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 (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.

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.

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.

Velocity of Entrainments Formed by High Velocity Air Jet Flow in Stagnant Water

2014 ◽  
Author(s):  
Masaaki Akabane ◽  
Yasuo Koizumi ◽  
Akihiro Uchibori ◽  
Hideki Kamide ◽  
Hiroyuki Ohshima
Keyword(s):  
High Speed ◽  
Rectangular Cross Section ◽  
Video Camera ◽  
Flow State ◽  
Entrainment Velocity ◽  
Air Jet ◽  
Test Vessel ◽  
Jet Velocity ◽  
Visualization Experiments ◽  
Inception Point

This study was intended to examine sodium entrainment behavior in the case that a hole was formed on a tube wall in the steam generator of a fast breeder reactor and high pressure and high temperature water jetted out into sodium. Flow visualization experiments of an air jet in liquid were performed. The test vessel was 270 mm wide, 5 mm depth and 300 mm high. The air jet was blown vertically upward into stagnant liquid in the test vessel from a rectangular cross-section nozzle of 1 mm wide, 5 mm depth and 20 mm long which was located at the bottom of the test vessel. A flow state of the jet in the liquid was recorded with a high speed video camera at the fastest 150,000 frame/s. The test liquid was water and kerosene. Filament-like ears and wisps pulled out from the wavy interface were noticed on the interface between liquid and the air jet. The ears and the wisps were broken off and entrained into the air jet. The droplets broke up to small entrainments. This process seemed quite similar to the entrainment process in the annular dispersed flow in a pipe. Entrainment was initiated at a little bit downstream from the nozzle outlet. The entrainment inception point moved downstream as the air jet velocity increased. Axial directional entrainment velocity increased as the air jet velocity increased and the entrainment proceeded downstream. Transversal directional entrainment velocity was much slower than the axial directional entrainment velocity. The variation of the entrainment velocity in the transversal direction was not so prominent. The entrainments produced at the interface of the air jet moved to gather at the center portion of the air jet as those were accelerated.

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.

Entrainment Into High Speed Air Jet Blowing Out From a Hole to Stagnant Water

2013 ◽  
Author(s):  
Yasuo Koizumi ◽  
Kohei Nago ◽  
Akihiro Uchibori ◽  
Hideki Kamide ◽  
Hiroyuku Ohshima
Keyword(s):  
High Speed ◽  
Open Space ◽  
Two Phase Flow ◽  
Video Camera ◽  
Diameter Distribution ◽  
Phase Flow ◽  
Flow State ◽  
Two Phase ◽  
Air Jet ◽  
Test Vessel

Flow visualization experiments of an air jet in liquid were performed. The test vessel was 270 mm wide, 5 mm depth and 300 mm high. The air jet was blown vertically upward into stagnant liquid in the test vessel from a nozzle of 1 mm wide, 5 mm depth and 20 mm long which was located at the bottom of the test vessel. A flow state of the jet in the liquid was recorded with a high speed video camera at fastest 5×105 f/s. The test liquid was water and kerosene. Experiments were performed at atmospheric pressure and ambient temperature. Filament-like ears and wisps pulled out from the wavy interface were noticed on the interface between liquid and the air jet. The ears and wisps were broken off and entrained into the air jet. The droplets broke up to small entrainments. This process seemed quite similar to the entrainment process in the annular dispersed flow in a pipe. As the air jet velocity increased, the number of entrainments created by the air jet increased lineally and the smaller entrainments increased. The correlation for the entrainment diameter distribution which was developed for the annular dispersed two-phase flow in a pipe predicted well the present results. The correlations for the entrainment diameter developed for entrainments in the annular dispersed two-phase flow in a pipe and for droplets that were blown out into open space above a water pool by a nitrogen gas jet that blew into water vertically upwards considerably underpredicted the experimental results. Measured entrainment rates were considerably lower than the prediction of the correlation for the annular dispersed two-phase flow in a pipe.

Holes and Entrainment in Stratocumulus

2005 ◽  
Vol 62 (2) ◽  
pp. 443-459 ◽  
Author(s):  
H. Gerber ◽  
G. Frick ◽  
S. P. Malinowski ◽  
J-L. Brenguier ◽  
F. Burnet
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Evaporative Cooling ◽  
Length Distribution ◽  
Relative Length ◽  
Minimal Amount ◽  
Entrainment Rate ◽  
Conditional Sampling ◽  
Free Atmosphere ◽  
Average Width

Abstract Aircraft flights through stratocumulus clouds (Sc) during the Dynamics and Chemistry of Marine Stratocumulus II (DYCOMS-II) study off the California coast found narrow in-cloud regions with less liquid water content (LWC) and cooler temperatures than average background values. The regions are named cloud holes and are assumed to be a result of water evaporated by the entrainment of dryer air from above the Sc. While such features have been noted previously, this study provided a unique opportunity to investigate in much greater detail the nature of the holes, as well as their relationship to the entrainment rate, because high-speed temperature and LWC probes with maximum spatial resolution of 10 cm were flown together for the first time. Nine long-duration flights were made through mostly unbroken Sc for which conditional sampling was used to identify the location and size of the holes. The holes are concentrated near cloud top, their average width near cloud top is about 5 m, their relative length distribution is nearly constant for all flights, and they can penetrate hundreds of meters deep into the Sc before being lost by mixing. Entrainment velocities at cloud top are estimated from measurements of fluxes of reduced LWC and vapor mixing ratios in holes, the fraction of cloud area covered by holes, and the total water jump between cloud top and the free atmosphere. Rates as large as 10 mm s−1 are found for nocturnal flights, and these rates are about 3 times larger than for daytime flight segments. The rates correlate best with the size of the buoyancy jump above the Sc; the present conditional-sampling approach for measuring the rates gives larger rates than the “flux jump” rates determined by others for the same flights by a factor of about 2. The stability criterion for all Sc predicts thinning and breakup of the Sc, which does not occur. The minimal amount of cloud-top evaporative cooling caused by entrainment contributes little to the top-down convection dominated by radiative cooling during nocturnal flights; however, evaporative cooling caused by the mixing of holes as they subduct with the large-scale eddy circulation in the Sc may contribute, but with an as-of-yet unknown amount.

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