Solid Flow Research Articles

CFD-DEM study of reactive gas-solid flows with cohesive particles in a high temperature polymerization fluidized bed

The cohesive particles are commonly encountered in high temperature polymerization fluidized bed reactors. However, detailed studies on the effect of cohesiveness on the hydrodynamics, heat transfer, and reaction characteristics in such reactors have been rarely reported. In this work, a CFD-DEM approach coupled with solid bridge force model and polymerization reaction kinetics model is established to simulate the reactive gas–solid flows with cohesive particles. The results demonstrate that cohesive particle agglomeration significantly increases the inhomogeneity of concentration and velocity fields, and hinders particle circulation. The hindered particle circulation further results in pronounced temperature inhomogeneity. Moreover, the local hot spots are readily formed in the agglomerates, which expand and deteriorate rapidly if not controlled promptly. Besides, how the cohesion model parameters, namely contact time and maximum cohesive force limitation, affect the onset temperature and the severity of particle agglomeration is revealed. The established model extends the particle-scale study of cohesive gas–solid flows to reactive systems.

Study on prediction and optimization of gas–solid erosion on S-Zorb reactor distribution plate

Adsorption desulfurization of catalytic gasoline (S Zorb) is an important desulfurization measure that is performed to meet the environmental protection requirements before the final product oil is sold in the market. The desulfurization reactor is a gas–solid two-phase flow environment composed of high-temperature and high-pressure hydrogen-oil mixed gas and sorbent particles; erosion prominently occurs on the reactor distribution plate. This study selects the typical gas–solid two-phase flow conditions and defines the erosion mechanism of the gas–solid two-phase flow environment for the plastic material of E347. Moreover, an S Zorb desulfurization reactor model is constructed, the CFD-DEM model is adopted to predict the wall erosion characteristics in a gas–solid two-phase flow environment, typical erosion laws are obtained via calculations. The erosion laws under the influence of variable parameters are studied based on the orthogonal test, the orthogonal test results show the best parameter combination, the parameter combination yields the maximum erosion rate and high erosion area that are 29.9% and 17.3%, respectively, lower than the existing values. Moreover, an optimum scheme of the inner structure parameters of the reactor is determined for reducing erosion rate and area.

Modification of dispersed systems and its effect of the internal corrosion of hydrotransports

Studies The impact of the modification of dispersed systems of kinematic and dynamic parameters of hydraulic windows, as well as wear in pressure pipes, taking into account the variability of the mechanical composition and the number of hydraulic windows. It is recommended for the modifying additives of the GosIpol resin for dispersed systems and its movements in the cylindrical pipes. The current model that takes into account the concentration of turbidity in the stream and the structural composition of dispersed systems, developed methods of calculation in the process of hydrotransport of modified dispersed systems. The method of calculating the rate of internal corrosion of hydrotransports, specific pressure losses for fluid and solid flow and the effect of variability of the mechanical composition of particles and concentration of turbidity to the flow rate and power of the modified dispersion system is justified, the dependence of the hydraulic friction coefficient from the flow movement mode, taking into account the variability of the solid flow concentration in modified dispersed systems of hydrotransport.

2D multi-phase-field lattice Boltzmann simulations of semi-solid shear deformation

The deformation of solid–liquid coexistence regions strongly affects the formation of solidification defects in casting applications. Thus, understanding the mechanism of semi-solid deformation is crucial. This study used the multi-phase-field lattice Boltzmann model (MPF-LBM), which can simulate polycrystalline solidification with solid motion and liquid flow, to simulate two-dimensional semi-solid shear deformation with various grain shapes and solid fractions. It was concluded that the MPF-LBM could express the characteristic behaviors of semi-solid deformation, such as the Reynolds’ dilatancy and shear band, depending on the grain shape and solid fraction.

A Field High Resolution Measurement Method for Irregular Surface Electrostatic Potential

Characterized by noninvasiveness and high sensitivity, the noncontact electrostatic testing technology has been widely used in scientific research and engineering practices such as electrostatic charge imaging, high-voltage insulator analysis, biological sensing, and gas—solid two-phase flow parameter measurement. However, in many practical applications, scanning electric potential microscope (SEPM) technologies focusing on high spatial resolution cannot meet the testing requirements of charged objects with irregular 3-D structures and flexible activities. Based on the principle of direct inductive electrostatic potential measurement and a six-axis robot arm, a 3-D scanning method for noncontact electrostatic potential measurement is proposed in this article. A low-noise electrostatic potential sensor with both high sensitivity and high accuracy was designed via positive feedback circuit technology. A calibration system was built, which has an adjustable excitation signal, progressive spatial accuracy, and variable 3-D attitude. The experimental data verify the effectiveness of this method. The correlation between the signal characteristics and the physical size of the calibration device was statistically analyzed. The effects of parameters such as the amplitude and frequency of the excitation signal, speed, and normal distance of the robot arm scanning on the resolution of the test results were investigated. The testing results show that the 3-D spatial resolution of dc and low-frequency ac potential distribution reached 200 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> .

Study on Dust Migration Law and Spray Dust Suppression Technology in Fully Mechanized Mining Face

To effectively solve the problem of high dust concentration during coal cutting and frame shifting in fully mechanized mining faces, based on the theory of gas–solid two-phase flow, a geometric model of a fully mechanized mining face was established by using COMSOL numerical simulation software. Simulations were performed for the movement characteristics of wind flow and the law of dust diffusion. Results show that the air flow at the junction of the working face, the air inlet, the hydraulic support moving area, and the vicinity of the shearer has accelerated movement, and the maximum wind speed zone of about 3 m/s can be formed. Under the influence of wind flow, dust particles above 35 μm settle faster, while dust particles below 35 μm are very vulnerable to the influence of wind flow, and the settling speed is slower. Using a custom experimental platform, the atomization characteristics and wind resistance of a pressure fan nozzle, a supersonic nozzle, and an ultrasonic nozzle were tested, and the nozzle that was suitable for the scheme was selected and applied in the field. Comparing the dust concentration before and after the application of the dust removal scheme at the sampling point, results show that the dust removal efficiency of the proposed scheme exceeds 85%, and the treatment effect is good.

Concentration Profile Measurement of Liquid–Solid Two-Phase Horizontal Pipe Flow Using Ultrasound Doppler

Concentration measurement of multiphase flow is essential to flow assurance and monitoring in industrial processes. The concentration profile is a quantitative parameter to diagnose the multiphase flow states and has drawn wide attention from researchers. An ultrasound Doppler technique is adopted to measure the concentration profile of liquid-solid two-phase horizontal pipe flow. A Bayesian inference based on the Differential Evolution Adaptive Metropolis sampling algorithm is proposed to solve the statistical inversion of the concentration profile. The posterior probability distributions of the solid concentration are sampled, and the final concentration profile is chosen with the maximum a posteriori probability. An experimental platform is built for liquid-solid two-phase flow experiments and ultrasound concentration profile measurement. The measured concentration profiles are verified with a maximum mean absolute error of 8.14%.

MANAGEMENT EFFICIENCY FOR CERTAIN TYPES OF PLASTIC WASTE

The issue of segregating plastic waste from the general stream of municipal solid waste and its recycling and disposal is a pressing environmental and socio-economic problem. Given that existing plastic waste recycling facilities in Ukraine are underutilized and partially operate on imported raw materials, the problem of separating and processing certain types of plastic waste from Ukraine's overall solid waste flow is extremely urgent. Plastic wastes are categorized by disposal complexity into three groups: 1.With good properties (clean, sorted, easily disposed of, and up to 90% of similar materials can be used during recycling); 2. With medium properties (containing a certain amount of pollutants, that require sorting, and their processing involves additional costs such as selection, washing, etc., resulting in only 20-30% of their initial quantity being recycled); 3. Difficult-to-dispose wastes (heavily contaminated and mixed, their processing is often not cost-effective). Polyethylene is one of the most common types of plastic wastes in Ukraine, accounting for 34% of all plastic waste. It was discovered that low-pressure or high-density polyethylene is one of the most marketable types of secondary raw materials in Ukraine, making the separation and collection of this type of plastic waste economically beneficial. The aim of the study is to justify the possibilities of extracting and disposing of plastic waste from the flow of municipal solid wastes in specific cities of Ukraine. This has been implemented by the public organization "City of the Future" in partnership with the Odesa State Environmental University.

Analyzing the Tumor-Immune Microenvironment by Flow Cytometry.

Flow cytometry is an essential tool for studying the tumor-immune microenvironment. It allows us to quickly quantify and identify multiple cell types in a heterogeneous sample. This chapter provides an overview of the flow cytometry instrumentation and a discussion of the appropriate considerations and steps in building a reproducible flow cytometry staining panel. We present an updated lymphoid tissue and solid tumor-infiltrating leucocyte flow cytometry staining protocol and an example of flow cytometry data analysis.

Fluid flow and heat transfer in microchannel devices for cooling applications: Experimental and numerical approaches

• Two phase flow in microchannels is characterized by numerical and experimental approaches. • Transition from bubbly flow to slug plug flow is numerically predicted but transition from bubbly flow to churn flow is not. • The proposed numerical tool is sensitive enough to capture particular effects of the studied parameters. Microchannel heat sinks are pointed to have a great potential in cooling systems. This paper presents a systematic study to develop a microchannel heat sink to be used in cooling applications. Particular emphasis is given to PV panels cooling. A systematic experimental approach is used to optimize the heat sink geometry. Then the potential advantage of using flow boiling conditions is explored in both numerical and experimental approaches. The two-phase flow is characterized in two different sets of conditions. In the experimental approach, a constrained bubble flow was observed with a stable pattern and bubble frequency in the narrower channel. In the wider channel a bubbly flow was observed with increased bubble diameters. Numerical simulations were also performed in order to examine the first transient stages of the two-phase flow development close to the inlet of the considered microchannels assuming an initial arbitrary distribution of nucleation sites. For this purpose, a previously developed and validated numerical simulation framework was utilised. The proposed customized tool has been developed in the general context of OpenFOAM CFD Toolbox and it accounts for phase-change (boiling/condensation) as well as for Conjugate Heat Transfer between solid and two-phase flow domains. The numerical predictions reveal that the proposed tool is sensitive enough to capture the effects of channel aspect ratio, applied heat flux and applied mass flux on the generated transient bubble dynamics and the associated heat transfer characteristics and it can constitute an important tool for quantifying the underpinned complex physical mechanisms, providing further insight into the experimental observations and measurements.

Manufacturing of urea co-crystals by spiral gas–solid two-phase flow (S-GSF) based on spiral jet mills: a continuous, solvent-free, and scalable mechanochemical method

A S-GSF method based on spiral jet mills for the continuous, solvent-free, and scalable mechanochemical preparation of four urea co-crystals for the first time.

Data-driven identification of coherent structures in gas–solid system using proper orthogonal decomposition and dynamic mode decomposition

Spatiotemporal coherent structures are critical in quantifying the hydrodynamics of dense gas–solid flows. In this study, two data-driven methods, proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD), are applied to identify and characterize the dominant spatiotemporal coherent structures in a bubbling fluidized bed. It is found that (i) with the same number of modes (or coherent structures), POD captures more defined energy than DMD; (ii) the main coherent structure of POD is symmetric and confirms the existence of bubble-emulsion two-phase structure; (iii) the coherent structures with a frequency of 0 Hz in DMD analysis can construct the mean flow field more reasonably than POD; and (iv) POD reconstructs the transient flow fields more accurately with the same number of modes. This study offers insights into the coherent structures in gas–solid systems.

Velocity distribution and hydrodynamic drag in turbulent flow

This work aims to study the vertical velocity distribution in the near-wall layer of a pipe, channel, and boundary layer of a flat plate because these issues are of great practical and theoretical importance. Until now, engineering calculations of turbulent flows have been based on empirical formulas derived in the last century. The theory of turbulent fluid motion has not been completed, and the issues of velocity distribution and hydraulic resistance remain open for further study. It is known that velocity distribution in the flow is intricately linked to hydraulic resistance. Therefore, the study’s objectives also include determining the position of the point of maximum turbulent tangential stresses and comparing the change in tangential stresses with the logarithmic velocity profile. Based on calculation and analytical methods, we have researched the distribution of the turbulent component of the tangential stress along the depth of the flow. Derived an expression determining the position of the maximum point of the turbulent component of the tangential stress for smooth tubes. The contribution of the viscous component of the tangential stress at different points along the flow depth has been evaluated. The calculation results determining the position of the maximum point of the turbulent component of the tangential stress were compared with experimental data on velocity distribution in the flow. With the decrease of the hydraulic resistance coefficient, the point of maximum turbulent tangential stresses shifts towards the solid flow boundary. Based on the results of comparing the maximum turbulent tangential stresses with the total tangential stress, we can conclude that the contribution of the viscous component of the tangential stress to the total amount of friction and its influence on velocity distribution is significant. The angular coefficient of the velocity profile for the flow core is determined.

Energy analysis of the convective drying of iron ore fines

Drying operations in iron ore processing plants have a particularly high energy demand due to the massive solid flow rates employed in this industry. A 33 full-factorial design was applied to investigate the effects of air temperature, airflow velocity, and solids load on the drying time and the specific energy consumption (SEC) of the convective drying of iron ore fines in a fixed bed. The results demonstrated that each drying air condition was associated with an optimal solids load that minimized the SEC. A load of 73 g (bed height of about 0.8 cm) was identified and validated as the optimal condition in terms of energy consumption for the configuration with the highest air temperature (90?C) and airflow velocity (4.5 m/s). This condition resulted in a drying time of 29.0 s and a corresponding SEC of 12.8 MJ/kg to reduce the moisture from 0.11 kg water/kg dry solids to a target of 0.05 kg water/kg dry solids. Identifying the optimum values for the process variables should assist in designing and operating energy-efficient convective dryers for iron ore fines.

Experimental study of humidity influence on triboelectric charging of particle-laden duct flows

Electrostatic charge on powders arises during pneumatic transport due to particle–particle and particle–surface interactions via triboelectrification. This is a potential threat to the safety of industrial production and the source of numerous fires and dust explosions in the past. Triboelectric charges are affected by environmental conditions, such as ambient temperature and relative humidity. In this work, we experimentally investigated the influence of ambient humidity on the particle charge of gas–solid flows in a square-shaped duct. Monodisperse PMMA particles are fed into a fully developed airflow in a PMMA duct and then pass through a metallic duct section. The charge of particles is measured at the outlet of the metallic duct via a Faraday cup. By measuring the electrostatic charge under various environmental conditions, we observed that the electrostatic charge first increases with the humidity and then decreases when the humidity becomes higher.

Machine Learning and Data-Driven Modeling to Discover the Bed Expansion Ratio Correlation for Gas–Liquid–Solid Three-Phase Flows

Machine Learning and Data-Driven Modeling to Discover the Bed Expansion Ratio Correlation for Gas–Liquid–Solid Three-Phase Flows

Three-dimensional full-loop numerical simulation of coal and sludge co-combustion in a circulating fluidized bed

The Dense Discrete Phase Model (DDPM) method is used to simulate the co-combustion process of coal and sludge over the full-loop circulating fluidized bed in a three-dimensional (3D) Eulerian-Lagrangian framework. Both heterogeneous (fuel conversion through pyrolysis and char combustion) and homogeneous reactions (e.g. volatile combustion) are considered. Comparison of the predicted pressure profile, flue gas composition and bed temperature with measurements show good agreement and validate the DDPM methodology for accurate description of the gas–solid flow and combustion process over the full-loop circulating fluidized bed. The results of coal and sludge co-combustion are analysed qualitatively and quantitatively in terms of flow characteristics, gas composition, reaction rate profile, and particle combustion characteristics. Due to the lower density and higher volatile content of the sludge, as the coal-to-sludge feeding ratio decreases, the combustion reaction rate is gradually skewed upwards in the furnace, shifting up also the corresponding gas concentration profiles. For the given fuel sizes, the faster devolatilization rate of coal yields a shorter burnout time than that of the sludge particles. Our work provides an intuitive perspective to the fluidized bed community to boost comprehension on the coal and sludge co-combustion in a full-loop circulating fluidized bed.

Analysis of gas–solid two-phase flow and structure optimization of mobile shot blasting machine recovery device

To address the problem of low efficiency of recycling process waste by gas–solid two-phase flow of the shot blasting machine recycling device, a method and structure by increasing the negative pressure value and optimizing the outlet pipe position are proposed. Computational fluid dynamics (CFD), discrete element method (DEM) and discrete phase model (DPM) were used to study the waste recovery efficiency at different pressure outlet conditions and outlet pipe locations. The validity of the model was verified by velocity tests at the outlet and inlet compared with simulations. The effect of particle size and particle generation rate on solid particle recovery efficiency was further investigated by analyzing the flow field distribution of the recovery unit. The results show that the maximum velocity of the gas phase in the recovery device increases with the increase of the absolute value of the outlet pressure, when the outlet pressure is -6500 Pa, the maximum velocity is 67.59 m/s. When the absolute value of the outlet pressure is greater than 6000 Pa, a small amount of steel shot particles is discharged from the recovery bin under the action of the outlet pressure, resulting in the loss of steel shot particles. After the outlet pipe position optimization, the steel shot particle recovery efficiency increased by 10% and the waste particle recovery efficiency increased by 18.9%.

On-site and high-resolution spectrophotometric measurement of total dissolved sulfide in natural waters

Reliable high-resolution data is essential for understanding the aquatic sulfur biogeochemical processes. However, the accurate quantification of total dissolved sulfide (TDS) remains challenging due to its low concentration and vulnerability to oxidation. Furthermore, the frequency and the spatial coverage of TDS measurements are constrained by the cost of the laboratory analysis. In this study, an automated portable system was developed for on-site real-time measurement of trace TDS in natural waters. This system was based on the classic methylene blue (MB) spectrophotometric assay combined with on-line solid phase extraction (SPE) and flow injection analysis (FIA). A commercially available weak-cation-exchange cartridge was used as the SPE sorbent. Experimental parameters affecting the performance of the proposed system were optimized. Under the optimized conditions, linear calibration range of 0.02–2.50 μmol L−1 was obtained with a sample loading volume of 5.0 mL and a sample throughput of 12 h−1. The limit of detection could be lowered to 0.003 μmol L−1 by pre-concentrating 10.0 mL sample. The precision, determined as the relative standard deviation (RSD), was <2.75 % (n = 11) and the recoveries from spiked samples ranged from 54.4 % to 97.5 % with RSDs of 1.1–2.3 % (n = 3). Furthermore, the FIA-SPE-MB system was successfully deployed in the Taihu Lake for continuous 48 h monitoring of variations in TDS, demonstrating the applicability of this system for on-site TDS measurement in natural waters.

Numerical investigation on the combustion characteristics of aluminum powder fuel in a supersonic cavity-based combustor

In order to explore the propulsion performance and combustion organization rules of powder fueled scramjets, research on powder fuel combustion characteristics in a supersonic cavity-based combustion chamber is conducted. The numerical simulation method based on the Euler-Lagrange framework for supersonic gas–solid two-phase turbulent flow and combustion is established, and the rationality and accuracy of the adopted method are verified by the comparison with experimental data. The structural feature and flame patterns in the combustion chamber under different air–fuel ratio conditions are compared and analyzed. The influence law of air–fuel ratio on the combustion characteristic of powder fuel is obtained. The results indicate that the powder fuel can achieve stable combustion in the supersonic airflow. The interior of the cavity and the shear layer, near the boundary layer of the expansion section are the main flame distribution areas. With the increase of the air–fuel ratio, the total pressure loss along the combustion chamber gradually decreases. While the combustion efficiency of powder particles exhibits an opposite trend. Overall, it is beneficial to have a lower air–fuel ratio in the supersonic cavity-based combustor.