Transient Multiphase Flow Research Articles

Entropy production during the drying process of milk droplets in an industrial spray dryer

Development of high energy efficiency spray dryers is of great importance for the future of the dairy powder industry. The present research studied energy efficiency in an industrial scale spray dryer with the second law of thermodynamics. The entropy production rate is computed from the CFD modeling results of the transient multi-phase flow in the spray dryer. Influences of particle size, inlet air flowrate and inlet air temperature on the entropy production rate are analyzed. The results show that large particles produce more entropy per unit mass on dry basis. To decrease the moisture content of product powders, it will produce more entropy by increasing inlet mass flowrate than by increasing the air temperature. The study shows that the second law of thermodynamics is a potential tool for optimizing dryer operation and design.

A Fundamental Model of Particle Deposition Incorporated in CFD Simulations of an Industrial Milk Spray Dryer

Particle deposition is an important, undesirable problem during the operation of spray dryers. A new mathematical model of particle deposition has been developed and implemented in the computational fluid dynamics (CFD) software FLUENT. The pseudo Ohnesorge number Oh* and Weber number We* have been used to formulate the model to the determine possibility of particle deposition. The reentrainment of the particles back into the dryer chamber was determined according to the wall shear stress. The transient multiphase flow process in an industrial spray dryer that produces around 9 tonnes of milk powder per hour was simulated to validate the deposition model. The numerical results show that reentrainment of particles into the dryer chamber is significant at the chamber walls. The deposition intensity has been found to be higher near the adjunctions of the ceiling wall, the vertical wall, and the conical wall because of smaller wall shear stress. The distribution of wall temperature, Oh* and We*, which has important influence on wall deposition, has been obtained from the numerical results. More experimental and computational work is required for future validations.

Predicting hydrate plug formation in oil-dominated flowlines

This work describes the development and application of a transient multiphase flow simulator which incorporates hydrate formation kinetics and thermodynamics to predict plugging in multiphase oil production lines. The model (CSMHyK v. 2.0) is shown to predict the formation of hydrate plugs in two industrial scale flowloops, by combining well known engineering correlations with state-of-the-art measurements. The experimental measurements described here allowed two fitted parameters to be eliminated. Applications of the model are demonstrated by forecasting hydrate formation rates in industrial flowlines. Further developments have allowed hydrate formation in systems with varying concentrations of salt or monoethylene glycol to be simulated by adjusting the hydrate equilibrium P– T curve as the concentration of inhibitor changes.

Numerical Investigation of the Transient Multiphase Flow in an Ironmaking Blast Furnace

Discrete particle simulation (DPS) has been applied to multiphase flow modelling in an ironmaking blast furnace (BF), including burden distribution at the top, gas–solid flow in the BF shaft and raceway, and liquid–solid flow in the hearth. In this work, the approach is further extended to take into account the transient features of gas and particle flow coupled with liquid tapping operation. In the simulation, two types of particles of coke and ore with different physical properties are considered, together with different shapes of the cohesive zone and the shrinkage of size of ore particles in the cohesive zone to present ore reduction. The simulated results show that the flow of both solid and gas phases varies spatially and temporally, particularly in the cohesive zone. Gas flow is strongly affected by the layered structure of ore and coke particles in the cohesive zone. A coke-free zone can form in the hearth, and the boundary profile between the coke-free zone and the coke bed depends on the amount of liquid accumulated in the hearth, gas and solid flow rates in the raceway, and coke consumption in different regions at the interface of liquid and the coke bed. The results show that the complicated transient multiphase-flow in a BF can be captured by the present approach which may be extended to account for heat transfer and chemical reaction in the future.

A Three-Dimensional Numerical Study of the Gas/Particle Interactions in an Industrial-Scale Spray Dryer for Milk Powder Production

Gas/particle interaction plays an important role in modern spray dryers and may have influences on wall deposition, agglomeration, powder degradation, etc. In the present study, the three-dimensional (3-D) transient multiphase flow in an industrial-scale spray dryer has been investigated using the CFD package FLUENT. The Eulerian–Lagrangian approach and two-way coupling method were used in the simulations. The reaction engineering approach (REA model) for milk particles has been implemented. Some new characteristics of the gas flow pattern and the particle behavior (e.g., temperature–time profiles) were identified from the numerical results; for example, the milk particles flow in such a way that makes the central jet oscillation more nonlinear. The discrete phase enhances the turbulence near the air/droplet inlet but damps it downstream. The transient turbulent flow causes significant uncertainties in the particle tracking, which presented some challenges in simulations. The study has highlighted the importance in performing 3-D transient simulations in order to understand the industrial-scale dryers.

Interaction between Supersonic Disintegrating Liquid Jets and Their Shock Waves

We used ultrafast x radiography and developed a novel multiphase numerical simulation to reveal the origin and the unique dynamics of the liquid-jet-generated shock waves and their interactions with the jets. Liquid-jet-generated shock waves are transiently correlated to the structural evolution of the disintegrating jets. The multiphase simulation revealed that the aerodynamic interaction between the liquid jet and the shock waves results in an intriguing ambient gas distribution in the vicinity of the shock front, as validated by the ultrafast x-radiography measurements. The excellent agreement between the data and the simulation suggests the combined experimental and computational approach should find broader applications in predicting and understanding dynamics of highly transient multiphase flows.

Evaluation of numerical modelling for a compact down-hole subsea gas-liquid separator for high gas content

This paper describes the computational fluid dynamics (CFD) modelling of a laboratory scale gas-liquid separator designed for high gas content. The separator consists of two concentric pipes with swirl tube in the annular space between the pipes. The gas-liquid mixture comes tangentially from the side inlet and the system works with a combination of gravity and centrifugal forces to achieve a high-efficient gas-liquid separation. Three dimensional transient multi-phase fluid flows were solved to predict the velocity and volume fraction of each phase. The standard k- turbulence model was used for turbulence closure. The performance of the gas-liquid separator was visually established for a range of gas flow rates (271–495 L/min), with volume fraction (VF) =0.874–0.985 by observing the liquid carry over (LCO) regime where liquid was carried out in the gas stream. The liquid and gas flow rates at which the LCO was observed defines the upper operational range of the separator. Air-water mixture was used in the numerical simulations to keep consistent with the experiments. The pressure between the inlet and exit was validated against the experiments for different air-water flow rate combinations. The values were matched reasonably well for high air flow rate (495 L/min, VF=0.985) but were under-predicted for low air flow rate (271 L/min, VF=0.874). The air and water were mixed upstream of the inlet in the experiments and the pressure was measured at the start of the inlet. In case of numerical simulation the air and water were mixed at the inlet. This might cause the deviation of pressure when the air flow rate was low.

Using Transient Inflow Performance Relationships to Model the Dynamic Interaction Between Reservoir and Wellbore During Pressure Testing

The fundamental understanding of the dynamic interactions between multiphase flow in the reservoir and that in the wellbore remains surprisingly weak. The classical way of dealing with these interactions is via inflow performance relationships (IPRs), where the inflow from the reservoir is related to the pressure at the bottom of the well, which is a function of the multiphase flow behavior in the well. A steady-state IPRs are normally adopted, but their use may be erroneous when transient multiphase flow conditions occur. The transient multiphase flow in the wellbore causes problems in well test interpretation when the well is shut-in at the surface and the bottomhole pressure is measured. The pressure buildup (PBU) data recorded during a test can be dominated by transient wellbore effects (e.g., phase change, flow reversal, and re-entry of the denser phase into the producing zone), making it difficult to distinguish between true reservoir features and transient wellbore artifacts. This paper introduces a method to derive the transient IPRs at bottomhole conditions in order to link the wellbore to the reservoir during PBU. A commercial numerical simulator was used to build a simplified reservoir model (single well, radial coordinates, homogeneous rock properties) using published data from a gas condensate field in the North Sea. In order to exclude wellbore effects from the investigation of the transient inflow from the reservoir, the simulation of the wellbore was omitted from the model. Rather than the traditional flow rate at surface conditions, bottomhole pressure was imposed to constrain the simulation. This procedure allowed the flow rate at the sand face to be different from zero during the early times of the PBU, even if the surface flow rate is equal to zero. As a result, a transient IPR at bottomhole conditions was obtained for the given field case and for a specific set of time intervals, time steps, and bottomhole pressure. In order to validate the above simulation approach, a preliminary evaluation of the required experimental setup was carried out. The setup would allow the investigation of the dynamic interaction between the reservoir, the near-wellbore region, and the well, represented by a pressured vessel, a cylindrical porous medium, and a vertical pipe, respectively.

Experimental and Numerical Investigation of Separator Pressure Fluctuation Effect on Terrain Slugging in a Hilly Terrain Two-Phase Flow Pipeline

Two-phase slug flow in horizontal and near horizontal pipes is a common occurrence in many engineering applications and industrial operations. The objective of this study is to experimentally investigate the effects of separator pressure fluctuations on terrain slugging and slug flow characteristics along and downstream of a hilly terrain pipeline. A further objective is to numerically simulate the flow behavior using a transient multiphase flow simulator to match the simulation predictions with the experimental data. Experimental results revealed that during the separator pressure decline, slug initiation is promoted due to the increase in slip velocity, which enhances the slug initiation mechanisms at the lower elbow. On the other hand, during the separator pressure increase, the analyses show slug suppression. In terms of slug flow characteristics, the mean slug velocity, mean slug length, and maximum slug length increased during the separator pressure decline condition and decreased during the separator pressure increase condition. Furthermore, separator pressure has a significant decreasing effect on slug frequency, maximum slug length, and slug length variance downstream of the hilly terrain section. The statistical analysis shows mixed results of decreasing and increasing trends on mean slug lengths under the fluctuated separator pressure when compared with constant separator pressure conditions. The numerical simulation results showed a close match of liquid holdup downstream of the lower elbow and a fair match at the lower elbow. Furthermore, the model was successful in matching the pressure fluctuation at the lower elbow of the experimental data.

Enhanced Local Void and Temperature Measurements for Highly Transient Multiphase Flows

We introduce a novel combined-temperature-and-conductivity needle probe measuring system for local void fraction measurements in multiphase-flow experiments. The system is able to deal with direct sheathed microthermocouples as well as open thermocouples. It consists of a thermoneedle probe connected to a special electronic circuit using an ac measuring technique for the conductivity measurements and a high-gain instrumentation amplifier with very high common-mode rejection for the amplification of the Seebeck voltage generated by the microthermocouple. After system buildup and calibration, the system has been tested in different experiments. In a dropping experiment, the time constant of the temperature measurement of the needle probe system was determined as 3.6 ms. Additionally, steam-water and gas-steam-water flow experiments have been carried out to demonstrate the system performance.

The Virtual Well Engineer – A Real – Time Surveillance Tool for Managed Pressure Drilling Operations

Well engineers face ever increasing technical challenge of drilling in complex environments and the use of Managed Pressure Drilling(MPD) techniques to control annular pressure for improved drilling performance in the oil industry has growing interest[1-4]. Understanding hole cleaning and controlling annular pressure in this complex environment is becoming increasingly important for a range of applications. The Virtual Well Engineer[VWE] has been identified as the engineering tool to address these issues in order to deliver a successful MPD operation. The VWE is the product name for a suite of well planning , monitoring and simulation packages with focus on Managed Pressure Drilling includng underbalanced drilling that allows the well engineering team to interact with virtual reality. Recent works initiated by the Well Engineering Group at The Robert Gordon University have extended the knowledge of multiphase flow in a drilling annulus through the tracking of the transient multiphase flow pattern prevailing and effects on hole cleaning , the pressure profiles and identification of hot spots in concentric and eccentric annular sections . The mechanistic models developed at RGU form the core algorithms for the VWE. This paper presents the architecture and functional capabilities of the VWE – HydraulicsDTS™ , which is used in simulating well operations.

Externally guided underfill encapsulation and subsequent filler particle migration during electronics packaging

We present a numerical study of the transient multiphase flow of a liquid encapsulant in a microgap formed between parallel plates with special reference to electronics packaging. The surface tension and polarization forces are assumed to drive the fluid flow. The governing equations are solved using the volume of fluid model within the framework of the finite volume method in order to predict the free surface front of the encapsulant together with the time and spatial evolution of filler particle concentration during the underfill process. The numerical results are found to be in good agreement with available reported experimental data. The influence of the polarization force is found to reduce the encapsulant fill time, increase the flow length and distribute the filler particles to a larger flow length. The new process has practical implications, such as overcoming the partial curing of underfill epoxy before the flow is complete.

Multiphase Production Control: Application to Slug Flow

TACITE, developed at IFP, is a compositional software able to simulate the behaviour of transient multiphase flow in production pipelines and wells with process equipment such as controllers, valves, separators, lateral injectors, productivity index or bundles. This paper presents first the set of partial differential equations that are solved in this software. Then, the different models (thermodynamic, hydrodynamic, thermal and numerical) are briefly described. Through a field case example, we illustrate that the use of a transient simulator, such TACITE, is essential in the engineering design phase. For instance, it can be used to test control schemes for multiphase production installation. We also illustrate the importance of the compositional approach that has been developed in this code. This example deals with the Dunbar pipeline in which undesirable transient phenomena called severe sluggingcan occur. The simulation results of different production schemes that can prevent severe slugging occuring are presented and their efficiency is analysed.

Neural Networks Tools for Improving Tacite Hydrodynamic Simulation of Multiphase Flow Behavior in Pipelines

Transient multiphase flow simulators are generally used to dimension the production scheme. One of the problems encountered is to predict accurately the pressure drop and the liquid holdup. This can be solved using an accurate numerical scheme and an appropriate thermodynamic behavior linked to an accurate and robust hydrodynamic model. In the Tacite Code, developed by IFP, a mechanistic hydrodynamic model has been developed. This model is able to predict the flow regime, the phase velocities and the local pressure drop for all slopes and all diameters. It contains closure laws based on flow regimes. This mechanistic model has been validated against various data banks. The two limitations of such an hydrodynamic model may be its mathematical disturbance (continuity, derivability are not always guaranteed) and the time consuming. This can be troublesome when using an accurate numerical scheme that requires derivative computation and for real time purposes. This paper presents a neural network based approach to efficiently replace the hydrodynamic module in the two phase model with the following two objectives: - to avoid discontinuity problems during hydrodynamic computations;- to reduce significantly computational time. This method was tested with experimental and simulated data. The results given in this paper prove the relevancy of this approach.

BRICK - A One-Dimensional Simulation Tool for Multiphase Flow in Vessels

A new one-dimensional model suitable for practically orientated simulations of transient multiphase flows within vessels is presented. It is based on a specially developed particle-in-cell method. The equations of transport are solved without numerical simulation. Flexible interfaces allow an easy implementation of additional correlations and models for special phenomena. There is also an interface which enables foam models to be implemented.

Fluids Transport Optimization Using Seabed Separation

Terrain slugging is extremely likely to occur sometime during the life of a deep subsea pipeline/riser system. But, can the terrain slugs be mitigated? In this study, we performed transient multiphase flow simulations to explore the feasibility of sea floor separation to mitigate terrain slugging and to optimize fluid transport from wellhead to downstream processing. We considered the effects of separator location and separation efficiency on production system behavior. We found that there is an optimal amount of gas underflow into the liquid line and there is an optimum location for subsea separator. Our study also covered how the operational transient processes, such as startup and shutdown, would affect the performance of the pipeline/separator system. It is necessary to have a good understanding of the performance of subsea separation system before a reliable one can be designed. The results of this study are aimed toward improving the design of sea floor processing for ultra-deepwater production. [S0195-0738(00)00403-9]

Combustion of unconfined hydrocarbon vapor-droplet clouds

Formation, evolution, and combustion of vapor-droplet clouds resulting from releases of hydrocarbon fuels into the open atmosphere have been studied. The fuels considered range from highly volatile pressure-liquefied gases undergoing flash evaporation upon discharge into the atmosphere (propane), to those which are liquids at normal storage conditions but may flash if heated above the boiling point prior to the release (pentane, octane). Transient multiphase flows of reacting air-vapor-droplet mixtures were calculated numerically with allowance for turbulent combustion, soot formation and oxidation, and radiative heat transfer, as well as mass, momentum, and energy exchange between the gaseous and dispersed phases. Vertical two-phase outflows of vapor-droplet mixtures were studied with ignition occurring at some elevation above the fuel source. Burning two-phase clouds rapidly assume nearly spherical shape. The internal structure, size, and lifetime of the resulting fireballs are presented and discussed. Length, velocity, and timescales corresponding to the two principal stages of the process (outflow prior to ignition, fireball evolution) are introduced and used for interpretation of the calculated results. Evolution of burning clouds is mainly governed by the initial momentum created by the fuel source and by the buoyancy of the gas in the fireball, the relative importance of these being characterized by the Froude number, defined as the square of the ratio of fuel injection velocity to the characteristic buoyancy-related velocity. We show that despite the differences in the fuel properties and release types, the non-dimensional fireball lifetime depends primarily on the Froude number, while the influence of other factors proves to be much less important. The calculated fireball sizes, dynamics of ascent, burning times, and radiative fractions are compared with the experimental data available, and reasonable agreement between these is demonstrated.

SIMMER-III applications to fuel–coolant interactions

The main purpose of the fast reactor safety analysis code, SIMMER-III, is to provide a numerical simulation of complex multiphase, multicomponent flow problems essential to investigate core disruptive accidents in liquid-metal fast reactors (LMFRs). However, the code is designed to be sufficiently flexible to be applied to a variety of multiphase flows, in addition to LMFR safety issues. In the present study, some typical experiments relating to fuel–coolant interactions (FCIs) have been analyzed by SIMMER-III to demonstrate that the code is applicable to such complex and highly transient multiphase flow situations. It is shown that SIMMER-III can reproduce the premixing phase both in water and sodium systems as well as the propagation of steam explosion. It is thus demonstrated the code is basically capable of simulating integral multiphase thermal-hydraulic problems included in FCI experiments.

Sizing Wet-Gas Pipelines and Slug Catchers With Steady-State Multiphase Flow Simulations

The design of wet-gas pipelines and slug catchers requires multiphase flow simulations, both steady-state and transient. However, steady-state simulation is often inadequately conducted and its potential not fully utilized. This paper shows how mechanistic steady-state simulation models can be used to obtain not only pressure drop, liquid holdup and flow regime, but also to extract important operational information such as pig transit time, pig exit speed, liquid buildup rate behind the pig, and the time for the pipeline to return to a steady-state after pigging. A well-designed set of steady-state simulations helps to determine pipeline size, slug catcher size, and pigging frequency. It also serves as a starting point for subsequent transient multiphase flow simulations.

Workshop on "Measuring techniques for steady state and transient multiphase flows"

Workshop on "Measuring techniques for steady state and transient multiphase flows"