Phase Distribution Measurements during Transient Bubbly Two‐Phase Flow in a Vertical Pipe

An experimental procedure for investigating transient bubble flow for an adiabatic air/water system with vertical upward flow in a pipe is presented. The results of the measured local transient two‐phase flow parameters are shown along a pipe length of approx. four meters. From the measured radial phase distributions under steady and under transient conditions one can draw conclusions about the interfacial forces. Here, the effects indicate the action of forces such as a transverse lift force and a time dependent force like the virtual mass force during the transient. For modelling the transverse lift force which seems to play a dominant role for that flow regime the formulation of Zun was chosen and it was implemented into the commercial CFD‐Code Fluent Release 4.4.4 via user‐defined subroutines. Finally, results from the simulation of the steady states of start and end conditions of an experimental measured transient are shown.     

Distribution of Two‐Phase Flow across 2.7‐mm Vertically Split U‐Type Junctions

A visual observation of the two‐phase flow across vertically split U‐type junctions and its flow redistribution inside two 2.7‐mm diameter smooth tubes with curvature ratios (2R/D) of 3 and 7, respectively, are reported. The range of mass flux is between 100 and 700 kg/m²s and quality (x) ranges from 0.001 to 0.5. The ratio of liquid distribution between the upper and lower outlet legs is related to the inlet flow pattern, but its influence is reduced at higher mass flux. The difference in liquid flow rates in the lower and upper legs is significantly affected by gravity at a small inlet mass flux, but this difference becomes less profound when the inlet mass flux is increased. The difference between the liquid flux in the upper and lower leg is reduced for the smaller curvature radius due to the reduced effect of gravity between the upper and lower legs. However, there is no consistent trend of gas flow distribution across the U‐type junction as compared to liquid flow distribution. The air mass flux in the upper and lower legs always increase with an increase in both gas quality and the total mass flux.     

Accuracy of Safety Valve Two‐Phase Mass Flow Capacity Sizing

The method specified in ISO/CD 4126–10 exhibits the highest accuracy compared to other models used in industry and academia. At the same time it allows for an oversizing of the necessary relief area under all test conditions. The average or statistical reproductive accuracy is characterized by an unacceptable logarithmic scatter of about 80 %.     

Pressure Drop in Liquid‐liquid Two Phase Horizontal Flow: Experiment and Prediction

The present study is aimed at an investigation of the pressure drop characteristics during the simultaneous flow of a kerosene‐water mixture through a horizontal pipe of 0.025 m diameter. Measurements of pressure gradient were made for different combinations of phase superficial velocities ranging from 0.03–2 m/s such that the regimes encountered were smooth stratified, wavy stratified, three layer flow, plug flow and oil dispersed in water, and water flow patterns. A model was developed, which considered the energy minimization and pressure equalization of both phases.     

Two‐Phase Sequential Simulation of a Fluidized Bed Reformer

A two‐phase flow model is adapted in order to predict the performance of a fluidized bed reformer using the sequential modular simulator. Since there are physical and chemical phenomena interacting in the reformer, two sub‐models appear to be necessary to describe the overall model. These are the hydrodynamic and reaction sub‐models. The hydrodynamic sub‐model is based on the dynamic two‐phase model and the reaction sub‐model is derived from the literature. In the overall model, the bed is divided into several sections. At each section, the flow of the gas is considered as plug flow through the bubble phase and to be perfectly mixed through the emulsion phase. Two sets of experimental data from the literature at different hydrodynamic regimes were used in order to validate the proposed model. A close agreement was observed between the model predictions and the experimental data. The model proposed in this work may be used as a framework for the development of sophisticated models for non‐ideal reactors inside process simulators.     

Homogeneous Tubular‐Flow Process for Monoolein Preparation

Esterification of fatty acids with glycerol is characterized by negligible solubility of the two liquid phases. The reactions to mono‐, di‐ and triglycerides taking place in the fatty acid phase, are limited by chemical equilibrium. The scope of this study is to investigate in a tubular reactor the conversion of a homogeneous mixture of oleic acid and glycerol in tert‐butanol. The liquid composition in this study was 1 mol of oleic acid, 6 mol of glycerol and 14 mol of tert‐butanol. Experiments were conducted in a tubular reactor at 35 atm over a temperature range of 200–240 °C and residence times of 0.7–17.6 h to determine the kinetics and the chemical equilibrium. The selectivity to monoolein was >95 mol %. A reversible second order reaction fits the data well.     

A Two‐Phase Non‐Isothermal PEFC Model: Theory and Validation

A two‐dimensional, non‐isothermal, two‐phase model of a polymer electrolyte fuel cell (PEFC) is presented. The model is developed for conditions where variations in the streamwise direction are negligible. In addition, experiments were conducted with a segmented cell comprised of net flow fields. The, experimentally obtained, current distributions were used to validate the PEFC model developed. The PEFC model includes species transport and the phase change of water, coupled with conservation of momentum and mass, in the porous backing of the cathode, and conservation of charge and heat throughout the fuel cell. The current density in the active layer at the cathode is modelled with an agglomerate model, and the contact resistance for heat transfer over the material boundaries is taken into account. Good agreement was obtained between the modelled and experimental polarization curves. A temperature difference of 6 °C between the bipolar plate and active layer on the cathode, and a liquid saturation of 6% at the active layer in the cathode were observed at 1 A cm^–2.     

Generation of Two‐Phase Air‐Water Flow with Fine Microbubbles

Aiming at the development of a low‐cost technology for multipurpose water and surface treatment in the chemical industry and beyond, using microbubbles, a novel scheme of liquid‐gas interaction within a specially designed bubble generator was tested. Its efficiency for the production of microbubbles with a size distribution in the micron range is confirmed. The basic element of the device is a vortex chamber with water supply through tangential ducts, while the gas (air) is introduced in a highly turbulent swirling flow of water in radial direction through the orifice in the gas supply duct, located on the chamber axis. Bubble diameters, bubble velocities in the pipe flow and effect of the output pressure on the bubble size distribution were studied.     

Experimental Investigation on the Holdup Distribution of Oil‐Water Two‐Phase Flow in Horizontal Parallel Tubes

An experimental investigation was conducted to study the holdup distribution of oil and water two‐phase flow in two parallel tubes with unequal tube diameter. Tests were performed using white oil (of viscosity 52 mPa s and density 860 kg/m³) and tap water as liquid phases at room temperature and atmospheric outlet pressure. Measurements were taken of water flow rates from 0.5 to 12.5 m³/h and input oil volume fractions from 3 to 94 %. Results showed that there were different flow pattern maps between the run and bypass tubes when oil‐water two‐phase flow is found in the parallel tubes. At low input fluid flow rates, a large deviation could be found on the average oil holdup between the bypass and the run tubes. However, with increased input oil fraction at constant water flow rate, the holdup at the bypass tube became close to that at the run tube. Furthermore, experimental data showed that there was no significant variation in flow pattern and holdup between the run and main tubes. In order to calculate the holdup in the form of segregated flow, the drift flux model has been used here.     

Numerical Simulation of the Two‐Phase Fluid Field in a Gas‐Around‐Liquid Spray Nozzle

A new gas‐around‐liquid spray nozzle (GLSN) was designed, and the two‐phase flow fluid field in this nozzle was simulated numerically. Flow characteristics under different structural parameters were obtained by changing the L/D ratio of the premixing chamber, incident angle, and inlet pressures. Increasing the L/D ratio and incident angle improved flow characteristics such as atomization flow, outlet velocity, and turbulence intensity. The nozzle performed optimally at an L/D ratio of 0.5 and incident angle of 60°. The atomization flow decreased with higher gas pressure and increased with higher liquid pressure. The outlet velocity mainly depended on the inlet gas pressure, not on the inlet liquid pressure. These results provide an indication for optimum structures and parameters of the GLSN.     

Interior Ballistics Two‐Phase Reactive Flow Model Applied to Small Caliber Projectile‐Gun System

Multi‐dimensional multi‐component two‐phase flow modeling of solid propellant combustion in weapons is the new trend of the interior ballistics codes. Most of these codes are designated to large caliber guns and rockets simulation. Only a small number of investigations on small‐caliber gun have been recently reported, where the need of high‐performance and reliable small‐caliber guns stimulated significant interest in developing techniques to understand the phenomenology of small‐caliber ballistics and predict the behavior and the performance of this type of weapons. In this paper, a numerical model describing the combustion of solid propellant in small‐caliber gun is presented. The governing equations with customize parameters were derived in the form of coupled, non‐linear axisymmetric partial differential equations. They were further implemented into the CFD code Fluent. A numerical test showed that Fluent is able to handle correctly the interaction between the moving projectile and the combustion gases in the chamber. The interior ballistics curves along with the performance of small‐caliber gun 5.56 mm were adequately predicted. The numerical results were in agreement with the experimental results.     

Droplet Size in Two‐Phase Liquid Dispersed Pipeline Flows

Few experimental data exists on drop size distribution during dispersed liquid‐liquid pipeline flows. In the majority of cases dilute dispersions have been used and the results have mainly been compared with models for drop breakup. A review of this work shows that the Rosin‐Rammler distribution represents satisfactorily the existing experimental data. However, the commonly used Hinze model (Hinze, 1955) often underpredicts the experimentally found maximum drop sizes. Later models, many of which are developments of the Hinze one, are also unable to predict the resulting maximum drop size for a wide range of experimental conditions. A more comprehensive database is needed for the further development and refinement of theoretical models.     

Simulation and Experimental Validation of Two‐Phase Flow in an Aerosol Counter‐Flow Reactor using Computational Fluid Dynamics

A simulation of the hydrodynamic behavior of an aerosol‐counter flow reactor was conducted using an Euler‐Lagrange method. The simulation results were then verified with experiments. The process simulated was a separation process required during the production of biodiesel (fatty acid methyl ester). In this process, the liquid ester/glycerol phases are continuously injected through a hollow cone nozzle with an overpressure of 10⁶ Pa into the reactor, operated at 15000 Pa. The liquid is atomized because of the pressure drop and a liquid particle spray is generated with an inlet velocity of 44.72 m/s. Water vapor of temperature 333 K is injected tangentially through two side, gas inlets with an inlet velocity of 1.2 m/s. Excess methanol is subjected to a mass transfer from the liquid phase into the gas phase, which is withdrawn through the head of the reactor and condensed in an external condenser unit. The stripping of the methanol off the liquid leads to a sharp interface between the glycerol and the ester phase, which can then be easily separated by gravity or pumping. The gas velocity field, pressure field and the liquid particle trajectories were calculated successfully. Simulated dwell time distribution curves were derived and analyzed with the open‐open vessel dispersion model. Experimental dwell time distribution curves were measured, analyzed with the open‐open vessel dispersion model, and compared with the simulated curves. A good consistency between simulated and measured Bodenstein numbers was achieved, but 25 % of the simulated particles exited at the reactor's head, contrary to experimental observations. The difference between simulated and measured dwell times was within one order of magnitude.     

Dry Cleaning of Fine Coal Based on Gas‐Solid Two‐Phase Flow: A Review

Dry cleaning of coal becomes increasingly significant to improve energy efficiency and reduce air pollutant emissions. Fine coal dry cleaning processes are mostly based on gas‐solid two‐phase flow and mainly classified into the following three categories. Modified air‐dense medium‐fluidized bed cleaning has high cleaning accuracy, but confronts the problems of product purification and medium recovery. Density‐segregation gas‐fluidized bed cleaning does not use artificial medium solids and is characterized by a simple process and stable performance. However, its cleaning accuracy is relatively low. Air table cleaning also uses no artificial medium and separates fine coal depending on the differences in density and coefficient of friction. Its cleaning accuracy is approximate to that of density‐segregation gas‐fluidized bed cleaning but has more influential factors.     

Computational Fluid Dynamics Modeling of Gas‐Liquid Two‐Phase Flow around a Spherical Particle

Microscale studies, which can provide basic information for meso‐ and macroscale studies, are essential for the realization of flow characteristics of a packed bed. In the present study, the effects of gas velocity, liquid velocity, liquid‐solid contact angle, and liquid viscosity on the flow behavior were parametrically investigated for gas‐liquid two‐phase flow around a spherical particle, using computational fluid dynamics (CFD) methodology in combination with the volume‐of‐fluid (VOF) model. The VOF model was first validated and proved to be in good agreement with the experimental data. The simulation results show that the film thickness decreases with increasing gas velocity. This trend is more obvious with increasing operating pressure. With increasing liquid velocity, the film thickness tends to be uniform on the particle surface. The flow regime can change from film flow to transition flow to bubble flow with increasing contact angle. In addition, only at relatively high values does the liquid viscosity affect the residence time of the liquid on the particle surface.     

Modeling of Two‐Phase Flashing Flow of Multicomponent Mixtures in Large Diameter Pipes

A two‐phase flashing flow model is developed to predict the distributions of pressure, temperature, velocity and evaporation rate in a transfer line, which is a typical example of a two‐phase flow pipe in the petrochemical industry. The model is proposed based on the pressure drop model and the multi‐stage flash model. The results indicate that pressure drop, temperature drop, and change of evaporation rate mainly occur in the transition section and the junction site of the transfer line. The predictions of the model have been tested with reliable field data and the good agreement obtained may lead to a better understanding of the two‐phase flashing flow phenomenon, as well as demonstrating the feasibility of applying the model into the design and optimization of pipelines.     

Two‐Phase Flow with Mass Transfer in Bubble Columns

Bubble columns are widely used in the chemical and biochemical industries. In these reactors a gaseous phase is dispersed into a continuous liquid phase thus the rising bubble swarm induces a circulating flow field. For the dimension of these reactors the local interfacial area and the residence time of the liquid and the gaseous phase are key parameters. In this paper an Euler‐Euler approach is used to calculate the flow field in bubble columns numerically. Therefore a transport equation for the mean bubble volume based on a population balance equation approach is coupled with the balance equations for mass and momentum. The calculations are performed for three‐dimensional, instationary flow fields in cylindrical bubble columns considering the homogeneous and the heterogeneous flow regime. For the interphase mass transfer the physical absorption of the gaseous phase into the liquid is assumed. The back mixing in the gaseous and liquid phase is calculated from the local and time dependent concentration of a tracer.