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Transition from bubbly to slug flow is a well-known phenomenon. In the channel with a swirler, a transition to slug flow at a lower gas superficial velocity than in the same channel without the swirler was observed in this work. The transition phenomenon from bubble flow to slug flow under the effect of swirl in a circular pipe was observed and investigated. Compared to the flow pattern (maintaining the bubble flow along a streamwise direction) in a non-swirling flow, we observe that bubble flow is transformed to a gas column downstream of the swirler, then broken up, and finally separated into gas slugs in the streamwise direction. The dynamic condition for the occurrence of a liquid bridge is proposed, then combined with a swirl decay model of a gas–liquid two-phase swirling flow; thus, the axial position for the transition from a gas column to a slug flow along the streamwise direction can be predicted. Whether slug flow always remains along the streamwise direction is closely related to its size. Under the effect of swirl, the void fraction is decreased and the pressure drop is increased compared with that in a non-swirling flow, and gradually approximates the values of a non-swirling flow along the streamwise direction.

The erosion of particles is one of the main reasons of damage to the multiphase flow pipelines in black water treatment systems. In this study, the particle erosion of liquid–solid–gas multiphase bubble flow in a horizontal-vertical-upward elbow was analysed. The optical microscope, scanning electron microscope (SEM) and white light interference microscope were used for detection of failed pipe samples. An erosion simulation method based on the volume of fluid (VOF) model and discrete phase model (DPM) was adopted to study the influencing factors on the erosion. The results showed that the particles and bubbles lead to lots of pits and furrows on the pipe surfaces, and the erosion at the outer elbow is relatively severe due to the effect of multiphase bubble flow. The most severe damage occurred at θ = 25° of the elbow, and erosion rate is positively correlated with the particle diameter, volume fraction and inlet velocity.

Results of experimental and numerical investigations of heat transfer and wall shear stress, in upward bubble flow in a flat inclined channel, are presented. The hydrodynamic structure is measured using the electrochemical method with miniature friction sensors. Miniature platinum thermoresistors are employed to measure the wall temperature. The set of RANS equations is used to account for the feedback effect of bubbles on mean and fluctuating flow parameters. It is shown that we can observe a significant dependence of shear stress and heat transfer on angle of channel inclination, in the bubble gas-liquid flow. The largest values of wall shear stress and heat transfer correspond to channel inclination angles of 30–50°. Intensification of wall shear stress in inclined two-phase bubble flow leads to values of 30%, and up to 15% for heat transfer. For inclination angles close to horizontal, suppression of shear stress and heat transfer of 10% and 25% respectively, was registered. Bubble size distributions along the channel length were obtained for different regimes of two-phase flow.

Under pressure-driven conditions of gas, the bubble size was experimentally studied in different types of T-junction microchannels having widths of 300 μm and heights of 100 μm. The bubble length increases with the flow rate, and we observed that it also increased with the driving pressure. This was proved through the published formulas for the bubble flow pressure difference using the experimental results. Three types of downstream channels—normal, movable, and deformed walls (of different lengths)—were used to study emerging bubbles, and a nonlinear relationship was observed between them. The channel type directly influenced the bubble size by affecting the resistance of the channel with bubbles. Furthermore, the difference between the resistances of a normal channel and a deformed channel with the same typical dimension was determined using a comparator structure between two parallel channels to evaluate the effect of flow resistance on bubble generation. The adjustment of the flow rate at downstream will give feedback to the bubble generation in the double T-junction channel.

The experiments on the air-water two-phase flow patterns in a 24 mm diameter vertical circular pipe under both static and rolling conditions were conducted. The superficial velocities were in the range of 0.05–4.07 m/s and 0.02–20.55 m/s for water and air, respectively. Five typical flow pattern morphologies resulting from a rolling motion were observed: dispersed bubbles; bubbles; slug; churn; and annular flow. Flow pattern transitions were identified by analysis of visual images and a bubble chord-length probability distribution function (PDF). The static experimental data was used to validate existing flow pattern transition models that were then modified to fit rolling conditions by considering the additional forces caused by rolling motion. These models also agreed well with the experimental data. Investigation of the influence of the rolling motion on flow pattern transition showed that, as the rolling amplitude increases, the formation of dispersed bubble flow requires a higher superficial liquid velocity. It was also found that, the greater the rolling amplitude, the larger region of churn. The rolling period, however, has little impact on flow pattern transitions.

The goal of this study was to determine feasible numbering-up laws to model the gas–liquid distribution in multiple microchannels. Comb-like microchannels were constructed by closely arranging eight capillaries of 0.5-mm inner diameter. The air–water flow in the parallel microchannels was recorded by a high speed CCD camera. After collecting and analyzing a very large number of images, the flow patterns were classified into two zones, zone I and zone II, which were the bubble flow and phase splitting zones, respectively. A model was established to describe the mean sizes and velocities of bubbles and liquid slugs in the two zones at different inlet flow rates of air and water, as well as to distinguish the two-zone operating limits by determining inlet flow rate intervals of the fluids. The calculated results agreed well with the experimental data. Therefore, the model showed a potential application to numbering up comb-like microchannels.

The early characteristic of the pressure buildup test is usually dominated by wellbore storage effect. These wellbore phase redistribution effects, which are transient in nature, including phase re-injection, bubble flow and hammering effect, sometimes lead to the pressure oscillation in early pressure buildup. And, these phenomena are characterized with the changing wellbore storage effect. But the present changing wellbore storage models vary with time monotonically, which could not describe these periodic processes. This paper presents a new changing wellbore storage model for analysis of the pressure oscillation process at wellbore or near wellbore region during the pressure buildup test. First, the physical processes of the phase re-injection, bubble flow and hammering effect are analyzed for reasons of the pressure oscillation. Then, a periodic correlation is introduced to describe these processes based on experiments. Finally, a new model is proposed by taking account of the combination of the Fair model and a cosine function. Then, the Stehfest algorithm and Crump algorithm are used to simulate the process of pressure oscillation. The results show that Stehfest algorithm has a significant error on high frequency pressure oscillation, but Crump algorithm could simulate the whole process of pressure oscillation more accurately than that of Stehfest algorithm. When the pressure oscillation occurs in the well test, the pressure and pressure derivative of the proposed model could match the experimental data and oil field data very well. With this model, the pressure oscillation in the pressure buildup test can be understood and predicted better. And the proposed model is a supplement to the phase redistribution model and yields an insight into the corresponding impact on well test transient pressure behavior.

The gas hold-up variation and regime transition were investigated with different liquid viscosities ranging from 1.0 mPa s to 31.5 mPa s using a 0.15-m-in-diameter bubble column. In contrast to common observations, the gas hold-up graph with the superficial gas velocity could be categorized into three flow regimes: homogeneous, pseudo-homogeneous and heterogeneous flow regimes. The formation of large bubbles caused a transition from the homogeneous to the pseudo-homogenous flow regime, in which large bubbles rose vertically without oscillatory turbulence. According to the results from the dynamic gas disengagement (DGD) technique, large bubbles began to form at the transition superficial gas velocity to the pseudo-homogeneous flow regime. The transition to a heterogeneous flow regime was initiated by the turbulent movement of large bubbles. The transition superficial velocities to pseudo-homogeneous and heterogeneous flow regimes, u t1 and u t2 , decreased with increasing liquid viscosity below a critical viscosity and converged to a certain value above that viscosity. However, the correlations from the literatures could not make a reasonable estimation of the transition superficial velocities because they did not consider the possible transition to a pseudo-homogeneous flow regime. Therefore, the two transition points should be predicted separately.

To optimize membrane bioreactor (MBR) equipment specifications and operating conditions in order to reduce the aeration rate, we investigated effects of the flat sheet membrane clearance and the bubble diameter on the shear stress on the membrane surface. The results were obtained using an apparatus consisting of a visible-channel, simulated-flat sheet MBR, in which the membrane clearance and bubble diameter could be varied. The shear stress on the simulated membrane surface was measured directly. We found that large bubbles with two-dimensional amorphous shapes between the membranes could make the shear stress large in comparison to the case of bubbles smaller than the membrane clearance. Moreover, we determined how to get the local maximum shear stress in the case of large bubbles. We developed a dimensionless index, consisting essentially of the membrane clearance and the bubble diameter that can be applied to describe the condition for maximizing the shear stress. Because the parameters of this index are easily obtainable, it is of significant benefit for effectively designing the operating conditions and equipment specifications of MBRs to promote scouring.

A horizontal tubular loop bioreactor (HTLB) was used for production of biomass from natural gas. Hydrodynamic characterizations (mixing time and gas hold up) and mass transfer coefficients were considered in the HTLB (L=2.2 m, H=0.4 m and D=0.03 m) as functions of design parameters, i.e., horizontal length to diameter ratio (L/D) and volume of gas–liquid separator (S) as well as operational parameters, i.e., superficial gas and liquid velocities (UsG, UsL). In addition, flow regime in different gas and liquid flow rates was investigated. It was observed from experimental results that UsL has remarkable effects on gas hold up and kLa due to its influence on mixing time. The volumetric mass transfer coefficients for oxygen ( k L a O 2 ) and methane ( k L a CH 4 ) were determined at different geometrical and operational factors. In average, the amount of oxygen consumption for metabolism is approximately 1.4 times higher than that of methane. In bubble flow regime, the HTLB was used for biomass production, too. A gas mixture of 50% methane and 50% oxygen (based on results of dry cell weight, optical density and doubling time) was the best gas mixture inlet for biomass production. The empirical correlations for mixing time, gas hold up and kLa in terms of UsG, UsL, L/D and volume of gas–liquid separator were obtained and expressed separately.

Target vessel wall being damaged by pitting caused by pressure waves generated when pulsed high-power beams are injected is a crucial issue in the realization of a pulsed high-power mercury target for spallation neutron sources. The injection of micro-bubbles into mercury is a prospective technology for use in mitigating the pressure wave and the resulting pitting. The bubble flow field in an actual target vessel was numerically examined and the optimal conditions for bubble injection were investigated. The results indicated the possibility of the bubbles being distributed over the core regions when they are injected in the appropriate position according to their diameter.

A method of evaluation of spatial dispersion of structures is presented. A quantitative parameter measuring spatial dispersion is introduced. It is shown that this parameter indeed measures spatial dispersion. A classification of bubble flow structures based on values of this parameter is proposed. An example of application of the method to real flow structures is presented.

Experiments were performed to study the hydrodynamic characteristics of ebullate-bed systems operated under conditions of high pressure and temperature. The effects of these variables on bed porosity and the liquid minimum fluidization velocity were determined and a correlation has been proposed as a criteria for determining flow regime transitions between the dispersed and coalesced bubble flow regimes. The bed porosity has been described with the pseudo-fluid model. The minimum fluidization velocity data were contrasted with predictions from empirical correlations reported in the literature.

A two-phase flow in a rectangular bubble column of 100×20 mm cross-section and 1.5 mm height was studied using a high-speed video system. Series of images were taken at different elevations at a frequency of 500 Hz. The images were processed using a bubble recognition algorithm. In such a way, an individual bubble in the gas swarm could be tracked. The time-averaged velocity profiles and the turbulent diffusion coefficients were derived as a function of the superficial gas velocity. The lateral displacement of bubbles travelling over a certain vertical distance was transformed into a probability density distribution in order to measure the turbulent diffusion coefficient of the gaseous phase. The shape of the distributions obtained was found to fit well to the Gaussian standard distribution. The dispersion coefficients were observed to grow proportionally to the square root of the vertical distance. The diffusion coefficients were calculated from the proportionality factor and were compared with some correlations published in the literature. The experiments were performed for superficial gas velocities ranging from 1 to 6 mm/s. The bubbles were generated either by a porous sparger or a set of capillaries placed at the bottom of the column. The measurements were taken at different heights between 1 and 1.2 m where the bubble cloud was occupying the entire cross-section.

A lattice Boltzmann method for two-phase immiscible fluids with large density differences is proposed. The difficulty in the treatment of large density difference is resolved by using the projection method. The method can be applied to simulate two-phase fluid flows with the density ratio up to 1000. To show the validity of the method, we apply the method to the simulations of capillary waves, binary droplet collisions, and bubble flows. In capillary waves, the angular frequencies of the oscillation of an ellipsoidal droplet are obtained in good agreement with theoretical ones. In the simulations of binary droplet collisions, coalescence collision and two different types of separating collisions, namely reflexive and stretching separations, can be simulated, and the boundaries of the three types of collisions are in good agreement with an available theoretical prediction. In the bubble flows, the effect of mobility on the coalescence of two rising bubbles is investigated. The behavior of many bubbles in a square duct is also simulated.

We demonstrate a “coarse time-stepper” based approach for the extraction of continuum-level stability and bifurcation information from kinetic theory based, LB simulations. Acting directly on the LB simulator, we sidestep the necessity of deriving macroscopic, explicitly closed continuum conservation equations. The approach is used to analyze the dynamics and the oscillatory instability of two-dimensional periodic arrays of gas bubbles rising in a liquid. ? 2004 Elsevier Ltd. All rights reserved.

In this study, the measurement of gas holdup using an ultrasonic level sensor was proposed. Moreover, the semi-empirical equation proposed by Nicklin, Wilkes, and Davidson (1962) to calculate the gas holdup in a Newtonian liquid under slug flow conditions in a bubble column was modified for use with a non-Newtonian liquid having a yield stress.

On the basis of the experimental results along with those available in the literature (1678 experimental data from five liquid systems, covering 10 different packings, from three sources) with a wide range of variables, a generalized approach is developed to identify the flow regime transitions viz., bubble flow, dispersed bubble flow and pulse flow in cocurrent two-phase (gas–liquid) upflow through packed beds. New correlations for the estimation of frictional pressure drop involving all the fundamental and operating variables are also presented for the three regimes of operation. This present correlations are more accurate than those previously reported.

New constitutive models for the interfacial forces acting on bubbles were developed for accurately predicting the lateral phase distribution in turbulent bubbly two-phase flow in vertical channels. Several experimental measurements have revealed that the lateral void profile in bubbly two-phase flow varies from the void peaking near the wall to the almost flat distributions as the liquid velocity increases. However, within the authors' knowledge, the effect of liquid velocity on the void profile has not been successfully predicted by the existing models; this would indicate the strong limitation of the existing multidimensional two-phase flow models. In view of these, the validity of the present constitutive models was tested in varied conditions of the liquid velocity as well as the bubble size. Since several assumptions were required in the models mainly due to the insufficient knowledge of the bubble motion, further improvements should still be needed. Nevertheless, the predicted lateral phase distributions were found to be in reasonably good agreement with available experimental data. It is hence expected that the present constitutive models can effectively be used in the practical applications and also be the base of the more sophisticated ones.

A series of experiments on two-phase gas-liquid flow patterns in a test tube with a length of 356 mm and an inside diameter of 10 mm were performed aboard the Mir Space Station in August 1999. Carbogal and air were used as the liquid and the gas phase, respectively. In the present paper, the experimental results at the background microgravity environment of the Mir Space Station (no more than 10(-5)g) were reported. Five kinds of flow patterns, namely dispersed bubble flow, bubble flow, slug flow, slug-annular transitional flow, and annular flow, were observed in the space experiment. Due to the small length-to-diameter ratio of the test tube used in the present study, the observed flow patterns should be considered to be developing ones. The experimental results were compared with the model proposed previously which accounts for the entrance effects on the flow pattern transitions. A good agreement between the predictions and the experimental data was obtained. Some widely used models developed based on the analysis of fully developed two-phase flow at microgravity were also compared with the present data in order to make evaluations of these models and to have some insights on the flow evolution.

Flow pattern and the bubble velocity in 2– 8 mm diameter inclined tubes were studied in the present work. Experimental observations show that the flow pattern is elongated bubble flow and no small dispersed bubbles exist in the liquid slug in conditions of 0.168– 0.672 m s −1 superficial liquid velocity and 0.04– 0.32 m s −1 superficial gas velocity. The shape of the gas slug in tube is influenced by the diameter of tube, the flow rate, and the inclination angle. Furthermore, the length of gas slug increases with the superficial gas velocity. The length of gas slug in the inclined tube is longer than that in the vertical or horizontal tube, and the gas slug velocity in the inclined tube is faster than that in the vertical or horizontal tube.

Resume Dans la presente etude, nous nous proposons une formulation du frottement parietal dans un ecoulement diphasique gaz–liquide a bulles, bidimensionnel, ascendant, vertical, stationnaire et pleinement developpe. Cette approche est fondee, d'une part sur le modele a deux fluides et d'autre part, sur l'hypothese d'ecoulement quasi parallele etabli. Les modeles de turbulence jouent un role essentiel dans celle-ci. La comparaison du modele avec les donnees experimentales (dont nous disposons) montre un accord satisfaisant. D'autres etudes experimentales (sur la structure de la couche limite et le frottement parietal), en particulier a taux de vide eleves, sont souhaitables pour examiner davantage la validite du modele.

Resume Cette note presente une methode d'identification des configurations d'un ecoulement diphasique eau-air en conduite horizontale. Le diagnostic repose sur la caracterisation de signaux a partir de trois parametres (frequence, espace et forme). Apres avoir discute des resultats obtenus avec differentes analyses, on montre qu'une methode prenant en compte la distribution spatiale du contenu spectral est la mieux adaptee pour la distinction quantitative de tous les regimes. Les donnees sur la repartition geometrique des constituants sont obtenues grâce a la configuration particuliere de la sonde de mesure dont sont issus les signaux. Ainsi, une classification des differents regimes d'ecoulement a pu etre etablie en fonction des nouveaux parametres retenus.

The results presented in this paper demonstrate the ability of the PFGSE-NMR to obtain a complete characterization of two-phase flows. Different methods are proposed to characterize air-water flows in different regimes: stationary two-phase flows and flows in transient condition. Finally a modified PFGSE is proposed to analyze the fluctuations in stationary air-water bubbly flows.

An experimental rig was constructed that enabled vertical co-current two-phase flow to be studied in a 0.026m i.d. tube. For vertical air-water flow, pressure loss fluctuation characteristics were useful in helping to identify phase patterns present and ensuring consistent operational conditions. Details are presented on the semi-annular flow regime which formed between churn and annular flows. Liquid hold-up was measured using the quick closing valve technique. Measurements showed the liquid hold-up to be flow regime dependent in agreement with published work. Prediction was achieved by the Nicklin46 and Bonnecaze19 relations for intermittent flow and the Spedding-Chen relation17 for annular type flows.

Based on an analysis of the physical mechanism, a new model is developed for the transitions for slug flow to churn flow in vertical pipes. The transition is attributed to the wake effect of Taylor bubbles on highly aerated liquid slugs. The new model is compared with existing models and published experimental data. It is in better agreement with experimental data than existing models.

Resume Cette etude vise a la comprehension des mecanismes fondamentaux gouvernant les interactions et la coalescence des bulles dans les fluides rheologiquement complexes. La dependance de la vitesse ascensionnelle sur la periode d'injection montre que de fortes interactions existent entre les bulles et qu'elles sont d'autant plus importantes que l'elasticite du fluide est prononcee. Une approche originale, appelee simulation rheologique, demontre que ces interactions sont conditionnees par la competition dynamique entre la creation et la relaxation des contraintes. Une application de la theorie du chaos permet de confirmer le caractere chaotique de la coalescence des bulles.

The present work involves an experimental study of bubble flow in a flat horizontal sudden expansion. This study consists of two parts which are interdependent and complementary. Here in the first part, the qualitative study by visualization shows that the bubble flow changes from a dissymetric configuration to a symmetric configuration beyond a certain volumetric quality x. The quantitative study involves evolutions of the pressure and the void fraction downstream of the singularity for a quasi-symmetric bubble flow.

Contrary to Kocamustafaougullari et al's conclusions, their experimental void and velocity profiles for horizontal bubbly flow are in fact compatible with a relationship assumed by Beattie between local void fraction and local velocity. Moreover, predictions based on the assumption (an independence of velocity profile on void profile and equations for (i) voidage profile, (ii) a two-phase “universal” velocity profile, (iii) a two-phase version of the smooth tube friction factor equation and (iv) average void fraction) are also supported by results of the experimental study. Some apparent inconsistencies in the data were uncovered while assessing their compatibility with the theory.

This paper is concerned with the nonlinear theory of bubbly liquids introduced by Eringen [8]. We study uniqueness and continuous dependence upon initial state and supply terms of smooth thermodynamic processes.

An experimental investigation of the influence of horizontal tubes on the bubble behaviour and through-flow velocity of gas inside bubbles was carried out and the influence of pressure and fluidization velocity was studied. The visible bubble flow rate and the gas velocity through the bubbles were measured simultaneously in a pressurized fluidized bed, using capacitance and Pitot-static pressures probes respectively. Silica sand with a mean particle diameter of 0.7 mm was fluidized at pressures between 01. and 1.6 MPa, in a bed of 0.2 × 0.3 m cross-section. Six different horizontal tube configurations were used and comparisons were made with results obtained in the same bed operated without tubes. The results from the bed with tubes show that the influence of pressure and fluidization velocity is basically the same as in the bed without tubes; an increase in pressure and fluidization velocity increases the bubble activity. At low excess gas velocities, the influence of immersed tubes on the bubble behaviour is less pronounced than at high excess gas velocities. Measurements and visual observations show that a small tube pitch gives a more uniform distribution of the visible bubble flow over the bed cross-section. At a combination of high pressure, high excess gas velocity and a large tube pitch, a preferred bubble path was observed in the centre of the bed cross-section. The pressure probe measurements show that the through-flow velocity of gas inside the bubbles is in most cases higher when tubes are present in the bed. The through-flow velocity consistently decreases with increasing pressure in the bed without tubes. The tendency is largely the same at a low excess gas velocity when tubes are present, but at a high excess gas velocity the through-flow velocity first decreases and then increases as the pressure is increased.

In column flotation scale-up and modelling, gas holdup is usually considered as a constant in the collection zone of the column. However, it was found that the gas holdup may decrease by one-half over a depth of about 10 m in the column, due to the expansion of individual bubbles resulting from the reduction of hydrostatic head. Conventional methods have failed to predict this phenomenon. A new approach is used in this study to estimate the axial gas holdup profiles. By considering bubbly flow characterization and the force balance on a rising bubble swarm systems, a model has been developed to relate the gas holdup to the column height and gas flowrates. A good agreement between the model and literature data was obtained.

A new method is described in this study to estimate the average bubble size in flotation columns, based on the bubble flow characterization in gas-liquid systems. It was found that if other operating conditions are fixed, higher gas holdups in the column do not necessarily mean that smaller bubbles are produced when comparing with the different frothers used, due to the contamination factor effect on bubbles. Unlike in single bubble systems, the surface tension of the solution cannot be used as a criterion to predict the average size of bubbles produced in the column in the presence of different frothers. Comparisons with photographically measured mean bubble size and literature data were made to confirm the feasibility of the proposed method. The effects of superficial gas and liquid velocities, as well as frother type and concentration on bubble size are discussed.

The paper describes the experimental and theoretical investigations on (1) the variation of fluidized bed expansion with gas flow rate, particle size, temperature and the presence of immersed surfaces, and (2) the visible bubble flow rate and its relation to the excess gas flow rate. Both experiments conducted by the authors and literature data are analysed.

In a fluidized-bed combustor one technique to reduce the output while retaining the bed temperature constant is to uncover tubes near the surface of the bed as the superficial velocity is descreased. A prediction of the bed expansion has been developed which is based on a first-principles model of gas flow through the bed. In a large-particle bed where the bubble rise velocity is of the same order as the minimum-fluidization velocity, the two-phase model for gas flow is in serious error. A large fraction of the gas flow is found to pass through bubbles which are erupting at the bed surface. The gas flow for this case has been predicted by using previously published results by the present authors of the multidimensional numerical solution for the bed containing a cavity at the surface. The predicated bed expansion vs superficial velocity was calculated for several different tube geometries. The results were compared to experimental results for these geometries which were measured in the MIT 1.2 m wide cold bed model of the TVA bubbling fluidized-bed combustor. The predicted bed expansion closely follows the measured results while predictions based on the two-phase model give poor agreement with the measurements. The model also gives good results for open beds and for the expansion of beds with an upper surface above the top banks.

The mechanism of heat transfer from a bubbling liquid pool to an inclined side wall is considered. The process is relevant to the question of Mark-I liner melt-through due to contact with a high-temperature melt of reactor core materials, the bubbling being due to the decomposition of the concrete floor. We demonstrate experimentally that the recirculation caused by the two-phase lift creates a single-phase (liquid) boundary-layer flow along the inclined boundary which is responsible for heat transfer. An initial attempt to analytically quantify this process is also presented.

The distribution of gas flow between bubbles and the dense phase in a fludized bed is considered. By deriving general equations for gas and solids continuity in a freely-bubbling fluidized bed, the possible contributions to the invisible gas flow are formulated. It is shown that the gross assumptions inherent in “two-phase theories” of fluidization are not justified. Measurements of visible bubble flow and bubble volume fraction can give nothing more than estimates for the gas flow through the two phases.

Causes d'erreurs dans la mesure des debits, realisation d'un nouveau debitmetre pour He, N 2 ou un autre gaz

A model for predicting the liquid recirculation rate in gas-lift reactors was developed. The model relies on experimentally determined correlations for mean gas holdup and frictional pressure drop in two phase bubble flow. Model predictions were found to agree well with experimental measurements of liquid recirculation.

A glow-discharge probe has been developed for measuring bubble-phase parameters of gas-fluidized beds. A low-cost, multichannel electronics has been set up and preliminary tests for probe calibration have been carried out. Probe performances appear to be comparable with those of capacitance probes, while its disturbing effect on the bubble flow pattern is at the minimum level for intrusive measuring techniques, due to the slender, needle-shaped detecting electrode.

The separate determination of single component velocities in two-phase flow systems by statistical methods requires signals, which are proportional to the individual flow patterns. Suitable values can be measured by optical transmission techniques with simultaneous absorption and scattering of visible or infrared radiation. Under turbulent flow conditions there is usually only low correlation of measured quantities, especially for a greater sensor distance in flow direction. Therefore, the efficiencies of different statistical methods for transit time determination with respect to single component velocities are compared in this investigation, utilising an extended diffusion model for the transport process. An application to bubble flow is discussed.

Narrow size cuts of particles in the range 40–260 μm have been examined by X-rays when fluidised by air. No discontinuity in behaviour was observed with decreasing particle size. The bubbles behave the same in all materials except that their velocity increases with decreasing particle size. The visible bubble flow is generally less than the excess over minimum fluidisation flow. Almost all flow occurs interstitially near the bottom of the bed but the proportion decreases with height to approach Umf near the top of the bed. Appreciable changes in dense phase voidage occur with fine particles and this varies with bed height.

Momentum and heat transfer process in a two-phase air-water bubble flow is investigated experimentally to confirm the applicability of the theoretical model proposed in Part 1 of this study. Comparisons are made between the measurements and the predictions for both velocity and temperature profiles, and then satisfactory agreement is obtained. Also, the results for bubble flow simulation are presented to clarify the interrelationship of the frictional pressure gradient and the heat transfer coefficient with the void fraction profile.

The expansion of freely bubbling gas fluidised beds has been investigated experimentally in a 12-in. diameter bed and the influence of bed depth, gas velocity, particle size and particle-size distribution has been studied. Results are compared with theoretical predictions and new light is thrown on the assumptions inherent in the two-phase theory of fluidisation. In particular there is evidence to support the view that the visible bubble flow rate is less than the difference between the total flow rate and that necessary for minimum fluidisation.

The various factors contributing to the motion of the bubbles in two-phase flow are analysed. A theory is presented which shows that the velocity of the bubbles consists of a component equal to the superficial liquid velocity, a component equal to the superficial gas velocity and component due to buoyancy. A simple experiment in support of the theory (involving direct measurement of the buoyancy component of velocity by suddenly stopping the flow of gas and timing the rise of the swarm of bubbles) is described. The energy losses associated with two-phase gas-liquid flow are discussed at some length, and it is shown that in bubble flow “the energy loss due to slip” is closely related to the buoyancy component of bubble velocity.

Theory is given to predict the value of k in the equation for a bubbling fluidised bed U=kU0+QB/A; here U is the superficial fludising velocity, U=UO at incipient fluidisation, QB is the observed bubble flow, and A the cross-sectional area of the bed. In the simple two-phase theory, k=1; but the theory herein, assuming constant voidage fraction between the bubbles, shows that for a regular array of bubbles, k=1+eb for a two-dimensional system, provided eb=volume of all bubbles/bed volume, is small. It is inferred that for a three-dimensional system, k=1+2eb. Thus the simple two-phase theory, though not strictly correct, is not much in error; the error is likely to be largest when U is not much greater than UO, and particularly just above the distributor of a fluidised bed.

Observations are reported on the two-phase bubble flow of air rising through a stationary water phase. Distinctly different results have been measured for tap water and for distilled water. The difference in these results is attributed to the presence of an extremely small quantity of an unknown surface-active contaminant. Both the nature and the axial distribution of the contaminant are shown to be important in determining the ultimate flow regime.