A RELAP5/MOD3 Model for the Estimation of Air Pull-Through for a Draining Tank

2004 ◽  
Author(s):  
D. S. Lucas ◽  
R. Riemke
Keyword(s):  
Air Entrainment ◽  
Air Bubble ◽  
Vortex Model ◽  
Pull Through ◽  
Entrained Air

An air pull-through vortex model was implemented in RELAP5/MOD3 to investigate air-entrainment from a draining tank. Surge tanks covered by an air bubble are vulnerable to the entrainment of air into the liquid. If such a system is connected to a pump the possibility of entrained air from draining resulting in cavitation and pump degradation is possible.

A Condition for an Air Entrainment by Breaking the Surface Waves at the Free Surface

2005 ◽  
Author(s):  
Ho-Yun Nam ◽  
Jong-Man Kim ◽  
Byoung-Hae Choi ◽  
Jong-Hyeun Choi
Keyword(s):  
Free Surface ◽  
Surface Wave ◽  
Water Flow Rate ◽  
Air Entrainment ◽  
Vessel Diameter ◽  
Test Facility ◽  
Critical Conditions ◽  
Air Bubble ◽  
Water Test ◽  
Entrained Air

An experimental study has been carried out to measure the critical conditions for the inception of an air entrainment by breaking the surface wave at the free surface in the water test facility. The experimental parameters are the vessel diameter, the nozzle diameter, the mean water-level and the water flow rate. More than 400 experimental data which show whether the air is entrained or not at a given experimental condition are obtained, and an experimental correlation that describes the air entrainment condition is developed. The correlation is described by the ratio between the diameter and height of the vessel, the ratio between the diameter of the nozzle and the height of the vessel, the modified Froude number and a modified Weber number. In this experiment two cases of air entrainment are observed. One case is that the air entrainment occurred due to the destruction of the surface wave from the center, and the other case is due to the crash of the water wave to the vessel wall. Theses two cases occur irregularly and the entrained air bubble distributes uniformly in the water.

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.

Air Entrainment and Bubble Generation by a Hydrofoil in a Turbulent Channel Flow

2019 ◽  
Author(s):  
Ichiro Kumagai ◽  
Kakeru Taguchi ◽  
Chiharu Kawakita ◽  
Tatsuya Hamada ◽  
Yuichi Murai
Keyword(s):  
Channel Flow ◽  
Flow Rate ◽  
High Speed ◽  
Air Flow ◽  
Air Entrainment ◽  
Air Bubbles ◽  
Air Flow Rate ◽  
Bubble Generation ◽  
Gas Liquid Flow ◽  
Entrained Air

Abstract Air entrainment and bubble generation by a hydrofoil bubble generator for ship drag reduction have been investigated using a small high-speed channel tunnel with the gap of 20 mm in National Maritime Research Institute (NMRI). A hydrofoil (NACA4412, chord length = 40 mm) was installed in the channel and an air induction pipe was placed above the hydrofoil. The flow rate of the entrained air was quantitatively measured by thermal air flow sensors at the inlet of the air induction pipe. The gas-liquid flow around the hydrofoil was visualized by a backlight method and recorded by a high-speed video camera. As the flow velocity in the channel increased, the negative pressure generated above the suction side of the hydrofoil lowered the hydrostatic pressure in the channel, then the atmospheric air was entrained into the channel flow. The entrained air was broken into small air bubbles by the turbulent flow in the channel. The threshold of air entrainment, the air flow rate, and gas-liquid flow pattern depends on Reynolds number, angle of attack (AOA), and hydrofoil type. We identified at least three modes of air entrainment behavior: intermittent air entrainment, stable air entrainment, and air entrainment with a ventilated cavity. At high flow speed in our experimental condition (9 m/s), a large volume of air bubbles was generated by this hydrofoil system (e.g. air flow rate was 50 l/min for NACA4412 at AOA 16 degrees), which has a high potential to reduce ship drag.

Effect of Entrained Air on Cavitation Damage

1974 ◽  
Vol 1 (1) ◽  
pp. 97-107 ◽  
Author(s):  
S. O. Russell ◽  
G. J. Sheehan
Keyword(s):  
High Velocity ◽  
Additional Data ◽  
Air Entrainment ◽  
Test Facility ◽  
Hydraulic Structures ◽  
Cavitation Damage ◽  
Water Flows ◽  
Velocity Flow ◽  
High Head ◽  
Entrained Air

When water flows at high velocity over a surface, quite small boundary irregularities may trigger cavitation which can, in turn, cause extensive damage. Concrete surfaces downstream from high head outlet gates are particularly vulnerable to cavitation damage.Operating experience and previous experimental work suggest that cavitation damage can be greatly reduced and, in some cases, eliminated by entrained air in the water.Experiments were carried out with a special high head test facility in Vancouver to obtain additional data on the effect of air entrainment. These tests confirmed its effectiveness. In this paper, previous evidence is reviewed, the experiments are described, and the results presented. Finally suggestions are made about the design of hydraulic structures which involve high velocity flow.

scholarly journals Universal mechanism for air entrainment during liquid impact

2016 ◽  
Vol 789 ◽  
pp. 708-725 ◽  
Author(s):  
Maurice H. W. Hendrix ◽  
Wilco Bouwhuis ◽  
Devaraj van der Meer ◽  
Detlef Lohse ◽  
Jacco H. Snoeijer
Keyword(s):  
Experimental Data ◽  
Air Entrainment ◽  
Stokes Number ◽  
Liquid Pool ◽  
Boundary Integral ◽  
Boundary Integral Method ◽  
Rigid Sphere ◽  
Entrained Air ◽  
The Impact ◽  
Universal Mechanism

When a millimetre-sized liquid drop approaches a deep liquid pool, both the interface of the drop and the pool deform before the drop touches the pool. The build-up of air pressure prior to coalescence is responsible for this deformation. Due to this deformation, air can be entrained at the bottom of the drop during the impact. We quantify the amount of entrained air numerically, using the boundary integral method for potential flow for the drop and the pool, coupled to viscous lubrication theory for the air film that has to be squeezed out during impact. We compare our results with various experimental data and find excellent agreement for the amount of air that is entrapped during impact onto a pool. Next, the impact of a rigid sphere onto a pool is numerically investigated and the air that is entrapped in this case also matches with available experimental data. In both cases of drop and sphere impact onto a pool the numerical air bubble volume $V_{b}$ is found to be in agreement with the theoretical scaling $V_{b}/V_{drop/sphere}\sim \mathit{St}^{-4/3}$, where $\mathit{St}$ is the Stokes number. This is the same scaling as has been found for drop impact onto a solid surface in previous research. This implies a universal mechanism for air entrainment for these different impact scenarios, which has been suggested in recent experimental work, but is now further elucidated with numerical results.

scholarly journals A Study of Bubble Entrainment as Related to Runner Velocity in Aluminum Sand Castings Using the Cosworth Process

2007 ◽  
Vol 539-543 ◽  
pp. 398-403 ◽  
Author(s):  
John C. Burford ◽  
Jerry Sokolowski
Keyword(s):  
Transient Flow ◽  
Metal Flow ◽  
Critical Value ◽  
Low Velocity ◽  
Air Bubble ◽  
Aluminum Castings ◽  
Bubble Entrainment ◽  
Open Production ◽  
Entrained Air ◽  
Flow Experiences

Traditional gravity pour down-sprue methods of filling moulds in the making of aluminum castings inherently lead to oxide and air bubble entrainment. The reason for this is found in the high velocities the metal flow experiences during the filling of a mould. The Nemak Windsor Aluminum Plant (WAP) produces cylinder blocks using the low-pressure Cosworth process, which includes low velocity up-hill filling of the sand mould package. This doctrine is followed in all except one part of the process: the runner system. The nature of the resulting defect is generally known as Head Deck Porosity. Runners were cast full in open production runners at three different velocities with the resulting quickly chilled castings analyzed using X-ray radioscopy, and Scanning Electron Microscopy. Results reveal that the subject bubble porosity is indeed the result of air entrained during initial transient flow within the production runner system whose velocity is higher than the critical value of 0.5ms-1. This theoretical value is corroborated by experimental results. In addition, a new "sessile" runner of optimized shape, filled at a velocity slower than the critical value, is proposed and analyzed using Magmasoft mould fill modelling software. The design can potentially replace the existing runner providing a casting free of entrained air.

Construction and Evaluation of a Versatile Graphite Filament Atomizer for Atomic Absorption Spectrometry

1972 ◽  
Vol 26 (6) ◽  
pp. 606-611 ◽  
Author(s):  
C. J. Molnar ◽  
R. D. Reeves ◽  
J. D. Winefordner ◽  
M. T. Glenn ◽  
J. R. Ahlstrom ◽  
...  
Keyword(s):  
Atomic Absorption ◽  
Air Entrainment ◽  
Absorption Spectrometry ◽  
Ambient Air ◽  
Atomic Fluorescence ◽  
Fluorescence Studies ◽  
Absorption Studies ◽  
Entrained Air ◽  
Graphite Rod ◽  
Absorption Measurements

A simple, versatile atomizer of the electrically heated graphite rod type is described and used for atomic absorption studies. The atomizer utilizes a burner head (directly under the rod) to produce a H2-Ar-entrained air flame; the flame is primarily useful in minimizing ambient air entrainment in order to maintain a highly reducing environment directly above the rod where atomic absorption measurements are generally taken. Temperature profiles of the H2-Ar-entrained air flames and also the temperatures of the graphite rod at various currents were measured, and appropriate plots are given. Several types of graphite and several different ways of holding liquid samples on the atomizer were also compared. Detection limits and analytical curves of aqueous solutions of Ag, As, Au, Cr, Cu, Fe, Mg, Ni, and Pb and oil-based solutions of Ag, Cu, and Fe are given. This atomizer should be of even greater use for atomic fluorescence studies.

Effects of Entrained Air on the Performance of a Horizontal Axial-Flow Pump

1983 ◽  
Vol 105 (4) ◽  
pp. 382-388 ◽  
Author(s):  
Mitsukiyo Murakami ◽  
Kiyoshi Minemura
Keyword(s):  
Weber Number ◽  
Radial Flow ◽  
Liquid Flow Rate ◽  
Axial Flow ◽  
Analytical Models ◽  
Air Bubble ◽  
Axial Flow Pump ◽  
Entrained Air ◽  
Air Void ◽  
Flow Pump

The performance of an axial-flow pump was investigated under air-admitting conditions and the results were compared with those obtained for radial-flow pumps investigated in our previous studies. For the axial-flow pump we measured head as a function of impeller speed, liquid flow rate, and air void fraction. Flow visualization was performed and we correlated air bubble size as a function of Weber number based on mean impeller velocity. Overall flow patterns and the locations of air coalesence within the impeller were observed and diagrammed. These data contribute to earlier data obtained by ourselves and others to develop analytical models to predict pump performance degradation due to air admittance.

scholarly journals Shortwave infrared imaging setup to study entrained air bubble dynamics in a MEMS-based piezo-acoustic inkjet printhead

2019 ◽  
Vol 60 (8) ◽  
Author(s):  
Arjan Fraters ◽  
Tim Segers ◽  
Marc van den Berg ◽  
Hans Reinten ◽  
Herman Wijshoff ◽  
...  
Keyword(s):  
Bubble Dynamics ◽  
Infrared Imaging ◽  
Air Bubble ◽  
Entrained Air ◽  
Shortwave Infrared ◽  
Inkjet Printhead ◽  
Imaging Setup

scholarly journals Volume of Fluid Computations of Gas Entrainment and Void Fraction for Plunging Liquid Jets to Aerate Wastewater

2020 ◽  
Vol 4 (4) ◽  
pp. 56
Author(s):  
Ali Bahadar
Keyword(s):  
Void Fraction ◽  
Volume Fraction ◽  
Piecewise Linear ◽  
Industrial Effluents ◽  
Air Entrainment ◽  
Interfacial Area ◽  
Volume Of Fluid ◽  
Liquid Jets ◽  
Entrainment Rate ◽  
Entrained Air

Among various mechanisms for enhancing the interfacial area between gases and liquids, a vertical liquid jet striking a still liquid is considered an effective method. This method has vast industrial and environmental applications, where a significant application of this method is to aerate industrial effluents and wastewater treatment. Despite the huge interest and experimental and numerical efforts made by the academic and scientific community in this topic, there is still a need of further study to realize improved theoretical and computational schemes to narrow the gap between the measured and the computed entrained air. The present study is a numerical attempt to highlight the air being entrained by water jet when it intrudes into a still water surface in a tank by the application of a Volume of Fluid (VOF) scheme. The VOF scheme, along with a piecewise linear interface construction (PLIC) algorithm, is useful to follow the interface of the air and water bubbly plume and thus can provide an estimate of the volume fraction for the gas and the liquid. Dimensionless scaling derived from the Fronde number and Reynolds number along with geometric similarities due to the liquid jet’s length and nozzle diameter have been incorporated to validate the experimental data on air entrainment, penetration and void fraction. The VOF simulations for void fraction and air-water mixing and air jet’s penetration into the water were found more comparable to the measured values than those obtained using empirical and Euler-Euler methods. Although, small overestimates of air entrainment rate compared to the experiments have been found, however, VOF was found effective in reducing the gap between measurements and simulations.

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