Phase Superficial Velocity Research Articles

Experimental Investigations on Carryover in a Gravity Separation-Based Steam Drum

Advanced heavy water reactor (AHWR) is a natural circulation-based, light water-cooled, heavy water-moderated pressure tube type of nuclear reactor. In AHWR, the steam separation takes place in horizontal steam drums purely based on gravity separation principle. It is a known fact that efficiency of gravity separation is affected by the carryover phenomenon, i.e., conveyance of water droplets by the steam. To minimize the carryover, it is advised to reduce the superficial velocities of phases. Lowering the flow velocities also results in to lower pressure drop, which is very much desired. However, careful attention must be given to carryover phenomenon during design. An experimental test facility known as air–water loop (AWL) simulating the scaled down steam drum of AHWR with air–water mixture has been designed and experimental work performed on carryover phenomenon is presented here. Comparison of measured entrainment fraction with existing correlations and other visual observations are described. Numerical simulations with Euler–Lagrangian method have been carried out for which droplet size distribution measured experimentally is used as an input.

Bed expansion characteristics in sound assisted fluidization of Geldart's group A powder

Intrinsic bed expansion characteristics in a sound assisted fluidization of Geldart's group A powder were investigated. To obtain an accurate bed expansion data, a 1-valve and 2-valve bed collapse experiment, together with a bed collapse model for a correct interpretation of bed collapse curves, was used. It was found that a total bed voidage and a dense phase for the sound assisted fluidization were varied with an inlet superficial velocity in the same fashion as those for a conventional fluidization. Besides, the voidage with respect to the inlet superficial velocity of the sound assisted fluidization was found to be lower, in comparison with those of the conventional fluidization and was independent on a sound frequency. On the other hand, dense phase voidage and its superficial velocity relations of the sound assisted fluidization at the different sound frequencies were approximately on the same trend as that for the conventional fluidization. And, a minimum bubbling point, defined using the dense phase voidage and the dense phase superficial velocity characteristic curve, was also unaffected by the sound vibration force. These findings suggested that the sound vibrational force tended to create more cavity or bubble phase in the fluidized bed, rather than changing a hydrodynamics relation in the dense phase. Therefore, the same equilibrium of force as that of the conventional fluidization can still be applied for the sound assisted fluidization, as well as stability criteria. Finally, it was proved that the modified revised Ergun drag force correlation, applicable for the conventional fluidization, can describe well the dense phase voidage and the dense phase superficial velocity characteristic curves of the sound assisted fluidization. Likewise, the stability criterion, proposed by Cherntongchai and Brandani in 2013, can predict excellently the minimum bubbling points for the sound assisted fluidized bed.

Flow measurement of oil-in-water flows in vertical low flow rate and high water-cut flow conditions

This paper reports on the flow measurement of oil-in-water flows with low flow rare and high water-cut in vertical 20mm inner diameter pipe. By using arc type conductivity sensor (ATCS) and cross-correlation flow meter (CCFM) based on conductance method, water holdup and mixture velocity are obtained. Afterward, oil-in-water flows drift-flux model is established to predict individual phase superficial velocity. The research results show that ATCS has high resolution on water holdup and CCFM performs well in mixture velocity measurement. Based on drift-flux model, individual phase superficial velocity can be predicted with high accuracy.

Continuous Wave Ultrasonic Doppler Modeling for Oil–Gas–Water Three-Phase Flow Velocity Measurement

Oil–gas–water three-phase flow is the most commonly seen fluid in petroleum production and transportation process. Flow velocity measurement of each individual phase is important to estimate the production condition and monitor the operation safety. The continuous wave ultrasonic Doppler (CWUD) technique has a high potential to measure the velocity of multiphase flow in a non-intrusive manner. However, this technique lacks proper measurement models for three-phase flow velocity measurement. In this paper, a one-sided CWUD sensor with 1-MHz center frequency was used for transmitting and receiving the acoustical signal that contains rich flow velocity information of the dispersed phases. By analyzing the momentum balance between different phases and modifying a two-fluid model into three-phase flow, a novel theoretical model to estimate the individual phase superficial flow velocity was established. Experiments were performed in a 50-mm inner diameter pipe, and two typical flow patterns (water dominated dispersed plug flow, oil dominated dispersed plug flow) were generated by adjusting the inlet flow rate of the three phases. By analyzing the ultrasound signal, the flow velocity of dispersed phases can be extracted. After using proposed theoretical model, the phase’s superficial velocities can be calculated. The results show that the mean relative error can achieve within 5%. The proposed theoretical model explains the characteristic and mechanism of ultrasound Doppler frequency shift in three-phase flow, which can be applied in similar flow conditions to obtain acceptable accuracy.

Flow Measurement of Oil-in-Water Emulsions Using Arc-Type Conductivity Probes and Electromagnetic Flowmeter

This paper reports on the flow measurement of oil-in-water emulsions using arc-type conductivity probes (ATCP) and electromagnetic flowmeter (EMF). With the aid of finite-element method, we first optimize the geometry parameters of ATCP through examining its sensitivity field distribution. Afterward, an experiment of oil-in-water emulsions with low velocity and high water cut is implemented in a 20-mm inner diameter vertical upward pipe. A comparative study in water holdup measurement characteristic between ATCP and vertical multiple electrode array conductance sensor is conducted by extracting their respective generalized conductance. The effect of water cut on the measurement in mixture velocity using EMF is investigated as well. Based on water holdup and mixture velocity from ATCP and EMF, oil-in-water emulsions drift-flux model is established to predict individual phase superficial velocities. The research results show that a high resolution in water holdup as well as high predicted accuracies in mixture velocity and individual phase superficial velocities can be achieved with the combination measurement system composed by ATCP and EMF.

Hydrodynamics of a pilot plant spray extraction column

The hydrodynamic characteristics of the liquid-liquid system of toluene-water in a pilot plant spray extraction column were experimentally determined. The experimental data for hydrodynamic characteristics such as the dispersed phase holdup, mean droplet size, and the axial dispersion coefficient were obtained. The dispersed phase superficial velocity had a great influence on toluene holdup. At the same time, a strong effect of the continuous phase superficial velocity on the dispersed phase holdup was evident. The dispersed phase holdup had a tendency to increase when the ratio of the dispersed phase superficial velocity and characteristic velocity increased. The Sauter mean droplet diameter decreased with increasing dispersed phase superficial velocity when the continuous phase superficial velocity remained constant. In contrast, it was not affected by the changes in the continuous phase superficial velocity while the dispersed phase superficial velocity remained constant. It was concluded that the Peclet number increased as a result of an increase of the Reynolds number.

CFD study of oil-in-water two-phase flow in horizontal and vertical pipes

The effectiveness of the classical Lagrangian method implemented in 3D CFD solver to simulate highly turbulent vertical and horizontal liquid-liquid dispersed flows where intensive turbulent migration of droplets make the flow behaviour complex is in the focus of the study. Dispersed oil-in-water two-phase pipe flow is analysed numerically using CFD solver ANSYS Fluent where a three-dimensional mathematical model of two-phase flow in pipes is developed. The Euler-Lagrange scheme is employed to resolve the interaction between the fluid (water) and droplet (oil) phases. The flow field of the continuous fluid phase is calculated by solving the Reynolds-averaged Navier-Stokes (RANS) conservation equations that are coupled with a high Reynolds number k-ε turbulence model and standard wall function. The Lagrangian method is used to resolve the motion of oil droplets. The drag, gravity, buoyancy and shear-lift forces are considered. The shear-lift force is of primary focus and is modelled and incorporated into the governing equations of the solver through the User Define Function (UDF) option as the external program. The two-way coupling procedure is employed. Here, droplet breakup and coalescence are not modelled. Mean droplet size is calculated using analytical methods. The model is validated with high level of accuracy against published experiments where the frictional pressure drop in vertical and horizontal dispersed oil-water flows is measured. The effect of mixture flow velocity and fluid phase superficial velocity on the droplet dynamics in vertical and horizontal pipes is investigated numerically. The transition from dispersed two-phase flow to stratified flow regime is analysed for the case of horizontal pipe flow. It has been found that the shear-lift force has much higher importance for the adequate flow representation as compared to the break-up/coalescence phenomena in the case of highly turbulent liquid-liquid dispersed pipe flows.

Drop behaviour characteristics in different operating regimes in an L‐shaped pulsed sieve‐plate column

AbstractIn this study, the influence of different operating regimes on drop behaviour in an L‐shaped pulsed sieve‐plate column has been investigated and the effects of pulsation intensity and phase superficial velocities on drop diameters are evaluated. The toluene‐water system with 0.03 L/L (3 vol%) acetone as a mass transfer agent is used. Experimental observations reveal that with increasing pulsation intensity, drop sizes slightly decrease and by reaching to the end of mixer‐settler regime, they significantly decrease followed by a mild decrease in the dispersion regime. Moreover, it is observed that mean drop size firstly varies inversely as both phase superficial velocities change, while it slightly increases with further increase in superficial velocities. Finally, some of the most recommended correlations are compared to the experimental data. It is revealed that these correlations show the highest deviation in the lower end of the mixer‐settler regime (> 40 %), while in the dispersion regime it becomes < 15 %, indicating that they are only applicable in the region of practical regimes. Accordingly, two of these correlations are modified in order to cover different operating regimes by means of two correlations proposed to predict the transition regime in each section of the column. The AARE values of the modified correlations are found to be < 14.7 %.

Measurement of gas phase characteristics in bubbly oil-gas-water flows using bi-optical fiber and high-resolution conductance probes

In the present study, experiments are carried out to investigate local gas phase characteristics of bubbly oil-gas-water flows in a vertical upward pipe with small inner diameter (ID). Bi-optical fiber probe signals at different radial positions and leading and rear half-ring conductance sensor fluctuation signals are collected in a 20mm ID test pipe. Then flow parameters, including local gas volume fraction, gas velocity and bubble size distribution are extracted according to optical probe signals. The results show that the gas phase superficial velocity, mixture superficial velocity of oil and water as well as mixing ratio of oil and water all have significant impacts on the distribution of gas phase flow parameters. Additionally, in order to validate the results obtained from optical probe signals, multi-scale cross entropy (MSCE) algorithm is applied to analyze signals of high-resolution half-ring conductance sensor to uncover the dynamical instability of oil-gas-water bubbly flows under different flow conditions.

Experimental investigation of two-phase flow patterns in minichannels at horizontal orientation

Two-phase flow is the simplest case of multiphase flow in which two phases are present for a pure component. The mini channel is considered as diameter below 3.0–0.2 mm and conventional channel is considered diameter above 3.0 mm. An experiment was conducted to study the adiabatic two-phase flow patterns in the circular test section with inner diameter of 1.1, 1.63, 2.0, 2.43 and 3.0 mm for horizontal orientation using air and water as a fluid. Different types of flow patterns found in the experiment. The parameters that affect most of these patterns and their transitions are channel size, phase superficial velocities (air and liquid) and surface tension. The superficial velocity of liquid and gas ranges from 0.01 to 66.70 and 0.01 to 3 m/s respectively. Two-phase flow pattern photos were recorded using a high speed CMOS camera. In this experiment different flow patterns were identified for different tube diameters that confirm the diameter effect on flow patterns in two-phase flows. Stratified flow was not observed for tube diameters less than 3.0 mm. Similarly, wavy-annular flow pattern was not observed in 1.6 and 1.0 mm diameter tubes due to the surface-tension effect and decrease in tube diameter. Buoyancy effects were clearly visible in 2.43 and 3.0 mm diameter tubes flow pattern. It has also observed that as the test-section diameter decreases the transition lines shift towards the higher gas and liquid velocity. However, the result of flow pattern lines in the present study has good agreement with the some of the existing flow patterns maps.

Upward flow of air-oil-water mixture in vertical pipe

The results of an experimental study into three-phase air-oil-water flow carried out in a vertical pipe with 0.03m diameter are reported. The experiments were conducted with the input superficial phase velocity: water from 0.02 to 1.07m/s, oil from 0.001 to 0.63m/s and gas from 0.01 to 16.40m/s. In order to investigate the influence of gas injection on an oil-water two-phase flow, the mean in situ phase fraction and pressure drop were measured. This was accompanied by performing flow pattern observations. Consequently, new methods were obtained with a practical potential for application in phase fraction and pressure drop predictions of gas-liquid-liquid three-phase flow through a vertical pipe. A good conformity between calculated and measured data in this work was obtained.

A study on hydrodynamic characteristics in a Φ38 pulsed extraction column by four‐sensor optical fiber probe

Accurate prediction of dispersed phase droplet behavior is crucial to the design and scaling‐up of an extraction column. In this article, the dispersed droplet velocity algorithm and the diameter algorithm in a liquid–liquid two‐phase flow have been developed based on the bubble velocity model in gas–liquid two‐phase flow of Lucas [Measurement Science & Technology. 749, 758(2005)] and Shen [International Journal of Multiphase Flow. 593, 617(2005)]. Hydrodynamic characteristics, including droplet diameter, holdup and droplet velocity, were measured using a self‐made four‐sensor optical fiber probe in a 38 mm‐diameter pulsed sieve‐plate extraction column. Water and kerosene were used as continuous and dispersed phases, respectively. The influences of the pulsed intensity, the continuous and dispersed phase superficial velocities on the hydrodynamic characteristics were investigated. The experimental results show that it is reliable to use a four‐sensor optical probe to measure the hydrodynamic characteristics of a pulsed extraction column. © 2016 American Institute of Chemical Engineers AIChE J, 63: 801–811, 2017

Differential pressure method for measuring water holdup of oil–water two-phase flow with low velocity and high water-cut

This paper is devoted to measuring water holdup of oil–water two-phase flow with low velocity and high water-cut through differential pressure method. At first, we carry out vertical upward oil–water two-phase flow experiment in a 20mm inner diameter pipe to obtain the response of differential pressure sensor, and use Vertical Multiple Electrode Array conductance sensor (VMEA) as well as Adaptive Optimal Kernel Time–Frequency Representation (AOK TFR) algorithm to identify 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). Then the water holdup is extracted from the differential pressure sensor response by calculating frictional gradient loss, and the water holdup measured is compared with the set value by using the method of quick closing valve. Finally, we using drift-flux model predict the individual phase superficial velocities based on the flow pattern classification and water holdup. The research results show that differential pressure method proves to be an effective approach to investigate flow characteristics in oil–water two-phase flow with low velocity and high water-cut.

HYDRODYNAMICS OF PLATE COLUMN FOR ENZYMATIC REACTIONS OF OIL

This work describes the hydrodynamics of a plate column of 5 cm inner diameter and 2.75 m height, operated in a semi-batch manner using an oil-water system especially important for enzymatic catalyzed reactions. The parameters such as dispersed phase superficial velocity, plate orifice size, number of nozzles, nozzle size and plate spacing, affecting the dispersed phase hold up, were investigated. It was observed that the orifice plate produced an uneven change in drop diameter and hence nozzles were used to study the hydrodynamics. The total and dynamic hold ups determined were increased with an increase in dispersed phase superficial velocity, while decreased with an increase in a nozzle size. The total hold up decreased, while dynamic hold up slightly increased with an increase in plate spacing. Correlations obtained are found to be appropriate for the estimation of the total hold up and dynamic hold up.

Experimental investigation on the heat transfer characteristics and flow pattern in vertical narrow channels heated from one side

Experimental investigation for the flow boiling of water in a vertical rectangular channel was conducted to reveal the boiling heat transfer mechanism and flow patterns map aspects. The onset of nucleate boiling went upward with the increasing of the working fluid mass flow rate or the decreasing of the inlet working fluid temperature. As the vapour quality was increased, the local heat transfer coefficient increased first, then decreased, followed by various flow patterns. The test data from other researchers had a similar pattern transition for the bubble-slug flow and the slug-annular flow. Flow pattern transition model analysis was performed to make the comparison with current test data. The slug-annular and churn-annular transition models showed a close trend with current data except that the vapor phase superficial velocity of flow pattern transition was much higher than that of experimental data.

Experimental investigation of annular two-phase flow splitting at a microimpacting T-junction

An experimental study was conducted in order to investigate the phase split of annular two-phase flow at a horizontal microimpacting T-junction with the square cross section of 0.5×0.5mm2. A high speed record camera was used to help elucidate the fluid dynamics at the junction. Nitrogen and water at 120kPa (abs) and room temperature of 22°C were used as the test fluids. The inlet superficial velocities of gas and liquid varied from 13 to 30m/s and from 0.018 to 0.08m/s, respectively, covering a wide range of the inlet qualities between 0.23 and 0.58. The aqueous solutions of sodium dodecysulfate (SDS) and carboxymethyl cellulose (CMC) with different mass concentrations were employed to study the effect of surface tension and viscous force on phase split, respectively. Experimental results showed that, the phase split of annular flow at microimpacting T-junctions was less affected by either the inlet phase superficial velocities or the viscous force, but varied largely with surface tension. Besides, the phase maldistribution of annular flow was smaller than that of slug flow and slug–annular flow at microimpacting T-junctions. Furthermore, when the present data were compared to those of mini- and macro-sized junctions at similar flow conditions, it was found that the phase maldistribution at microimpacting T-junctions was the smallest. Finally, good agreement was obtained between the present experimental data and a modification of an existing model.

Fluid flow and mass transfer characteristics of enhanced CO2 capture in a minichannel reactor

CO2 absorption using amine solvents can be significantly enhanced by the use of microscale reactors having high surface area to volume ratio. The present paper reports an experimental investigation of the fluid flow and mass transfer characteristics during reactive gas–liquid absorption in a minichannel reactor. Absorption of CO2 mixed with N2 into aqueous diethanolamine was studied in a channel having hydraulic diameter of 762μm and a circular cross-sectional geometry. High-speed imaging of the two-phase flow was conducted to visualize the flow regimes. Image-processing analysis of the acquired flow patterns was performed to determine the interfacial area. The performance of the reactor was studied with respect to the absorption efficiency, pressure drop, mass transfer coefficient, interfacial area, enhancement factor, and Sherwood number. Parametric studies investigating the effects of phase superficial velocity, liquid reactant concentration, and CO2 concentration in the gas phase were performed and are discussed. High levels of absorption efficiency, close to 100%, were observed under certain operating conditions. An empirical model for the Sherwood number was developed and compared against experimental data. The mass transfer coefficient was found to be higher at reduced channel lengths, which was attributed to improved utilization of the absorption capacity of the amine solution for a given reactor volume. The presently achieved values of mass transfer coefficient and specific interfacial area are between 1 and 4 orders of magnitude higher than those reported for most conventional absorption systems.

Flow patterns and gas fractions of air–oil and air–water flow in pipe bends

An experimental study of two-phase flow in a 180° pipe bends with 0.016, 0.022 and 0.03m and the curvature radii of 0.11, 0.154, 0.21m, respectively have been carried out. The experiments were conducted under the input superficial phase velocity: air from 0.038 to 5.4ms−1, water from 0.018 to 0.92ms−1 and oil from 0.014 to 0.92ms−1. The conducted research involved the observation of the forming flow patterns and determination of average volumetric in situ gas fraction. On the basis of the results of experimental flow map was created for gas–liquid flow and a method of calculating gas fractions was established.

Effect of a Polymer Additive on Heat Transfer and Pressure Drop Behaviors of Upward Air–Water Flow in an Inclined Smooth Circular Tube

This article presents an experimental study of the effect of polyacrylamide (PAM) on heat transfer and frictional pressure drop behaviors of upward air–water two-phase flow in an inclined smooth circular tube with an upward inclination angle of 8 degrees from the horizontal direction. The test tube has an inside diameter of 40 mm and an outside diameter of 48 mm. A PAM water solution with a concentration of 300 ppm was used in the experiments. The liquid phase superficial velocities are 0.52, 1.02, and 1.46 m/s and the gas-phase superficial velocities are from 1.79 to 6.54 m/s. Heat transfer tests were performed by cooling the air–water flow inside the test tube through its wall using the cooling water with a heat transfer length of 3 m, and two-phase pressure drops were measured over a length of 3.1 m. Results show that the air–water two-phase frictional pressure drops can be reduced from 26.2% to 42.7%, while the two-phase heat transfer coefficients can be reduced from 39.7% to 80.8% with addition of PAM. Furthermore, new proposed physical mechanisms of the two-phase frictional pressure drop and heat transfer reductions are used to explain the experimental results.

Dispersed Phase Holdup in a Tall and Low Plate Free Area Liquid Pulsed Sieve-Plate Extraction Column

Dispersed phase holdup is studied in a tall and low plate free area pulsed sieve-plate extraction column. The 5.0 cm internal diameter column consists of 80 number of plates with percent free area of 13.5. The effects of pulse velocity (product of amplitude and frequency), superficial phase velocities, and solute addition are studied for five liquid-liquid systems with a wide range of interfacial tensions. The experimental holdup data is tested against the most widely recommended correlations and a new correlation has been developed that best fits the data.