Effect of Physical Properties on Gas Entrainment Rate From Free Surface by Vortex (2nd Report)

2014 ◽  
Author(s):  
Yasuo Koizumi ◽  
Naosuke Ohte ◽  
Hideki Kamide ◽  
Shuji Ohno ◽  
Kei Ito
Keyword(s):  
Surface Tension ◽  
Free Surface ◽  
High Speed ◽  
Silicone Oil ◽  
Liquid Velocity ◽  
Test Fluid ◽  
Entrainment Rate ◽  
Flow State ◽  
Exit Velocity ◽  
Gas Entrainment

A sodium-cooled fast breeder reactor is now at the developing stage in Japan. One concern for safety is cover gas entrainment into the sodium coolant. The gas entrainment rate into liquid by the vortex formed on the free surface was examined experimentally. Four kinds of test fluid were used; water at 25 °C, water at 60 °C, 20 cSt silicone oil and kerosene. Gas was air. The flow state of gas entrainment was visually observed by using a high speed video camera. The gas entrainment rate into liquid was measured. Following conclusions were obtained. When exit velocity was low, bubble-type gas entrainment occurred. As the exit velocity increased, the gas entrainment type turned from the bubble type to a vortex type and gas entrainment rate considerably increased. The relation between gas entrainment rate and liquid velocity was mainly affected by the viscosity of liquid. As viscosity became large, higher exit velocity was required to get the same gas entrainment rate. The effect of surface tension on the gas entertainment rate was minor or little. No systematic trend by the surface tension was noticed in the gas entrainment rate. Present results of the onset of the bubble type gas entrainment are well expressed with both the modified Baum and the modified Takahashi et al. correlation although the modified Takahashi et al. correlation provides a little better prediction than the modified Baum correlation. A flow state at the outlet piping has significant effect on the gas entrainment rate. The dimension of the outlet piping may become important to consider the gas entrainment rate in the vortex type region.

Measurement of Gas Entrainment Rate From Free Surface by Vortex

2012 ◽  
Author(s):  
Yasuo Koizumi ◽  
Naosuke Ohte ◽  
Kamide Hideki ◽  
Shuji Ohno ◽  
Kei Ito
Keyword(s):  
Free Surface ◽  
High Speed ◽  
Silicone Oil ◽  
Liquid Velocity ◽  
Liquid Level ◽  
Test Fluid ◽  
Entrainment Rate ◽  
Flow State ◽  
Gas Entrainment ◽  
Test Vessel

A sodium-cooled fast breeder reactor is now at the developing stage in Japan. One concern for safety is cover gas entrainment into the sodium coolant. The gas entrainment rate into liquid by the vortex formed on the free surface was examined experimentally. Liquid flowed into a cylindrical vessel from a wall tangentially. Swirl flow was formed in the vessel, and then liquid drained from the bottom outlet of the vessel. A hollow vortex was formed on the free surface in the test vessel. Air was entrained under the free surface of the vortex and carried away from the bottom of the vessel. The flow state of the gas entrainment was visually observed by using a high speed video camera. The gas entrainment rate into liquid was measured. In the present experiments, test fluid was changed from water in the previous experiments to 20 cSt silicone oil. The liquid level in the test vessel was 25 mm in the present experiments. Only the vortex-type gas-entrainment was observed as in the previous experiments since the liquid level was low. The flow state observed at the flow visualization section of the outlet pipe was only a semi-annular flow. The initiation of the gas entrainment was delayed in the case of silicone oil compared with the case of water. The increasing rate of the gas entrainment to the liquid velocity is milder in the case of silicone oil than in the case of water.

Effect of Physical Properties on Gas Entrainment Rate From Free Surface by Vortex

2013 ◽  
Author(s):  
Ohte Naosuke ◽  
Yasuo Koizumi ◽  
Hideki Kamide ◽  
Shuji Ohno ◽  
Kei Ito
Keyword(s):  
Surface Tension ◽  
Free Surface ◽  
Liquid Velocity ◽  
Wave Length ◽  
Test Fluid ◽  
Instability Wave ◽  
Entrainment Rate ◽  
Helmholtz Instability ◽  
Gas Entrainment ◽  
Bottom Outlet

Gas entrainment rate into liquid by a vortex formed on free surface was examined experimentally. Four kinds of test fluid were used; water at 25 °C, water at 60 °C, 20 cSt silicone oil and kerosene. Gas was air. The flow state of gas entrainment was visually observed by using a high speed video camera. The gas entrainment rate into liquid was measured. When liquid velocity was low, bubble-type gas entrainment occurred. As the liquid velocity increased, the gas entrainment type turned from the bubble type to a vortex type and gas entrainment rate considerably increased. The relation between gas entrainment rate and liquid velocity was mainly affected by the viscosity of liquid. As viscosity became large, higher liquid velocity was required to get the same gas entrainment rate. The effect of surface tension on the gas entertainment rate was minor or little. No systematic trend by the surface tension was noticed in the gas entrainment rate As liquid velocity increased, vortex became deep in the test vessel without gas entrainment occurrence and eventually a vortex tip reached a bottom outlet. After the vortex tip reached the bottom outlet, the tip penetrated into an outlet piping. Vortex growing speed becomes slow. Then, bubble-type gas entrainment was initiated from the vortex tip. A further increase in liquid velocity resulted in a transition from the bubble-type gas entrainment to vortex-type gas entrainment. By assuming that liquid flow was free falling film flow in an outlet pipe, liquid velocity was derived. The Kelvin-Helmholtz instability wave length was calculated for this liquid velocity. The wavelength that was observed at the vortex tip interface in the condition that bubbles were torn off from the tip was close to the Kelvin-Helmholtz instability wave length in both bubble-type and vortex-type gas entrainment.

Study on Gas Entrainment Rate Into Liquid From Free Surface by Vortex

2010 ◽  
Author(s):  
Yasuo Koizumi ◽  
Kei Ito ◽  
Hiroyuki Ohshima ◽  
Hiroyasu Ohtake
Keyword(s):  
Free Surface ◽  
High Speed ◽  
Bubbly Flow ◽  
Video Camera ◽  
Swirl Flow ◽  
Entrainment Rate ◽  
Flow State ◽  
Gas Entrainment ◽  
High Speed Video Camera ◽  
Bottom Outlet

The gas entrainment rate into liquid by the vortex formed on the free surface was examined experimentally. Water flowed into a cylindrical vessel from a wall tangentially. Swirl flow was formed in the vessel, and then water left from the bottom outlet of the vessel. The flow state of the entrainment was visually observed by using a high speed video camera. The gas entrainment rate into water was measured. A stable vortex was formed in the test vessel. Whether the bottom of the vortex reached the bottom outlet of the vessel was dependent on the downward velocity of water; the velocity at the bottom outlet. Before the vortex tip reached the bottom of the vessel, bubbles were periodically torn off from the bottom tip of the vortex and the bubble-type gas entrainment was observed. After the bottom of the vortex reached the bottom of the vessel, the gas entrainment turned to the vortex-type gas entrainment. When the gas entrainment turned to the vortex-type gas entrainment, the flow state in the outlet pipe changed from the bubbly flow to the churn flow. After the gas entrainment varied from the bubble-type to the vortex-type, the gas entrainment rate increased drastically. The downward water velocities at the initiation of the bubble-type gas entrainment and at the transition from the bubble-type to the vortex-type gas entrainment became fast as the liquid level in the vessel became deep. The Kelvin-Helmholtz instability did not explain the bubble torn-off from the vortex tip.

Numerical investigation of shear-flow free-surface turbulence and air entrainment at large Froude and Weber numbers

2019 ◽  
Vol 880 ◽  
pp. 209-238 ◽  
Author(s):  
Xiangming Yu ◽  
Kelli Hendrickson ◽  
Bryce K. Campbell ◽  
Dick K. P. Yue
Keyword(s):  
Surface Tension ◽  
Free Surface ◽  
Shear Flow ◽  
Power Law ◽  
Outer Surface ◽  
Air Entrainment ◽  
Entrainment Rate ◽  
Surface Layers ◽  
Surface Turbulence ◽  
Free Surface Turbulence

We investigate two-phase free-surface turbulence (FST) associated with an underlying shear flow under the condition of strong turbulence (SFST) characterized by large Froude ($Fr$) and Weber ($We$) numbers. We perform direct numerical simulations of three-dimensional viscous flows with air and water phases. In contrast to weak FST (WFST) with small free-surface distortions and anisotropic underlying turbulence with distinct inner/outer surface layers, we find SFST to be characterized by large surface deformation and breaking accompanied by substantial air entrainment. The interface inner/outer surface layers disappear under SFST, resulting in nearly isotropic turbulence with ${\sim}k^{-5/3}$ scaling of turbulence kinetic energy near the interface (where $k$ is wavenumber). The SFST air entrainment is observed to occur over a range of scales following a power law of slope $-10/3$. We derive this using a simple energy argument. The bubble size spectrum in the volume follows this power law (and slope) initially, but deviates from this in time due to a combination of ongoing broad-scale entrainment and bubble fragmentation by turbulence. For varying $Fr$ and $We$, we find that air entrainment is suppressed below critical values $Fr_{cr}$ and $We_{cr}$. When $Fr^{2}>Fr_{cr}^{2}$ and $We>We_{cr}$, the entrainment rate scales as $Fr^{2}$ when gravity dominates surface tension in the bubble formation process, while the entrainment rate scales linearly with $We$ when surface tension dominates.

Physical Modeling of Gas Jet-Liquid Free Surface in Steelmaking Processes

2009 ◽  
Vol 1243 ◽  
Author(s):  
J. Solórzano-López ◽  
R. Zenit ◽  
C. González-Rivera ◽  
M. A. Ramírez-Argáez
Keyword(s):  
Free Surface ◽  
High Speed ◽  
Gas Flow ◽  
Liquid Velocity ◽  
Gas Jet ◽  
Main Process ◽  
Process Variables ◽  
Dimensionless Numbers ◽  
Liquid Free Surface ◽  
Vector Maps

ABSTRACTGas jets play a key role in several steelmaking processes as in the Basic Oxygen Furnace (BOF) or in the Electric Arc Furnace (EAF). They improve heat, mass and momentum transfer in the liquid bath, improve mixing of chemical species and govern the formation of foaming slag in EAF. In this work experimental measurements are performed to determine the dimensions of the cavity formed at the liquid free surface when a gas jet impinges on it as well as liquid velocity vector maps measured in the zone affected by the gas jet. Cavities are measured using a high speed camera while the vector maps are determined using a Particle Image Velocimetry (PIV) technique. Both velocities and cavities are determined as a function of the main process variables: gas flow rate, distance from the nozzle to the free surface and lance angle. Cavity dimensions (depth and diameter) are statistically treated as a function of the process variables and also as a function of the adequate dimensionless numbers that govern these phenomena. It is found that Froude number and Weber number control the depression geometry.

scholarly journals Short-term dynamics of a density interface following an impact

2007 ◽  
Vol 577 ◽  
pp. 241-250 ◽  
Author(s):  
A. ANTKOWIAK ◽  
N. BREMOND ◽  
S. LE DIZÈS ◽  
E. VILLERMAUX
Keyword(s):  
Surface Tension ◽  
High Speed ◽  
Liquid Velocity ◽  
Short Term ◽  
Liquid Surface Tension ◽  
Image Velocimetry ◽  
Interface Curvature ◽  
Impulse Pressure ◽  
The Impact ◽  
Wetting Liquid

A tube filled with a perfectly wetting liquid falls axially under its own weight. In its gravity-free reference frame, the liquid interface is deformed by surface tension into a hemispherical shape. On impact of the tube on a rigid floor, the interface curvature reverses violently, forming a concentrated jet. If the contact angle at the tube wall is such that the interface is flat, the liquid rebounds as a whole with the tube, with no deformation. We analyse this phenomenon using an impulse pressure description, providing an exact description of the initial liquid velocity field at the impact, supported by high-speed image velocimetry measurements. This initial dynamics is insensitive to liquid surface tension and viscosity.

scholarly journals Numerical Investigation of Unsteady Cavitation Dynamics over a NACA66 Hydrofoil near a Free Surface

2020 ◽  
Vol 8 (5) ◽  
pp. 341 ◽  
Author(s):  
Tiezhi Sun ◽  
Qingmo Xie ◽  
Li Zou ◽  
Hao Wang ◽  
Chang Xu
Keyword(s):  
Free Surface ◽  
High Speed ◽  
Energy Content ◽  
Dynamic Mode Decomposition ◽  
Dynamic Mode ◽  
Flow State ◽  
Characteristic Mode ◽  
Mode Decomposition ◽  
Cavitation Intensity ◽  
Lift And Drag

Cavitation is a typical and unavoidable phenomenon for small waterline ships and high-speed vehicles. It creates a highly complex multiphase flow near the free surface and is primarily represented by the free surface-cavitation interaction. In this paper, the large-eddy method and Schnerr-Sauer cavitation model are combined to address the effects of a free surface on the cavitation dynamics of a NACA66 hydrofoil. The numerical method is validated by comparing the cavitation morphology and pressure with available experimental data. The results show that the presence of a free surface affects the cavitation evolution and hydrodynamic load characteristics. Compared with the non-free surface case for the same cavitation number, the free surface suppresses the cavitation intensity and increases the frequency of cavitation shedding. Furthermore, an improved dynamic mode decomposition method is applied to investigate the unsteady cavitation flow features. The results show a correlation between the characteristic mode and the flow state. Meanwhile, the presence of a free surface is found to reduce the energy content in each order mode and results in smaller scale of the coherent structure in higher-order modes. Moreover, with increasing distance from the hydrofoil to the free surface, the cavitation intensity increases, as well as the average lift and drag coefficients. In particular, significant free-surface unsteady fluctuations are observed in the wake region.

scholarly journals Modeling of the Free-Surface Vortex-Driven Bubble Entrainment into Water

Water ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 709
Author(s):  
Ryan Anugrah Putra ◽  
Dirk Lucas
Keyword(s):  
Free Surface ◽  
Bubble Size ◽  
Dynamics Simulation ◽  
Entrainment Rate ◽  
Modeling Framework ◽  
Two Phase ◽  
Gas Entrainment ◽  
Free Surface Vortex ◽  
Bubble Entrainment ◽  
Surface Vortex

The recently developed GENTOP (Generalized Two Phase Flow) concept, which is based on the multifield Euler‒Euler approach, was applied to model a free-surface vortex—a flow situation that is relevant for hydraulic intake. A new bubble entrainment model has been developed and implemented in the concept. In general, satisfactory agreement with the experimental data can be achieved. However, the gas entrainment can be significantly affected by several parameters or models used in the CFD (Computational Fluid Dynamics) simulation. The scale of curvature correction C s c a l e in the turbulence model, the coefficient in the entrainment model C e n t , and the assigned bubble size to be entrained have a significant influence on the gas entrainment rate. The gas entrainment increases with higher C s c a l e values, which can be attributed to the stronger rotation captured by the simulation. A smaller bubble size gives higher gas entrainment, while a larger bubble size leads to a smaller entrainment. The results also show that the gas entrainment can be controlled by adjusting the entrainment coefficient C e n t . Based on the modeling framework presented in this paper, further improvement of the physical modeling of the entrainment process should be done.

A Thermocapillary Convection Experiment in Microgravity

1995 ◽  
Vol 117 (3) ◽  
pp. 611-618 ◽  
Author(s):  
Y. Kamotani ◽  
S. Ostrach ◽  
A. Pline
Keyword(s):  
Surface Tension ◽  
Free Surface ◽  
Temperature Distribution ◽  
Laser Beam ◽  
Thermocapillary Convection ◽  
Silicone Oil ◽  
Free Surfaces ◽  
Numerical Predictions ◽  
Liquid Free Surface ◽  
Infrared Imager

Results are reported of the Surface Tension Driven Convection Experiment (STDCE) aboard the USML-1 Spacelab, which was launched on June 25, 1992. In the experiment, 10 cSt silicone oil was placed in an open 10-cm-dia circular container, which was 5 cm deep. The fluid was heated either by a cylinderical heater (1.11 cm diameter) located along the container centerline or by a CO2 laser beam to induce thermocapillary flow. Several thermistor probes were placed in the fluid to measure the temperature distribution. The temperature distribution along the liquid-free surface was measured by an infrared imager. Tests were conducted over a range of heating powers, laser-beam diameters, and free surface shapes. An extensive numerical modeling of the flow was conducted in conjunction with the experiments. Some results of the temperature measurements with flat free surfaces are presented in this paper and they are shown to agree well with the numerical predictions.

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