Superficial Velocity Research Articles

Novel correlations for the liquid holdup in a gas-liquid slug flow

This paper introduces novel equations for calculating the slug unit liquid holdup (average liquid holdup) and the slug liquid holdup (slug holdup) in liquid-gas slug flow. The equations were tested across various pipe diameters, incline angles, fluid viscosities and densities, system pressures, and liquid and gas flow rates. The correlation utilizes two dimensionless numbers and displays a self-similar nonlinear symmetrical sigmoidal trend. The two parameters used are the ratio of the no-slip liquid holdup to the in-situ liquid holdup and the ratio of liquid superficial velocity to gas superficial velocity. When the superficial velocities ratio is high, all data converge to a single value of approximatly1 for the no-slip to in-situ liquid holdup ratio. The present unified correlations are simple to implement in any slug flow model. It employs defined parameters, and it has already been tested for varying pipe diameters, inclinations, and fluid viscosities that range from water to 962 cP. The presented correlations are unified and unique and not found in public literature. The suggested correlations exhibit superior performance compared to existing correlations and models.

Experimental investigation of countercurrent flow limitation (CCFL) in a 1/19 scale of VVER-1000 geometry

Countercurrent flow limitation (CCFL) has been experimentally considered in a VVER-1000 hot-leg. The proposed test facility consists of a hot-leg pipe, a reactor vessel simulator (RVs), and a steam generator simulator (SGs). It was designed and constructed based on power-to-volume scaling approach by preserving the Froud number in the hot leg. The scaling ratio was considered 1/19 of the Bushehr NPP (VVER-1000) geometry. The hot leg of the proposed facility provides good optical observation of the gas/liquid interface. The SG simulator has also a side view for optical observation. Experimental results were captured at atmospheric pressure with air/water as fluid. CCFL was obtained by analyzing the pressure differences between RV and SG simulators.This CCFL data was compared with empirical data and correlations available in the literature. With increasing liquid superficial velocity, the gas superficial velocity curve is continuously decreased, which is consistent with Navarro's results. In this study, an experimental correlation is proposed and compared to other correlations. It was very close to the Navarro and Richter correlations.The results of experimental investigations clarified the onset of the CCFL phenomenon in a Bushehr NPP (VVER-1000) hot-leg geometry. Moreover, the achieved patterns and behaviors of the air/water mixture would be used in computational fluid dynamics (CFD) code validations.

Thermodynamic and kinetic analysis on the biomass syngas fueled chemical looping hydrogen generation process in fixed bed reactor

Because of its simple structure and easy operation, the fixed bed reactor is widely used in the chemical looping process to assess the performance of oxygen carriers (OC) or to evaluate new chemical looping technologies. However, the systematic investigation of the redox behavior and temperature evolution during the chemical looping hydrogen generation (CLHG) process in the fixed bed reactor under different conditions, which is crucial for process optimization and reactor design, has received less attention. In the present work, the redox characteristics of the CLHG process with biomass syngas as the fuel in a fixed bed reactor were investigated and analyzed from a perspective of thermodynamics and kinetics. Results showed that high redox temperature (>800 °C) favors the fuel conversion due to the improved reaction kinetics and favorable thermodynamics. A space velocity in the range of 0.12–0.5 s−1 and superficial velocity of 0.008–0.075 m/s can provide enough reaction time meanwhile enhance the external diffusion of fuel gas, achieving high reduction degree of OC and further high H2 yield (3.4 mmol/g Fe2O3) and high H2 energy efficiency (45 %). Moreover, a violent OC bed temperature rise (100 °C) was observed in the air oxidization stage, which can be mitigated by diluting the Fe2O3 content and decreasing the air flow rate. Finally, the reaction front and flow front moving behavior were discussed in detail for a better understanding of the CLHG process.

Performance Rating and Flow Analysis of an Experimental Airborne Drag-Type VAWT Employing Rotating Mesh

This paper presents the results of a performance analysis conducted on an experimental airborne vertical axis wind turbine (VAWT), specifically focusing on the MAGENN Air Rotor System (MARS) project. During its development phase, the company claimed that MARS could generate a power output of 100 kW under wind velocities of 12 m/s. However, no further information or numerical models supporting this claim were found in the literature. Extending our prior conference work, the main objective of our study is to assess the accuracy of the stated rated power output and to develop a comprehensive numerical model to analyze the airflow dynamics around this unique airborne rotor configuration. The innovative design of the solid model, resembling yacht sails, was developed using images in the related web pages and literature, announcing the power coefficient (Cp) as 0.21. In this study, results cover 12 m/s wind and flat terrain wind velocities (3, 5, 6, and 9 m/s) with varying rotational velocities. Through meticulous calculations for the atypical blade design, optimal rotational velocities and an expected Tip Speed Ratio (TSR) of around 1.0 were determined. Introducing the Centroid Speed Ratio (CSR), which is the ratio of the sail blade centroid and the superficial wind velocities for varied wind speeds, the findings indicate an average power generation potential of 90 kW at 1.4 rad/s for 12 m/s and approximately 16 kW at a 300 m altitude for a 6 m/s wind velocity.

Bed structure of CNT agglomerates in gas–solid fluidized beds

In this study, the bed structure according to the flow regime of fine particles in gas–solid fluidized beds was studied by measuring the pressure drop and heat transfer coefficient. Two types of carbon nanotube (CNT) agglomerates with behavior similar to Geldart A and Geldart B and two types of glass bead (GB) particles corresponding to Geldart A and Geldart B classification were used. CNTs fluidized in the form of agglomerates, and in some CNT agglomerates, a homogeneous expansion regime with suppressed generation of bubbles, were observed. In the homogeneous expansion regime of CNT agglomerates, the relationship between superficial velocity and voidage was consistent with the Richardson–Zaki equation, and had a higher n value than that of Geldart A particles and fumed silica agglomerates. In this regime, small-diameter channels coexisted, and due to unstable fluidization at low superficial velocity, intermittent bed collapse occurred. In the homogeneous expansion regime of GB particles, the heat transfer coefficient remained constant, and as bubbles were generated, the heat transfer coefficient increased. On the other hand, as the superficial velocity increased, the heat transfer coefficient of CNT agglomerates continuously increased, regardless of the flow regime transition. In the homogeneous expansion regime of CNT agglomerates, unlike Geldart A particles, movement of agglomerates within the bed was confirmed, and a dynamic bed structure was present, in which the movement increased according to the superficial velocity.

Two-Phase Flow Patterns of Air – Water and Oil in Mini Channel Against Horizontal Position

Two-phase flow is the simplest form of multi-phase flow or multi-component flow. Inside a two-phase flow, two phases or components flow simultaneously. The most important thing to ensure is not to let a flow pattern occur that can increase the flow pressure to increase very extremely so that it will damage the piping system or channel, both on the mini, small channels, and large channels. The flow pattern’s main parameters include superficial velocity, fluid density, and viscosity. Therefore, it is crucial to examine how influential these parameters are in forming flow patterns. This experimental study used an acrylic pipe 160 mm long with a diameter of 1.6 mm in a horizontal position. The liquid solution used is a water-coconut oil emulsion of 350 mg/dl and a water-oil emulsion of 500 mg/dl. The superficial velocity of the gas (JG) = 0.083 m/s - 76.604 m/s and the superficial velocity of the liquid (JL) = 0.041 m/s - 4.145 m/s. The resulting Flow Pattern is Plug, Slug Annular, Annular, and churn. Changes in the mixture of water emulsions and coconut oil have little effect on the flow pattern of a plug, slug annular, and annular and significantly affect the flow pattern of churn. This significant influence occurs because the variation in the mixture of water and oil emulsions greatly affects the difference in viscosity of liquids, namely 130.00 Cp and 161.66 Cp, thus affecting the type of flow pattern. In this study, a bubbly flow pattern was not found. This case was due to the absence of laminar to turbulent transitions because higher oil concentrations resulted in lower Reynolds values.

Air-lift characteristics of rock core mass in gas–liquid–solid mixed flow

The air-lift reverse circulation drilling method enables efficient and continuous core extraction. However, the flow characteristics of gas–liquid–solid mixtures during core mass transport are complex, and developing a model to predict performance remains challenging. The flow characteristics of gas–liquid–solid mixtures inside the drill pipe are numerically analyzed by calculating the mixing transport of the core during the airlift process. By solving the momentum equations for multiphase flow, the distribution of physical quantities of three phases and pressure along the depth was calculated, and the laws of influence of the operating parameters on the transport characteristics of the core were analyzed. The results show that the drilling performance is related to the geometric parameters of the pipe and core, drilling speed, and depth. When the submergence ratio is increased to 0.9, the maximum liquid-phase superficial velocity is increased by 109% compared with that when the submergence ratio is 0.6. The size of the annular space gap 67 formed between the core and the pipe wall is the key to the core's mechanical properties, and the differential pressure gradient force increases with increasing core diameter. An increase in well depth reduces the fluid flow. In addition, increasing the pipe diameter improves drilling performance due to reduced friction losses, which elevates the air flow rate required for air-lift reverse circulation operation.

Effect of perforation density distribution on production of perforated horizontal wellbore

To address the issue of horizontal well production affected by the distribution of perforation density in the wellbore, a numerical model for simulating two-phase flow in a horizontal well is established under two perforation density distribution conditions (i.e. increasing the perforation density at inlet and outlet sections respectively). The simulation results are compared with experimental results to verify the reliability of the numerical simulation method. The behaviors of the total pressure drop, superficial velocity of air-water two-phase flow, void fraction, liquid film thickness, air production and liquid production that occur with various flow patterns are investigated under two perforation density distribution conditions based on the numerical model. The total pressure drop, superficial velocity of the mixture and void fraction increase with the air flow rate when the water flow rate is constant. The liquid film thickness decreases when the air flow rate increases. The liquid and air productions increase when the perforation density increases at the inlet section compared with increasing the perforation density at the outlet section of the perforated horizontal wellbore. It is noted that the air production increases with the air flow rate. Liquid production increases with the bubble flow and begins to decrease at the transition point of the slug–stratified flow, then increases through the stratified wave flow. The normalized liquid flux is higher when the perforation density increases at the inlet section, and increases with the radial air flow rate.

Continuous turbulent liquid-liquid emulsification using open-cell solid foams: Experimental investigation and modelling

The study investigates the efficiency of liquid-liquid emulsification using three types of open-cell solid foams. Initially, the pressure drop profiles revealed the non-negligible impact of the inertial term at a low viscosity of the continuous phase, with profiles becoming more linear at higher viscosities. The Darcy-Forchheimer model effectively predicted pressure drops with a maximum mean relative error of 14%. Emulsification performance (seen as a decrease in the droplet size) was then evaluated by varying dispersed phase viscosity, superficial fluid flow velocity and foam insert packing length, comparing results with structured static mixers (SMX+). The droplet size of the dispersed phase rapidly decreased within the first foam inserts before stabilizing at a length of 175 mm. Under the same superficial velocity, the mean droplet diameter is correlated to the foam's mean pore size. SMX+ mixers exhibited emulsification capability comparable to solid foam with the largest pores, while medium and small pore foams produced smaller droplets. Finally, the Middleman's correlation with viscosity correction accurately predicted mean droplet size at equilibrium and across various scenarios.

Spatio-temporal void fraction visualization in air-water two-phase flow regime transitions by combination of convolutional neural network and long short-term memory implemented into multiple current-voltage (MCV-CNN_LSTM)

Spatio-temporal void fraction in air-water two-phase flow regime transitions has been visualized by combination of convolutional neural network and long short-term memory implemented into multiple -current-voltage (MCV-CNN_LSTM). The MCV-ML is composed of two components, which are MCV-CNN_LSTM training and evaluation. In the first component, four steps are carried out as 1) true void fraction α measurement was conducted by wire-mesh sensor (WMS) as objective variables, 2) simulated MCV voltage U calculation by simulation of MCV measurement for explanatory variable, 3) CNN_LSTM training instance generation, and 4) CNN_LSTM model training and testing. In the second component, two additional steps are experimentally conducted which are 5) actual MCV voltage V measurement by MCV for input of trained ML, and 6) spatio-temporal void fraction α prediction. For the dataset generation, the experiment was conducted on air-water two phase flow regime transitions in vertical pipe with an inner diameter of 25 mm and a length of 350 mm from the elbow. The superficial velocity of liquid and gas phase are varied to present the flow regime transition of bubbly to slug flow. As a result, the estimated spatio-temporal void fraction αˆ by MCV-CNN_LSTM enables the visualization of detailed gas distribution in vertical upward two-phase flow. The spatial averaged instantaneous void fraction measured by WMS and estimated by MCV-CNN_LSTM show qualitative agreement in normalized cross correlation (INCC) of 0.364 on its temporal variation.

Water vapor effects on attrition and elemental migration of iron‐based oxygen carrier in chemical looping combustion

AbstractChemical looping combustion (CLC) offers a novel approach to simultaneous power generation and carbon capture. However, the commercial viability of CLC depends on durable and cost‐effective oxygen carriers (OCs). This study assesses the impact of water vapor (WV) on the attrition of red mud OC, crucial for industrial CLC deployment. Findings indicate a significant reduction in the average attrition rate, from 0.06%/h to 0.03%/h, attributed to the limitation of Fe2O3 reduction, resulting in reduced volumetric and temperature changes in the presence of WV. A developed volume‐based model reveals attrition contributions in the order of chemical > mechanical >> thermal stresses, influencing OC particle surface morphology. Remarkably, the formation of the iron‐oxide layer remains unaffected by WV, reducing agents (CO or H2), or superficial velocities, suggesting scalable iron recovery from attrition with enhanced flexibility in future applications.

Modeling and analysis of particle behavior in fluidized bed bioreactors during non-Newtonian sewage treatment

The stability of biofilms attached to support particles plays a crucial role in fluidized bed bioreactors (FBBRs) when treating non-Newtonian sewage. Biofilm instability is governed by particle-particle (P-P) and particle-wall (P-W) collisions. This paper presents a numerical study of particle behavior in a FBBR using a combined approach of computational fluid dynamics (CFD) and discrete element method (DEM) tailored for non-Newtonian flow systems. Following validation, the CFD-DEM model is utilized to quantify the FBBR performance regarding bed expansion, void fraction distribution, and P-P/W interactions. The impacts of three variables are examined, including sewage superficial velocity and two rheological properties, i.e., sewage temperature and solid concentration. The results reveal that increasing sewage superficial velocity and sewage solid concentration or decreasing sewage temperature, leads to a transition in particle flow from symmetrical to asymmetrical in the radial direction, along with a circulating flow at the lower part of the bed. The relationships between the variables and the bed expansion, uniformity, and P-P/W interactions are also established, identifying optimum conditions to enhance bed uniformity and reduce P-P/W interactions. Overall, the findings demonstrate the value of the CFD-DEM model for understanding, designing, and optimizing FBBRs.

Predictive Model of Restart-Up Pressure Drop after Shutdown for Heavy Oil-Water Ring Transportation Pipeline.

Aiming at the problem of restart-up for a heavy oil-water ring transportation pipeline due to instability and damage of the water ring, based on the self-developed design of a small indoor loop simulation experimental device and taking four kinds of ordinary heavy oil in the Lvda oilfield as the research object, the change trend of restart-up pressure drop with time is experimentally studied when the pipeline is restarted-up after shutdown at a constant water flow. On the basis of the regression analysis of the orthogonal restart-up experimental data of four factors (oil holdup, oil viscosity, standstill period, and water cleaning superficial velocity) and mixed levels by the statistical product and service solutions statistical analysis software, a multivariate nonlinear restart-up maximum pressure drop prediction model is established. Through analysis of the characteristics of each stage of the restart-up process, an exponential decay model of restart-up pressure drop with time is created. The research results show that the variations in restart-up pressure drop with time can be divided into two stages: the attenuation stage and the equilibrium stage. The predicted value of restart-up pressure drop with time is in good agreement with the measured one, and the goodness of fit is very close to 1. The maximum restart-up pressure drop rises along with the increase in oil holdup, oil viscosity, standstill period, and water cleaning superficial velocity. The restart-up time prolongs with the increase in oil holdup, oil viscosity, and standstill period but shortens with the increase in water cleaning superficial velocity.

Influence of a restriction on flow patterns, void fraction, and pressure drop in gas–liquid pipe flow

Subsurface safety valves play an important role in the hydrocarbon production process. The Brazilian industry is suffering significant losses due to the reduction of the useful life of this device, not to mention the risks associated with the operation and the environment. One possible reason for the failure of the subsurface safety valve’s reliability prediction may be the occurrence of two-phase flow in the well. For this reason, a set of twenty horizontal two-phase flow experiments was carefully designed to evaluate the influence of a simplified internal reduction in a steel pipe. Superficial velocities were considered in the range of 0.1 m/s and 2.0 m/s for water and, 0.33 m/s and 7.47 m/s for compressed air. The experiments were carried out in 2″-i.d. and 2-m-long steel pipes, being a tube with restriction and another without restriction. Both tubes have an upstream development length of 126 pipe diameters. Gamma-ray densitometry and a differential pressure transducer were used to measure void fraction and pressure drop, and a visualization window was used to observe the flow patterns. Among the main findings are the effects of void fraction and mixture velocity on pressure gradient, with different impacts on the restricted pipe (RP) compared to the unrestricted pipe (UP). The presence of the restriction generated significant changes in the upstream flow: the lengths of the liquid slugs were increased, appeased by the increase in local pressure necessary to overcome the resistance produced by the restriction. Downstream, the change was reflected in the rise of void fraction and decrease of slip ratio between the phases.

Experimental investigation of two-phase flow development through two-stage orifices

In this study, the effect of flow development length on two-stage flow orifices at an intermittent flow condition was investigated. Experiments were carried out for two-stage orifices with area ratio of 0.25–0.14 and with 1, 3, and 5D spacing between orifices. Also, experiments were carried out on single-stage orifices of the same area ratios under the same inlet flow conditions. The data suggested that restricting the flow in stages, with the smaller area of the restriction in the final stage, reduced the flow separation, enhance the mixing and improve flow development downstream as the spacing increased. Also, the total pressure drop of the two-stage orifice found to decrease as the spacing decreased especially at low gas superficial velocity. Finally, a new approach to correlate the total pressure drop was proposed and successfully implemented in order to determine the pressure drop multiplier of two-stage orifice with varying spacing.

Shaping of MIL-53-Al and MIL-101 MOF for CO2/CH4, CO2/N2 and CH4/N2 separation

Metal-organic frameworks (MOF) are promising materials for gas storage and separation. The formulation and shaping of MOFs in mechanically stable bead forms is an essential requirement for their practical application as an adsorbent for gas and liquid mixture separations. In this work, MIL-53-Al and MIL-101 MOF beads are synthesized using sodium alginate as a binder, and calcium chloride as a gelling agent. The synthesized MIL-53-Al and MIL-101 MOF beads are characterized by powder X-ray diffraction (PXRD), BET surface area, porosity analysis from N2 uptake data at 77 K, FTIR, TGA, and scanning electron microscopy (SEM). The isothermal equilibrium adsorption uptake of CH4 and N2 gases is measured up to 10 bar pressure while the CO2 equilibrium uptake is measured up to 1 bar at 298 and 313 K respectively. The isotherm data of all adsorbates are fitted in Dual Site Langmuir (DSL) isotherm equations. The adsorption selectivity for CH4/N2, CO2/CH4, and CO2/N2 binary systems are predicted using the Ideal Adsorbed Solution Theory (IAST) method. The dynamic column breakthrough experiments are carried out on MIL-53-Al beads for CH4/N2 (30:70 and 50:50 v/v), CO2/CH4 (45:55 v/v) and CO2/N2 (15: 85 v/v) feed mixtures. The IAST selectivity and breakthrough time obtained under the same superficial velocity, pressure, and temperature conditions follow the order CO2/N2 > CO2 /CH4 > CH4/N2. The MIL-53-Al beads show higher CH4/N2, CO2/CH4, and CO2/N2 selectivity for the targeted mixtures than MIL-101 beads.

Experimental Study on Gas-Liquid Two-Phase Stratified Flow at High Pressure in a Horizontal Pipe

This study investigates wave-stratified flow in a horizontal pipe at high pressure, and flow characteristics are obtained, such as flow pattern map, liquid film thickness, and pressure drop. Compared with a flow pattern map of a gas-liquid two-phase flow carried out at atmosphere, stratified flow zone is depressed with increasing system pressure and the critical gas superficial velocity decreases for smooth-wave-stratified flow transition, while the critical liquid superficial velocity increases for stratified-intermittent transition. On one hand, the compressed air results in an increase in momentum transfer between gas and liquid phases, which accounts for the smaller gas superficial velocity that is encountered in both smooth-wave and stratified-annular flow transition at higher pressure. One the other hand, it slows down the liquid below the crest, and it makes the interface wave crest unstable and split for the vortex shedding behind the wave crest, which accounts for flow regime transition in gas-liquid two-phase flows in pipelines. As a result, stratified-intermittent flow transition is depressed and delayed. The pressure influence on the liquid film profile is analyzed, and relationships between film thickness and dimensionless numbers are studied, such as liquid Weber number and gas Weber number. Friction factors on different interfaces at high pressure are studied, and new empirical formulas are deduced.

Two-phase Upward Flow-Induced Vibrations in U-bend under Different Orientations

U-bends are frequently employed in industries to change the direction of fluid flow. Flow Induced Vibrations (FIV) are very prominent due to internal two-phase flow and vary with U-bend orientation. Potential possibilities of spatial orientations of a U-bend make it impractical to predict these vibrations using an experimental approach. This study investigates the two-phase flow-induced vibrations for 0°, 30°, 60° and 90° upward flow in a U-bend using CFD. In-plane and out-of-plane directional vibrational data was gathered for these four orientations of U-bend. For constant superficial velocities with void fraction of 0.5, impact of orientation on slug frequencies was observed with Fast Fourier Transformation. In-plane (x-axis) forces applied at the outlet bend significantly increase 39% compared to the corresponding forces at the inlet bend. Forces at the outlet bend along the y-axis (out-of-plane) were reduced by 26%, but the forces along the z-axis show a more moderate decrease of 7%. This study provides significant data essential to forming a correlation of two-phase flow-induced vibrations with multiple upward flow U-bend orientations.

Experimental study on leakage characteristics of gas-liquid two-phase flow in a horizontal pipe

Oil and gas pipeline leakage accidents caused by aging and third-party damage have increased, resulting in polluting the ecological environment and jeopardizing life and property safety. A detailed and systematic investigation on the leak characteristics of oil and gas two-phase pipelines is significantly urgent. The leak experiments were performed on a horizontal tube with a diameter of 32 mm. There was a 3 mm round leakage hole at the bottom of the tube. The distance of the leakage hole from the pipe inlet was 4.8 m. Three inlet flow patterns, including stratified flow, slug flow, and annular flow via adjusting the gas superficial velocity (1.73 m/s ≤ USG ≤ 24.19 m/s) and liquid superficial velocity (0.017 m/s ≤ USL ≤ 0.415 m/s), were obtained. The conclusions point out that the type of leakage, whether it is mainly liquid or both gas and liquid, depends on the USG. The degree of phase separation in stratified flow is the greatest among the three inlet flow patterns, with a maximal phase separation efficiency (η) of 0.403. Slug flow has the least phase separation degree. Interestingly, the η is directly proportional to the inlet mass fraction only for slug flow. The harmonic frequency that appeared in the power spectral density curves for the pressure difference of leakage hole in slug flow, indicates that leakage is not a standard periodic event. The liquid velocity loss is primarily related to the gas leakage mechanism. These findings can provide new insights into two-phase pipeline leak detection and accident consequence prediction.

Area averaging of packed bed in continua conservation equations in axial flow

AbstractA novel averaging of the conservation equations for axial flow in packed beds is presented to express the momentum, continuity, and energy equations in terms of the cross‐sectional averages of concentration, temperature, and superficial velocity. The model integrates the radial fluctuations of the intrinsic variables into the partial differential equations of the model and presents a method for the design and analysis of catalytic reactors at a broad range of Reynolds numbers without the necessity of adjusting the operating conditions to minimize the impact of the radial profiles of velocity, concentration, and temperature. Since the control of the industrial reactors is dependent on the average values of the concentration and temperature, the model can be directly employed for design, optimization, and control processes with the added advantage of time and cost savings for both the numerical resolution and laboratory testing expenses. The model is limited to reaction systems with Péclet numbers of less than 700 with an average void fraction of for which the ratio of the bed length‐to‐particle diameter to particle Péclet number exceeds . The model was applied to the simulation of steam methane reforming (SMR). The results indicate that the average equations predict the responses of the SMR properly and thus the model could be reliably utilized for process design, operation, and control.