Multiphase Flow Analysis Research Articles

A Robust Bubble Growth Solution Scheme for Implementation in CFD Analysis of Multiphase Flows

Although the full form of the Rayleigh–Plesset (RP) equation more accurately depicts the bubble behavior in a cavitating flow than its reduced form, it finds much less application than the latter in the computational fluid dynamic (CFD) simulation due to its high stiffness. The traditional variable time-step scheme for the full form RP equation is difficult to be integrated with the CFD program since it requires a tiny time step at the singularity point for convergence and this step size may be incompatible with time marching of conservation equations. This paper presents two stable and efficient numerical solution schemes based on the finite difference method and Euler method so that the full-form RP equation can be better accepted by the CFD program. By employing a truncation bubble radius to approximate the minimum bubble size in the collapse stage, the proposed schemes solve for the bubble radius and wall velocity in an explicit way. The proposed solution schemes are more robust for a wide range of ambient pressure profiles than the traditional schemes and avoid excessive refinement on the time step at the singularity point. Since the proposed solution scheme can calculate the effects of the second-order term, liquid viscosity, and surface tension on the bubble evolution, it provides a more accurate estimation of the wall velocity for the vaporization or condensation rate, which is widely used in the cavitation model in the CFD simulation. The legitimacy of the solution schemes is manifested by the agreement between the results from these schemes and established ones from the literature. The proposed solution schemes are more robust in face of a wide range of ambient pressure profiles.

Computational analysis of multiphase flow of non-Newtonian fluid through inclined channel: heat transfer analysis with perturbation method

Computational analysis of multiphase flow of non-Newtonian fluid through inclined channel: heat transfer analysis with perturbation method

Performance Analysis of Internal Ballistic Multiphase Flow of Composite Charge Structure

Different charge structures have different interior ballistic performance. Existing research is based on experimental measurements or the lumped parameter method to obtain limited ballistic characteristics, which indirectly impacts the analysis of the parameters’ distribution, requiring a complex modeling solution process. Besides this, the ignition performance of different charge structures needs to be further explored. The disadvantages of previous studies have limited the feasibility of further optimization of the composite charge structure. In this paper, we apply a two-dimensional two-phase flow method based on the Eulerian–Lagrangian model to study the performance of different composite charge structures. First, we establish the mathematical model of different particle types based on interior ballistics, which is directly related to the research foundation of subsequent ballistic performance. Next, we investigate the multi-scale reaction flow of complex charge structures by the two-phase flow method and obtain the distribution of parameters in the chamber. Finally, we conduct a study with different particle charge parameters to explore the sensitivity of ballistic characteristics to structural parameters. The results show that the tubular propellant has good ignition performance in different charge structures, and the ignition consistency can be improved by charging tubular propellant in the center of the chamber. However, more tubular propellants are ineffective at significantly improving ignition performance, and result in a decrease in combustion chamber pressure. These results may be promising for the optimization of various charge structures.

Visualization of multiphase pulsatile blood over single phase blood flow in a patient specific stenosed left coronary artery using image processing technique.

Coronary arteries disease has been reported as one of the principal roots of deaths worldwide. The aim of this study is to analyze the multiphase pulsatile blood flow in the left coronary artery tree with stenosis. The 3D left coronary artery model was reconstructed using 2D computerized tomography (CT) scan images. The Red Blood Cell (RBC) and varying hemodynamic parameters for single and multiphase blood flow conditions were analyzed. Results asserted that the multiphase blood flow modeling has a maximum velocity of 1.017 m/s and1.339 m/s at the stenosed region during the systolic and diastolic phases respectively. The increase in Wall Shear Stress (WSS) observed at the stenosed region during the diastole phase as compared during the systolic phase. It was also observed that the highest Oscillatory Shear Index (OSI) regions are found in the downstream area of stenosis and across the bifurcations. The increase in RBCs velocity from 0.45 m/s to 0.6 m/s across the stenosis was also noticed. The computational multiphase blood flow analysis improves the understanding and accuracy of the complex flow conditions of blood elements (RBC and Plasma) and provides the progression of the disease development in the coronary arteries. This study helps to enhance the diagnosis of the blocked (stenosed) arteries more precisely compared to the single-phase blood flow modeling.

손상 선박 기름 유출량 추정을 위한 수치해석과 이론식의 비교 연구

This paper provides the results of numerical and theoretical predictions of oil outflows from damaged single-hull and double-hull ships.Theoretical equations derived from the unsteady Bernoulli equation and a CFD method for multi-phase flow analysis were used to estimate the oil outflow rate from cargo tank. The predicted oil outflow rate from a single-hull cargo tank damaged due to grounding and collision accidents showed a good agreement with the available experimental results in both numerical and theoretical analyses. However, in the case of the double-hull conditions, the time variation of the amount of water and oil mixture inside the ballast tank predicted by the theoretical equation showed some different behavior from the numerical results. The reason was that the interaction of the oil flow with the water inflow in the ballast tank was not reflected in the theoretical equations. In the problems of the initial pressure condition in the cargo and ballast tanks, the oil outflow and water inflow were delayed at the pressure condition that the tanks were sealed. When the flow interaction between the oil and water in the ballast tank was less complicated, the theoretical and the numerical results showed a good agreement with each other.

Mathematical Model for Predicting the Development of Two-Phase Flow in a Horizontal Pipe

Prediction of the flow pattern is a central problms in multi-phase flow analysis. It is a vital point for researchers to accurately predict which flow pattern category types will occur at different flow rates. For this purpose, a mathematical model using the MATLAB (R2017b) computer program is developed for the prediction of gas-liquid two-phase flow patterns in a horizontal pipe with an inner diameter of 30mm under standard conditions. The properties of the air-water two-phase, the pipe geometry, and the flow rates of phases are defined to initiate the operating conditions. The mass flow rates of air and water changed from 0.002 to 0.004 kg/s and 0.672 to 1.334 kg/s, respectively. The impact of properties of the fluid and pipe diameters on two-phase flow configuration is considered to predict the impact of fluid properties on the flow pattern. The findings indicate that as the mass flux increases, the pipe diameters decrease, affecting the configuration of the flow pattern types. The mathematical model�s predicted results are validated by comparing with previous studies. In addition, good agreement is obtained when the predicted results are compared to the ongoing experiment of this research.

Flow Structure and Slipstream Characteristics of an Axial Flow Hydraulic Turbine with a Collection Device in an Open Channel

The axial flow hydraulic turbine with a collection device can be simply installed in the flowing water of an open channel with shallow water depth to generate electricity, and the power output is increased by collecting and increasing the velocity of the flow. When the power output of this hydraulic turbine is insufficient, it is necessary to install several turbines in series with the flow in narrow channels, and it is necessary to establish a guideline for appropriate installation intervals. In this study, the relationship between the velocity distribution and the vortex structure inside and outside the hydraulic turbine was investigated by experiments and multiphase flow analysis considering free surface in order to clarify the slipstream characteristics of this hydraulic turbine in an open channel with shallow water depth. As a result, it was clarified that the axial flow velocity behind the brim recovered rapidly due to the momentum exchange between the flow passing through the outside of the hydraulic turbine and the flow passing through the inside of the hydraulic turbine. It was also discovered that all the major vortices disappeared at a position 9 times the runner diameter in the downstream direction from the runner center, and more than 70% of the axial flow velocity was recovered in the entire width direction.

Simulation and Analysis of Multiphase Flow in a Novel Deepwater Closed-Cycle Riserless Drilling Method With a Subsea pump+gas Combined Lift

Recently, deepwater resource exploration has grown rapidly. Because the conditions of marine environment and seabed geology are more complex, deepwater drilling needs to numerous confront challenges, such as more complicated wellbore situations, low drilling efficiency, and high cost. Advanced novel drilling methods serve as significant impetus to facilitate the rapid advancement in deepwater oil-and-gas exploration and development. However, adopting riserless drilling methods may pollute marine environment and yield poor wall protective effects, while drilling methods with risers may suffer from relatively high cost and risk. Based on these dilemmas, in this study, a novel deepwater closed-cycle riserless drilling method with a subsea pump + gas combined lift is proposed. The proposed novel closed-cycle method has also established a multiphase flow drilling model and analyzed the effects of drilling fluid displacement, gas injection displacement, gas injection site and seawater depth on the multiphase flow in the wellbore. The simulation results revealed the following: As the gas migrates upward along the pipeline, its flow velocity first increases slowly and then rapidly owing to the volume expansion of gas. Larger displacement of drilling fluid demands greater working power of the subsea lifting pump, which is characterized by a nonlinear relationship. The gas injection displacement can effectively mitigate the load-bearing capacity of the pump, and increasing gas injection displacement leads to a decreased subsea lifting pump working power requirement; the decreasing effect on pump power load is more significant in the case of low gas injection displacement. Increasing the depth of gas injection sites reduces the subsea pump working with a decreasing slope with respect to the power descent. Finally, the subsea pump lifting power demand increases approximately linearly with an increasing seawater depth. Subsequently, an optimization method of hydraulic parameters for deepwater closed-cycle riserless drilling was proposed, which provides a theoretical foundation for the selection of subsea pumping power as well as the optimization of gas injection sites and displacement.

Prediction of incipient cavitation in micro tubular propeller turbine

Abstract Cavitation is a phenomenon that cavities or bubbles form in a liquid when static pressure falls below the vapor pressure. It can damage the machine, hence it is recommended to be avoided in the design and operation of the machine. In this study, the cavitation characteristics were numerically investigated with a change in the flow rate of a micro tubular propeller turbine. Here, the rotational speed was set to the value corresponding to the best efficiency point for each flow rate. A multiphase flow analysis incorporating water and water vapor was conducted, using the Zwart-Gerber-Belamri (ZGB) model as the cavitation model. Results show that the tip clearance is the first region where the cavitation starts to occur as the flow rate increases. At this time, the Thoma number was found to be 1.178. The second region where the cavitation occurs with further increases in the flow rate is in the vicinity of the leading edge. It turned out that the leading edge cavitation occurs when the Thoma number is below 1.111. As the tip clearance increases, the range of the flow rate that cavitation does not occur increases, but it reduces turbine performance. Therefore, the selection of appropriate tip clearance given the operating flow rate range and performance needs to be considered.

Analytical Study of Unsteady Boiling Characteristics of Steam Generator

Currently, research on the efficiency of the film heater, which is a surface heating element, is being actively conducted as it is a potential alternative to the sheath heater. However, research on the heat transfer phenomenon and the performance of the film heater is insufficient. In this study, the performance of the sheath heater and the film heater were compared and analyzed, and the heat transfer pattern according to the arrangement of the heating wire was analyzed. To inspect the heat transfer performance, the external heat transfer and internal flow characteristics of the steam generator were determined, and a study on the performance of the steam generator according to each design variable was conducted. The Eulerian multiphase model was used to conduct the multiphase flow analysis, and the wall boiling model was used to conduct the phase change analysis. Among the models analyzed in this study, the model in which the heating wire was arranged along the flow path and the length of the induction was extended by 50% showed the best performance. Compared to the base model, the steam generation time was improved by 33.3% and the steam ejection time was improved by 17%. These times were improved because the heating wire arrangement of the film heater was optimized along the fluid channel. The U-shaped heating wire arrangement enabled a stable steam injection, and in the case of the normal film heater and fluid channel following heater, a large portion of the heating wire was located around the center. Consequently, steam was formed at the center of the housing. We believe that the results of this study can be applied to various fields in consideration of the advantages of the film heater package, free pattern design of printing, and economy.

Clearance Fit Design of a Hydraulic Cylinder with Particle Polluted by Hydraulic Oil

In hydraulic cylinder systems, oil pollution results in wear and leakage of hydraulic cylinder components. In accordance with the actual working conditions of a certain type of hydraulic cylinder, the technology of fluid–solid thermal coupling and multiphase flow analysis is applied to analyze the heat–fluid–solid coupling of hydraulic cylinder under the condition of particle polluted by hydraulic oil. The distribution law of the heat field of hydraulic cylinder was obtained through analysis. The results show the effect of heat flow on the partial load effect. The distribution rules of particles in the hydraulic cylinder were obtained under the influence of different gaps and particle pollutants. The damage rate of the hydraulic cylinder under these working conditions was analyzed by optimizing the plunger and cylinder clearance fit and providing important technical support to solve the problem of hydraulic oil leakage in hydraulic cylinders.

Microscopic Visualization and Quantification of Molten Aluminum Alloy Flow Inside Die Cavity by Multiphase Flow Analysis

Microscopic Visualization and Quantification of Molten Aluminum Alloy Flow Inside Die Cavity by Multiphase Flow Analysis

Analysis of Multiphase Flow and Heat and Mass Transfer for Ammonium Chloride Crystallization of the High-Pressure Heat Exchanger in Hydrogenation Unit.

The corrosion failure of the high-pressure heat exchanger in a petrochemical enterprise was simulated. A multiphase flow and heat and mass transfer simulation shows that the vortex core with a higher gas phase content and lower temperature is the region of easy crystallization, located on both sides of the center of the tube. The crystallization process occurs in the gas phase. As the reaction progresses, the crystallization range spreads from the tube wall to the center of the tube bundle, and the inner diameter of the tube bundle decreases continuously. In Fluent, a user-defined function, based on the ammonium chloride crystallization reaction, is loaded. The results show that crystallization first occurs in the tube bundles on both sides of the center of the tube and that the corrosion is aggravated by the erosion wall surface of crystal particles at the elbow, which is consistent with the actual corrosion failure location.

Numerical analysis of multiphase flow of couple stress fluid thermally effected by moving surface

The study of multiphase flows gained much importance because of its extensive applications in nature and industry. These flows possess two or more thermodynamic phases, for example, one component phase (e.g., water vapors and water flow) or several components phase (e.g., water and oil flow). The most common example of multiphase flow in the context of the oil industry is petroleum. Further blood flow, porous structures, fluidized bed, bubbly flow in nuclear reactors, and fiber suspension in the paper industry are some significant examples of multiphase flows. In this paper, we considered the Couette flow of non-Newtonian (couple stress) fluid with variable magnetic field and thermal conductivity effects between parallel walls of the channel. The upper wall of the channel is in constant motion while the lower wall is in a fixed position. The variable viscosity effects with the suspension of hafnium particles are also discussed by taking Vogel’s viscosity case. The shooting method based on the R–K method is applied to obtain the numerical solution of the current problem. A comparison between Newtonian and non-Newtonian fluids is presented by sketching graphs. The variations in flow and temperature of fluid against various involved factors, including variable viscosity, wall temperature, thermal radiations, variable magnetic field, and thermal conductivity are sketched and also physically described. It is observed that variable viscosity parameter elevated both velocity and temperature profiles while wall temperature parameter decelerated both fields. Further, noticed that the variable thermal conductivity and variable magnetic field impede the velocity of the fluid and also retarded the temperature field. Our attempt is not just useful to investigate the mechanical and industrial multiphase flows but also delivers important results to fill the gap in the existing literature.

Defocusing PIV and ridge-detection algorithm for the analysis of flows laden with non-spherical particles

In this preliminary work, the feasibility of the combination of a volumetric velocimetry technique such as Defocusing Particle Image Velocimetry and a particle phase-discrimination methodology based on ridge detection algorithm for the analysis of turbulent multiphase flows with non-spherical fiber-like particles is discussed. Experimental results of a dilute suspension of fibers in an open-channel apparatus are provided.

Numerical analysis of multiphase flow in chemical looping reforming process for hydrogen production and CO2 capture

Numerical analysis of multiphase flow in chemical looping reforming process for hydrogen production and CO2 capture

A micromechanical hydro-mechanical-damage coupled model for layered rocks considering multi-scale structures

An anisotropic Hydro-Mechanical-Damage coupled model was established in the framework of thermodynamics for saturated layered rocks, which contain arbitrarily-distributed cracks of smaller scales and orientated bedding planes of much larger scales. The proposed model considers the anisotropic damage growth and frictional sliding of cracks and shear sliding and dilatancy of bedding planes, as well as the interaction between cracks and bedding planes. Numerical implementation of the nonlinear coupled model was developed based on TOUGHREACT, which is a well-established simulator for multiphase fluid flow and reactive transport analysis. The proposed model was first validated with laboratory water injection test results on rock blocks, and then used to study the effects of injection rates, in situ stresses and bedding planes on fluid injection processes at the field scale, demonstrating the importance to consider the variation of multi-scale structures for better understanding the coupled Hydro-Mechanical responses in layered rocks.

Dual evolution mixed variational analysis of multiphase flow in the subsurface

Dual evolution mixed variational formulations of multiphase flow models in the subsurface are established and analyzed. Specifically, compositional multiphase flow of a triphasic water–oil–gas multicomponent flow is treated, with a dual Gibbs oil–gas mass transfer model. Qualitative analysis of the mixed variational models is performed applying composition duality principles and methods. For multiphysics as well as parallel computing, macro-hybrid variational reformulations are considered. Dual semi-implicit time-marching schemes are presented as semi-discrete approximations for the flow-transport variational models, as well as for a precondition augmented exactly penalized dual Gibbs optimality variational formulation, which are all implementable as parallel proximal penalty–duality algorithms. In this manner, bases for fully discrete non-conforming macro-hybrid mixed finite element numerical realizations are rendered.

Impact of Specific Number of Air to Clinker on Clinker Cooling Process in Grate Coolers in a Cement Plant

The impact of specific number of airs to clinker on a clinker cooling process in grate coolers in a cement plant was investigated. Clinker cooling process is a complex process due to the vast number of interacting operating parameters such as: clinker cooler length, ambient temperature, clinker cooler width, clinker cooler drives speed, clinker cooler fan speed, clinker and air mass flow rates, and clinker density and air densities. This research examines heat transfer and multiphase fluid flow analysis as relating to specific number of air to clinker in a clinker cooling system. It employs a physical “dimensionally scaled-down” model. A 3D model of the clinker bed was developed using SolidWorks 2014 based on geometric parameters adopted in the scaled conceptual design after an existing running clinker cooler. The designed model was scaled down by ratio 25:1, that is, existing cooler being twenty-five times higher than the modelled with length 1.3 m, width 0.3 m and variable clinker bed height of 0.3 m, 0.4m and 0.6m as geometric dimensions. Numerical experimentation done involved high temperature clinker entering the clinker cooler from the heating-up furnace (HUF) at 1350 °C, specific numbers of 2.2041 and 1.7959 Nm3/kg clk, air inlet temperature of 32 °C, inlet mass flow rate of air at 0.45 kg/s at clinker 0.15 kg/s. It was observed that at a specific number of 2.2041 Nm3/kg clk at a bed height 0.6 m an optimal energy recoverable efficiency of 70% was recovered into the system and with an improved lower outlet clinker temperature of 68 °C. While, at a specific number of 1.7959 Nm3/kg clk and at a clinker bed height of 0.3 m, the lowest recoverable efficiency of 57.52% was recovered into the modelled clinker cooler and with highest outlet clinker temperature of 168.7 °C. Hence, specific number of airs to clinker also plays a significant role in clinker cooler performance.

Numerical study on the sloshing flows in a prismatic tank using natural frequency of the prismatic shapes

In this numerical study, a 2D prismatic tank - subjected under horizontal excitation - is used to analyse the sloshing characteristics for a specific range of Reynolds number, from 2.5 × 104 to 2.0 × 105. Three models of geometric variable δ1 - namely, δ1 = 50 mm, δ1 = 150 mm and δ1 = 250 mm - are used to observe the effects of the lower chamfered shape of the prismatic tank, where the Reynolds number for each δ1 ranges from 2.5 × 104 to 2.0 × 105 (12 cases). The volume of fluid (VOF) method is used for the multi-phase flow analysis. The fast Fourier transform (FFT) technique is used to analyse the frequency components of excitation force and the magnitude of the amplitude spectrum. The results show that the sloshing wave fluctuation becomes small when the geometric variable δ1 is larger. Also, the FFT technique shows that the resonance does not occur due to frequencies which are not integral multiple of the excitation frequency. Moreover, for the sloshing load analysis, the free surface length is an important parameter than the shapes of the lower section.