Electroresistivity Probe Research Articles

Measurement of bubble size distribution in activated sludge bubble column bioreactor

Bubble size, bubble rise velocity and the corresponding distributions were directly measured by a dual-tip electro resistivity probe and to present empirical correlations to estimate the average bubble size and bubble rise velocity in activated sludge. Experiments were conducted in a 9cm diameter bubble column while superficial gas velocity was in range of 0.5–7cm/s. Four samples of activated sludge with mixed liquor suspended solid (MLSS) concentrations from 1.082 to 10.82g/L were used in the experiments. It was found that increasing the MLSS concentration resulted in increase in the bubble chord length and bubble rise velocity and decrease in the gas hold up. It was shown that in the homogeneous regime, the probability distributions of bubble chord length and bubble rise velocity are sharp and unimodal. To estimate bubble size and bubble rise velocity in activated sludge, correlations were developed which includes effect of MLSS concentration besides physical properties and operating conditions. The experimental results of this study were compared with the proposed correlations in literature obtained in two and three phase bubble column. It was shown that neither of the previous correlations can predict the bubble size and bubble rise velocity in the activated sludge system properly while the proposed correlation in this work shows a good precision for estimating these parameters.

Round gas jets submerged in water

Water submerged gas jets are characterized by the interplay of inertia and buoyancy forces and can exhibit diverse behaviors ranging from bubbly plumes to stable jets. In this work, direct measurements of the interfacial behavior of water-submerged gas jets, with Mach numbers ranging from subsonic to supersonic, were performed using high-speed digital photography and shadowgraphs. The results indicate that the jets have a preferential pinch-off position that can be attributed and correspond to the location of the maximum streamwise-velocity turbulence fluctuations. A new, experimentally determined jet penetration distance is proposed; the jetting length is taken as the jet length corresponding to a 99% probability of the gas-jet outer boundary being attached to the orifice during the sampling period. Using the shadowgraph analysis and this criterion, we determined that the electro-resistivity probe measurements, previously used to determine the jet penetration length, may be significantly biased. This is attributed to the inability of the probe measurements to distinguish between a continuous gas jet and advecting bubbles. In addition, based on a simple force-balance of the jet cross-section, we introduce a new scaling relationship for the jet penetration distance. This relationship shows that the jetting length scales with the square of the Froude number and compares well with the experimental observations. Finally, measurements of the gas jet boundary acceleration coupled with estimations of the internal gas jet velocity suggest that both Rayleigh–Taylor and Kelvin–Helmholtz mechanisms are nearly equally responsible for governing the jet boundary dynamics.

Separation and Hydrodynamic Performance of Air-Kerosene-Water System by Bubble Column

The separation of emulsified kerosene in water (concentration 250-750ppm) was investigated in a bubble column15.6 cm diameter and 120 cm height. The effective behaviors of bubble characteristics (bubble diameter, bubble rise velocity and air hold-up) on the removal efficiency were measured by electroresistivity probe. The effects of kerosene concentration, air flow rate,bubble diameter, liquid height, liquid viscosity, NaCl concentration, and alum on the removal rate were found. The experimental results showed that the removal efficiency increased with increasing air flow rate (1.09-2.6cm/s) and decreased with increasing CMC concentration. The results also showed that adding anionic surfactants (SLES and SDBS) leads to increase removal rate. The the flotation process was found to be first order kinetics. New correlations of air holdup and bubble diameter using dimensionless groups were derived.

Characterization of Bubble Properties in Slurry Bubble Columns Using a Triple Electroresistivity Probe

A triple electroresistivity probe was newly developed to detect the bubbles whose centers moved upwards through it and to measure their rise velocities and sizes (central chord lengths). The probe was designed based on the directional coincidence of the probe axis with the bubble motion, as required to determine the bubble velocity, as well as on the positional determination of the bubble chord detected, as required to obtain the chord length. The conventional double probe has a difficulty in sampling its signals for the bubbles moving vertically and in determining which chord of the individual bubble is detected. The measurements of the behaviors of bubbles with the triple probe were made for two different sizes of normal bubble columns and an external loop airlift bubble column with the liquid and solid phases performed batchwise under a wide range of operating conditions. An analysis of the signal sequences obtained by the probe was proposed which considered the effects exerted by the complicated behaviors of both bubbles and particles. The method gave the results on the local bubble frequency and gas holdup, as well as on distributions of the bubble central chord length and bubble rise velocity at a given radial position of the column. These results suggested an enhanced interaction between bubbles, such as their coalescence and breakup, due to the presence of solid particles. The radial profiles of the bubble frequency, the gas holdup and the mean bubble size and rise velocity, were found to depend on the bubble column type, operating conditions and physical properties of liquid and solid particles.

06/01241 Experimental study of the resulting flow of plume-thermosiphon interaction: application to chimney problems: Zinoubi, J. et al. Applied Thermal Engineering, 2005, 25, (4), 533–544

This paper describes the mean gas fraction distribution in the two-phase flow of a gas–liquid bubble plume set to develop adjacent either to a wall or to another bubble plume. When this happens, the plume exhibits a type of Coanda effect, bending either towards the wall or the other plume. The local mean gas fraction measurements are carried out using the electro-resistivity probe technique in an air–water system. The deflection angle of the plumes is shown to present a dependence on the modified Weber and Froude numbers of the bubbles. A Gaussian distribution for the mean gas fraction profile, observed to exist for axisymmetric single plumes, is shown not to occur in flow geometries where the Coanda effect is allowed to set in. The transition zone between the downstream flow where two Gaussian plumes are observed and the far upstream flow where the plumes are seen to merge onto a single plume is characterized. Photographs of the flow are shown to illustrate the phenomenon. Results are present for two- and three-dimensional mean gas fraction distributions. In addition, a simple theory based on integral methods is advanced for the prediction of the plume deflection angle; the theory considers a variable entrainment co-efficient.

Bubble plumes and the Coanda effect

This paper describes the mean gas fraction distribution in the two-phase flow of a gas–liquid bubble plume set to develop adjacent either to a wall or to another bubble plume. When this happens, the plume exhibits a type of Coanda effect, bending either towards the wall or the other plume. The local mean gas fraction measurements are carried out using the electro-resistivity probe technique in an air–water system. The deflection angle of the plumes is shown to present a dependence on the modified Weber and Froude numbers of the bubbles. A Gaussian distribution for the mean gas fraction profile, observed to exist for axisymmetric single plumes, is shown not to occur in flow geometries where the Coanda effect is allowed to set in. The transition zone between the downstream flow where two Gaussian plumes are observed and the far upstream flow where the plumes are seen to merge onto a single plume is characterized. Photographs of the flow are shown to illustrate the phenomenon. Results are present for two- and three-dimensional mean gas fraction distributions. In addition, a simple theory based on integral methods is advanced for the prediction of the plume deflection angle; the theory considers a variable entrainment co-efficient.

Bubble and liquid flow characteristics during horizontal cold gas injection into a water bath

In refining processes such as the AOD process cold gas is blown horizontally into the molten metal bath of the processes. The spatial distribution of bubbles in the bath is one of the important factors influencing the efficiency of the processes. In this study, a water model study was carried out to understand the characteristics of bubbles and liquid flow generated by horizontal gas injection. The bubble and liquid flow characteristics were measured using an electro-resistivity probe and a laser Doppler velocimeter, respectively. In the flow field near the nozzle the bubble characteristics for the horizontal cold gas injection can be predicted by empirical equations derived for isothermal gas injection systems. The liquid flow characteristics could not be measured in this region. On the other hand, in the region far from the nozzle the two characteristics for the cold gas injection became different from those for the isothermal gas injection because of enhanced buoyancy force acting on expanding cold bubbles due to heat transfer.

Gas holdup in a three-phase magneto-fluidized bed

The influence of magnetic field on local gas holdup, ε g and average gas holdup ε ̄ g has been studied in a three-phase (gas–liquid–solid) magneto-fluidized bed using electroresistivity probe technique and quick closing valve technique, respectively. The local gas holdup shows a linear variation with dimensionless radius at low gas velocities and parabolic variation at high gas velocities with maximum at the centre and minimum at the wall. Higher values of ε g are obtained in presence of field than in absence of magnetic field. Average gas holdup ε ̄ g decreases with field intensity upto H=52.8 Oe and shows an increase beyond this field intensity. The ε ̄ g values obtained by first fluidizing the bed and then magnetizing it have been found to be higher than those obtained by reversing this sequence.

Effects of pore diameter, bath surface pressure, and nozzle diameter on the bubble formation from a porous nozzle

The effects of the pore diameter, bath surface pressure, and nozzle diameter on the bubble formation from a porous bottom nozzle placed in a water bath and on the behavior of rising bubbles were investigated with still and high-speed video cameras and a two-needle electroresistivity probe. Three types of bubble dispersion patterns were observed with respect to gas flow rate, and they were named the low, medium, and high gas flow rate regimes. The transition boundaries between these gas flow rate regimes were expressed in terms of the superficial velocity at the nozzle exit, i.e., the volumetric gas flow rate per unit nozzle surface area. These transition boundaries were dependent on the pore diameter but hardly dependent on the bath surface pressure and the porous nozzle diameter. The characteristics of rising bubbles in each gas flow rate regime were investigated as functions of the three parameters.

Mixing time and fluid flow phenomena in liquids of varying kinematic viscosities agitated by bottom gas injection

A model experiment was carried out to investigate the mixing condition and related fluid flow phenomena in a slag layer of metal-refining processes agitated by bottom gas injection. Silicone oil was used as a model for the molten slag. Mixing time in a silicone oil bath was measured with a newly developed laser optical sensor. Measured mixing time values increased with an increase in the kinematic viscosity of the silicone oil. In order to explain the relation between mixing time and the kinematic viscosity of silicone oil, the rising velocity of bubbles and the vertical and horizontal velocities of silicone oil flow were measured with an electroresistivity probe and a laser Doppler velocimeter, respectively. The increase in the mixing time with the kinematic viscosity of silicone oil was caused mainly by the suppression of upward motion of bubbles and silicone oil in the bubbling jet region. An empirical correlation for the mixing time was derived as a function of the kinematic viscosity of silicone oil, in addition to conventionally used parameters such as the gas flow rate, bath diameter, and bath depth.

Development of a Laser Optical Sensor for Measuring Bubble Characteristics in an Oily Liquid Bath.

Oily liquids such as silicone oil and normal pentane have been commonly used as the model for top slag to investigate the role of the top slag on the mixing in the bath of various refining processes. An electroresistivity probe is a powerful tool for measuring bubble characteristics in a bath filled with a liquid of high electrical conductivity and it is extensively used in water model experiments. Unfortunately, the electrical conductivity of oily liquids is very low, and accordingly, the electroresistivity probe looses its validity in oily liquid baths. Considering these circumstances, a two-channel laser optical sensor was developed to measure the bubble characteristics in oily liquid baths. Gas holdup, mean bubble rising velocity and mean bubble chord length were measured accurately, whereas measurement of bubble frequency was disturbed by Doppler signals originating from the bubble surface.

Coanda Effect on Bubble Characteristics in a Bubbling Jet Rising Near the Side Wall of a Cylindrical Vessel.

Experimental investigation was carried out on the behavior of an air–water bubbling jet generated vertically upward by air injection through a single-hole nozzle placed near the side wall of a cylindrical vessel. The bubbling jet was pulled towards the side wall, attached to it at a certain vertical distance from the nozzle top, and afterwards rose along it. Such a phenomenon was caused through the Coanda effect. The vertical distance from the nozzle top to the attachment position was defined as the attachment length. This length was closely associated with the gas flow rate and the horizontal distance between the nozzle top and the side wall. The inner diameter of the nozzle, however, exerted a negligibly small effect on the attachment length. Bubble characteristics represented by bubble frequency, gas holdup, mean bubble rising velocity and mean bubble chord length were measured with a two-needle electroresistivity probe. The horizontal distributions of the bubble frequency and gas holdup were similar in the vertical region above the attachment position.

Bubble and liquid flow characteristics in a wood’s metal bath stirred by bottom helium gas injection

A model study was carried out to elucidate bubble and liquid flow characteristics in the reactor of metals refining processes stirred by gas injection. Wood’s metal with a melting temperature of 70 °C was used as the model of molten metal. Helium gas was injected into the bath through a centered single-hole bottom nozzle to form a vertical bubbling jet along the centerline of the bath. The bubble characteristics specified by gas holdup, bubble frequency, and so on were measured using a two-needle electroresistivity probe, and the liquid flow characteristics, such as the axial and radial mean velocity components, were measured with a magnet probe. In the axial region far from the nozzle exit, where the disintegration of rising bubbles takes place and the radial distribution of gas holdup follows a Gaussian distribution, the axial mean velocity and turbulence components of liquid flow in the vertical direction are predicted approximately by empirical correlations derived originally for a water-air system, although the physical properties of the two systems are significantly different from each other. Under these same conditions, those turbulent parameters in high-temperature metals refining processes should thus be accurately predicted by the same empirical correlations.

The shape of bubbles rising near the nozzle exit in molten metal baths

A previously developed multineedle electroresistivity probe was used to investigate the shape of bubbles generated at the exit of a central single-hole bottom nozzle in molten Wood’s metal and mercury baths. This probe is capable of detecting the vertical cross section of rising bubbles. The shape of bubbles just after the detachment from the nozzle exit was correlated as a function of a modified Reynolds number and a modified Weber number. Furthermore, the relations between the shape of bubbles and the radial distributions of bubble characteristics specified by gas holdup, bubble frequency, etc. were derived. As a result, it is possible to predict the shape of the bubbles by measuring the bubble characteristics with a conventional two-needle electroresistivity probe.

Development of a multineedle electroresistivity probe for measuring bubble characteristics in molten metal baths

Precise information on the behavior of rising bubbles in molten metals is of essential importance for the enhancement of current metal-refining processes as well as the development of new refining processes agitated by gas injection. In particular, the total interfacial area between bubbles and molten metal is a key parameter, but it cannot be evaluated unless the shape of bubbles is given. Getting information on the shape of rising bubbles has been very difficult for nontransparent liquids. In this study, we developed a multineedle electroresistivity probe to detect the shape of bubbles rising in molten metal baths. The accuracy of the presently developed probe was examined for water-air and Wood’s metal-He systems using a conventional two-needle electroresistivity probe and a high-speed video camera.

Phase-resolved measurements in a gas-injected liquid bath

The local phase volume fraction, bubble frequency, bubble velocity and phase resolved temperature distributions were measured in vertical air-injected water and air-injected multifluor™ inert fluid baths under different injection conditions. An electroresistivity probe was employed for determination of the local volume fraction, bubble arrival frequency and bubble velocity. The phase resolved temperatures were measured using a microthermocouple. The phase resolved temperature measurements are reported for the first time in these types of flow systems. The measurements showed that in the region close to the injection point, the gradients of the flow variables exhibit steep changes in radial and axial directions.

Model study of bubble and liquid-flow characteristics in a bottom blown bath under reduced pressure

Gas injection techniques are widely used in metals refining processes. Pressure on the bath surface of reactors is sometimes highly reduced to enhance the efficiency of refining. Many fundamental and practical investigations have been made to clarify the effects of reduced surface pressure on the mixing time and reaction rates of decarburization or desulfurization in the bath. However, details of these effects are not fully understood yet. Since the mixing time and chemical reaction rates are closely associated with fluid flow phenomena in the bath, information on, for example, the total surface area of bubbles rising in the bath and liquid flow induced by the buoyancy force of the bubbles should be accumulated as much as possible. In this study, the so-called water-model experiments were carried out to reveal the effects of reduced surface pressure on the bubble and liquidflow characteristics using a two-needle electroresistivity probe and a two-dimensional laser Doppler velocimeter. At an axial position near the nozzle, each bubble expanded to a volume corresponding to the hydrostatic pressure. The bubble and liquid-flow characteristics in the axial region located farther than this axial position were found to be approximately the same as those obtained under an atmospheric surface pressure.

Bubble Characteristics in Molten Copper Bath with Gas Injection.

Bubble characteristics in a molten copper bath at 1250°C agitated by Ar gas injection were measured using a newly developed electroresistivity probe. The bubble characteristics are specified by gas holdup (void fraction) α, bubble frequency fB, mean bubble rising velocity uB^- and mean bubble diameter dB^-. Ar gas was injected through a centered single-hole bottom nozzle or an L-type lance at the same temperature as the bath. The Ar gas flow rate was 50 or 100 cm3/s (at 1250°C), which was adjusted using a mass flow controller. Measured values of α, fB, uB^- and dB^- were compared with their respective empirical correlations for these quantities proposed previously on the basis of the cold model experiments. Good agreement between the measured values and empirical correlations was seen in the bath, except near the nozzle exit.

Bubble and liquid flow characteristics in a vertical bubbling jet

A vertical bubbling jet was formed in a cylindrical water bath by injecting air from a centric single-hole nozzle. Bubble characteristics, such as gas holdup (void fraction), bubble frequency, mean bubble rising velocity, mean chord length, were measured using a two-needle electro-resistivity probe. In addition, liquid flow characteristics, represented by the axial mean velocity, rms values of axial and radial turbulence components, Reynolds shear stress, effective kinematic viscosity, skewness and flatness factors for axial and radial turbulence components, were measured with a two-dimensional laser Doppler velocimeter. The flow field in the bubbling jet was essentially classified into two regions with respect to the axial distance from the nozzle exit. One is located near the nozzle where the inertia force of injected gas plays an important role. The other is located far from the nozzle in which the buoyancy force of bubbles governs the flow. In this study the experimental results of liquid flow characteristics in the latter region were compared with those for a single-phase round jet. Turbulence production in the bubbling jet was found to mainly occur in the wake of bubbles and to be approximately two times as large as the turbulence production in the single-phase round jet. The turbulence structures for the two jets also were different from each other.

Measurement of bubble characteristics in a molten iron bath at 1600 °C using an electroresistivity probe

A two-needle, electroresistivity probe was developed to measure bubble characteristics such as gas holdup, bubble frequency, and bubble rising velocity in a molten iron bath at 1600 °C. The probe’s electrode was made of a 0.5-mm platinum wire coated with ZrO2 cement and an outer coat of alumina as insulator. The life of this probe at 1600 °C was 15 to 20 minutes, making it possible to systematically measure bubble characteristics. The measured values of the bubble characteristics were compared with their respective empirical correlations derived from cold model experiments. Good agreement between the measured values and the empirical correlations was seen for each bubble characteristic. This electroresistivity probe allows us to measure bubble characteristics in actual metallurgical reactors with gas injection at high bath temperatures.