  
Pradyumna Ghosh
Keyword(s):  
Heat Transfer ◽  
Brownian Motion ◽  
Pressure Drop ◽  
Laminar Flow ◽  
Computational Model ◽  
Flow Regime ◽  
Cfd Simulation ◽  
Computational Results ◽  
Heat Transfer Characteristics ◽  
Simulation Process

CFD simulation of the heat transfer and pressure drop characteristics of different nanofluids in a minichannel flow has been explained using FLUENT version 6.3.26. Different nanofluids with nanoparticles of Al2O3, CuO, SiO2, and TiO2have been used in the simulation process. A comparison of the experimental and computational results has been made for the heat transfer and pressure drop characteristics for the case of Al2O3-water nanofluid for the laminar flow. Also, computations have been made by considering Brownian motion as well as without considering Brownian motion of the nanoparticles. After verification of the computational model with the experimental results for Al2O3-water nanofluid, the simulations were performed for the same experimental readings for different nanofluids in the laminar flow regime to find out the heat transfer and pressure drop characteristics.

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.

Transition Criteria for Laminar to Turbulent Flow for Yield Power Law (YPL) Fluids Based on Stability Analysis

2013 ◽  
Author(s):  
Goktug Kalayci ◽  
Evren M. Ozbayoglu ◽  
Stefan Z. Miska ◽  
Mengjiao Yu ◽  
Nicholas Takach ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Stability Analysis ◽  
Pressure Drop ◽  
Laminar Flow ◽  
Friction Factor ◽  
Yield Stress ◽  
Flow Regime ◽  
Power Law ◽  
Laminar Flow Regime

It is well known that a Newtonian fluid with the presence of solid particles in suspension behaves non-Newtonian. Higher the solid content, more significant the yield stress of the fluid. Determination of the hydraulic behavior of fluids having a significant yield stress is a challenging task. For engineering purposes, pressure drop within the system, during pipeline transportation, has to be estimated carefully and accurately. Flow regime plays a vital role during hydraulic calculations. The inaccurate determination of flow regime can lead us to large errors in frictional pressure drop calculations and ultimately leads to error in designing and flow assurance point of view, since hydraulic calculations are including a friction factor term, which is a direct function of flow regime. In general, Reynolds number is the main parameter used by the industry for determining the flow regime, and the friction factor. This approach works reasonably accurate for Newtonian fluids. However, as the yield stress of the fluid increases, this conventional technique for determining the flow regime is not as accurate. Although many approaches have been introduced for estimating the flow regime for non-Newtonian fluids, there exists a lack of information and confidence of such predictions for fluids having high yield stress, such as Yield Power Law (YPL) fluids (i.e., Herchel-Bulkley). (1)τ=τy+Kγm This study presents an analytical solution for predicting the transition from laminar to non-laminar flow regime based on Ryan & Johnson’s approach using the stability analysis and equation of motion for YPL fluids. Comparing with the experimental results for YPL fluids under different flow conditions, including laminar and non-laminar flow regimes, show that presented approach gives a better estimation of the transition from laminar to non-laminar flow regime than conventional Reynolds number approach. In some cases, it is observed that although the Reynolds number is high, flow is still laminar, which is predicted accurately using the presented model. This study provides a higher accuracy in estimating the flow regime, which leads to a higher confidence in hydraulic designs and determining limitations of the system in concern.

scholarly journals Influence of Capillary Number on the droplet Shape, Film Thickness, and Pressure Drop in a Liquid-Liquid Taylor Flow inside a Microcapillary

2019 ◽  
Vol 4 (6) ◽  
pp. 1407-1419
Author(s):  
S. V. B. Vivekanand ◽  
S. Chandrasekhar ◽  
V. R. K. Raju
Keyword(s):  
Fluid Flow ◽  
Pressure Drop ◽  
Film Thickness ◽  
Flow Regime ◽  
Capillary Number ◽  
Slug Flow ◽  
Internal Diameter ◽  
Droplet Shape ◽  
Taylor Flow ◽  
Circular Microchannel

Numerical analysis of a two-dimensional, axisymmetric, incompressible, laminar liquid-liquid Taylor flow inside a vertical circular microchannel is carried out in the present study. The focus is laid on fluid flow characteristics in the slug flow regime. Although many researchers have performed numerical and experimental studies of two-phase flows in narrow channels, their efforts seem to have been fairly successful in explaining the underlying mechanisms of fluid flow phenomena, especially for slug flow regime. Here, an attempt has been made to explore the hydrodynamics of such flows. In the present study, dodecane and Pd5 have been used as the carrier phases and water is used as the discontinuous phase. The internal diameter of the circular microchannel is 1.5 mm with its wall being insulated. The flow and volume fraction equations are solved by the finite volume approach (FVM). The volume of fluid (VOF) method has been adopted for capturing the interface. The effect of Capillary number on film thickness and interfacial pressure drop is explained. The film thickness is found to increase with Capillary number and is also found to be in a close match with the models available in the literature. The pressure drop per unit length obtained from the CFD study is compared with a standard model available in the literature. The pressure drop across the unit cell is found to be following the phenomenological model. It is observed that the pressure drop at the interface has the highest contribution to the total pressure drop in contrast to the other pressure drops in the channel, with ~50-55% in dodecane-water and ~55-62% in Pd5-water systems. Besides, the distribution of the velocity, axial, and wall pressure fields inside the microcapillary are also discussed.

Investigation and Development of Proposed General Pressure Drop and Heat Transfer Correlations for Laminar Flow in a Toroidal Coiled Tube System

2004 ◽  
Author(s):  
Anthony J. Bowman ◽  
Hyunjae Park
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Laminar Flow ◽  
Friction Factor ◽  
Radius Of Curvature ◽  
Straight Tube ◽  
Coiled Tube ◽  
Tube Heat Exchanger ◽  
Curved Tube

In this paper, the laminar flow pressure drop and heat transfer correlations published and applied to plain, coiled tube heat exchanger systems are extensively investigated. It was found that most correlations obtained for toroidal geometric systems have been applied to the analysis of helical and spiral tube systems. While toroidal (and helical) coils have a constant radius of curvature about the coil center-point (and center-line), spiral coils have a continuously varying radius of curvature, in which the flow does not reach a typical fully developed flow condition. The centrifugal forces, arising from the curved flow path, contribute to the enhancement of heat transfer (at the cost of additional pressure drop) over straight tube heat exchangers of the same length. In this paper, using published correlations and available experimental test data for pressure drop and heat transfer in toroidal tube systems, the proposed general correlations are developed by using a filtered-mean multiple regression method. The Coiling Influence Factors for the friction factor and heat transfer, CIFf and CIFh, respectively; defined and used in the authors’ previous works [1,2,3] it was found that the deviations between the proposed and published correlations are within about 3% for friction factor and 5–20% for heat transfer, depending on working fluid. In order to assess the validity of applying the generalized correlations developed in this work for toroidal tube systems, onto other curved tube systems, a numerical analysis of toroidal coil systems, using the commercially available CFD package (Fluent 6) has been explicitly performed. A comparison is made between the CFD result for average heat transfer (CIFh) with that predicted by the proposed general correlation for toroidal coils and available experimental data. As an extension of this work, a comparison of curved tube over straight tube heat exchanger effectiveness is made to highlight its use as a design optimization parameter and motivation for additional coiled tube heat exchanger research.

Two-Phase Pressure Drop in the Intermittent Flow Regime for Noncircular Microchannels

2002 ◽  
Author(s):  
Srinivas Garimella ◽  
Jesse D. Killion ◽  
John W. Coleman
Keyword(s):  
Pressure Drop ◽  
Flow Regime ◽  
Intermittent Flow ◽  
Average Error ◽  
Two Phase ◽  
Pressure Drops ◽  
Mass Fluxes ◽  
Tube Shape ◽  
Measured Pressure ◽  
Phase Pressure

This paper reports the development of an experimentally validated model for pressure drop during intermittent flow of condensing refrigerant R134a in horizontal, noncircular microchannels. Two-phase pressure drops were measured in six noncircular channels ranging in hydraulic diameter from 0.42 mm to 0.84 mm. The tube shapes included square, rectangular, triangular, barrel-shaped, and others. For each tube under consideration, pressure drop measurements were taken over the entire range of qualities from vapor to liquid at five different refrigerant mass fluxes between 150 kg/m2s and 750 kg/m2s. Results from previous work by the authors were used to select the data that correspond to the intermittent flow regime; generally, these points had qualities less than 25%. The pressure drop model previously developed by the authors for circular microchannels was used as the basis for the model presented in this paper. The model includes the contributions of the liquid slug, the vapor bubble, and the transitions between the bubbles and slugs. Slug frequency was estimated using a simple correlation for non-dimensional unit-cell length. The model predicts the experimentally measured pressure drops for the noncircular tube shapes under consideration with 90% of the predictions within ±28% of the measurements (average error 16.5%), which is shown to be much better than the predictions of other models in the literature. The effects of tube shape on condensation pressure drop are also illustrated in the paper.

An Expermentally Validated Model for Two-Phase Pressure Drop in the Intermittent Flow Regime for Noncircular Microchannels

2003 ◽  
Vol 125 (5) ◽  
pp. 887-894 ◽  
Author(s):  
Srinivas Garimella ◽  
Jesse D. Killion ◽  
John W. Coleman
Keyword(s):  
Pressure Drop ◽  
Flow Regime ◽  
Intermittent Flow ◽  
Average Error ◽  
Two Phase ◽  
Pressure Drops ◽  
Mass Fluxes ◽  
Tube Shape ◽  
Measured Pressure ◽  
Phase Pressure

This paper reports the development of an experimentally validated model for pressure drop during intermittent flow of condensing refrigerant R134a in horizontal, noncircular microchannels. Two-phase pressure drops were measured in six noncircular channels ranging in hydraulic diameter from 0.42 mm to 0.84 mm. The tube shapes included square, rectangular, triangular, barrel-shaped, and others. For each tube under consideration, pressure drop measurements were taken over the entire range of qualities from vapor to liquid at five different refrigerant mass fluxes between 150 kg/m2s and 750 kg/m2s. Results from previous work by the authors were used to select the data that correspond to the intermittent flow regime; generally, these points had qualities less than 25%. The pressure drop model previously developed by the authors for circular microchannels was used as the basis for the model presented in this paper. Using the observed slug/bubble flow pattern for these conditions, the model includes the contributions of the liquid slug, the vapor bubble, and the transitions between the bubble and slugs. A simple correlation for nondimensional unit-cell length was used to estimate the slug frequency. The model successfully predicts the experimentally measured pressure drops for the noncircular tube shapes under consideration with 90% of the predictions within ±28% of the measurements (average error 16.5%), which is shown to be much better than the predictions of other models in the literature. The effects of tube shape on condensation pressure drop are also illustrated in the paper.

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