scholarly journals Gravity Driven Bubbly Flows: The Role of Vortical Structures

2003 ◽  
Author(s):  
Robert F. Mudde
Keyword(s):  
Liquid Flow ◽  
Large Scale ◽  
Bubble Column ◽  
Bubbly Flow ◽  
Low Frequency ◽  
Fine Tuning ◽  
Large Scale Circulation ◽  
Vortical Structures ◽  
Gravity Driven ◽  
Air Lift

Gravity driven bubbles are found in many industrial applications. Two typical reactors are the bubble column, in which the liquid is stagnant and the air lift reactor in which the liquid circulates, under the action of gravity, through the reactor. These reactors are attractive for a number of reasons: they have no moving parts and are thus low in maintenance; the size can be enormous (diameters of several meters, heights of tens of meters) allowing large volume flows to be processed; good mixing and heat transfer characteristics, etc. Our knowledge about the structure of the flow induced is rather limited. This makes design, fine tuning of operation and scale up still difficult. The two-phase flow in a bubble reactor is complicated. In the bubble columns, the liquid exhibits a large-scale circulation in a time averaged sense, with upward flow in the center and downward flow in the wall region. The first reliable data on this large-scale circulation date back to the work of Hills (174). In 1984, Franz et al. reported on the motion of what was later called vortical structures, eddy like structures (with sizes on the order of the column diameter) that move through the bubbly mixture. These vortical structures have been research more extensive during the last ten year by e.g. Fan and coworkers, Dudukovic and coworkers and Mudde & Van den Akker. The structures are found for a wide range of gas fractions, ranging from a few percent to well above 20%. The vortical structures seem to be a universal feature of the gravity driven bubble flows as they were also found in air lift reactors. For this reactor it has been reported that the liquid flow behaves more or less like the superposition of a net liquid flow and the complicated flow features found in the bubble column. The similarities will be high lighted. The vortical structures have important consequences for e.g. the (pseudo-)turbulence and the mixing in the bubbly flow. In 2-dimensional equipment they appear very regular and a separation between the low frequency fluctuations and the high frequency ‘turbulence’ is easily made. However, in 3-dimensional columns the situation is more complicated. LDA data show that the vortical structures are still responsible for a the occurrence of low frequency oscillations (on the order of 0.1Hz), but they are no longer appearing regularly and a separation of frequencies is no longer possible. Finally, the newest experiment seem to show that the vortical structures can be suppressed up to gas fraction of (at least) 10%. These new experiments suggest that the gravity driven bubbly flow is not inherently unstable, but rather sensitive to the conditions at the gas inlet.

Unsteady measurements in a separated and reattaching flow

1984 ◽  
Vol 144 ◽  
pp. 13-46 ◽  
Author(s):  
N. J. Cherry ◽  
R. Hillier ◽  
M. E. M. P. Latour
Keyword(s):  
Shear Layer ◽  
Large Scale ◽  
Separation Bubble ◽  
Scale Up ◽  
Three Dimensional ◽  
Low Frequency ◽  
Vortical Structures ◽  
Large Scale Structures ◽  
Bubble Length ◽  
Low Frequency Motion

Measurements of fluctuating pressure and velocity, together with instantaneous smoke-flow visualizations, are presented in order to reveal the unsteady structure of a separated and reattaching flow. It is shown that throughout the separation bubble a low-frequency motion can be detected which appears to be similar to that found in other studies of separation. This effect is most significant close to separation, where it leads to a weak flapping of the shear layer. Lateral correlation scales of this low-frequency motion are less than the reattachment length, however; it appears that its timescale is about equal to the characteristic timescale for the shear layer and bubble to change between various shedding phases. These phases were defined by the following observations: shedding of pseudoperiodic trains of vortical structures from the reattachment zone, with a characteristic spacing between structures of typically 60% to 80% of the bubble length; a large-scale but irregular shedding of vorticity; and a relatively quiescent phase with the absence of any large-scale shedding structures and a significant ‘necking’ of the shear layer downstream of reattachment.Spanwise correlations of velocity in the shear layer show on average an almost linear growth of spanwise scale up to reattachment. It appears that the shear layer reaches a fully three-dimensional state soon after separation. The reattachment process does not itself appear to impose an immediate extra three-dimensionalizing effect upon the large-scale structures.

Correlation Between a Local Void Fraction and Dissolved Gas Concentration in a Bubble Column by Using a Newly Developed Photoelectric Optical Fiber Probe

2011 ◽  
Author(s):  
Masahiro Yamada ◽  
Takayuki Saito
Keyword(s):  
Optical Fiber ◽  
Large Scale ◽  
Bubble Column ◽  
Bubbly Flow ◽  
Co2 Concentration ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Optical Fiber Probe ◽  
Void Fractions ◽  
Increase Rate

A bubble column is frequently used in various industrial plants for the purpose of dissolving gases into liquid phases. Clarifying a relationship between the mass transfer mechanism and the structure of the bubbly flow is important in order to improve the efficiency of the gas absorption. In the present study, we discuss a correlation between the concentration transportation and the large-scale structure of the bubbly flow, by using a newly developed photoelectric optical fiber probe (POFP). The POFP has two functions of electrical concentration measurement and optical bubble measurement; i.e. measurement of the time-spatial correlation of the bubble swarms and the concentration transportation is achieved simultaneously by using a pair of the POFPs. A bubble column of 380 mm in inner diameter and 1500 mm in height was employed. We pumped a mixture gas of CO2 and pure air into the bubble column through a perforated plate. Based on the fluctuation characteristics of the void fractions, the flow field in the column was divided into three zones: bottom, middle and upper zones. A long-period fluctuation of the void fractions fades out toward the upper zone of the bubble column. Simultaneously, we measured local CO2 concentrations. In the bottom zone, the increase rate of the concentration significantly differed by position. In contrast, in the upper zone, little difference in the increase rate was observed by position. The differences in the increase rate of the CO2 concentration faded out toward the upper zone. Furthermore, the fluctuations of the CO2 concentration showed a very close correlation with the fluctuations of the void fraction. We will discuss correlations between the mass transportation characteristics and the large-scale structure of the bubbly flows (i.e. the gas-phase and liquid-phase large-scale structure).

Footprints of Tropical Cyclones in WNP Summer Monsoon Variability

2020 ◽  
Author(s):  
Huang-Hsiung Hsu
Keyword(s):  
Climate Variability ◽  
Tropical Cyclones ◽  
Large Scale ◽  
Climate Models ◽  
Southern Oscillation ◽  
Intraseasonal Oscillation ◽  
Low Frequency ◽  
Monsoon Trough ◽  
Teleconnection Pattern ◽  
Large Scale Circulation

<p>Tropical cyclones (TCs) in the western North Pacific (WNP) are modulated by large-scale circulation systems such monsoon trough, intraseasonal oscillation, teleconnection pattern, El Niño and Southern Oscillation, and some interdecadal oscillations. While the low-frequency, large-scale circulation produces a clustering effect on TCs, the latter in return leave marked footprints in climate mean state and variability because of large amplitudes in circulation and strong heating. In this study, we applied PV inversion technique to remove TCs from reanalysis and evaluate their contribution to mean circulation and climate variability. It is found that the mean climatological circulation (e.g., low-level monsoon trough and upper-tropospheric anticyclone) would be much weaker with TCs removed. Intraseasonal and interannual variance of certain variables could decrease by as much as 40–50 percent. An accompanied study indicated that TCs had slowed down the sea surface warming in the WNP for the past few decades because of TC-induced cooling. Our results suggest that TC effect has to be considered to understand the climate variability in the tropical atmosphere and ocean. The ensemble effect of TCs, at least in the statistical sense, has to be resolved in climate models to better simulate climate variability and produce more reliable climate projection in the TC-prone regions.</p>

scholarly journals Climatological Large-Scale Circulation Patterns over The Middle Americas Region

Atmosphere ◽  
2020 ◽  
Vol 11 (7) ◽  
pp. 745
Author(s):  
Carlos A. Ochoa-Moya ◽  
Yoel A. Cala-Pérez ◽  
Yanet Díaz-Esteban ◽  
Christopher L. Castro ◽  
Paulina Ordoñez-Peréz ◽  
...  
Keyword(s):  
Large Scale ◽  
Low Frequency ◽  
North American Monsoon ◽  
Large Scale Circulation ◽  
Western Atlantic ◽  
Near Surface ◽  
Synoptic Classification ◽  
Atmospheric Circulation Patterns ◽  
The North ◽  
Circulation Patterns

In this study, twenty large-scale circulation patterns are identified to generate a synoptic classification of Weather Types (WT) over a region that comprises Mexico, the Intra-Americas Seas, Central America, and northern South America. This classification is performed using Self-Organizing Maps (SOMs) with mean sea-level pressure standardized anomalies from reanalysis. The influence of quasi-permanent pressure centers over the region, such as North Atlantic Subtropical High (NASH) and North Pacific High (NPH) are well captured. Seasonal variability of high-pressure centers for dry (November–April) and wet (May–October) periods over the entire region are also well represented in amplitude and pattern among the WTs. The NASH influence and intensification of the Caribbean low-level jet and the North American monsoon system is well captured. During the dry period, a strong trough wind advects cold air masses from mid-latitudes to the subtropics over the western Atlantic Ocean. High-frequency transitions among WTs tend to cluster around the nearest neighbors in SOM space, while low-frequency transitions occur along columns instead of rows in the SOM matrix. Low-frequency transitions are related to intraseasonal and seasonal scales. The constructed catalog can identify near-surface atmospheric circulation patterns from a unified perspective of synoptic climate variability, and it is in high agreement with previous studies for the region.

scholarly journals A Numerical Simulation of Unsteady Two-phase Gas-Liquid Flow in a Large-scale Air-lift Pump.

1999 ◽  
Vol 115 (6) ◽  
pp. 437-442 ◽  
Author(s):  
Nobuo HATAKEYAMA ◽  
Hiroshi TAKAHASHI ◽  
Takayuki SAITO ◽  
Tadashi MASUYAMA
Keyword(s):  
Numerical Simulation ◽  
Liquid Flow ◽  
Large Scale ◽  
Two Phase ◽  
Gas Liquid Flow ◽  
Air Lift

Rossby–Khantadze electromagnetic planetary vortical motions in the ionospheric E-layer

2011 ◽  
Vol 77 (6) ◽  
pp. 813-828 ◽  
Author(s):  
T. D. KALADZE ◽  
L. V. TSAMALASHVILI ◽  
L. Z. KAHLON
Keyword(s):  
Geomagnetic Field ◽  
Electromagnetic Waves ◽  
Large Scale ◽  
Low Frequency ◽  
Vortical Structures ◽  
Linear Waves ◽  
E Region ◽  
Propagation Properties ◽  
The Waves ◽  
Linear Propagation

AbstractIt is shown that in the earth's conductive ionospheric E-region, large-scale ultra low-frequency Rossby and Khantadze electromagnetic waves can propagate. Along with the prevalent effect of Hall conductivity for these waves, the latitudinal inhomogeneity of both the earth's angular velocity and the geomagnetic field becomes essential. Action of these effects leads to the coupled propagation of electromagnetic Rossby and Khantadze modes. Linear propagation properties of these waves are given in detail. It is shown that the waves lose the dispersing property for large values of wave numbers. Corresponding nonlinear solitary vortical structures are constructed. Conditions for such self-organization are given. It is shown that nonlinear large-scale vortices generate the stronger pulses of the geomagnetic field than the corresponding linear waves. Previous investigations are revised.

scholarly journals Seasonal-to-Subseasonal Model Forecast Performance during Agricultural Drought Transition Periods in the U.S. Corn Belt

2017 ◽  
Vol 145 (9) ◽  
pp. 3687-3708 ◽  
Author(s):  
Nicholas J. Schiraldi ◽  
Paul E. Roundy
Keyword(s):  
Large Scale ◽  
Low Frequency ◽  
Seasonal Prediction ◽  
Agricultural Drought ◽  
Corn Belt ◽  
Model Errors ◽  
Large Scale Circulation ◽  
Forecast Performance ◽  
Circulation Patterns ◽  
The U.S

The prediction of drought onset and decay in the U.S. Corn Belt region (CBR) on seasonal-to-subseasonal time scales has not been well studied. This study utilizes the subseasonal-to-seasonal prediction archive to assess model errors in large-scale circulation patterns associated with agricultural drought transition periods, targeting models used by the European Centre for Medium-Range Forecasts, National Centers for Environmental Prediction, and Australian Bureau of Meteorology. An analysis of the seasonal cycle of bias for geopotential anomalies at 200 hPa and net radiation at the top of the atmosphere in each model is presented and used to subtract the long-term bias from each model. Model fields are decomposed into three spectral bands—low frequency (periods > 100 days), intraseasonal (periods 20–100 days), and synoptic (periods < 20 days)—to demonstrate each model’s ability to predict patterns associated with agricultural drought transition periods in each band. Results demonstrate that ECMWF and NCEP struggle in predicting the large-scale circulation patterns associated with 20-day agricultural drought and onset transitions, but are more skillful in predicting the patterns associated with 60-day agricultural drought onset and decay events at reforecast hour lead window 360–480 (F360–F480). BoM was not skillful in predicting the circulation patterns associated with either type of drought transition. Results also demonstrate that the errors associated with these events are no worse than historical errors for the target study period.

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