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.

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.

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.

scholarly journals On the incidence of Kelvin-Helmholtz instability for mass exchange process at the Earth’s magnetopause

2002 ◽  
Vol 20 (6) ◽  
pp. 757-769 ◽  
Author(s):  
R. Smets ◽  
D. Delcourt ◽  
G. Chanteur ◽  
T. E. Moore
Keyword(s):  
Mass Transfer ◽  
Solar Wind ◽  
Test Particle ◽  
Exchange Process ◽  
Wave Length ◽  
Velocity Shear ◽  
Mhd Waves ◽  
Instability Wave ◽  
Ion Leakage ◽  
Helmholtz Instability

Abstract. Due to the velocity shear imposed by the solar wind flowing around the magnetosphere, the magnetopause flanks are preferred regions for the development of a Kelvin-Helmholtz instability. Since its efficiency for momentum transfer across the magnetopause has already been established, we investigate its efficiency for mass transfer. Using nonresistive magnetohydrodynamic simulations to describe the magnetic field shape in the instability region, we use test-particle calculations to analyse particle dynamics. We show that the magnetopause thickness and the instability wave-length are too large to lead to nonadiabatic motion of thermal electrons from the magnetosphere. On the other hand, the large mass of H+, He+ and O+ ions leads to such nonadiabatic motion and we thus propose the Kelvin-Helmholtz instability as a mechanism for either magnetospheric ion leakage into the magnetosheath or solar wind ion entry in the magnetosphere. Test-particle calculations are performed in a dimensionless way to discuss the case of each type of ion. The crossing rate is of the order of 10%. This rate is anti-correlated with shear velocity and instability wavelength. It increases with the magnetic shear. The crossing regions at the magnetopause are narrow and localized in the vicinity of the instability wave front. As a Kelvin-Helmholtz instability allows for mass transfer through the magnetopause without any resistivity, we propose it as an alternate process to reconnection for mass transfer through magnetic boundaries. Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; MHD waves and instabilities) – Space plasma physics (numerical simulation studies)

Study on the Collapse of Water Jet

2011 ◽  
Author(s):  
Ryuhei Ikuta ◽  
Yasuo Koizumi ◽  
Hiroyuki Yoshida ◽  
Kazuyuki Takase
Keyword(s):  
Flow Velocity ◽  
High Speed ◽  
Wave Length ◽  
Water Jet ◽  
Instability Wave ◽  
Helmholtz Instability ◽  
Experimental Conditions ◽  
Small Perturbations ◽  
Dispersed Flow ◽  
Lower Position

Collapse of a water jet flowing out from a nozzle to the atmosphere was examined. The diameters of nozzles used in the experiments were 3, 6 and 8 mm. The flow state of the water jet was recorded with a high speed video camera. The collapse length was derived from recorded images. When the flow velocity was quite low, the surface of the water jet was smooth and small perturbations appeared at the lower position of the water jet. As the flow velocity was increased, the position where the small perturbations appeared came close to the nozzle outlet. The perturbations grew as these went downstream and lumps of water were formed at the lower position. When the flow velocity was further increased, successive waves came around on the surface of the water jet. The collapse of the water jet occurred in such a state that the lump of water was torn off from the jet. When the water jet velocity was high, the jet turned into a dispersed flow and the collapse occurred. The agreement of the measured results and the predicted results was poor. It was considered that the instability of the surface of the water jet seemed important for the jet collapse in the present experimental range. The Kelvin-Helmholtz instability wave length was compared with the measured wave length on the water jet. When the wave length reached the Kelvin-Helmholtz instability wave length, the jet collapse occurred except the case that the transition to the dispersed flow caused the jet collapse. The air rolling into the water jet was not observed in the present experimental conditions. The two-phase region was not formed inside the water jet contrary to what is explained in the literature.

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.

Collapse Limit of Water Jetting With Surface Condensation in Steam Injector

2010 ◽  
Author(s):  
Ryuhei Ikuta ◽  
Yasuo Koizumi ◽  
Hiroyuki Yoshida
Keyword(s):  
Flow Velocity ◽  
High Speed ◽  
Wave Length ◽  
Water Jet ◽  
Instability Wave ◽  
Flow State ◽  
Helmholtz Instability ◽  
Small Perturbations ◽  
Dispersed Flow ◽  
Lower Position

Collapse of a water jet flowing out from a nozzle to the atmosphere was examined. The diameters of nozzles used in the experiments were 3, 6 and 8 mm. The flow state of the water jet was recorded with a high speed video camera. The collapse length was derived from recorded images. When the flow velocity was quite low, the surface of the water jet was smooth and small perturbations appeared at the lower position of the water jet. As the flow velocity was increased, the position where the small perturbations appeared came close to the nozzle outlet. The perturbations grew as these went downstream and lumps of water were formed at the lower position. When the flow velocity was further increased, successive waves came around on the surface of the water jet. The collapse of the water jet occurred in such a state that the lump of water was torn off from the jet. When the water jet velocity was high, the jet turned into a dispersed flow and the collapse occurred. The agreement of the measured results and the predicted results was poor. It was considered that the instability of the surface of the water jet seemed important for the jet collapse in the present experimental range. The Kelvin-Helmholtz instability wave length was compared with the measured wave length on the water jet. When the wave length reached the Kelvin-Helmholtz instability wave length, the jet collapse occurred except the case that the transition to the dispersed flow caused the jet collapse.

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