Gas-liquid simulation of an airlift bubble column reactor

The simulation of two-phase flow for an experimental airlift reactor (32-l volume) using commercially available software from Fluent Incorporated is presented here (http://www.fluent.co.uk). Data from the simulation is compared with the experimental data obtained by the tracking of a magnetic particle and analysis of the pressure drop to determine the gas hold-up. Comparisons between vertical velocity and gas hold-up were made for a series of experiments where the superficial gas velocity in the riser was adjusted between 0.01 and 0.075 m s-1. © 2003 Elsevier B.V. All rights reserved.

Gas-liquid-solid flow modelling in a bubble column

An alternative approach to the modelling of solid-liquid and gas-liquid-solid flows for a 5:1 height to width aspect ratio bubble column is presented here. A modified transport equation for the volume fraction of a dispersed phase has been developed for the investigation of turbulent buoyancy driven flows (Chem. Eng. Proc., in press). In this study, a modified transport equation has been employed for discrete phase motion considering both solid-liquid and gas-liquid-solid flows. The modelling of the three-phase flow in a bubble column was achieved in the following case: injecting a slug of solid particles into the column for 10 s at a velocity of 0.1 m s-1 and then the gas phase flow was initiated with a superficial gas velocity of 0.02 cm s-1. © 2003 Elsevier B.V. All rights reserved.

The modelling of buoyancy driven flow in bubble columns

Using the analogy between lateral convection of heat and the two-phase flow in bubble columns, alternative turbulence modelling methods were analysed. The k-ε turbulence and Reynolds stress models were used to predict the buoyant motion of fluids where a density difference arises due to the introduction of heat or a discrete phase. A large height to width aspect ratio cavity was employed in the transport of heat and it was shown that the Reynolds stress model with the use of velocity profiles including the laminar flow solution resulted in turbulent vortices developing. The turbulence models were then applied to the simulation of gas-liquid flow for a 5:1 height to width aspect ratio bubble column. In the case of a gas superficial velocity of 0.02 m s-1 it was determined that employing the Reynolds stress model yielded the most realistic simulation results. © 2003 Elsevier B.V. All rights reserved.

Three-dimensional gas-liquid simulation of an airlift bubble column reactor

Basic hydrodynamic parameters of an airlift reactor with internal loop were estimated experimentally and simulated using commercially available CFD software from Fluent. Circulation velocity in a 32-dm(3)-airlift reactor was measured using the magnetic tracer method, meanwhile the gas hold-up was obtained by analysis of the pressure drop using the method of inverted U-tube manometers. Comparison of simulated (in two and three dimensions) and experimental data was performed at different superficial gas velocities in the riser.

CFD and bubble column reactors:simulation and experiment

The simulation of two-phase flow in bubble columns using commercially available software fromFluent Incorporated is presented here. Data from a bubble column with a ratio of height to thecolumn diameter of 5 : 1 are compared with simulations and experimental results for time-averaged velocity and Reynolds stress proles are used to validate transient, two-dimensional simulations.The models are based on multiphase biological reactors with applications in the food industry. An example case of the mass transfer of oxygen through the liquid phase is also presented.

Intragranular nucleation of austenite

The mechanism of intragranular nucleation of austenite in a duplex stainless steel (Fe-23.1 Cr-6.1 Ni-3.1 Mo-O.165 N-0.017 C, wt.%) weld metal and heat-affected zone (HAZ) has been examined. In the weld metal the acicular austenite is found to nucleate intragranularly on inclusions and subsequent plates form sympathetically resulting in a fine interlocked microstructure. Austenite plates adopt the Kurdjumov-Sachs orientation relationship with the ferrite matrix and grow with diffusion-controlled mechanism as evident from partitioning of substitutional alloying elements. At least one set of fine intrinsic dislocations on the austenite/ferrite interphase interfaces is observed suggesting that the boundaries are semi-coherent. The high cooling rates involved in the HAZ result in a supersaturated ferrite matrix where precipitation of intragranular austenite occurs as a result of reheating associated with subsequent passes. Austenite particles in the HAZ nucleate preferentially away from gain boundary austenite allotriomorphs indicating that intragranular precipitation is favoured by the supersaturated matrix.

Initial nucleation study and new technique for sublimation growth of AlN on SiC substrate

Single crystal platelets of AlN were successfully grown on 6H-SiC(0001) by a novel technique designed to suppress SiC decomposition, promote two-dimensional growth, and eliminate cracking in the AlN. X-ray diffractometry and synchrotron white beam X-ray topography demonstrate that the final AlN single crystal is of high structural quality.

Effect of oscillatory flow on nucleation kinetics of butyl paraben

More than 165 induction times of butyl paraben-ethanol solution in a batch moving fluid oscillation baffled crystallizer with various amplitudes (1-9 mm) and frequencies (1.0-9.0 Hz) have been determined to study the effect of COBR operating conditions on nucleation. The induction time decreases with increasing amplitude and frequency at power density below about 500 W/m3; however, a further increase of the frequency and amplitude leads to an increase of the induction time. The interfacial energies and pre-exponential factors in both homogeneous and heterogeneous nucleation are determined by classical nucleation theory at oscillatory frequency 2.0 Hz and amplitudes of 3 or 5 mm both with and without net flow. To capture the shear rate conditions in oscillatory flow crystallizers, a large eddy simulation approach in a computational fluid dynamics framework is applied. Under ideal conditions the shear rate distribution shows spatial and temporal periodicity and radial symmetry. The spatial distributions of the shear rate indicate an increase of average and maximum values of the shear rate with increasing amplitude and frequency. In continuous operation, net flow enhances the shear rate at most time points, promoting nucleation. The mechanism of the shear rate influence on nucleation is discussed.

Buborékok és legendák. Válságok és válságmagyarázatok - a tulipánmánia és a Déltengeri Társaság, I. rész (Bubbles and myths, crises and explanations: tulip mania and the South Sea bubble. I.)

A 2007 óta kibontakozó válság újból divatba hozta a korai buborékok és válságok témáját. A jelenlegi válság nyomán újraéledtek a makroökónómiai viták, kétségessé vált a "nagy mérséklődés" és az újklasszikus szintézis érvényessége. Az 1634-1637 közötti holland tulipánmánia - mint az első buborék - sokféle értelmezése ismeretes: a tömeghisztéria kitörésétől a hatékony pénzügyi piacok korai példáján át a kulturális sokkig. Áttekintve ezeket, a cikk visszavezeti a tulipánmánia közismert anekdotikus leírásait az eredeti forrásokig, és megmutatja, milyen módon és céllal használták fel ezeket a közgazdászok és történészek saját elemzéseikben. / === / The accounts of early bubbles and crises are becoming fashionable again in economic discourse during the recent downturn. The article, having looked at the revival of macroeconomic debate provoked by the failure of current theory, sums up various interpretations of the Dutch tulip mania of 1634-7. These range from an outburst of popular madness, through an early example of an efficient financial market, to an instance of culture shock. Some well-known anecdotes about tulip mania are traced back to their original sources, and the article explores the various patterns and intentions in the use economists and historians have made of them.

Buborékok és legendák. Válságok és válságmagyarázatok - II/1. rész. A Déltengeri Társaság (Bubbles and myths crises and explanations II/1.: the South Sea bubble)

A cikk a tulipánmániával foglalkozó tanulmány folytatása (Madarász [2009]). A Déltengeri Társaság 1720-as fellendülése és kipukkadása mindmáig egyike a pénzügyi történelem leghíresebb és leggyakrabban emlegetett buborékainak. A közgazdaságtanban a buborék sokáig nem volt fontos téma, de az utóbbi időben ismét divatba jött. A tanulmány először a buborékmetafora néhány irodalmi példáját mutatja be, majd összefoglalja az angol államadósság kialakulását, a korai modern fiskális-militarista állam létrejöttét és a pénzügyi forradalom különböző interpretációit. A Déltengeri Társaság történetének, az adósság-részvény csere lebonyolításának és a korabeli vélemények spektrumának ismertetése után áttekintést ad arról, milyen módon és céllal használták fel az 1720-as eseményeket közgazdászok és történészek saját magyarázataikban. Ezek skálája a tudatos csalástól a befektetők irracionális mániáján át a racionális buborék kialakulásáig terjed. / === / The first part of the study (published here in 2009) was devoted to "tulipmania". This article continues the account of early bubbles and crises with the 1720 boom and bust of the South Sea Company, which is to this day one of the best known and most cited examples in history. For several decades, bubbles were not seen as an important issue in economic and financial theory, but recent events have focused attention on them again. The author introduces some historical examples of the bubble metaphor in literature, before giving an account of the emergence of British public debt and the fiscal-military state, and summarizing various interpretations of the financial revolution. An account of the South Sea Bubble, a detailed description of the debt-equity swap, and citations from some contemporary investors and observers are followed by an overview of the way the events of 1720 were used subsequently by various economists and historians in their own theorizing and explanations. The interpretations placed on it range from deliberate fraud, through irrational investment mania, to the emergence of a rational bubble.

Buborékok és legendák. Válságok és válságmagyarázatok II/2. rész. A Déltengeri Társaság (Bubbles and myths crises and explanations II/2.: the South Sea bubble)

A cikk a tulipánmániával foglalkozó tanulmány folytatása (Madarász [2009]). A Déltengeri Társaság 1720-as fellendülése és kipukkadása mindmáig egyike a pénzügyi történelem leghíresebb és leggyakrabban emlegetett buborékainak. A közgazdaságtanban a buborék sokáig nem volt fontos téma, de az utóbbi időben ismét divatba jött. A tanulmány először a buborékmetafora néhány irodalmi példáját mutatja be, majd összefoglalja az angol államadósság kialakulását, a korai modern fiskális-militarista állam létrejöttét és a pénzügyi forradalom különböző interpretációit. A Déltengeri Társaság történetének, az adósság-részvény csere lebonyolításának és a korabeli vélemények spektrumának ismertetése után áttekintést ad arról, milyen módon és céllal használták fel az 1720-as eseményeket közgazdászok és történészek saját magyarázataikban. Ezek skálája a tudatos csalástól a befektetők irracionális mániáján át a racionális buborék kialakulásáig terjed. / === / The first part of the study (published here in 2009) was devoted to "tulip-mania". This article continues the account of early bubbles and crises with the 1720 boom and bust of the South Sea Company, which remains to this day one of the best known and most cited examples in history. For several decades, bubbles were not seen as an important issue in economic and financial theory, but recent events have focused attention on them again. The author introduces some historical examples of the bubble metaphor in literature, before describing the emergence of British public debt and the fiscal/military state, and summarizing various interpretations of the financial revolution. An account of the South Sea Bubble, a detailed description of the debt-equity swap, and citations from some contemporary investors and observers are followed by an overview of how the events of 1720 were used subsequently by various economists and historians in their theorizing and explanations. Such interpretations range from deliberate fraud, through irrational investment mania, to the emergence of a rational bubble.

Pore-water concentration of chloride in sediment cores and equilibrium temperatures and gas bubble analysis at ROV stations from the Vodyanitskii mud volcano

Vodyanitskii mud volcano is located at a depth of about 2070 m in the Sorokin Trough, Black sea. It is a 500-m wide and 20-m high cone surrounded by a depression, which is typical of many mud volcanoes in the Black Sea. 75 kHz sidescan sonar show different generations of mud flows that include mud breccia, authigenic carbonates, and gas hydrates that were sampled by gravity coring. The fluids that flow through or erupt with the mud are enriched in chloride (up to 650 mmol L**-1 at 150-cm sediment depth) suggesting a deep source, which is similar to the fluids of the close-by Dvurechenskii mud volcano. Direct observation with the remotely operated vehicle Quest revealed gas bubbles emanating at two distinct sites at the crest of the mud volcano, which confirms earlier observations of bubble-induced hydroacoustic anomalies in echosounder records. The sediments at the main bubble emission site show a thermal anomaly with temperatures at 60 cm sediment depth that were 0.9 °C warmer than the bottom water. Chemical and isotopic analyses of the emanated gas revealed that it consisted primarily of methane (99.8%) and was of microbial origin (dD-CH4 = -170.8 per mil (SMOW), d13C-CH4 = -61.0 per mil (V-PDB), d13C-C2H6 = -44.0 per mil (V-PDB)). The gas flux was estimated using the video observations of the ROV. Assuming that the flux is constant with time, about 0.9 ± 0.5 x 10**6 mol of methane is released every year. This value is of the same order-of-magnitude as reported fluxes of dissolved methane released with pore water at other mud volcanoes. This suggests that bubble emanation is a significant pathway transporting methane from the sediments into the water column.

Lily with bubble gum

General note: Title and date provided by Bettye Lane.

Bubble Growth From First Principals

We consider the simplest relevant problem in the foaming of molten plastics, the growth of a single bubble in a sea of highly viscous Newtonian fluid, and without interference from other bubbles. This simplest problem has defied accurate solution from first principles. Despite plenty of research on foaming, classical approaches from first principles have neglected the temperature rise in the surrounding fluid, and we find that this oversimplification greatly accelerates bubble growth prediction. We use a transport phenomena approach to analyze the growth of a solitary bubble, expanding under its own pressure. We consider a bubble of ideal gas growing without the accelerating contribution from mass transfer into the bubble. We explore the roles of viscous forces, fluid inertia, and viscous dissipation. We find that bubble growth depends upon the nucleus radius and nucleus pressure. We begin with a detailed examination of the classical approaches (thermodynamics without viscous heating). Our failure to fit experimental data with these classical approaches, sets up the second part of our paper, a novel exploration of the essential decelerating role of viscous heating. We explore both isothermal and adiabatic bubble expansion, and also the decelerating role of surface tension. The adiabatic analysis accounts for the slight deceleration due to the cooling of the expanding gas, which depends on gas polyatomicity. We also explore the pressure profile, and the components of the extra stress tensor, in the fluid surrounding the growing bubble. These stresses can eventually be frozen into foamed plastics. We find that our new theory compares well with measured bubble behavior.