Modeling the Onset of Gas Entrainment in a Single Downward Discharge From a Stratified Gas-Liquid Region With Liquid Crossflow

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
R. C. Bowden ◽  
I. G. Hassan
Keyword(s):  
Experimental Data ◽  
Froude Number ◽  
Liquid Region ◽  
Flow Conditions ◽  
Critical Height ◽  
High Discharge ◽  
Gas Entrainment ◽  
Model Predictions ◽  
Pipe Inlet ◽  
Made In

The critical height at the onset of gas entrainment, in a single downward oriented discharge from a stratified gas-liquid region with liquid crossflow, was modeled. The assumptions made in the development of the model reduced the problem to that of a potential flow. The discharge was modeled as a point-sink while the crossflow was said to be uniform at the main pipe inlet. The potential function was determined from a superposition of known solutions for a point-sink and uniform flow. The resulting system of three equations demonstrated that the flow field was dominated by the discharge and crossflow Froude numbers. The system was solved numerically and provided a relationship between the geometry, flow conditions, dip location, and critical height. The model predicted that the critical height increased with the discharge Froude number and decreased with the crossflow Froude number. With no imposed crossflow, the model prediction demonstrated agreement with transient and quasisteady experimental data to within ±30%. Existing experimental correlations showed inconsistent crossflow effects on the critical height and disagreed with the model predictions at high discharge Froude numbers.

Experimental Investigation on the Onset of Gas Entrainment from a Stratified Two-Phase Region Through Multiple Branches Mounted on a Curved Surface

2006 ◽  
Vol 128 (4) ◽  
pp. 726-733 ◽  
Author(s):  
Tariq Ahmad ◽  
Ibrahim Hassan
Keyword(s):  
Experimental Data ◽  
Experimental Investigation ◽  
Froude Number ◽  
Hydraulic Resistance ◽  
Numerical Models ◽  
Phase Region ◽  
Critical Height ◽  
Two Phase ◽  
Gas Entrainment ◽  
Wide Range

An experimental investigation has been carried out to simulate the onset of gas entrainment phenomenon from a stratified region through branches located on a semicircular wall configuration, in close dimensional resemblance with a Canada Deuterium and Uranium (CANDU) header-feeder system. New experimental data for the onset of gas entrainment was developed during single and multiple discharge from an air/water stratified region over a wide range of Froude numbers (0 to 100), in order to thoroughly understand the onset of gas entrainment phenomenon. It was found that the critical height at the onset of gas entrainment (single or simultaneous) was a function of the corresponding Froude number of each branch, the vertical distance between the centerlines of the branches (for multiple discharge), the hydraulic resistance of the discharging lines, as well as the orientation of the branches and their diameter with respect to the main header. Concerning multiple discharge comparisons, at intermediate Fr values (1<Fr<10) the data deviates, however at higher Fr values (>10) there is convergence. The present data are necessary in validating future analytical and numerical models of the onset of gas entrainment for a curved geometry, particularly at low Froude numbers.

A Hybrid Model to Predict the Onset of Gas Entrainment With Surface Tension Effects

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
W. Saleh ◽  
R. C. Bowden ◽  
I. G. Hassan ◽  
L. Kadem
Keyword(s):  
Experimental Data ◽  
Surface Tension ◽  
Three Dimensional ◽  
Radius Of Curvature ◽  
Liquid Region ◽  
Two Dimensional ◽  
Poor Agreement ◽  
Critical Height ◽  
Gas Entrainment ◽  
Good Agreement

The onset of gas entrainment in a single downward discharge, from a stratified gas-liquid region, was modeled. The discharge was modeled as a point-sink and Kelvin–Laplace’s equation was used to incorporate surface tension effects. Consequently, a criterion to characterize the dip radius of curvature, at the onset of gas entrainment, was required. The dip geometry was experimentally investigated and a correlation was developed relating the dip radius of curvature to the discharge Froude number. The correlation was used in conjunction with the theoretical model. It was found that the predicted critical height demonstrated good agreement with experimental data with the three-dimensional point-sink approach, while poor agreement using the two-dimensional finite-branch approach was found. The inclusion of surface tension improved the model’s capability to predict the critical height, particularly at discharge Froude numbers below 1.

Modeling of the Onset of Gas Entrainment Through a Finite-Side Branch

2003 ◽  
Vol 125 (5) ◽  
pp. 902-909 ◽  
Author(s):  
M. Ahmed ◽  
I. Hassan ◽  
N. Esmail
Keyword(s):  
Froude Number ◽  
Three Dimensional ◽  
Phase Region ◽  
Side Branch ◽  
Critical Height ◽  
Two Phase ◽  
Gas Entrainment ◽  
Branch Model ◽  
Predicted Values ◽  
New Criterion

A theoretical investigation has been conducted for the prediction of the critical height at the onset of gas entrainment during single discharge from a stratified, two-phase region through a side branch with a finite diameter. Two different models have been developed, a simplified point-sink model and a three-dimensional finite-branch model. The two models are based on a new criterion for the onset of gas entrainment. The results of the predicted critical heights at the onset of gas entrainment showed that the finite-branch model approaches the physical limits at low Froude numbers. However, as the values of the Froude number increased, the predictions of both models eventually converged to the same value. Based on the results of the models, the critical height corresponding to the onset of gas entrainment was found to be a function of Froude number and fluid densities. The results of both models are compared with available experimental data. The comparisons illustrate a very good agreement between the measured and predicted values.

Influence of Wall Inclination Angles on the Onset of Gas Entrainment During Single and Dual Discharges From a Reservoir

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
M. Ahmed
Keyword(s):  
Froude Number ◽  
Inclination Angle ◽  
Phase Region ◽  
Critical Height ◽  
Two Phase ◽  
Gas Entrainment ◽  
Inclination Angles ◽  
Mass Flow Rates ◽  
Predicted Values ◽  
New Criterion

A theoretical analysis was carried out to predict the influences of wall inclination angles of large reservoirs on the onset of gas entrainment during single and dual discharges from a stratified two-phase region. The findings reveal that when the wall inclination angle differs from zero, along with low values of Froude number, two distinct flow regimes occur: the gas-entrainment and no gas-entrainment regimes. A new criterion has been developed to predict the critical Froude number at the transition from the gas-entrainment to the no-gas-entrainment regime. The critical Froude number is defined as a function of the wall inclination angle for a single discharge. For dual discharge, the critical Froude number is found to be dependent on the wall inclination angle, the separating distance between the centerlines of the two branches, as well as the Froude number of the second branch. Furthermore, four different flow regions are mapped, representing the flow regime, as well as the two-phase flow for each branch. These maps serve to predict the flow regions, mass flow rates, and quality during single and dual two-phase discharges. For the gas-entrainment regime, the predicted values of the critical height at the onset of gas entrainment are compared with the experimental data reported in literatures. Comparisons showed good concurrence between the measured and predicted results. Furthermore, the influence of the wall inclination angle on the flow regions, the predicted critical height, and the location of the gas entrainment are presented and discussed at different values of independent variables.

Modeling of the Onset of Gas Entrainment Through a Finite-Side Branch

2002 ◽  
Author(s):  
M. Ahmed ◽  
I. Hassan ◽  
N. Esmail
Keyword(s):  
Froude Number ◽  
Phase Region ◽  
Side Branch ◽  
Critical Height ◽  
Two Phase ◽  
Gas Entrainment ◽  
Branch Model ◽  
Single Discharge ◽  
Predicted Values ◽  
New Criterion

A theoretical investigation has been conducted for the prediction of the critical height at the onset of gas entrainment during single discharge from a stratified two-phase region through a side branch with a finite diameter. Two different models have been developed including a new criterion for the onset of gas entrainment, a simplified point-sink model and a finite-branch model. The results of the predicted critical heights at the onset of gas entrainment showed that the finite-branch model approaches the physical limits at low Froude numbers. However, as the values of the Froude number increased, the predicted values of both models eventually converged to the same value. Based on the results of the models, the critical height corresponding to the onset of gas entrainment was found to be a function of Froude number and fluid densities. The results of both models are compared with available experimental data. The comparisons illustrate a very good agreement between the measured and predicted values.

Modeling of the Onset of Gas Entrainment From a Stratified Two-Phase Region Through Branches on a Curved Surface

2005 ◽  
Vol 128 (4) ◽  
pp. 717-725 ◽  
Author(s):  
A. F. Andaleeb ◽  
I. Hassan ◽  
W. Saleh ◽  
T. Ahmad
Keyword(s):  
Froude Number ◽  
Phase Region ◽  
Data Sets ◽  
Critical Height ◽  
Two Phase ◽  
Gas Entrainment ◽  
Physical Limit ◽  
Predicted Values ◽  
Branch Size ◽  
Feeder Configuration

The present investigation is focused on the onset phenomena from a stratified two-phase region through a single branch located on a semi-circular wall, resembling a circular reservoir of a CANDU header-feeder configuration. Two different models have been developed, over the whole range of branch Froude number, to predict the critical height at the onset of gas-entrainment. The results showed that there is both a maximum and a minimum physical limit of prediction, which depends on the branch size and configuration. Also, at a distinct range of Froude numbers within the physical limits, the predicted values of both models collaborated to the same values. The critical height corresponding to the onset of gas entrainment was found to be a function of the branch orientation and Froude number. Three different experimental data sets at branch orientation angles of zero, 45, and 90 degrees were used to validate the present models. A good concurrence was illustrated between the experimental and theoretical values.

scholarly journals Implementation of the BEM skewed-wake model within the multibody aero-elastic solver Cp-Lambda

2020 ◽  
Vol 173 ◽  
pp. 02004
Author(s):  
Igor Petrović ◽  
Filippo Campagnolo ◽  
Tadej Kosel ◽  
Carlo L. Bottasso
Keyword(s):  
Experimental Data ◽  
Wind Tunnel ◽  
Wind Turbine ◽  
Flow Conditions ◽  
Aerodynamic Loads ◽  
Model Predictions ◽  
Wind Tunnel Data ◽  
Wake Model ◽  
Nrel Phase Vi ◽  
Local Variability

To account for the problem of an azimuthally constant induction in the BEM method, which influences on incorrectly predicted aerodynamic loads in the yawed flow, a skewed-wake model implementation to the BEM method has been performed. The numerical aerodynamic loads have been compared with the wind tunnel data of the NREL Phase VI and against another numerical campaign. At first, the model predictions have been validated against experimental data performed with aligned flow conditions, showing a reasonable match. Successively, the model predictions are validated against experimental results obtained with the wind turbine yawed. Results show, a possible better prediction of loads at yawed flow with Skewed-Wake correction, however the method does not overall correlate better, compared to the BEM method with implemented local variability of the induction factor.

Venturi tube and single pipe inlet as gas distributors in hydrogenation of rape seed oil

1987 ◽  
Vol 52 (12) ◽  
pp. 2876-2885
Author(s):  
Milan Rylek ◽  
Petr Svoboda ◽  
Jiří Souček
Keyword(s):  
Seed Oil ◽  
Venturi Tube ◽  
Stirred Tank ◽  
Hydrogenation Rate ◽  
Rape Seed ◽  
Tank Reactor ◽  
Scale Unit ◽  
Single Pipe ◽  
Pipe Inlet ◽  
Made In

The effect of hydrogenation conditions on rate of hydrogenation of rape seed oil was studied in a laboratory stirred tank reactor of 250 ml volume, with nickel on kieselguhr catalyst within the range of conditions (150 ⪬ t(°C) ⪬ 190), (0.1 ⪬ P(MPa) ⪬ 1.0), and (0.01 ⪬ cNi(%) ⪬ 0.37). On the basis of these results a comparison of the effect of a Venturi tube and single pipe gas inlet as gas distributors on hydrogenation rate was made in a bench scale unit of 5 l volume.

scholarly journals An approach to the modeling of a virtual thermal manikin

2014 ◽  
Vol 18 (4) ◽  
pp. 1413-1423 ◽  
Author(s):  
Dragan Ruzic ◽  
Sinisa Bikic
Keyword(s):  
Turbulence Models ◽  
Thermal Conditions ◽  
Heat Fluxes ◽  
Thermal Manikin ◽  
Flow Conditions ◽  
Body Segments ◽  
Nominal Size ◽  
Natural Flow ◽  
Good Agreement ◽  
Made In

The aim of the research described in this paper, is to make a virtual thermal manikin that would be simple, but also robust and reliable. The virtual thermal manikin was made in order to investigate thermal conditions inside vehicle cabins. The main parameters of the presented numerical model that were investigated in this paper are mesh characteristics and turbulence models. Heat fluxes on the manikin's body segments obtained from the simulations were compared with published results, from three different experiments done on physical thermal manikins. The presented virtual thermal manikin, meshed with surface elements of 0.035 m in nominal size (around 13,600 surface elements) and in conjunction with the two-layer RANS Realizable k-? turbulence model, had generally good agreement with experimental data in both forced and natural flow conditions.

scholarly journals Through what mechanisms do protected areas affect environmental and social outcomes?

2015 ◽  
Vol 370 (1681) ◽  
pp. 20140267 ◽  
Author(s):  
Paul J. Ferraro ◽  
Merlin M. Hanauer
Keyword(s):  
Experimental Data ◽  
Protected Areas ◽  
Empirical Evidence ◽  
Strong Evidence ◽  
Protected Area ◽  
Evidence Base ◽  
Social Outcomes ◽  
Causal Effects ◽  
The Past ◽  
Made In

To develop effective protected area policies, scholars and practitioners must better understand the mechanisms through which protected areas affect social and environmental outcomes. With strong evidence about mechanisms, the key elements of success can be strengthened, and the key elements of failure can be eliminated or repaired. Unfortunately, empirical evidence about these mechanisms is limited, and little guidance for quantifying them exists. This essay assesses what mechanisms have been hypothesized, what empirical evidence exists for their relative contributions and what advances have been made in the past decade for estimating mechanism causal effects from non-experimental data. The essay concludes with a proposed agenda for building an evidence base about protected area mechanisms.

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