Solid-liquid Two-phase Flow Research Articles

Influence of the internal structure of straight microchannels on inertial transport behavior of particles

The rapid advancement of Micro-Electro-Mechanical Systems (MEMS) technology has established microfluidics as a pivotal field. This technology marks the onset of a new era in various applications, including drug testing, cell culture, and disease monitoring, underscoring its extensive practicality and potential for future exploration. This research delves into the intricate behavior of particle inertial migration within microchannels, particularly focusing on the impact of different channel structures and Reynolds numbers (Re). Our studies reveal that particles in microchannels with one-sided sharp-cornered microstructures migrate towards the sharp corner at a relative position of 0.4 under low flow rates, and towards the straight wall side at a relative position of 0.8 under high flow rates. The migration pattern of equilibrium positions varies with different arrangements of sharp-corner structures, achieving stability at the channel's center only when the sharp corners are symmetrically arranged on both sides. Our investigation into the shape of microstructures indicates that sharp-cornered structures generate a more stable secondary flow compared to rectangular and semi-circular structures, preventing particle aggregation at the outlet. To address the challenges associated with handling variable cross-section geometries and solid-wall boundaries in dissipative particle dynamics methods effectively, we have developed a dissipative particle dynamics model specifically for analyzing such microchannels. Building upon our previous research, this model introduces a conservative force coefficient for particles within the microstructured region and an interaction zone that only involves repulsive forces, aligning well with experimental outcomes. Through the study of microstructures' geometric shapes, this paper offers guidance for designing microchannels for particle enrichment. Furthermore, the dissipative particle dynamics model established for the particle flow and solid structure interaction within microstructured channels provides insights into the mesoscale dynamics of liquid-solid two-phase flow and particle motion. In conclusion, this paper aims to enhance particle motion sample preparation techniques, thereby broadening the scope of microfluidic applications in the biomedical field.

Study on Wear Characteristics of a Guide Vane Centrifugal Pump Based on CFD–DEM

Guide vane submersible centrifugal pumps are a kind of submersible pump, and the fluid inside the pump is often mixed with gravel and other impurities during operation, affecting the pump’s operating efficiency and life expectancy. However, past studies on solid–liquid two-phase flow (STF) and wear characteristics in guided vane centrifugal pumps have been limited to the particle trajectory and wear region distribution. These studies have lacked research on the effect of particles on the fluid flow and the specific amount of wear on the overflow components. Additionally, most of them have used the DPM discrete-phase model, which does not consider the particle–particle and particle–wall interactions. This paper is based on the CFD–DEM method, combined with the Archard wear model. A solid–liquid two-phase flow simulation is carried out for pumps with different particle sizes and particle shapes to analyze the particle movement inside the pump, the wear distribution and average wear amount of the overflow components, and the effect of particles on the turbulent kinetic energy of the fluid. The results show that the particles mainly collide with the leading and trailing edges of the impeller blades and the leading edge of the guide vane blades and form a buildup at the trailing edge of the concave surface of the guide vane blades, resulting in the wear being mainly distributed in these regions. With an increase in particle size and a decrease in sphericity, the average wear on the overflow components increases. The change of particle size directly affects the resistance of the fluid and the structure of the flow field, which has a large impact on the fluid flow pattern and generates large turbulent kinetic energy fluctuations. The shape of the particles only changes the structure of the local flow field, which has a small impact on the fluid flow pattern.

Study on Proppant Transport and Placement in Shale Gas Main Fractures

In this paper, based on the background of a deep shale reservoir, a solid–liquid two-phase flow model suitable for proppant and fracturing fluid flow was established based on the Euler method, and a large-scale fracture model was established. Based on field parameters, a proppant transport experiment was conducted. Then, on the basis of the experimental fracture model, proppant transport simulation under different influencing factors was carried out. The results show that the laboratory experiment was in good agreement with the simulated results. The process of proppant accumulation in fractures can be divided into three stages according to the characteristics of sand banks. The displacement mainly affects the sedimentation distance of the proppant in the first stage, and the viscosity of the fracturing fluid represents the strength of the fluid sand carrying performance. Compared with 40/70 mesh proppant, 70/140 mesh proppant is more easily fluidizable, the fracture width has less influence on proppant migration and placement, and the perforation location only affects the accumulation pattern at the fracture entrance, but has less influence on proppant placement in the remote well zone.

Numerical analysis of coarse particle two-phase flow in deep-sea mining vertical pipe transport with forced vibration

Exploring the dynamics and flow characteristics of coarse particles within vertical lifting pipes is essential to ensure safe and efficient pipeline transportation. This study combines computational fluid dynamics (CFD) and the discrete element method (DEM) to investigate the behavior of coarse particle solid–liquid two-phase flow in a vertical pipe utilized for deep-sea mining under forced vibration and compares it with that in stationary pipes. This study examined the effects of pipe amplitude, vibration frequency, and initial internal flow velocity separately. The amplitude values tested were 0D (static), 1D, 2D, 3D, and 4D, where D represents pipe diameter. The vibration frequencies of 0 Hz (static), 0.25 Hz, 0.5 Hz, 1 Hz, and 2 Hz were tested, respectively. Finally, initial velocities of 1 m/s, 2 m/s, 3 m/s, and 4 m/s were tested. Compared with stationary pipes, particle-induced turbulence gradually disrupts the flow field, leading to a more dispersed particle volume distribution during pipe vibration. An increase in the amplitude and vibration frequency of the pipe results in an augmentation of the pressure drop within the pipe. By comparing the results of the vibrating pipe with those of the stationary pipe, the effect of the pipe vibration gradually weakened as the initial velocity increased.

Study of solid-liquid two-phase flow model of drilling fluids for analyzing mud cake formation

Mud cake is formed by the accumulation of particles on the surface and inside of the well wall during the filtration of drilling fluids, which is multiply affected by reservoir types, composition of drilling fluids, and wellbore conditions. Numerical simulation can provide a more comprehensive study than experiments, but the usual single-phase models of drilling fluid is difficult to simulate the non-homogeneous characteristics of mud cake. In this paper, the calculation method of interactions between particles and the drag force on particles with different sphericity in non-Newtonian fluid are derived. Therefore, a solid-liquid two-phase flow model of drilling fluid that describes the motion of solid and liquid phases, respectively, is constructed to investigate the influences of their properties on the dynamic non-homogeneous formation of mud cake in the real pore space of cores. The results show that the flow volume and velocity of the liquid phase are affected by the tortuosity of the pore channel, which in turn affects the entering number of particles. The influences of particle parameters on the entering number are radius > morphology > release velocity > free energy of the surface > density > release concentration. The solid-liquid two-phase flow model can refine the analysis to formulate the most applicable drilling fluids, which will significantly reduce the exploration and validation work of plugging experiments.

Simulation Analysis of Metallic Particles Movement in Typical Structure of Oil-immersed Power Transformer

The insulation performance of oil-immersed power transformers is closely involved with the movement of metal particle impurities, and the movement characteristics of metal particles are not only influenced by the electric field, but also by the oil flow. In this paper, a solid-liquid two-phase flow simulation model was constructed, and the effect of electric field on the motion of metal particles was considered. Firstly, the validity of the simulation model was verified by using the experimentally observed motion of metal particles in the horizontal oil channel between parallel flat plate electrodes, based on which the motion of metal particles in the typical oil channels of a 500kV power transformer was studied. It was found that when the metal particles passed through the oil flow inlet, the number of metal particles settling increased with the increase of particle size. All the metal particles with 1mm particle size sank in the oil flow inlet during the oil migration process, it was almost impossible to enter the low, medium and high voltage winding parts. Through the middle or upper end of the high voltage winding, the smaller particles (50μm, 150μm) would easily migrate with the oil flow and move faster; the larger particles (500μm) would move slower or be more easily deposited. This research holds significant practical implications in the engineering study of metal particle motion distribution within transformers.

Numerical Simulation on Erosion and Stress on a Small-Diameter Hydrajet Fracturing Tool.

Conventional hydrajet fracturing techniques are often frustrated when they are applied to some specific well types, such as casing-damaged and small-diameter wells. It is of great significance to investigate the erosion and stress on a small-diameter hydrajet fracturing tool during its service and clarify the relevant influencing factors. Based on the solid-liquid two-phase flow theory and erosion model, a numerical simulation was conducted on the erosion and stress on a small-diameter hydrajet fracturing tool by using the computational fluid dynamics approach in order to understand how the inlet flow rate, particle size, and particle mass concentration affect the erosion and stress on the tool. The results show that the erosion on the small-diameter hydrajet fracturing tool is generally a cutting erosion of proppant particles on the tool body. Such erosion occurs on the lower wall of the nozzle, and the erosion at the upper-0° nozzle is higher in rate and smaller in area than that at the lower-180° nozzle. The maximum stress of the small-diameter hydrajet fracturing tool is concentrated on the upper and lower walls of the upper and lower nozzles, especially the lower part inside the upper nozzle. The maximum erosion rate, average erosion rate, and maximum stress on the wall near the nozzle during fracturing increase as the inlet flow rate and particle mass concentration increase and decrease as the proppant particle size increases.

Comparative analysis of internal flow characteristics and particle trajectories of centrifugal pumps with different impeller structures under solid-liquid two-phase flow conditions

The disc pump is a non-conventional centrifugal pump that utilizes centrifugal force and boundary layer effects to transport fluids. This pump is widely used in industries such as petrochemicals. However, due to the presence of particles in the solid-liquid two-phase flow, it causes wear and performance degradation of the pump’s flow components. However, due to the presence of particles in the solid-liquid two-phase flow, it can cause wear and performance degradation of the pump components. To study the internal flow characteristics of solid-liquid flow and the particle trajectory in a bladed disc pump, numerical simulation method was adopted to perform steady-state numerical simulation of spherical particles with different diameters (0.1 mm, 0.25 mm, 0.4 mm) in the bladed disc pump. The results indicate that compared to conventional centrifugal pumps, the performance of the bladed disc pump is lower. The variation in particle diameter has a minor influence on the intensity of the internal flow field in the bladed disc pump. The particle trajectories inside the impeller of the bladed disc pump are more chaotic, with larger diameter particles exhibiting a wider range of trajectory variations, while smaller diameter particles maintain relatively stable motion trajectories.

Particle distribution and two-phase flow characteristics of twin-screw pump during solid-liquid transfer

The twin-screw pump is a kind of positive displacement machinery with smooth pressure and flow pulsation and strong self-priming ability, which is widely used in the fields of oilfield production, marine engineering, and other fields. However, in the process of conveying liquid-phase media, it is difficult to avoid the inclusion of solid impurities and grit, resulting in wear of the pump casing and rotor, and the pump’s pressurization capacity is reduced or even shut down. At present, the solid-liquid two-phase flow characteristics within the twin-screw pump have not been clarified, which hinders the study of particle wear in the pump. In this paper, a solid-liquid two-phase flow study is carried out on a twin-screw pump through numerical simulation and experimental testing. The distribution of particles with different diameters in the rotor domain with the liquid-phase transport process is explored by simulating the two-phase flow under different differential pressures and particle concentrations. The results show that the particles in the rotor domain are mainly distributed in the region away from the male and female rotor engagement, and the number of particles near the engagement is small but the velocity is higher under the influence of the clearance jets; the elevation of the differential pressure and the particle concentration increase the risk of the particles to collide with the rotor more frequently and at higher velocity; at different particle concentrations, new localized vortices are caused by particle conveying which compared to pure liquid transport, but there are also cases where the original vortices are suppressed. The results will provide a theoretical basis for further research on particle wear characteristics in twin-screw pumps.

Motion characteristics and wear analysis of particles in the clearances of a twin-screw pump

The rotors of twin-screw pumps would be worn by hard particles for deep-sea oil and gas mixture transport. It led to the destruction of the seal clearance and the deterioration of pump performance. Based on the Euler–Lagrange method and dynamic grid technology, the transient numerical simulation of solid–liquid two-phase flow in a twin-screw pump was carried out and validated by experiment. The motion characteristics of particles in the tip, interlobe, flank clearance, and the causes of rotor wear were clarified. The results revealed that the severe wear at rotor tips was caused by the particles when they enter the tip clearance rather than leaving the tip clearance with the leakage jet flow. Particles passing through the flank clearance had high velocity and contributed to the wear at rotor tips. The main flow in the tooth chamber was disturbed by the interlobe and flank clearance leakage, even resulting in local high-speed reflux near the engagement. With the increase in the particle concentration and diameter, the collision frequency between particles and rotor tips increased, aggravating the risk of wear at rotor tips. The research could reveal the motion nature of particles following the liquid phase and their wear mechanism in twin-screw pumps.

Comparative evaluation of sand erosion in reversible turbine at pump mode and turbine mode

During the operation of reversible pump turbine, the flow passing components are often worn by sediments. In this paper, Euler-Euler computational fluid dynamics (CFD) method is used to simulate the liquid-solid two-phase steady flow in several pump modes and turbine modes. Finnie models are used to predict possible wear conditions and further analyze the causes of component wear. Results show that runner is the most easily worn component, which is related to local high flow velocity. The runner erosion position is mainly concentrated in the middle part of the pressure side. The erosion position of guide vane and stay vane is mainly concentrated in the leading edge and trailing edge, which depends on the change of condition. By daily weighted, the turbine mode is found has higher erosion rate than that of pump mode. This study provides the scientific support of anti-erosion of pumped storage units.

The Numerical Investigation of Solid–Liquid Two-Phase Flow Characteristics Inside and Outside a Newly Designed 3D Sediment Trap

Sediment transport serves as a link for material exchange between land and sea. Using sediment traps, we can observe the capture and transport processes of sediments. Based on the sediment particle size distribution characteristics in Jiaozhou Bay, this paper analyzes the influence of a newly designed 3D sediment trap on the water–sand two-phase flow process inside and outside a trap device during its operation. Meanwhile, under a certain concentration condition, a numerical formula model is researched and proposed to evaluate the impact of the device’s structure, the environmental flow speed, and the particle size on particle capture efficiency. This model is based on the CFD-DPM coupling in Fluent 2021R1 software, and the particle filtration process is solved using a combination of porous media and UDF functions. Finally, by analyzing the distribution of sediment movement in the fluid domain, two concepts, namely the percentage of particles entering the tube and the effective capture rate, are proposed. Suggestions for optimizing the structure of the trap are put forward to achieve optimal capture effects.

Analysis of Solid-Liquid Two-Phase Flow in the Area of Rotor and Tailpipe

In order to study the internal flow state and wear law of a bulb cross-flow unit based on the particle non-uniform phase model in the Euler–Euler method, the solid-liquid two-phase flow condition of the hydraulic turbine under different solid-phase diameters, concentrations, and guide vane openings is calculated. The results show that (1) Under the same solid-phase physical parameters, the distribution of solid-phase concentration on the working surface of the blade is positively correlated with the opening degree of the guide vane, the concentration of the solid phase on the back of the blade is negatively correlated with the opening degree of the guide vane. (2) The addition of the solid phase changes the time-domain period of pressure pulsations at the rotor inlet and the tailpipe inlet under clear water conditions, and the tailpipe pressure pulsation coefficient decreases with increasing solid-phase concentration. The pressure pulsation coefficient increases with increasing solid-phase diameter and concentration at the inlet of the rotor. (3) Numerical simulation of the wear characteristics of cross-flow turbine by Finne’s wear model reveals that the two-phase flow condition with high concentration, large particle size and small openings has a more serious effect on turbine blade wear.

Study on Collection Performance of Hydraulic Polymetallic Nodule Collector Based on Solid–Liquid Two-Phase Flow Numerical Simulation

The hydraulic collector is an important device for collecting seafloor polymetallic nodules. In this study, a hydraulic polymetallic nodule collector with two acquisition nozzles and one transmission nozzle is described. The numerical model of the hydraulic collector is established based on the solid–liquid two-phase flow method, and it is verified by experimental tests. On this basis, the collection mechanism of the hydraulic collector is analyzed, and the effects of structural parameters and working parameters on its collection performance are explored. The results show that the collection height and slant angle of the acquisition nozzle are key factors for collection efficiency, with optimal heights below 150 mm and angles between 45 and 49∘. The recommended range for the center distance between the two acquisition confluence tubes is 650–730 mm. Excessive acquisition and transmission flow rates make a negligible contribution to improving the collection efficiency, but can also cause a significant increase in energy consumption. Therefore, the recommended ranges for acquisition and transmission flow rates are 140–160 m3/h and less than 80 m3/h, respectively. All of the results indicated that the parameters of the developed hydraulic collector were set reasonably, which thus ensured a balance between the collection efficiency and energy consumption.

Investigation on the Erosion Characteristics of Liquid–Solid Two-Phase Flow in Tee Pipes Based on CFD-DEM

Tee pipes are widely utilized in pipeline transportation, especially in subsea production systems and the chemical industry. The purpose of this research is to study the influences of gravity direction, conveying parameters and particle properties on the erosion distribution in tee junctions. Investigation using the CFD-DEM coupled method is conducted on the flow mechanisms and erosion characteristics in a tee junction under different flow conditions. Firstly, numerical calculations of liquid–solid two-phase flow in a vertical cylindrical pipe are performed, and the comparison between simulation results and experimental results is carried out. Then, the verified lift and erosion models are used for the numerical calculations of tee pipes. Flow mechanisms and erosion characteristics are numerically investigated through analysis of the velocity profiles, streamlines, and erosion contours. The results indicate that the gravity direction has a nonnegligible influence on the cross-sectional velocity profiles, particularly under the condition of high velocity and high particle concentration. The region with the maximum erosion rate occurred at the branch pipes, about three fourths of the pipe diameter away from the tee junction.

A novel transient hole cleaning algorithm for horizontal wells based on drift-flux model

With the continuous expansion of unconventional and offshore oil and gas fields, horizontal wells have become adopted as an economical and effective mining method. However, the inclined and horizontal sections make them prone to cuttings deposition in the wellbore, leading to the formation of a cuttings bed that adversely affects drilling operations. In this paper, we focus on the features of cuttings transport in the wellbore during drilling and propose a solid-liquid two-phase transient flow model by integrating the flow pattern and drift flux model. The model is discretized using a format based on the finite volume method and solved using a preprocessing method. It enables us to predict the flow parameters, cuttings bed distribution, and cuttings removal time in the wellbore of horizontal wells.To validate the model's effectiveness, we verify it using laboratory experimental data, which demonstrates its prediction accuracy. Furthermore, we use the established model to simulate the damage effect of the cuttings bed on the hole cleaning device during drilling. By comparing the complete return time of cuttings under different working conditions, we quantitatively analyze the hole cleaning device's effect and the backreaming operation's cleaning efficiency. The results indicate that the use of hole cleaning devices during drilling, backreaming, well washing, and other operations in the hole cleaning process can effectively suspend the cuttings deposited in the annulus, allowing them to return to the wellhead more quickly, which enhances the cleaning efficiency of the wellbore and reduces the overall construction time. Furthermore, by comparing and analyzing the effect of drilling flow rate, well cleaning flow rate, cutting particle size, temperature gradient and rate of penetration (ROP) on cuttings return efficiency, it was observed that the drilling flow rate and ROP have minimal impact on the time required for complete cuttings removal during drilling. However, cutting particle size has a significant impact on the effective distance of the hole cleaning tool. Meanwhile, the temperature gradient and the flow rate during the well cleaning has a decisive influence on the time needed for complete cuttings removal.

Experimental study on influence of particle shape on shockwave from collapse of cavitation bubble

The bubble dynamics under the influence of particles is an unavoidable issue in many cavitation applications, with a fundamental aspect being the shockwave affected by particles during bubble collapse. In our experiments, the method of spark-induced bubbles was used, while a high-speed camera and a piezoresistive pressure sensor were utilized to investigate how particle shape affects the evolution of shockwaves. Through the high-speed photography, we found that the presence of the particle altered the consistency of the liquid medium around the bubble, which result in the emitting of water hammer shockwave and implosion shockwave respectively during the collapse of the bubble. This stratification effect was closely related to the bubble-particle relative distance φ and particle shape δ. Specifically, when the bubble-particle relative distance φ < 1.34 e-0.10δ, particles disrupted the medium consistency around the bubbles and led to a nonspherical collapse and the consequent stratification of the shockwave. By measuring the stratified shockwave intensity affected by different particle shapes, we found that the stratified shockwave intensity experienced varying degrees of attenuation. Furthermore, as the particle shape δ increased, the attenuation of the particle on shockwave intensity gradually reduced. These new findings hold significant theoretical implications for elucidating cavitation erosion mechanisms in liquid–solid two-phase flows and applications and prevention strategies in liquid–solid two-phase cavitation fields.

A Review of the Settling Law of Drill Cuttings in Drilling Fluids

During the drilling process, cuttings settle under the action of gravity, which easily results in the formation of a cuttings bed, which then results in wellbore cleaning problems. The settling law of cuttings in drilling fluid is essentially a problem of solid–liquid two-phase settling. This study analyzes and summarizes the effects of the wall effect, the rheology of the fluid, particle shape irregularity, and particle concentration on the settling rate of particles and clarifies the problems faced by current research on the settling rate of particles and the development direction. Studies have shown that walls exert additional blocking effects on particles, thus reducing their settling velocity. The shear thinning effect of non-Newtonian fluids such as power-law fluids and Herschel–Bulkley fluids will reduce the viscosity of the liquid, thus increasing the settling velocity of the particles. Compared with spherical particles, irregular particles will obtain higher resistance in the fluid, leading to a decline in the particle settling velocity. The mutual interference between particles will result in an increase in the drag force on the particles and a decline in the settling velocity. However, when the particles are aggregated, the settling velocity will increase. This study can provide theoretical guidance for predicting the migration law of cuttings during the drilling of horizontal wells, and it has important significance for enriching the theory of solid–liquid two-phase flow.

Research on wear characteristics of U-shaped elbows based on CFD-DEM coupling

The C++ programming language is employed to improve the Computational Fluid Dynamics (CFD)- Discrete Element Method (DEM) coupling interface in this paper, the accuracy of solid-liquid two-phase flow numerical model are validated through experiments. Subsequently, the wear characteristics of the U-shaped elbows under different elbows spacing, bending diameter ratio, particle volume concentration, and particle size are investigated. The research results indicate that as the spacing between bends is increased, the phenomenon of particle sedimentation is intensified, and the maximum collision angle in elbow 2 is increased. The location of the maximum collision angle is closer to the outlet of elbow 2. However, both the collision frequency and wear rate are reduced due to the decrease in the number of particles. Smoother particle flow and a reduction in the collision angle and wear rate of particles on both bends are achieved by increasing the bend ratio. During the variation of the particle volume fraction from 0.5% to 7%, the increase in collision frequency and wear rate of both bends is slowed down. A greater decrease is observed in elbow 2, but the “shielding effect” is not observed. Furthermore, at low volume fractions, kinetic energy is lost by particles as they flow through elbow 1, resulting in a lower average wear rate in elbow 2 compared to elbow 1. Conversely, at high volume fractions, the opposite effect occurs. Finally, when keeping the particle volume fraction constant, an increase in the particle size leads to a smaller wear area in both bends. The wear rate in elbow 1 increases at a slower rate, while the wear rate in elbow 2 exhibits an initial increase followed by a decrease trend.

Numerical study on cylindrical particle solid–liquid two-phase flow in a slurry pump

Numerical study on cylindrical particle solid–liquid two-phase flow in a slurry pump