Holdup Measurements Research Articles

Mass transfer, gas hold-up and cell cultivation studies in a bottom agitated draft tube reactor and multiple impeller Rushton turbine configuration

Gas–liquid mass transfer is an important phenomenon in aerobic microbial cultivations, and the mass transfer performance of an industrial reactor strongly affects the overall process economics. Traditionally, industrial and laboratory bioreactors have been agitated with flat disc turbines (Rushton turbines) although there are many variants to this design. In addition, pneumatically agitated reactors such as bubble columns and airlift reactors have been studied and used by the industry.In this study we utilize an agitated draft tube reactor in cell cultivation and mass transfer studies. A standard reactor geometry agitated with three Rushton turbines was compared to Outotec OKTOP®9000 reactor which is a draft tube reactor agitated with a single impeller located just below the draft tube. The experiments included cell cultivation with Pichia pastoris yeast, determination of overall mass transfer coefficient by dynamic gassing in method and measurement of local gas hold-up by electrical impedance tomography (EIT). In addition, agitation power was estimated from the power consumption of the DC-motor.OKTOP®9000 reactor was found to have higher kL a values than the STR with similar agitation power and gas flowrate. The overall gas hold-up was similar in both geometries at same power inputs and gas flow rates. However, some significant differences were detected in the distribution of gas phase between the two geometries especially in the axial direction. Also changes in the gas dispersion regime can be detected from the spatial distribution of the gas hold-up measured by EIT. The cell cultivation experiments showed the applicability of this type of agitated draft tube reactor to bioprocesses although a direct comparison with Rushton geometry is not straightforward.

Effects of flow patterns and salinity on water holdup measurement of oil-water two-phase flow using a conductance method

Abstract This research investigates the effects of flow pattern and salinity of oil-water two-phase flow on water holdup measurement using a conductance method. Firstly, vertical upward oil-water two-phase flow experiment is conducted in a 20 mm inner diameter (ID) pipe, in which the salinities of aqueous solutions are set as 151 ppm, 1003 ppm, 2494 ppm and 4991 ppm respectively. Experimental water-cut and mixture velocity are set as 80–100% and 0.0184–0.2576 m/s. In the experiment, three different flow patterns, i.e., dispersed oil-in-water slug flow (D OS/W), dispersed oil-in-water flow (D O/W) and very fine dispersed oil-in-water flow (VFD O/W) are observed and recorded by a high speed camera. Meanwhile, we collect the response of Vertical Multiple Electrode Array (VMEA) conductance sensor excited by a sine voltage signal. The result shows that, for VFD O/W, the water holdup from VMEA sensor shows a satisfied agreement with that of quick closing valve (QCV) method under certain salinities, i.e., 1003 ppm as well as 2494 ppm. For D OS/W flow and D O/W flow characterized by dispersed oil droplets with various sizes, considerable deviations of water holdup between VMEA sensor and QCV method under four kinds of salinity aforementioned are presented. Afterward, according to experimental analysis along with theoretical deviation, it is concluded that the deviation of the measurement system reaches its minimum when reference resistance in the measurement circuit and salinity of the aqueous solution satisfy constraint conditions, and the accuracy of water holdup using the conductance method can be improved through adjusting reference resistance to match the salinity of water phase. Finally, the recurrence plot algorithm is utilized to identify typical flow patterns mentioned above and it shows satisfied results on comprehending the discrepancies among different flow patterns, demonstrating that the recurrence plot algorithm can be effectively applied in flow pattern identification regarding oil-water flows.

Design of Helical Capacitance Sensor for Holdup Measurement in Two-Phase Stratified Flow: A Sinusoidal Function Approach.

A 360° twisted helical capacitance sensor was developed for holdup measurement in horizontal two-phase stratified flow. Instead of suppressing nonlinear response, the sensor was optimized in such a way that a ‘sine-like’ function was displayed on top of the linear function. This concept of design had been implemented and verified in both software and hardware. A good agreement was achieved between the finite element model of proposed design and the approximation model (pure sinusoidal function), with a maximum difference of ±1.2%. In addition, the design parameters of the sensor were analysed and investigated. It was found that the error in symmetry of the sinusoidal function could be minimized by adjusting the pitch of helix. The experiments of air-water and oil-water stratified flows were carried out and validated the sinusoidal relationship with a maximum difference of ±1.2% and ±1.3% for the range of water holdup from 0.15 to 0.85. The proposed design concept therefore may pose a promising alternative for the optimization of capacitance sensor design.

A Four-Sector Conductance Method for Measuring and Characterizing Low-Velocity Oil–Water Two-Phase Flows

Measuring water holdup and characterizing the flow behavior of an oil–water two-phase flow is a contemporary and challenging problem of significant importance in industry. To address this problem, we develop a new method to design a new four-sector distributed conductance sensor. Specifically, we first use the finite-element method (FEM) to investigate the sensitivity distribution of the electric field and then calculate its response on the measurement electrodes. Based on the FEM analysis results, we extract two optimizing indexes to describe and find the optimum geometry for the four-sector distributed conductance sensor. We carry out oil–water two-phase flow experiments in a vertical upward pipe to validate the designed sensor implemented in the measurement of water holdup. In addition, we use the multivariate pseudo Wigner distribution (MPWD) method to analyze the multivariate signals from the four-sector distributed sensor. Our analytical and experimental results indicate that the four-sector distributed conductance sensor enables measuring water holdup and the MPWD allows uncovering local flow behavior revealing different oil–water flow patterns.

Experimental investigation on the influence of ethanol on bubble column hydrodynamics

We experimentally investigate the effect of ethanol (0.05% in mass) on the hydrodynamics of a large-diameter and large-scale bubble column. The bubble column is 5.3m in height, has an inner diameter of 0.24m, and we consider gas superficial velocities in the range of 0.004–0.20m/s. The experimental investigation consists of gas holdup measurements and image analysis. The gas holdup measurements are used to investigate the flow regime transition and the global bubble column hydrodynamics. The image analysis is used to investigate the bubble shapes and size distributions near the sparger and in the developed region of the column. The presence of ethanol increases the gas holdup, stabilizes the homogeneous regime and modifies the bubble shapes and size distributions. In particular, the addition of ethanol increases the mean bubble aspect ratio and decreases the bubble diameters. The results suggest that the addition of ethanol changes the bubble properties, which modifies the bubble size distribution and shapes, thus, stabilizing the homogeneous flow regime and, finally, increasing the gas holdup.

An on-line adaptive estimation method for water holdup measurement in oil–water two-phase flow with a conductance/capacitance sensor

Oil–water two-phase flow widely exists in industrial processes such as petroleum engineering and chemical engineering. Accurate and real-time measurement of water holdup is an important problem requiring urgent solutions. In this work, a conductance and capacitance combination sensor (CCCS) system with four conductance rings and two concave capacitance plates was validated for its measurement performance of in situ water holdup through dynamic experiments. An online adaptive weight Kalman estimation (OAWKE) fusion algorithm for the CCCS system is proposed to fuse the conductance measurement and capacitance measurement. The algorithm has fast and dynamic response for the water holdup measurement of oil–water two-phase flow and has improved measurement precision by the adaptive data fusion method. The OAWKE fusion algorithm also has the ability to deal with the abrupt change of water holdup during the measurement process. Therefore, in the low water conductivity condition (tap water), the CCCS system with the OAWKE fusion algorithm can dynamically estimate the real-time full range water holdup of oil–water two-phase flow, which has prospects in the petroleum industry.

A meta-analysis of empirical correlations for average gas hold-up in three-phase fluidized beds

Experimental measurements of the average gas hold-up, a key parameter in the design and operation of three-phase (gas–liquid–solid) fluidized beds, are extracted from a multitude of published studies, classified and correlated for the first time. A simple functional, based on power-law dependence of the average gas hold-up on a number of dimensionless variables, successfully correlates gas hold-up during gas flow in fluidized beds of spherical particles with pure water as the liquid phase. Best-fit parameters of such a functional result in prediction of more than 75% of the data with absolute relative error less than 20%, but are shown to depend on the morphology of three-phase flow and may be difficult to generalize.

Characterising gas behaviour during gas–liquid co-current up-flow in packed beds using magnetic resonance imaging

Magnetic resonance (MR) imaging techniques have been used to study gas phase dynamics during co-current up-flow in a column of inner diameter 43mm, packed with spherical non-porous elements of diameters of 1.8, 3 and 5mm. MR measurements of gas hold-up, bubble-size distribution, and bubble-rise velocities were made as a function of flow rate and packing size. Gas and liquid flow rates were studied in the range of 20–250cm3s−1 and 0–200cm3min−1, respectively. The gas hold-up within the beds was found to increase with gas flow rate, while decreasing with increasing packing size and to a lesser extent with increasing liquid flow rate. The gas hold-up can be separated into a dynamic gas hold-up, only weakly dependent on packing size and associated with bubbles rising up the bed, and a ‘static’ hold-up which refers to locations within the bed associated with temporally-invariant gas hold-up, over the measurement times of 512s, associated either with gas trapped within the void structure of the bed or with gas channels within the bed. This ‘static’ gas hold-up is strongly dependent on packing size, showing an increase with decreasing packing size. The dynamic gas hold-up is comprised of small bubbles – of order of the packing size – which have rise velocities of 10–40mms−1 and which move between the packing elements within the bed, along with much larger bubbles, or agglomerates of bubbles, which move with higher rise velocities (100–300mms−1). These ‘larger’ bubbles, which may exist as streams of smaller bubbles or ‘amoeboid’ bubbles, behave as a single large bubble in terms of the observed high rise velocity. Elongation of the bubbles in the direction of flow was observed for all packings.

Particle Velocity, Solids Hold-Up, and Solids Flux Distributions in Conical Spouted Beds Operating with Heavy Particles

Conical spouted beds operating with high-density particles have recently gained attention because of their potential use as nuclear fuel coaters for next-generation nuclear reactors. To design, scale-up, and manufacture these coaters, detailed investigation of local flow structure is of paramount importance. Therefore, in this study, local instantaneous particle velocity and solids hold-up and flux measurements were carried out in spouted beds having a wide range of cone angles (30°, 45°, 60°) using zirconia particles (dp = 0.5, 1 mm; ρp = 6050 kg/m3). Effects of axial height, particle diameter, conical angle, and static bed height on local flow behavior were investigated. Comparisons were also made with the results of low-density particle studies. It is shown that particle velocity decreases and solids hold-up and flux increase along the bed height in the spout. The solids circulation is augmented as particle diameter and conical angle are decreased and static bed height is increased.

Comprehensive experimental investigation of counter-current bubble column hydrodynamics: Holdup, flow regime transition, bubble size distributions and local flow properties

In this paper, we apply a variety of experimental techniques to investigate the influence of the counter-current mode on bubble column hydrodynamics. We study an air–water bubble column, which is 5.3m in height and has an inner diameter of 0.24m, and we consider gas superficial velocities in the range of 0.004–0.20m/s and liquid superficial velocities up to −0.09m/s. The experimental investigation consists of holdup, gas disengagement, image analysis and optical probe measurements. The holdup measurements are compared with the literature and are used to investigate the flow regime transition. The gas disengagement measurements are used to further investigate the flow regime transition and study the structure of the holdup curve. The image analysis is used to study the bubble shapes and size distributions near the sparger and in the developed region of the column; in particular, the image analysis is applied to different gas velocities in the homogeneous regime in both the batch and counter-current modes. The optical probe is used to acquire radial profiles of the local properties (i.e., local void fraction and bubble rise velocity) to study the flow properties and further investigate the flow regime transition. Comparing the results from the different techniques, the influence of the gas superficial velocity and the liquid superficial velocity is discussed considering all main aspects of the two-phase flow, from the local flow properties to the global flow features. The counter-current mode is found to increase the holdup, reduce the bubble rise velocity, destabilize the homogeneous regime and change the local flow properties.

Influence of internals on counter-current bubble column hydrodynamics: Holdup, flow regime transition and local flow properties

Bubble columns are frequently studied without considering internals (open tube bubble columns). However, in most industrial applications, internal devices are often added to control heat transfer, to foster bubble break-up or to limit liquid phase back mixing. These elements can have significant effects on the multiphase flow inside the bubble column reactor and the prediction of these effects is still hardly possible without experimentation. In this paper, we study experimentally a counter-current gas–liquid bubble column in the open tube and annular gap configurations. In the annular gap bubble column, two vertical internal tubes are considered. The column has an inner diameter of 0.24m, and the global and local hydrodynamic properties are studied using gas holdup measurements and a double-fiber optical probe. The gas holdup measurements are compared with the literature and used to investigate the flow regime transition. A double-fiber optical probe is used to acquire midpoint data and radial profiles of the local properties to study the flow properties and to further investigate the flow regime transition. The counter-current mode is found to increase the holdup, decrease the bubble velocity and cause regime transition at lower superficial gas velocity. The holdup curves in the annular gap and open tube configurations are similar in shape and values, suggesting that the presence of internals has a limited influence on the global hydrodynamic. In addition, it is found that the presence of the internals stabilizes the homogeneous regime in terms of transition gas velocity and holdup.

Nonlinear observability of grinding mill conditions

Abstract: A nonlinear observer model of a grinding mill is developed. The model distinguishes between the volumetric hold-up of water, solids, rocks and balls in the mill, where solids are all ore small enough to discharge through the end-discharge grate, and rocks are all ore too large to discharge. The model includes the discharge rate, abrasion rate of rocks and the abrasion rate of balls as parameters. It is shown that with mill discharge flow-rate, discharge density and volumetric hold-up measurements the model states and parameters are locally (weakly) nonlinearly observable, but not linearly observable. Although instrumentation at the mill discharge is not yet included in industrial circuits because of space restrictions, this study motivates the benefits to be gained from including instrumentation at the mill discharge. If mills are fitted with adequate measurement instrumentation at the discharge, important mill states and parameters can be estimated.

Bubble size distributions and shapes in annular gap bubble column

An understanding of the bubble properties, size distributions and shapes is of fundamental importance for comprehending flow dynamics and mass transfer phenomena in bubble column reactors. A large number of studies have focused on open tube bubble columns, and the knowledge concerning bubble columns with internals is still limited. This paper contributes to the existing discussion experimentally investigating a counter-current annular bubble column with 0.24m inner diameter and two internal pipes. The experimental investigation consists in holdup measurements and image analysis. The former is used for identifying the flow regime transition and studying the bubble column hydrodynamics, whereas the latter is used for investigating the bubble shapes and size distributions. The definition of the transition point is important because the size distribution and bubble shapes depend on the operating conditions and a change of the bubble properties is expected near the transition. The image analysis is applied at different superficial gas and liquid velocities, corresponding to a gas holdup between 2.9% and 9.6%. It is difficult to measure bubble size distribution accurately in large-diameter bubble columns owing to the overlapping of bubbles, even at low void fractions, and—in an annular gap bubble column—the fact that cap bubbles have also been reported in the homogeneous flow regime. The use of a bubble image analysis method to study the bubbly flows in a large-diameter annular gap bubble column is described. In the proposed method, each bubble is approximated and reconstructed using an ellipse. The proposed approach is used to quantify the bubble size distribution, as well as to study the bubble shape and orientation as function of the superficial gas and liquid velocities. The experimental data obtained are used to develop a correlation between non-dimensional parameters and aspect ratios. Also, the experimental data are compared with non-dimensional diagrams from the literature, revealing good agreement. Finally, the image analysis is used for supporting the flow regime transition prediction in the stability analysis method: the virtual mass formulation is obtained by using the aspect ratio correlation provided by the image analysis. The stability analysis—supported by the image analysis—was able to predict the transition point in very good agreement with experimental data and performed better than literature correlations.

Influence of electrolyte concentration on holdup, flow regime transition and local flow properties in a large scale bubble column

We experimentally investigate the influence of the electrolyte concentration on holdup, flow regime transition and local flow properties in a large scale bubble column, with air and water as working fluids. The column is 0.24 m inner diameter, 5.3 m height and the air is introduced by a spider sparger up to a superficial gas velocity of 0.2 m/s. The influence of five NaCl concentrations are investigated by using gas holdup and optical probe measurements. The gas holdup measurements are used for analysing the flow regime transition between the homogeneous and the transition regime and the optical probe is used for studying the local flow characteristics at different radial positions. The presence of NaCl - up to a critical concentration - increases the gas holdup. The increase in the gas holdup is due to the inhibition of the coalescence between the bubbles and, thus, the extension of the homogeneous regime. The results are in agreement with the previous literature on smaller bubble columns.

A methodology to quantify the uncertainty in liquid holdup measurements with wire mesh sensor

The uncertainty in the holdup measurements of a capacitance based WMS with 32×32 wires has been experimentally evaluated, and a methodology for its quantification is proposed for horizontal flow. Investigation is performed in laboratory and in-situ experiments under stagnant conditions with an emphasis on the effect of the mesh grid orientation on the measurements. Also, potential impact of misalignment in the pipe inclination is explored by slightly inclining the pipe for both tests. Finally, dynamic flow conditions are tested in a high pressure (1.37MPa) facility with horizontal stratified-wavy oil/air two-phase flow for gas and liquid superficial velocity ranges of 2.8m/s≤νSg≤6.9m/s and 0.01m/s≤vSL≤0.05m/s, respectively.The angle between the phase interface and the sensor wires is ineffective while the misalignment in the pipe inclination plays a major role in the deviations of the holdup measurements. Using the proposed methodology, the measurement uncertainty from laboratory tests is shown to follow a logarithmic increase as a function of the measured holdup for smaller holdup values (HL≤15%) and to be lower than 1.5% for HL>15%. This behavior is intrinsic to WMS and a representative of the measurement uncertainty in the actual flow loop installation.Under actual flow conditions, the holdup measurements of the trapped liquid by WMS show an offset compared to the measurements via flow imaging which can be corrected by using the uncertainty quantified in the laboratory tests. However, the dynamic measurements with WMS show a good agreement with the holdup of the trapped liquid volume within the quantified uncertainty bounds.

Assessing the Feasibility of Optical Probe in Phase Holdup Measurements and Flow Regime Identification

Abstract Despite the hydrodynamics of trickle beds experiencing pilot size, on the contrary, the possibility of measuring hydrodynamic parameters locally and for large scale and finding an indicator to pinpoint the flow regime from trickling to pulsing remains obscure, to assess the feasibility of getting such information the reactor bed was randomly packed with equal-sized spherical beads of 3 mm diameter. Gas and liquid holdup measurements and flow regime identification were achieved at various flow conditions from trickling to the pulsing regime by an optical probe method using time series processing method. This method is shown to be simple and efficient provides quantitative information about the gas and liquid holdup variation in different flow regime. The various experimental results were compared to available literature models and correlations for confrontation and recommendations. The trickle-to-pulse flow transition boundary shifted towards higher gas and liquid superficial velocities, aligning with the findings on a variation of holdup along the axial direction confirmed to broaden the trickle flow domain. [Correction added after online publication June 26, 2015: To unify the adjective everywhere in this manuscript, optic fiber probe was changed to optical probe.]

Annular Gap Bubble Column: Experimental Investigation and Computational Fluid Dynamics Modeling

This paper investigates the countercurrent gas–liquid flow in an annular gap bubble column with a 0.24 m inner diameter by using experimental and numerical investigations. The two-phase flow is studied experimentally using flow visualizations, gas holdup measurements, and double fiber optical probes in the following range of operating conditions: superficial air velocities up to 0.23 m/s and superficial water velocities up to −0.11 m/s, corresponding to gas holdups up to 29%. The flow visualizations were used to observe the flow patterns and to obtain the bubble size distribution (BSD). The gas holdup measurements were used for investigating the flow regime transitions, and the double fiber optical probes were used to study the local flow phenomena. A computational fluid dynamics (CFD) Eulerian two-fluid modeling of the column operating in the bubbly flow regime is proposed using the commercial software ansys fluent. The three-dimensional (3D) transient simulations have been performed considering a set of nondrag forces and polydispersity. It is shown that the errors in the global holdup and in the local properties are below 7% and 16%, respectively, in the range considered.

Experimental flow pattern map, slippage and time–frequency representation of oil–water two-phase flow in horizontal small diameter pipes

We detect the flow structures of a horizontal oil–water two-phase flow in a 20mm inner-diameter pipe using 8-channels radial mini-conductance probes. In particular, we present an experimental flow pattern map that includes 218 flow conditions and compare this map to the flow pattern transitional boundaries predicted by published models. In addition, using the Adaptive Optimal Kernel Time–Frequency Representation, we analyze the conductance fluctuating signals and characterize the flow pattern in terms of the total energy and dominant frequency. Based on the liquid holdup measurements using the quickly closing valve technology combined with three parallel-wire capacitance probes, we investigate the slip effect between the oil and water phases under various flow conditions. The results show that the flow structures greatly affect the slippage, and the slip ratio is sensitive to flow pattern variations.

Validation of high-resolution gamma-ray computed tomography for quantitative gas holdup measurements in centrifugal pumps

In this article, the capability of high-resolution gamma-ray computed tomography (HireCT) for quantitative gas–liquid phase distribution measurements in commercially available industrial pumps is experimentally investigated. The object of interest thereby operates under two-phase flow conditions. HireCT System comprises a collimated 137Cs isotopic source, a radiation detector arc with a multi-channel signal processing unit, and a rotary unit enabling CT scans of objects with diameters of up to 700 mm. The accuracy of gas holdup measurements was validated on a sophisticated modular test mockup replicating defined gas–liquid distributions, which are expected in impeller chambers of industrial centrifugal pumps under two-phase operation. Stationary as well as rotation-synchronized CT scanning techniques have been analyzed, which are both used to obtain sharply resolved gas phase distributions in rotating structures as well as non-rotating zones. A measuring accuracy of better than 1% absolute for variously distributed static gas holdups in the rotating frame has been verified with the modular test mockup using HireCT.

A New Model to Determine the Two-phase Drilling Fluid Behavior Through Horizontal Eccentric Annular Geometry, Part A: Flow Pattern Identification and Liquid Hold-up Estimation

Flow patterns, liquid holdup, and frictional pressure gradient are three importance parameters to study the multiphase drilling fluid behavior. Although two-phase fluid flow is studied in detail for pipes, there exists a lack of information about aerated fluid flow behavior inside a wellbore. This study aims to identify the flow patterns of gasified fluids flowing inside a horizontal annulus, and to develop a method for measurement of liquid holdup by using the image processing techniques. Experiments have been conducted at Middle East Technical University (METU) Multiphase Flow Loop using air-water mixtures with various in-situ flow velocities. A digital high-speed camera is used for recording each test dynamically for the identification of flow patterns and the measurement of liquid holdup.