Bubble Size Measurements Research Articles

Bubble size distribution and gas–liquid interfacial area in a modified downflow bubble column

Bubble size distribution and the gas–liquid specific interfacial area were measured as a function of axial location, nozzle diameter and superficial liquid and gas velocities in a modified bubble column reactor. The experimental measurements of bubble size and its distribution are analyzed with distribution model to gain insight into the breakup and coalescence mechanisms taking place. Axial profile of bubble number flux was estimated based on size distribution model incorporated with coalescence phenomena. Also correlation for Sauter mean bubble diameter has been developed with operating variables.

Measuring bubble size in aerated flow

Abstract The effect of reducing cavitation damage in high-speed flow structure not only relate with entrained air concentration, but also relate with air bubble density has been discovered in recent research. The air bubbles in aerated flow with diameter below then 0.2mm or 0.5mm plays important role in reducing cavitation damage. May be very little air concentration can protect construction free from cavitation erosion. Thereby, measuring bubble size must be emphasized in study of reducing cavitation damage. Measuring bubble size can use probe of needle-type and image usually. By analyses and application experience of velocimeter of air concentration probe of needle-type, suggesting of the median size of bubble d 50 adopt measuring data by probe directly, and calculate space distance and density of bubble. Although, the d 50 and space distance would be big then real size, and density small then real value. The measuring results have importance value for studying mechanism and establishing a new criterion on entrained air to reduce cavitation damage.

Model for Plateau border drainage of power-law fluid with mobile interface and its application to foam drainage

A model for drainage of a power-law fluid through a Plateau border is proposed which accounts for the actual Plateau border geometry and interfacial mobility. The non-dimensionalized Navier–Stokes equations have been solved using finite element method to obtain the contours of velocity within the Plateau border cross section and average Plateau border velocity in terms of dimensionless inverse surface viscosity and power-law rheological parameters. The velocity coefficient, the correction for the average velocity through a Plateau border of actual geometry compared to that for a simplified circular geometry of the same area of cross section, was expressed as a function of dimensionless inverse surface viscosity and flow behavior index of the power-law fluid. The results of this improved model for Plateau border drainage were then incorporated in a previously developed foam drainage model [G. Narsimhan, J. Food Eng. 14 (1991) 139] to predict the evolution of liquid holdup profiles in a standing foam. Foam drainage was found to be slower for actual Plateau border cross section compared to circular geometry and faster for higher interfacial mobility and larger bubble size. Evolution of liquid holdup profiles in a standing foam formed by whipping and stabilized by 0.1% β-lactoglobulin in the presence of xanthan gum when subjected to 16 g and 45 g centrifugal force fields was measured using magnetic resonance imaging for different xanthan gum concentrations. Drainage resulted in the formation of a separate liquid layer at the bottom at longer times. Measured bubble size, surface shear viscosity of β-lactoglobulin solutions and literature values of power-law parameters of xanthan gum solution were employed in the current model to predict the evolution of liquid holdup profile which compared well with the experimental data. Newtonian model for foam drainage for zero shear viscosity underpredicted drainage rates and did not agree with the experimental data.

Measuring bubble size in aerated flow

Measuring bubble size in aerated flow

Observation of fine particle aggregating behavior induced by high intensity conditioning using high speed CCD

Abstract The aggregating behavior between bubbles and particles induced by high intensity conditioning (HIC) was studied using high speed CCD technique. Bubble size measurement was conducted, and the attachment behavior between bubbles and particles in HIC cell and flotation cell were observed. The results show that in HIC cell, high intensity conditioning creates an advantage environment for the formation of small size bubble due to hydrodynamic cavitations, and these fine bubbles have high probability of bubble-particle collision, which will enhance fine particle flotation. The bubble-particle attachment experiments indicate that in high intensity conditioning cell, a lot of fine bubbles are produced in situ on the surface of fine particles, and most of fine particles are aggregated under the bridging action of fine bubbles. The observation of bubble-particle interaction in flotation cell illustrates that aggregates created by HIC can be loaded more easily by big air bubble in flotation cell than those created by normal conditioning.

Bubble size measurement in three-phase system using photograph technology

A special experiment setup was designed to observe the interaction between bubbles and particle in flotation cell and to analyze the bubble characteristics such as bubble size, distribution and bubble-loading efficiency. Bubbles in water-gas system and three-phase system were measured. The results indicate that with the current setup the bubbles as small as 10 µm can be easily distinguished. The average size of the bubbles generated under the given conditions in two-phase system is 410 µm at frother concentration of 0.004%, which is in good correspondence with the results of other works. The effect of frother on bubble size was probed. Increasing frother concentration from 0 to 0.004% causes a reduction of bubble size from 700 to 400 µm. The bubble loading efficiency was reported. The result indicates that the fine particle is more easily entrapped than the coarse particle. Some factors, which have effect on measurement accuracy were discussed. The aeration speed has a significant effect on the accuracy of results, if it surpasses 30 mL/s, and the image becomes unclear due to the entrapment of fine particle. Another factor, which can affect observing results, is the sampling position. At a wrong sampling position, the images become unclear.

Effect of Electrolyte Concentration on Bubble Size and Gas-Liquid Interfacial Area in Bubble Column

The optimum conditions of bubble column would be the ones that enhance mass transfer and this is accomplished by maximizing gas-liquid interfacial area. In the present work the effect of electrolyte concentration (aqueous solution of sodium chloride NaCl 0.005-0.015 gm/cm3) on bubble size, gas-liquid interfacial area and gas holdup at various superficial gas velocities (0.35-0.312 m/s)) in bubble column was studied. A series of experiments were also performed for air – distilled water system at various superficial gas velocities. The results for the two systems were compared and show a significant difference on gas-liquid interfacial area, bubble size and gas holdup. Digital camera for bubble size measurements was used and the fractional gas holdup was estimated using bed expansion. Correlation based on dimensionless groups for the prediction of bubble size, gas- liquid interfacial area and gas holdup is suggested. An agreement with available data was found

Evaluation of a Microcel TM sparger in the Red Dog column flotation cells

Column flotation cells have been installed in numerous base metal operations around the world. The majority of these cells utilize conventional air-only spargers to introduce air into the bottom of the column. The recent development of instruments to measure the bubble characteristics in these columns has provided a renewed understanding of column behaviour. These new tools provided insight into why the columns at Red Dog Mine had never performed up to expectations. After efforts to optimise the spargers failed to substantially change the bubble size and air efficiency, alternate sparger systems were investigated. The Metso Minerals CISA Microcel sparger system appeared promising and was selected for a full-scale plant trial. The Microcel sparger system was originally developed for the coal industry at the Virginia Centre for Coal and Minerals Processing. In October 2003, a Microcel was retrofitted into one of two 3.66 m diameter flotation columns in the zinc retreat circuit at Red Dog Mine. The operation of the two different sparger systems in parallel allowed a detailed comparison. This paper discusses the performance of the Microcel based on the data collected during several detailed surveys. Bubble size measurements carried out in the pulp zone using the McGill University bubble viewer showed a significant difference in bubble size. The mean Sauter diameter of the bubbles decreased from 3.4 mm for the jetting-type sparger to 1.9 mm for the Microcel sparger. The overall recovery and the recovery by size fraction for both valuable and gangue minerals were compared. Paired t-tests demonstrated that the Microcel column produced a higher concentrate grade (0.6% zinc absolute) and a higher unit recovery (2.8% zinc absolute) than the existing Canadian Process Technologies Inc (CPT) SlamJet column. These improvements provided a payback period of 1.5 months for the $109,000 investment.

Bubble characteristics in a two-dimensional vertically vibro-fluidized bed

Measurement of bubble size and local average bubble rise velocity was carried out in a vertically sinusoidal vibro-fluidized bed. Glass beads of Geldart group B particles were fluidized at different gas velocities, while the bed was vibrated at different frequencies and amplitudes to study their effects on the bubble behavior. This is compared with the case of no vibration in a two-dimensional bed and it is concluded that with vibration the local average bubble size, d bav, decreases significantly, especially at minimum bubbling velocity. The average bubble size increases slightly with increasing vibration frequency and amplitude. The local average bubble rise velocity is higher than that with no vibration, though with increasing vibration frequency and amplitude, it does not change significantly.

A PIV study of hydrodynamics in gas–liquid high throughput experimentation (HTE) reactors with eccentric impeller configurations

High-throughput experimentation (HTE) is used for the screening of novel catalyst formulations via miniature agitated gas–liquid reactors with vessel volumes of an order of magnitude below the laboratory scale. An investigation of the macroscopic hydrodynamic performance of a miniaturised unbaffled stirred vessel of diameter 45 mm for an air–water system has been carried out at gassing rates of 0.25 and 0.5 vvm (dispersed flow regime) using particle image velocimetry (PIV). Measurements of bubble size and gas hold-up were also made. Eccentric agitation was employed as a means of breaking solid body rotation within the vessel, using a 6-blade, up-pumping pitched blade turbine. The gas phase was introduced via sintered glass panel spargers mounted in the vessel base. Two different configurations were used: firstly where the sparger located directly below the impeller, and secondly where the sparger was located opposite the impeller on the other side of the vessel. Measured distributions of turbulent kinetic energy (TKE) for both gassed configurations were similar and showed significant differences to the ungassed case. Estimates of the gas–liquid interfacial area were at least 2–3 times higher than those found in conventional, lab-scale baffled vessels; this was attributed to the creation of very small bubbles at the sparger ( d 32 ≈ 100 μ m ).

Bubble size estimation in slurry bubble columns from pressure fluctuations

AbstractThe average large gas bubble size in slurry bubble columns is estimated using a spectral analysis method applied to measured pressure time series. A pressure time series measured in a bubble column consists of local pressure fluctuations and global pressure fluctuations. The local pressure fluctuations arise from the liquid velocity fluctuations induced by the large gas bubbles and by the changes in gas holdup. The standard deviation of these local pressure fluctuations is a measure of the average large bubble size. The coherence between the pressure time series measured at the sparger and at any other location in the column is used to separate the local pressure fluctuations from the global pressure fluctuations. The global pressure fluctuations are measured instantaneously throughout the column and form the coherent part of the pressure time series. The local pressure fluctuations, which are absent at the sparger, form the incoherent part of the pressure time series. In a 2‐D bubble column, a clear correlation is demonstrated between the incoherent standard deviation of the pressure time series and the average large gas bubble size obtained from video imaging. A good agreement is also found between this correlation and the 3‐D model proposed by Krishna et al. for predicting the average large bubble size in 3‐D (slurry) bubble columns. © 2005 American Institute of Chemical Engineers AIChE J, 2005

Effect of particle hydrophobicity on particle and water transport across a flotation froth

Froth recovery measurements have been conducted in both the presence (three-phase froth) and absence (two-phase froth) of particles of different contact angles in a specially modified laboratory flotation column. Increasing the particle hydrophobicity increased the flow rate of particles entering the froth, while the recovery of particles across the froth phase itself also increased for particle contact angles to 63° and at all vertical heights of the froth column. However, a further increase in the contact angle to 69° resulted in lower particle recovery across the froth phase. The reduced froth recovery for particles of 69° contact angle was linked to significant bubble coalescence within the froth phase. The reduced froth recovery occurred uniformly across the entire particle size range, and was, presumably, a result of particle detachment from coalescing bubbles. Water flow rates across the froth phase also varied with particle contact angle. The general trend was a decrease in the concentrate flow rate of water with increasing particle contact angle. An inverse relationship between water flow rate and bubble radius was also observed, possibly allowing prediction of water flow rate from bubble size measurements in the froth. Comparison of the froth structure, defined by bubble size, gas hold-up and bubble layer thickness, for two- and three-phase froths, at the same frother concentration, showed there was a relationship between water flow rate and froth structure.

Effect of liquid properties on the performance of bubble column reactors with fine pore spargers

This work is a study of the effect of liquid properties on the performance of bubble column reactors with fine pore spargers. Various liquids covering a range of surface tension and viscosity values are employed, while the gas phase is atmospheric air. A fast video technique is used for visual observations and, combined with image processing, is used for gas holdup and bubble size measurements. New data on average gas holdup values, bubble size distributions and Sauter diameters are presented and are consistent with existing physical models on coalescence/breakage. A correlation based on dimensionless groups for the prediction of gas holdup in the homogeneous regime is proposed and found to be in good agreement with available data.

Optical fibre probe measurements of bubbly flow in hydraulic jumps

This paper describes measurements of void fractions, bubble frequencies and bubble sizes in hydraulic jumps with Froude numbers 2.0, 2.4, 3.7 and 4.8. In each case data were obtained with a dual-tip optical fibre probe at a large number of points throughout the jump. Across the lower part of the flow, dominated by air entrainment into a region of turbulent shear, void fractions follow a Gaussian distribution. In the upper region, dominated by interactions with the free surface, the void fraction follows the form of an error function. The intersection between these two profiles provides a well-defined boundary between the two regions. Comparisons are made with measurements at higher Froude numbers [by Chanson, H., Brattberg, T., 2000. Experimental study of the air–water shear flow in a hydraulic jump. International Journal of Multiphase Flow 26, 583–607] revealing a very large measure of compatibility between the two sets of data.

X-ray 미세 영상기법을 이용한 미세기포의 크기 및 속도 동시 측정기술 개발

It is important to measure precisely the size and velocity of micro-bubbles used in various field. The synchrotron X-ray micro-imaging technique was employed to measure the size and velocity of micro-bubbles moving in an opaque tube simultaneously. Phase contrast images were obtained at interfaces of micro-bubbles between water and air due to their different refractive indices. The X-ray micro-imaging technique was found to measure an optical fiber with an accuracy of 0.2%. Micro-bubbles of 20-60~m diameter moving upward in an opaque tube (??=2.7mm) were tested to measure bubble size and up-rising velocity. For DI water, the measured velocity of micro-bubbles is nearly proportional to the square of bubble size, agreed well with the theoretical result. In addition, the synchrotron X-ray micro-imaging technique can measure accurately the size and velocity of several overlapped micro-bubbles.

A novel approach for estimating the average bubble size for foams flowing in vertical columns

Bubbles in flowing foams deform, coalesce, and rupture. The bubble size, however, determines to a great extent the functionality and mechanical properties of the foam. Often it is not possible to measure directly the bubble size in a flowing foam, either because the system or the foam itself is not transparent. In order to determine the average bubble size in a flowing foam, a novel approach to estimate the average bubble size was developed, based upon the overflowing foam liquid content and conductivity measurements. A flowing foam column with variable orifice diameters was designed and experiments were performed with different gas flowrates, orifice diameters and surfactant (Sodium dodecyl sulphate) concentrations. Image analysis was used to measure directly the bubble size in the foam. When progressively smaller orifices were inserted, more coalescence was observed, as well as a decrease in the overflowing liquid content and the foam conductivity. Estimating the bubble size from these measurements showed close agreement with the directly measured bubble sizes.

Optical Measurement of Bubbles: System Design and Application

Affordable high quality charge-coupled device (CCD) video cameras and image processing software are powerful tools for bubble measurements. Because of the wide variation between bubble populations, different bubble measurement systems (BMSs) are required depending upon the application. Two BMSs are described: a mini-BMS designed to observe the background bubble population from breaking waves, and a large-BMS designed to noninvasively determine the time-resolved bubble distribution inside dense bubble plumes and near the interface, as are details of the analysis techniques. Using the two systems in conjunction with each other allowed size distributions over the range 15-5000-μm radius to be obtained. The BMSs were designed for application to breaking-wave bubble plumes in the field or laboratory. Distributions measured by both BMSs in aerator-generated plumes agreed very well for the overlapping size range. Also presented are observations of bubble plumes produced by breaking waves in a large wind-wave flume, and calibration experiments showing the effect on measured bubble size due to blur induced by slow shutter speeds.

Novel application of computer vision to determine bubble size distributions in beer

Certain beers develop a large number of microbubbles during dispense which circulate in the beer as it stands in the glass rather than immediately rising to the surface. This phenomenon is often referred to as bubble haze. Experimentally determined bubble size distributions for these bubble hazes would be of very significant value to the brewing industry in terms of product control and development. However the majority of bubble measurement techniques are not appropriate for the analysis of bubbles in beer created during the dispense process. Therefore a novel application of computer vision for measuring bubble size distributions in beer has been developed. The technique incorporates a computer controlled charge coupled device camera to capture and save bubble images. The technique is also designed to be simple to use and relatively portable. The technique allows for the measurement of both bubble diameter and velocity. Data from the experiments has been analysed to predict rates of bubble nucleation, growth, and motion for a variety of experimental conditions.

New basis for measuring the size distribution of bubbles

The use of air bubbles of varying size distribution in ore and wastewater treatment, including conventional (froth) and dissolved air flotation (DAF), Jameson flotation cell and Microcel (among others), has attracted much interest recently. These flotation processes are governed by the physical characteristics of the bubbles as well as the particles, and therefore it is necessary to investigate accurately the size distribution of bubbles that are generated. A new method was developed to measure the bubble size distribution based on the bubbles’ capture (without movement) combining microscopy with digital image processing procedures. The technique (LTM-BSizer) employs a sampler to draw bubbles, rising in a column, into a special viewing chamber and exposes them to a digital camera after they have decelerated and stopped. Thus common problems related to the movement of bubbles, namely focus, illumination, photographic speed and bubbles overlapping are all overcome. Results obtained are in good correlation with some values reported with the traditional image analysis method and show that using this technique accurate size distributions can be produced conveniently and efficiently. The influence of some operational parameters on the formation of bubbles was studied. It is believed that the bubble size measurement technique developed in this study will assist understanding and improvement of the DAF and conventional fines and ultrafines mineral flotation, from both theoretical and practical viewpoints.

Autocatalytic Cyclohexane Oxidation in a Bubble Column Reactor

AbstractThe autocatalytic cyclohexane oxidation was investigated in a lab‐scale bubble column reactor with on‐line measurement of bubble sizes. Significant conversion was obtained at temperatures between 420 and 430 K. The main products were found to be cyclohexyl‐hydroperoxide, cyclohexanol and cyclohexanone. Rising oxygen concentrations favour the production of cyclohexanone. Temperature mainly affects the induction time. At conversion rates greater than 5 % bubble coalescence was inhibited, affecting bubble size distributions for gas hold‐ups above 1 %.