scholarly journals Modeling of Kinetics of Air Entrainment in Water Produced by Vertically Falling Water Flow

2014 ◽  
Vol 20 (3) ◽  
Author(s):  
Adelė VAIDELIENĖ ◽  
Arvaidas GALDIKAS ◽  
Paulius TERVYDIS
Keyword(s):  
Water Flow ◽  
Air Entrainment ◽  
Kinetics Of

Flow over a stepped chute with and without macro-roughness elements

2004 ◽  
Vol 31 (5) ◽  
pp. 880-891 ◽  
Author(s):  
Mehmet Ali Kökpinar
Keyword(s):  
Water Flow ◽  
High Speed ◽  
Length Distribution ◽  
Air Entrainment ◽  
Air Concentration ◽  
Bubble Frequency ◽  
Two Phase ◽  
Air Bubble ◽  
Roughness Elements ◽  
Stepped Chute

High-speed two-phase flows over a 30° stepped flume were experimentally investigated using macro-roughness elements. The roughness elements included combinations of steps and horizontal strips. Local values of air concentration, air bubble frequency, and mean chord lengths were measured by a fiber-optical instrumentation system in the air–water flow region. The range of unit discharge of water was varied from 0.06 to 0.20 m2/s. Three step configurations were studied: (i) without macro-roughness elements, (ii) with macro-roughness elements on each step, and (iii) with macro-roughness elements on each second step (AMR configuration). The results were compared in terms of onset flow conditions and internal air–water flow parameters such as local air concentration, mean air bubble chord length distribution, and air bubble frequency in the skimming flow regime. It was observed that the AMR configuration produced the maximum free-surface aeration among the other configurations. This alternative step geometry has potential for less cavitation damage than conventional step geometry because of the greater air entrainment.Key words: stepped chute, air-entrainment, air-water flow properties, macro-roughness elements, skimming flow.

scholarly journals Experimental investigations of air entrainment in transition and skimming flows down a stepped chute

2002 ◽  
Vol 29 (1) ◽  
pp. 145-156 ◽  
Author(s):  
H Chanson ◽  
L Toombes
Keyword(s):  
Free Surface ◽  
Water Flow ◽  
Air Entrainment ◽  
Stepped Spillway ◽  
Transition Flow ◽  
Flow Properties ◽  
Flow Measurements ◽  
Surface Aeration ◽  
Stepped Chute ◽  
Uniform Equilibrium

Stepped spillways have been used for about 3500 years. The last few decades have seen the development of new construction materials, design techniques, and applications, for example, embankment overtopping protection systems. Although it is commonly acknowledged that free-surface aeration is significant in stepped chutes, experimental data are scarce, often limited to very steep slopes (α ~ 50°). This paper presents an experimental study conducted in a large-size stepped chute (α = 22°, h = 0.1 m, W = 1 m). Observations demonstrate the existence of a transition flow pattern for intermediate flow rates between nappe and skimming flows. Detailed air–water flow measurements were conducted in both transition and skimming flows, immediately downstream of the inception point of free-surface aeration where uniform equilibrium flow conditions were not achieved. In skimming flows, a complete characterization is developed for the distributions of void fraction, bubble count rate, and velocity, and flow resistance data are compared with other studies. Transition flows exhibit significantly different air–water flow properties. They are highly aerated, requiring the design of comparatively high chute sidewalls.Key words: stepped spillway, air entrainment, two-phase flow properties, skimming flow, transition flow.

scholarly journals Assessment and Prediction of Air Entrainment and Geyser Formation in a Bottom Outlet: Field Observations and CFD Simulation

Fluids ◽  
2020 ◽  
Vol 5 (4) ◽  
pp. 203
Author(s):  
James Yang ◽  
Penghua Teng ◽  
Junhu Nan ◽  
Shicheng Li ◽  
Anders Ansell
Keyword(s):  
Water Flow ◽  
Cfd Simulation ◽  
Three Dimensional ◽  
Air Entrainment ◽  
Cfd Modeling ◽  
Two Phase ◽  
Gate Operation ◽  
Flow Features ◽  
Air Pockets ◽  
Bottom Outlet

Air entrainment at the intake of a bottom outlet often gives rise to air pockets in its conduit and formation of geysers. The outlet in question comprises a bulkhead gate, gate shaft, horizontal conduit, and exit. Operations show that it suffers from appreciable flow fluctuations and blowouts in the tailwater, which leads to gate operation restrictions. For the purpose of understanding the hydraulic phenomenon, both prototype discharge tests and three-dimensional computational fluid dynamics (CFD) modeling of two-phase flows are performed. The operational focus of the facility are small and large gate openings. The CFD results reveal that, with air entrained in the gate shaft, continual breakup and coalescence of air bubbles in the conduit typify the flow. At small openings below 1 meter, the air–water flow is characterized by either distinct blowouts of regular frequency or continuous air release. In terms of geyser behaviors inclusive of frequency, the agreement is good between field and numerical studies. At large openings, the gate becomes fully submerged, and the flow is discharged without air entrainment and blowouts. The paper showcases the air–water flow features in a typical bottom outlet layout in Sweden, which is intended to serve as an illustration of the study procedure for other similar outlets.

scholarly journals Experimental Characterization of Air Entrainment in Rectangular Free Falling Jets

Water ◽  
2020 ◽  
Vol 12 (6) ◽  
pp. 1773
Author(s):  
José M. Carrillo ◽  
Patricio R. Ortega ◽  
Luis G. Castillo ◽  
Juan T. García
Keyword(s):  
Phase Change ◽  
Water Flow ◽  
Void Fraction ◽  
Cross Sections ◽  
Scale Effects ◽  
Air Entrainment ◽  
Phase Detection ◽  
Detection Probe ◽  
Relative Differences ◽  
Free Falling

This experimental study presents an analysis of the air–water flow in rectangular free-falling jets. The measurements were obtained downstream of a 1.05 m wide sharp-crested weir. The properties of the air–water flow were registered in several cross-sections of the nappe. A conductivity phase detection probe was employed, sampling at 20 kHz. Three different specific flows were considered, with energy head over the crest of 0.080, 0.109 and 0.131 m to avoid scale effects. To analyze the flow properties, air–water parameters during the fall, such as the phase change spatial distribution, air–water phase change of frequency, Sauter mean diameter, bubble chord length, turbulent intensities and spectral analyses, were studied. The jet thickness behaviors (inner jet core and free surface) were also analyzed in the falling jet. The jet thickness related to a void fraction of 90% seems to be similar to the theoretical proposal obtained by Castillo et al. (2015), while the jet thickness related to a void fraction of 10% seems to be similar to the jet thickness due to gravitational effects. The results show relative differences in the behavior of the upper and lower sides of the nappe. The experimental data allow us to improve on and complement previous research.

The Problem of Predicting Rate of Heat Release in Diesel Engines

1969 ◽  
Vol 184 (10) ◽  
pp. 192-202 ◽  
Author(s):  
H. C. Grigg ◽  
M. H. Syed
Keyword(s):  
Diesel Engine ◽  
Heat Release ◽  
Chemical Kinetics ◽  
Diesel Engines ◽  
Turbulent Mixing ◽  
Air Entrainment ◽  
Experimental Results ◽  
Fuel Sprays ◽  
Rate Of Heat Release ◽  
Kinetics Of

Two simple models for the rate of heat release in diesel engines are described. The factors taken into account in the models are rate of entrainment of air into the fuel sprays, the rate of turbulent mixing of fuel and air within the spray, and the chemical kinetics of burning. The models differ in their treatment of the rate of air entrainment. Comparisons are made with experimental results for a diesel engine running at two speeds and a variety of turbocharging ratios. The overall agreement with experiment in respect of shape of rate of heat release diagram is good, with the exception of the naturally aspirated cases where the rate of air entrainment is too low.

Air-water flow in bottom outlets

2000 ◽  
Vol 27 (3) ◽  
pp. 454-462 ◽  
Author(s):  
Jürg Speerli ◽  
Willi H Hager
Keyword(s):  
Water Flow ◽  
High Velocity ◽  
Flow Characteristics ◽  
Design Procedure ◽  
Air Entrainment ◽  
Design Guidelines ◽  
Air Concentration ◽  
Tunnel Length ◽  
Mixture Flow ◽  
Bottom Outlets

Bottom outlets involve high-velocity air-water flow. Depending on the tunnel length, both air entrainment and air detrainment processes are significant. These processes are evaluated using a hydraulic model consisting of a long rectangular tunnel with a bottom slope larger than the critical slope. Expressions are presented for the maximum air concentration and its streamwise development along the tunnel. A prediction of mixture flow depth along the tunnel is developed. Design guidelines are presented relating to the flow pattern required, the air supply system, and the downstream submergence. The effect of tunnel length on the development of mixture flow characteristics is also outlined. A typical example shows the design procedure for bottom outlets.Key words: air entrainment, air-water flow, high-velocity flow, tunnel flow.

The water relations of hemlock (Tsuga canadensis). V. The localization of resistances to bulk water flow

1975 ◽  
Vol 53 (10) ◽  
pp. 1078-1084 ◽  
Author(s):  
M. T. Tyree ◽  
C. Caldwell ◽  
J. Dainty
Keyword(s):  
Activation Energy ◽  
Water Flow ◽  
Water Exchange ◽  
Careful Analysis ◽  
Bulk Water ◽  
Exponential Process ◽  
Measurable Amount ◽  
Pressure Bomb ◽  
Overall Resistance ◽  
Kinetics Of

The pressure-bomb technique has been used to measure the kinetics of water exchange while a plant enclosed in a pressure bomb evolves from one equilibrium balance pressure to another. In earlier studies two observations were made. (1) The kinetics of water exchange appeared to be described by an exponential process in which three populations of cells exchange water with apoplast independently of each other. (2) The temperature dependence of the tempo of water exchange yielded an activation energy of 25.9 ± 0.6 × 103 J/mol, which is higher than the activation energy for laminar flow of water in pipes (= 17 × 103 J/mol). These results have been repeated and a more careful analysis has been conducted involving infiltration of air spaces in leaves with water and the selective removal of the leaves. It now appears that the xylem network up to (but not including) the leaves contributes about two thirds of the resistance to water flow in whole shoots 15 to 40 g in fresh weight. Presumably leaves near the cut basal end of the shoot experience a smaller xylem resistance than leaves near the apex. The kinetics of water exchange from water in the air spaces of infiltrated shoots indicates that there is a barrier at the air–water interface of leaves that equals the normal shoot resistance to bulk water flow. The activation energy for water flow through the xylem alone was measured to be about 17 × 103 J/mol. Although the leaves contribute a measurable amount to the overall resistance to water flow, the mathematical description of the system is much more complicated than previously supposed.

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