Solid-liquid Flow Research Articles

Simulation of a macrosegregation benchmark in a cylindrical coordinate system with a meshless method

The main objective of the present paper is to define a new benchmark test for macrosegregation in axisymmetry and to verify a novel meshless method on it. The test case represents a solidification of Al4.5 wt%Cu alloy in two different types of geometries, a solid and a hollow cylinder, cooled at the vertical boundaries. The volume averaging method is used to formulate the coupled mass, energy, momentum, and species transport equations for solid-liquid flow. The lever rule is used for determination of liquid and solid fraction.The meshless numerical approach, verified in this paper, is called the diffuse approximate method. The method is formed by using the weighted least squares approximation, where the second-order polynomial basis and Gaussians are used as trial and weight functions, respectively. The method is localised with the use of subdomains, each containing thirteen computational nodes. The explicit Euler scheme is used to perform the temporal integration. The fractional step method is used to couple the pressure-velocity fields. The stability of the method is attained by an adaptive shift of the computational node and Gaussian weight in the upstream direction.Results are presented for three geometrically different simulations. The results are compared with the classical finite volume method. All results show a very good agreement with the finite volume method. The simulations are performed on a uniform equidistant node arrangements of different node densities and the convergence of the node spacing is evaluated and compared. The results can also be used as a benchmark for other numerical methods.

Numerical simulation and experimental study on eggshell membrane separation device

In order to provide theoretical guidance for separating egg membrane from eggshell by using mechanical agitation, CFD was used to explore the flow characteristics in stirred tank, using the Sliding Grid method to deal with the impeller rotational velocity zone in flow field, and using the Euler model to deal with liquid-solid two-phase flow. This study explored the influence of dish-shape bottom or flat-shape bottom, the clearance size between baffle and the side wall, and the axial height of impeller to bottom on suspension state of particles, solids holdup distribution, solid phase velocity and power number by CFD. Simulation results showed that better particles suspension effect in dish-shape tank can reduce particles accumulation at the bottom and power consumption. If there was a small clearance size (S) between the baffle and the side wall of the stirred tank, it would reduce particles accumulation at the bottom, and reduce the power consumption. However, too large S would decrease the suspension height of particles, not only cannot strengthen the main flow, but also lead to most fluid through clearance forming tangential flow, simulation results showed that S=6 mm was perfect. While decreased axial height of impeller (C) to bottom, particles accumulation at the bottom was decreased, but power consumption would increase, simulation results showed that C=H/5 (H is height of liquid surface) was perfect. According to the simulation results, the structure of the stirring tank was optimized. At the same time, the influences of stirring rotational velocity, stirring time, solid-liquid ratio and separating medium temperature on egg membrane recovery were also studied by experiment, and optimal parameter combination of factors was obtained. The experiment results showed while the stirring time was 17.1 min, stirring rotational velocity was 350 r/min, solid-liquid ratio was 1:17 g/mL, the separating medium temperature was 32°C, the membrane recovery rate can reach above 89%. The device improves the recovery and utilization of discarded eggshell, and provides a reference for the solid-liquid two-phase flow and related study. Keywords: liquid-solid two-phase flow, mechanical stirring, field characteristics, eggshell membrane separation DOI: 10.25165/j.ijabe.20191202.3058 Citation: Chi Y, Wang Y, Li M F, Ren J, Chi Y J. Numerical simulation and experimental study on eggshell membrane separation device. Int J Agric & Biol Eng, 2019; 12(2): 173–183.

Erosion of an Arrow-Type Check Valve Duo to Liquid–Solid Flow Based on Computational Fluid Dynamics

The computational model of an arrow-type check valve coupling with a combined continuous-phase and discrete-phase models has been used to predict the particle erosion of an arrow-type check valve by computational fluid dynamics method and Fluent software. The flow field distribution of liquid–solid flow is captured under various valve opening conditions. The effects of inlet velocity, particle flow rate and particle diameter are discussed, respectively, in detail, which are also captured the particle erosion of an arrow-type check valve under different flow parameters. The results reveal that the valve opening has an important effect on the pressure, velocity and turbulence intensity. However, the changes are not obvious as the valve opening is more than 15 mm. The results also indicate that the small cylinders of an arrow-type check valve are severe erosion, and erosion rate of an arrow-type check valve is most sensitive to the changes in inlet velocity especially when the speed is over 10 m/s. Compared with inlet velocity, the influence of particle flow rate and particle diameter on erosion is weak.

Numerical analysis of liquid-solid flow in tapered and cylindrical fluidized beds for wastewater treatment and biogas production

One of the most promising technologies employed for biological wastewater treatment and biogas production in recent years is the fluidized bed bioreactor, in which microorganisms immobilized on an inert particle surface convert organic effluents to biogases like methane and hydrogen at high rates. In order to ensure an appropriate biofilm thickness, it is important to know the hydrodynamics of these bioreactors. This study is focused on the investigation of the hydrodynamic characteristics of cylindrical and tapered fluidized bed reactors and evaluation of the influence of hydrodynamic variables on biofilm formation using Computational Fluid Dynamics tools. The Eulerian-Eulerian two-phase, transient, turbulent flow model was simulated in a cylindrical fluidized bed and also in 2.5° and 5° tapered fluidized beds, under conditions found in anaerobic fluidized bed bioreactors. Simulations were performed for a wide range of liquid superficial velocities using two-dimensional axisymmetric meshes. Results indicated that the tapered fluidized beds are superior to conventional cylindrical fluidized beds since a more uniform axial distribution was obtained, thereby providing a more stable operation. Better recirculation rates and a more uniform distribution of energy dissipation rate were observed for the 2.5° tapered fluidized bed operating under 7.83 cm/s. These characteristics induce the formation of particles with uniform biofilms. The tapered fluidized bed with a 5° taper angle operating under low superficial velocities provided lower energy dissipation rates, which can result in a lower erosive effect acting on the biofilm, generating thicker biofilms. Results presented in this paper emphasize the importance of using more sophisticated models, which can predict the details of the flow. These models enabled the identification of the geometric and operational conditions that can improve the operation of fluidized bed bioreactors.

Hydrological study and suspended sediment transport in the MACTA: Mekerra watershed (NW Algerian)

The aim of this work is hydrological study and quantification of solid suspended transport in Mekerra basin which is located in the northwest of Algeria, in order to understand and explain the mechanisms of sediment, their causes and their consequences. The quantitative and qualitative analysis of the liquid flows and solid flows measured at this representative basin over a period from 1988-2009 (station: Sidi Bel Abbes) has revealed relations between the solid transport of wadis and their streamflow, in fact average specific degradation is 117 t/km2/year. The relations of the concentrations-liquid flows through the use of hysteresis curves have made it possible to identify the main classes of evolution. The curved shape in eight forms seems to be the most frequent. It reflects instantaneous erosive action and transport of rapidly suspended sediments caused by short showers, violent on generally dry, fragile and poorly protected soils.

A Liquid-Solid Two-phase Flow Computational Fluid Dynamic Modelling of the Operational Characteristics Effects on the Cleaning Time of a Circulating Flow Loop

Flow loops and computational fluid dynamics are the main research approaches for resolving the hole-cleaning problems. Cutting transport phenomena can be considered as a Computational Fluid Dynamic (CFD) model by using Eulerian assumptions for the turbulent liquid-solid flow in concentric annuli. The effect of time along with the main operational characteristics on the hole-cleaning phenomena is not negligible but recent studies have had paid little attention to it. Poor near bit cleaning causes many problems such as bit balling, decline in the rate of penetration, pipe sticking, etc. In addition to the effect of inclination, drill pipe rotary speed, cutting size, nozzle velocity and fluid viscosity as well as the effect of the bit nozzle arrangement on the cutting transport process were discussed. The results demonstrate that at a critical inclination angle of 30 degrees the cutting transport is inefficient. For all sections, the effect of drill pipe rotary speed was negligible at high velocities. In the horizontal section, at low flow rates and high drill pipe rotation speeds, Newtonian viscous fluids or water has no effect on the time needed for initial hole-cleaning butby removing the drill pipe rotation speed in similar conditions, a dramatic influence on time is observed. In inclined annuli, increasing the cuttings size and decreasing the nozzle velocity result in having no cutting in the output. Under critical inclination (30 degrees) the effect of the nozzle angle pattern on the hole-cleaning time is negligible. However, for a vertical annulus, the nozzle angle significantly influences the cutting transport. The best performance is obtained when the nozzle angle was perpendicular to the drill pipe axes. Keywords: Two-phase flow, flow characteristics, CFD, jetting flow.

Experimental Study on Hydraulic Conveying Characteristics by Discharging Plates for Sediment Removal

In the hydraulic transportation of solid-liquid flow in the conduits, the authors have proposed that to place the discharging plates in the flow area is valid to transport particles piled up. In the previous paper, we examined the effects of interval length of discharging plates while the plates were used under the experimental condition that was these plates were not inserted particles bed. However, practically the discharging plates have been used under the circumstance that is these plates are inserted particles bed. Therefore, in this paper, we examined the effects of interval length of discharging plates while the plates were used under the experimental condition that was these plates were inserted particles bed. As a result, it was found that the optimum interval length of discharging plates in current installation depth of the discharging plates. In addition, it was revealed by the visualization of particles behavior that the circumstances of the scouring boundary change by the interval length of discharging plates.

On the numerical simulation of sand transport in liquid and multiphase pipelines

Sand deposition in pipelines represents one of the problems that can arise in oil and natural gas production and transport. The main problems that sand can cause include the pipeline obstruction with the relative production loss, the increase of the lines erosion and corrosion and the compromising of the structural integrity. Moreover, there is a limit in the amount of sand that can be separated and removed. Therefore, methods and strategies to reduce the production of sand are key factors for safety and economic risks. In general sand deposition problems occur in different flow systems such as sand–multiphase mixtures of gas-oil-water or two-phase mixtures. In order to elaborate an effective method able to predict the amount of sand and to have a reliable prediction of sand transport velocity and entrainment processes, several factors requires to be considered, including sand characteristics, sand concentration, flow regimes, fluid properties and pipe properties.This paper presents the results of a detailed testing on the performance of a new sand transport model implemented in one-dimensional dynamic multiphase code, performed by comparing numerical results with experimental data. This study deals with both liquid-solid flow as well as gas-liquid-solid flow. The results demonstrate a good agreement between numerical and experimental data for the sand-liquid flow and sand transport in stratified gas-liquid flow, while show that for the sand transport in gas-liquid slug flow improvements are necessary.

Mechanistic analysis of solid–liquid flow during injection

Direct injection of retinal cells into patients’ eyes is a new and improved therapeutic method to address cataracts, but one challenge is that the survival rate of cells during injection is very low. To solve this problem, in this study, the force distribution on retinal cells in injectors with two needle shapes was analysed by coupling the discrete element method with computational fluid dynamics and implementation of an immersed boundary method. Two injectors were considered: one with a straight needle and the other with a curved needle. The velocities of retinal cells in the injector with a straight needle were slightly higher than those in the injector with a curved needle. In addition, injection speed greatly affected the force distribution on retinal cells, with the retinal cells near the piston subjected to the highest forces during injection. The forces on retinal cells strengthened with increases in both retinal cell concentration and piston displacement.

Numerical study on liquid-solid flow characteristics in inverse circulating fluidized beds

The flow behavior of particles in inverse liquid-solid circulating fluidized beds was simulated using the Eulerian-Eulerian approach incorporating the kinetic theory of granular flow. The Syamlal-O’Brien drag model was used to account for the interphase interaction between the liquid and solids phases. A detailed description of the model equations used in this work has been presented. Predicted results were compared with the experimental data obtained by other group members. A good agreement between the numerical simulations and experimental results has been achieved. The inverse flow characteristics of particles were studied using a single type of particles and multiple types of particles with different densities under different liquid velocities and solids flow rates. The results indicated that for the particles with different densities, 950 kg/m3, 850 kg/m3 and 640 kg/m3, the cross-sectional average solids holdup along the axis was uniform and the radial flow structures at different bed heights were identical. Particles moved from the walls to the center at the top region of the bed. Such tendency diminished as the particles move downwards. The axial velocities of solid particles were higher in the center and lower near the walls. For the particles with a density of 28 kg/m3, due to the randomly generated vortexes of particles, the solids holdup radial distributions and the velocities of particles were more irregular. For the mixed particles with two different densities of 850 kg/m3 and 950 kg/m3, the trend of solids holdup radial distribution, and the trend of the lateral and axial velocities of each particle group were similar to those in the simulation using the single-density particles.

Influence of inclined plates on flow characteristics of a liquid-solid fluidised bed: A CFD-DEM study

An in-depth analysis of liquid-solid flow characteristics of a modified fluidised bed equipped with inclined channels has been conducted using a coupled model of computational fluid dynamics (CFD)-discrete element method (DEM). Specifically, the simulation results have provided local information on the two phase flow characteristics of the modified fluidised bed including solid distribution, particle velocity distribution and energy dissipation rate of the liquid flow. It is shown that the strong reflux of sediments from the inclined channel into the bottom vertical section induced intensive circulations of both solid particles and the liquid phase. As a result, solid distribution over the entire bed became more non-uniform as the fluidisation velocity increased. Moreover, the subsequent impingement of the liquid-solid flow onto channel walls resulted in a much higher energy dissipation rate of the liquid flow, indicating a higher energy loss when compared to conventional fluidised beds. Also, an optimum fluidisation velocity was identified at which the solid concentration of the sediment layer reached its peak. It was shown that smaller inclination angle led to lower bed expansions and greater solid reflux, resulting in stronger two-phase flow circulations in the vertical section. For fluidised beds with multiple inclined channels, the particle flow characteristics in individual inclined channels were observed to be rather similar with smaller overall particle velocities and more compact sediments. The predicted results of the CFD-DEM model were found to be in good agreement with the experimental data and those predicted by our kinematic model, with a maximum deviation of 12%. The CFD-DEM model presented here can be utilised to optimise the design and operation of liquid fluidised beds containing inclined channels.

Comparison of liquid-solid flow characteristics in upward and downward circulating fluidized beds by CFD approach

The flow behaviors of the particles in the upward and downward liquid-solid circulating fluidized beds were simulated by Eulerian-Eulerian approach incorporating the kinetic theory of granular flow. The Syamlal-O’Brien drag model was used to account for the interphase interaction between the liquid and solids phases. The numerical results agreed well with the experimental data obtained by other group members, successfully validating the numerical approach. The hydrodynamic characteristics of the particles with different densities and sizes in the upward and downward circulating fluidized beds were compared in detail under different liquid velocities and solids flow rates. The results indicated that there were many hydrodynamic similarities in the upward and downward circulating fluidized beds. However, due to the deviation of the standard drag curve, the drag force on the lighter particles in the downward liquid-solid circulating fluidized bed became different, leading to random and irregular particle flow behaviors. The predicted average solids holdups matched well with the results by an empirical model proposed by Sang and Zhu and the matching degree between the numerical results and the model was larger than 85%, further proving that the Sang and Zhu model is widely applicable.

Numerical Analysis of Solid-Liquid Two-Phase Abrasive Flow in Microcutting Polycrystalline Materials Based on Molecular Dynamics

Abrasive flow polishing plays an important role as a type of precision nanomachining technology. In this study, the polishing mechanism of abrasive flow was studied using numerical simulations based on molecular dynamics. In order to study the polishing mechanism of polycrystalline materials, the molecular dynamics simulation of three kinds of polycrystalline materials was carried out. The cutting force, energy, friction coefficient, and surface morphology (during the microcutting process) of the three workpiece materials were analyzed. The analysis shows that the adhesion of atoms in the contact area on the workpiece surface will be affected by liquid phase and the type of abrasive particles, and then the surface quality polished by the abrasive flow will also be influenced. The onset of an abrasive flow polishing process involving plastic deformation (including the nucleation and migration of dislocations, grain boundary shape deformation, and deformation twinning) was observed on the workpiece surface. Defects strongly competed with each other in the form of interactions of dislocations and the grain boundaries, resulting in the migration of twin boundaries. A further analysis of the numerical results for different cutting depths and abrasive properties of the workpiece materials will be useful for understanding the different cutting effects.

Three-dimensional Eulerian modeling of gas–liquid–solid flow with gas hydrate dissociation in a vertical pipe

The pipe transportation of gas hydrate-bearing sediments (GHBS)1GHBS—gas hydrate-bearing sediments;1 is one of the key problems in mechanical–thermal exploitation of gas hydrate (GH)2GH—gas hydrate.2 in marine stratum. It is a gas–liquid–solid (methane gas–seawater–GHBS particles) three-phase flow, accompanied by GH dissociation. In this study, a three-dimensional Eulerian model combined with the kinetic theory of granular flow (KTGF) was adopted to simulate the gas–liquid–solid flow with GH dissociation. The commercial CFD software FLUENT 16.2 was employed, considering the hydrodynamics, heat and mass transfer, and GH dissociation simultaneously. A kinetic model for GH dissociation in the GHBS particles is presented, considering the influence of multiphase flow on dissociation rate. The model can capture the transition from the initial liquid–solid two-phase flow to gas–liquid–solid three-phase flow, describing the distribution of the phase volume fraction, velocity, temperature, and dissociation rate. The interaction between GH dissociation and multiphase flow is discussed. The simulation results indicate that the continuous production of gas bubbles by GH dissociation leads to more violent fluctuations in the pressure gradient and a more marked elevation of the solid particles compared with the liquid–solid two-phase flow without GH dissociation. In addition, the effect of GH dissociation on the multiphase flow under different hydrate saturations was analyzed.

Three-dimensional numerical and experimental investigation of the behavior of solar salts within thermal storage devices during phase change

Experiments and three-dimensional computational simulations of melting and solidifying solar salts in an aluminum container are performed in order to obtain a fuller picture of the thermal and flow behavior of this commonly-used phase change material. A heating element is placed under a closed aluminum container filled with solar salts, both with and without aluminum fins. Accurate simulations are performed in part by identifying thermal properties that lead to the accurate reproduction of experimental results; the thermal properties of the solar salts are found to differ significantly from values in the literature. The numerical results are then used to describe the dynamics of the solid-liquid front and flow patterns within the container during melting and solidification. The combined experimental and computational results provide insight into the thermal, flow, and melt behavior of solar salts. The experimentally validated simulation capability can be used for the design of efficient thermal storage devices using solar salts.

Numerical analysis on mixing performance of logarithmic spiral impeller

Mixing performance of the solid-liquid two phase system in a mixing tank equipped with a logarithmic spiral impeller is studied with fluid dynamics software FLUENT. Based on the kinetic theory of granular flow, the basic control equations of the E-E model are established. A multiple reference frame (MRF) method and the RNG k-ε turbulence model are chosen to simulate solid-liquid flow performance and results are compared with that of the four blade turbine (MK) and the six blade turbine (PY). Research shows that the logarithmic helicoidal impeller improves solid-liquid axial-flow performance, and the concentration, power consumption and the mixing time of it are better compared with the PY and MK impellers. For a wide range of mixing velocities, the concentration of the sludge particles is always lower in the upper position to impeller than in the lower position. With the increase of velocity, the power consumption raises gradually, the uniformity of solid particle distribution decreases and the mixing time reduces.

Erosion-corrosion behavior and electrochemical performance of Hastelloy C22 coatings under impingement

The erosion-corrosion behavior of Hastelloy C22 coating prepared by multilayer laser cladding technology is investigated under impingement by solid-liquid flow. Three external factors are taken into consideration including fluid flow velocity, impact angle and erosion time. The total weight loss and corrosion current density increase with the increase in flow velocity. But the passive current density reduces when velocity is over 4 m/s. The combination effect of shear and normal stress leads to the maximum of total weight loss at 60°, but electrochemical measurements show lowest corrosion resistance at 30° due to dominant shear stress and highest value at 60° because of stronger protection of passive film. As expected, both weight loss and corrosion rate increase with erosion time extending. The microhardness of coating surface increases after impingement. The impact of solid particles on surface produces typical craters with different shapes and sizes. The low annual corrosion rate of Hastelloy C22 coating shows the efficacity of multilayer laser cladding technology.

Numerical simulation of hydrate slurry flow behavior in oil-water systems based on hydrate agglomeration modelling

Hydrate agglomeration in oil-water systems could lead to pipeline hydrate plugging. Dynamic modeling of pipeline hydrate particle agglomeration is of great importance to hydrate management. For this purpose, a dynamic model of hydrate agglomeration was established based on population balance equation, which took both hydrate agglomeration and hydrate breakage into consideration. The calculation methods of collision frequency, agglomeration efficiency, breakage frequency and particle size distribution function of the sub particles resulting from particle breakage were given and fully discussed in the dynamic model. Then, combined with several traditional solid-liquid flow models, the dynamic model was solved by the CFD software FLUENT 14.5 to simulate the influences of flow rate and hydrate volume fraction on pipeline hydrate slurry flow behavior in oil-water systems. The simulation results show that hydrate particle size distribution in pipeline flowing systems can be well described by log-normal distribution. Hydrate particle diameters and hydrate volume concentrations in the near wall region are larger than that in the center region of the pipeline. The proportion of large hydrate particles and the mean hydrate particle diameter in pipeline increase with the increase of flow rate and hydrate volume fraction. Hydrate particle diameter and pressure gradient in oil-water systems are larger than that in water systems.

Simulations of dense agitated solid–liquid suspensions – Effects of the distribution of particle sizes

We perform Eulerian-Lagrangian simulations of solid-liquid flow in a mixing tank. The simulations are three-dimensional and time dependent and in the transitional flow regime. The lattice-Boltzmann method is used to solve the volume-averaged Navier-Stokes equations. The overall solids volume fraction is of the order of 10%. Situations with the solids only partly suspended are compared to those with fully suspended solids. The emphasis is on the effect of the particle size distribution (PSD) on the suspension behavior. Four PSD’s all having the same d32 were investigated. It is harder to fully suspend particles with wider size distribution as compared to narrow distributions.

Simulation of solid-liquid flows in a stirred bead mill based on computational fluid dynamics (CFD)

The selection of simulation model is an important step in computational fluid dynamics (CFD) to obtain an agreement with experimental work. In addition, computational time and processor speed also influence the performance of the simulation results. Here, we report the simulation of solid-liquid flow in a bead mill using Eulerian model. Multiple Reference Frame (MRF) was also used to model the interaction between moving (shaft and disk) and stationary (chamber exclude shaft and disk) zones. Bead mill dimension was based on the experimental work of Yamada and Sakai (2013). The effect of shaft rotation speed of 1200 and 1800 rpm on the particle distribution and the flow field was discussed. For rotation speed of 1200 rpm, the particles spread evenly throughout the bead mill chamber. On the other hand, for the rotation speed of 1800 rpm, the particles tend to be thrown to the near wall region resulting in the dead zone and found no particle in the center region. The selected model agreed well to the experimental data with average discrepancies less than 10%. Furthermore, the simulation was run without excessive computational cost.