Solid Flow Research Articles

Integrating a bench scale phosphate flash dryer to a solar heating source: integration challenges and monitoring system development

Aiming to reduce the energetic consumption and greenhouse emissions, integrating the energy-intensive dryer to a solar loop constitutes the optimum solution. This paper investigates the feasibility to integrate a bench scale flash dryer to a solar heating source. Initially, the choice of the best heating source was made and the design was realized. Then, the best configuration of the gas/liquid heat exchanger was selected to design the exchange surface. Finally, the solar flash dryer was mathematically modeled to simulate the dryer performances at various conditions. The parabolic through collectors were selected, with a nominal power of 29kWth, were coupled to a spiral finned tube exchanger with 24 kW capacity. The integration showed a significant dependency of the drying air temperature on the climatic conditions (DNI and incidence angle). The drying tests, realized at the most favorable and unfavorable conditions, showed an important decrease in the moisture fraction to be eliminated, increasing from 1.8% to 3.5% when the air temperature drops from 155 °C to 110 °C. It was hence necessary to develop a regulation system to ensure a continuous solid flow rate.

Deep learning‐based tomographic imaging of ECT for characterizing particle distribution in circulating fluidized bed

AbstractThe gas and solids in a circulating fluidized bed (CFB) are heterogeneously dispersed and a multiscale flow regime may form both in time and space. Accurate measurement of the fluidizing process is significant for investigating the multiscale gas–solid flow characteristics and the design, optimization, and control of CFBs in various applications. This article develops a deep learning‐based tomographic imaging of electrical capacitance tomography (ECT) to characterize the particle concentration distribution in a CFB. The deep tomographic imaging approach is realized through training a well‐designed convolutional neural network (CNN) with the numerically built dataset. Simulation results demonstrate that the average values of the relative image errors reconstructed by CNN in the test set are 0.1110 and 0.1114 for the 60 and 100 mm pipes, respectively, which are better than the average values of 0.1819 and 0.2519 by the Landweber algorithm. With the verification of the trained model based on the prepared data can image the unseen typical flow patterns better than Landweber, it is further used to investigate the particle flow characteristics of a lab‐scale CFB. Experimental results reveal that the developed deep tomographic imaging of ECT can successfully measure the fluidized particle distribution in both the 60 and 100 mm pipes, showing good prediction and generality of the designed CNN model. A flow regime transformation from “annular” flow to “core‐annular” flow and pneumatic conveying is observed under the tested conditions. Besides, the flow regime would be highly affected by the fluidized gas flow rate and the initial bed height.

Investigation of gas-solid flow characteristics in a novel internal fluidized bed combustor by experiment and CPFD simulation

Based on the coal self-preheating combustion technology, this research proposed a novel internal fluidized bed combustor (IFBC) with an internal separator for stable preheating of fuel. In order to verify feasibility and operation stability of IFBC, cold experiment, electrical capacitance tomography (ECT) and computational particle fluid dynamic (CPFD) simulation were performed in a laboratory-scale IFBC. The effects of superficial air velocity (Ug) and return valve structure on the operation and gas-solid flow characteristics were investigated. The results revealed that the CPFD prediction agreed well with the experiment values. The pressure balance curve presented an “8″ shape distribution, and the particle volume fraction (PVF) showed ‘core-annular’ distribution features. With the increase of Ug, the PVF in the standpipe increased, and the discharge pattern of the return valve changed from continuous discharge to intermittent discharge, and the solid circulation flux showed a trend of increasing first and then decreasing. With the decrease of the outlet opening of return valve (Φ), the gas–solid flow behavior in standpipe experienced a transition from gas leakage, stabilizing material seal, and blocking state. For Ug = 2 m/s, Φ = 50 %, an effective solid seal in the return valve was established and IFBC has a stable circulation and operation.

Effect of the novel combined internal devices on gas−solid flow behavior in spouted beds

To reduce the flow dead zone in spouted beds (SBs), a novel multi-jet–axial swirl blade spouted bed (MJ-ASB SB) is proposed. Experimental verification and simulation analyses of the MJ-ASB SB, a conventional SB (CSB), and an integral multi-jet spout-fluidized bed (IMJSFB) were carried out. The simulation results showed that the combined structure resulted in more powerful turbulence, better radial mixing of particles in the spouting and annulus regions, and improved the flow−field uniformity. The intensification factor of the MJ-ASB SB was more than 20%, which was better than that of the IMJSFB, and the enhancement factors of the gas and particle velocities were four and five times those of the IMJSFB, respectively. Optimal structural parameters were obtained by analyzing the different structural parameters of the novel internal devices, and it was found that particle fluidization in the MJ-ASB SB was best when the height ratio ξ was 3, the width ratio was 1.3 and the rotation was clockwise.

Wear Regularity of Shotcrete Conveying Bend Based on CFD-DEM Simulation

To reveal the flow characteristics of shotcrete during pneumatic transportation, the numerical simulation of the gas–solid flow of shotcrete in the pipeline transportation process was carried out based on a CFD-DEM coupling simulation method. When the particle diameter increased from 7 mm to 12 mm, the maximum wear depth of the pipeline increased from 1.48 × 10−6 mm to 4.58 × 10−6 mm. With an increase in particle diameter, the maximum wear depth of the pipeline increased. Moreover, the wear position gradually concentrated to a fixed area with the increase in particle diameter. In the wind speed range of this simulation study, when the wind speed increased from 42 m/s to 52 m/s, the maximum wear depth of the pipeline increased from 2.53 × 10−6 mm to 5.26 × 10−6 mm. The change in wind speed had little effect on the wear location of the pipeline. However, the wear depth of the pipeline increased with the increase in wind speed. When the curvature radius increased from 200 mm to 250 mm, the maximum wear depth decreased from 5.83 × 10−6 mm to 4.47 × 10−6 mm. When the curvature radius increased to 300 mm, the maximum wear depth increased to 6.58 × 10−6 mm. Finally, according to the law of pipeline wear and combined with the actual situation of pipeline wear in engineering, measures were put forward to prevent or reduce the degree of pipeline wear.

Behavior of Gas–Solid Two-Phase Flow in a Backward Facing Step - Effect of Interparticle Collisions

Abstract This article presents a computational investigation of the dilute gas–solid flow's loss coefficient and reattachment length in a horizontally placed backward-facing step. The article's primary objective is to study the effect of the interparticle collision and three significant parameters, namely, inlet solid-phase volume fraction (αs=0.002, 0.005), particle size (dp = 70 μm and 200 μm), and solid-particle density (ρs = 1500 kg/m3 and 3000 kg/m3). The numerical procedure uses the Eulerian–Eulerian approach in conjunction with the Kinetic theory of Granular flow and the four-way coupling approach. The outcomes show that the loss coefficient and the reattachment length increase as the interparticle collision intensifies with the system. Moreover, these parameters show higher values with small particle sizes and higher solid-phase volume fractions. The reattachment length is higher with less dense solid particles and higher with heavier solid particles.

Solid Phase Macromixing Study in a Pilot-Scale Geldart Group B Circulating Fluidized Bed Riser Using Single Particle RTD and RPT Measurements

Solid flow in a Geldart’s group B circulating fluidized bed (CFB) riser is complex, and it exhibits backflow and recirculation in the riser. A single radioactive tracer particle is used to measure the overall and sectional residence time distribution in a CFB riser at a gas velocity of 7.6–9.2 m/s and a solid flux of 100–200 kg/m2s. At the same time, radioactive particle tracking (RPT) data are used to measure the trajectories of the tracer particle and its length distribution at the bottom and middle sections of the riser. Both residence time distribution (RTD) and trajectory length distribution data obtained from RPT and RTD experiments are processed and compared. Results show that the bottom section has higher back mixing than the middle section. The results also show that back mixing in both the sections reduces with an increase in the gas inlet velocity and reduces marginally with an increase in the solid flux. Results confirm that RPT and RTD data are highly correlated and can be used with the same accuracy to quantify the macromixing behavior of any process vessel/reactor.

Fluctuating characteristics of streamwise wind speed and total saltation mass flux in the near-neutral atmospheric surface layer

Eolian sand transport in the atmospheric surface layer (ASL) is a typical kind of gas–solid two-phase flow at a very high Reynolds number that fluctuates over a wide range of spatial and temporal scales. Based on the high-frequency time series of streamwise wind speed (u) and total saltation mass flux (q) measure at three different observation sites, the fluctuating characteristics of u and q in the near-neutral ASL have been analyzed. Our study suggests that the probability density function (PDF) of the normalized streamwise wind speed fluctuations at the height of approximately 0.5 m follows a standard normal distribution, and the PDF of the q presents a lognormal distribution in the near-neutral ASL during strong and steady wind-blown sand. The investigations on the premultiplied spectral of q and u show that, as the energy of very large-scale motions (VLSMs) increases, the influence of the VLSMs on q becomes more significant. In addition, the stochastic couplings between u and q have been analyzed by using space–time correlations and linear coherence spectrum. Our results suggest that the VLSMs have a significant effect on the low-frequency fluctuations of q in the near-neutral ASL.

Review of bubble dynamics on charged liquid–gas flow

When a fluid is subject to an electric field, it usually processes unique features compared to the conventional fluid that arises from coupling between charged particles and fluid interface. Based on this commonality, we defined the concept of “charged multiphase flow” and constructed a generalized charged multiphase flow system using the “Tai Chi Diagram” to analyze the properties and features of different study objects, with an emphasis on the bubble dynamics on the charged liquid–gas flow object, covering the processes of bubble generation, motion, and interaction, as well as the important dynamic behaviors, involved such as bubble deformation, coalescence, and breakup. Furthermore, in light of the special plasma–liquid interface phenomenon formed by the ionization of the gas/vapor phase in the liquid phase in strong electric fields, the traditional gas–liquid–solid three-phase flow system is expanded into a broader range of multiphase flow systems involving plasma, which enriches the theoretical and frontier scientific problems of the multiphase flow. In addition, technical innovations, remaining work, and future trends in the development of the charged liquid–gas flow, and their potential applications are discussed.

Modeling of radiation heat transfer in dense-bed flows of solids in indirectly heated rotary kilns

• modification and implementation of a DOM-radiation model which combines all required physical submodels to simulate heat radiation to dense beds of particles. • Full time and space resolved simulation of thermal conversion of wet moving bulk in a large-scale rotary kiln reactor. • Analytical validation of model and justification with laboratory-scale experiments. • Efficiency optimization of the numerical solver for industrial-scale and long-time simulations on parallel supercomputers. • Parameter studies for large-scale reactors to investigate conversion rate and product quality. This work presents further development and validation of the Discrete Ordinates Model for thermal radiation implemented in OpenFOAM® for application to packed beds of particles. The radiation model is an important part of a more comprehensive model for simulating the thermochemical conversion of the discrete phase (here for instance wet biomass particles). The comprehensive Eulerian-Lagrangian model is part of a three-dimensional, time-resolved simulation of the essential chemical and physical processes occurring within and in-between particles in a moving bed. For the thermal treatment of solid particles, convective and radiative heat transfer couple the energy exchange between the reactor wall, gas- and disperse phase. The original implementation of the finite volume Discrete Ordinate Model (fvDOM) present in OpenFOAM® is valid for a dilute particulate phase and neglects the effect of local opacity due to the existence of individual particles. In the present application, a dense-packed bed of the particulate phase exists in the reactor and, therefore, this direction-based radiation model is adjusted for a computational cell with arbitrary particle volume fractions. To validate the results with the present thermal radiation model, a simple test case is first presented, where a bed of particles is heated from the top of the computational domain. A second test case relates to an experimentally investigated laboratory-scale reactor. The results of the improved fvDOM are compared to the original implementation in OpenFOAM® and the more simple and computationally cheap P-1 radiation model. In the presence of a packed bed, the P-1 model largely overpredicts the radiative heat transfer while the original fvDOM underpredicts the heat flux by about 15 % for the first test case. The new improved model delivers results within 1% deviation at the expense of maximum of 10 % increase in the computational time. Large-scale parallel simulations of real setups are crucial tools to predict the efficiency of a process and improve the operational parameters. To achieve the pre-defined product quality at minimum cost, an example of the implemented radiation model in thermochemical conversion of wet biomass in a rotary drum is been given and the importance of the radiation heat transport to the bulk is highlighted.

Gas–solid flow characteristics of fluidized bed with binary particles

Gas–solid flow characteristics of fluidized bed with binary particles

Estimating the chemical composition of municipal solid waste using the inverse method

This research aims to perform and implement an inverse solution method in waste-to-energy power plants for carrying out solid waste analysis without sampling. For this purpose, a simple simulated experiment is defined to evaluate the stability and accuracy of the method, which is investigated by adding random errors to the results of the direct problem conducted by the Monte Carlo method. The inverse problem solution procedure is solved by obtaining data categories for measuring parameters. In addition, the coefficient matrix is created and the linearization method is employed. By assuming a 0.5 percent nitrogen content in municipal solid waste, the number of unknown parameters is reduced, and the problem is solvable. The regularization method is applied to obtain the stability of the answer. The procedure is done for a municipal solid waste analysis with different regularization parameters. The mean value error and variance of the obtained solution from each analysis are evaluated and the acceptable range for regularization parameters is determined. Also, the identified matrix parameters between 1 and 100 are examined in the constant regularization parameter, and the acceptable parameters are determined. The error in validation by simulated experiment for carbon, oxygen, hydrogen, sulfur, moisture, and ash content of municipal solid waste is 1.47, 3.81, 0.91, 0.22, 7.32, and 1.57 percent, respectively. In the next step, the developed procedure is applied to the Aradkooh waste-to-energy power plant in Tehran, Iran. The operating data are gathered from the power plant, and the municipal solid waste composition is estimated. Results indicate the feasibility of the proposed method, and the municipal solid waste composition and mass flow rate can be predicted indirectly by the flue gas analysis and some other measurements without needing to sample the municipal solid waste. According to the results, the carbon, oxygen, hydrogen, sulfur, moisture, and ash content of municipal solid waste in the Aradkooh power plant is 21.13, 41.96, 5.70, 0.01, 25.06, and 5.63 percent, respectively. Further, the mass flow rate of municipal solid waste and air are 0.53 and 2.5 kg per second. Finally, the sensitivity of the estimated municipal solid waste composition to errors is evaluated by error analysis.

Review of CFD-DEM Modeling of Wet Fluidized Bed Granulation and Coating Processes

Wet fluidized bed granulation and coating processes have been widely used in the pharmaceutical and food industries. The complex gas–solid flow coupled with heat and mass transfer in such processes made it hard to form complete control over the apparatuses. To serve better design, scaling-up, and optimization of granulators and coaters, the underlying micro-scale mechanisms must be clarified. Computational fluid dynamics coupled with the discrete element method (CFD-DEM) provides a useful tool to study in-depth the gas-solid hydrodynamics of the granulation and coating processes. This review firstly introduced the fundamental theory of CFD-DEM from governing equations, force calculation, and coupling schemes. Then the application of CFD-DEM in simulating wet fluidized bed granulation and coating was presented. Specifically, the research focus and the role of CFD-DEM in resolving issues were discussed. Finally, the outlook on the development of CFD-DEM in the context of granulation and coating was given.

Piezoelectric micropump with integrated elastomeric check valves: design, performance characterization and primary application for 3D cell culture.

This paper reports on the study of a piezoelectric actuated micropump with integrated elastomeric check valves that can transport small amounts of fluid in a highly controllable manner. The proposed micropump consists of a piezoelectric actuated fluid chamber with two integrated elastomeric check valves for regulating input and output flow direction, while restricting backflows. The actuation, fluid dynamic response and fluid-structure interactions at various working cycles are studied through a fully coupled multiphysics simulation (solid mechanics, electrostatic and fluid flow). The pump bodies are manufactured by micromachining of PMMA sheets, while the middle elastomeric membrane and diaphragm are fabricated by spin-coating PDMS. The experimental results confirm that the micropump can provide sufficiently low-velocity outflow for biomedical applications between 3.4 - 41.8µl/min. The performance of the micropump is improved significantly through a convenient geometric modification of an off-the-shelf piezoelectric brass disc. Furthermore, the combination of this micropump with the 3D cell-culture microfluidic chip realizes the dynamic culture of cells encapsulated in 3D hydrogels with a continuous flowing medium, which offers the potential for changing the traditional mode of 3D cell culture with a static supply of nutrition and factors.

Charge–velocity correlation transport equations in gas–solid flow with triboelectric effects

This paper is dedicated to the development of particle charge and velocity second-order moment transport equations for monodisperse particles in gas flow with a tribocharging effect. The full transport equations for the particle charge–velocity covariance and the charge variance are derived in the framework of the kinetic theory of granular flow assuming that the electrostatic interaction does not modify the collision dynamics. The collision integrals are solved without presuming the form of the electric part for the particle probability density function. The full second-order transport equation model is tested in a one-dimensional periodic domain. The results show that this model is able to capture more important physical mechanisms that are neglected by simple algebraic models proposed in the past. An in-depth analysis of the transport equations is also performed. This study reveals that, for sufficiently small covariance characteristic destruction time scales, the transient and third-order moments terms can be safely neglected. In addition, two different reduced-order models are proposed: a more general algebraic model that takes into account the variance effect and a semi-algebraic model that only resolves a transport equation for the charge variance coupled with an algebraic model for the covariance. The former could, however, lead to non-physical predictions in many cases, while the latter can be a suitable alternative only for a sufficiently small interparticle collision time. Finally, a simple chart based on test case simulations is proposed to show under which conditions a semi-algebraic model could be considered as a suitable alternative.

Simulation of fully coupled hydro-mechanical behavior based on an analogy between hydraulic fracturing and heat conduction

The hydraulic fracturing process involves complex coupling problems of the deformation and fracturing of solid and fluid flow in fractures. In this paper, a simple numerical tool for simulating the coupled hydro-mechanical behavior is developed by using an analogy between hydraulic fracturing and heat conduction. Using this analogy, the numerical implementation can be simply realized in the framework of a commercial finite element package ABAQUS with two user material subroutines to fully characterize the complex coupling problems of hydraulic fracturing. It is thus considerably simplified without any new development of user-defined element and fluid–solid solver but directly with the commercial finite element package. The proposed numerical tool along with the virtual crack method for elastic–brittle material is firstly verified by the classical 2D plain strain KGD analytical solution and then applied to several representative hydraulic fracturing problems and laboratory tests to illustrate its advantageous features. The present method is aiming to develop a useful numerical tool to study the coupled hydro-mechanical behavior of hydraulic fracturing. However, it is not limited to any specific materials and can be extended to other constitutive models that featured with the fully coupling problems of fluid and solid due to its simplicity.

Study of Flow Patterns in a Moving Bed Reactor for Chemical Looping Combustion Based on Machine Learning Methods

Abstract A tower-type moving bed can be used as the air reactor in a chemical looping combustion system because of its low-pressure drop and smooth operation. In our previous simulation, a quasi-two-dimensional numerical model was established using discrete element method (DEM) approach to investigate the velocity and solid residence time distributions in the moving bed. In this work, the flow patterns under different operating and structural parameters are studied and optimized via machine learning methods. The random Forest regression model is applied to evaluate the importance of each variable to the solid flow pattern, while the feed forward neural network is applied to buildup a high-accuracy model to predict the solid axial velocity in the moving bed without the requirement to understand the physical mechanisms. Results show that the solid mass flux has the least impact on the mass flow index, while the axial position has the dominant influence and what comes next is the wedge angle, reactor angle, and ratio of down-comer diameter to reactor diameter. Further, based on the established feed forward neural network model, relation between the effective transition position and structural parameters of the moving bed is built, which provides valuable guidance for optimization of the reactor configuration.

Analysis on the Quenching Deformation Characteristics of Light Cast Aluminum Alloy Wheels and Their Control Strategies

The purpose of this paper is to develop a new technology for controlling the quenching deformation of light cast aluminum alloy wheels. First, based on the existing wheel heat treatment process, a gas–liquid–solid multi-phase flow coupling model was established through the ANSYS Workbench platform to analyze the gas–liquid phase change, heat exchange on wheel surface and quenching deformation characteristics during the process of wheel immersion into the water. The results show that heat exchange characteristics of the wheel surface are comprehensively affected by wheel structure, quenching fluid flow field and gas–liquid phase transition. There are a lot of non-uniform heat exchange areas in the outer rim, spoke area and center area, which affect the overall deformation characteristics. Affected by spoke structure, the maximum deformation occurs at the outer and inner rim end faces farthest away from the wheel. Based on the above research, this paper independently develops a new deformation control strategy of spray and water immersion composite step process. Through spraying, the influence of spoke structural stiffness on the overall deformation characteristics of the wheel is effectively reduced, and the wheel deformation control is realized by meeting the mechanical properties of the wheel, with the maximum deformation reduction of 39.2%. This study provides a new option for the integrated control of deformation and mechanical properties of aluminum alloy wheels.

Sonographic prediction of intraductal papillary carcinoma with partially cystic breast lesions

BackgroundIntraductal papillary carcinoma (IDPC) is a rare but fatal disease. Preoperative ultrasound diagnosis of IDPC remains challenging and meaningful. The aim of the study was to determine an effective ultrasound model to predict intraductal papillary carcinoma (IDPC) in patients with partially cystic breast lesions on ultrasound.MethodsWe reviewed female patients with breast nodules who underwent biopsy or surgery between 2004 and 2019, and pathological results were used as the reference standard. We finally included 21 IDPC patients with partially cystic lesions on preoperative ultrasound matched to 40 patients with intraductal papilloma. The association of ultrasound features with IDPC was analysed.ResultsPosterior echo enhancement (P < 0.001), tumour size (P = 0.002), irregular shape (P = 0.003), wide base (P = 0.003), solid-mainly component (P = 0.013), rich Doppler flow (P < 0.001) and multiple lesions (P = 0.044) were associated with IDPC by univariate analysis. Based on univariate analysis, variables were included in the regression analysis to obtain independent factors. The regression analysis showed that microcalcification, multiple lesions, posterior echo enhancement, wide base of solid components and rich colour Doppler flow were predictors for IDPC (P < 0.001). The collective model of the independent factors (microcalcification, multiple lesions, posterior echo enhancement, wide base of solid components and rich colour Doppler flow) could predict IDPC with an area under the curve (AUC) of 0.99 (95% CI 0.95–1.00). The collective model had a better net benefit demonstrated by the decision curve.ConclusionUltrasonic features may be an applicable model for predicting IDPC with partially cystic breast lesions on ultrasound and has a better potential to facilitate decision-making preoperatively.

Effect of swirling spouting intensification structure on semi-dry desulfurization process in 3D spouted beds

The swirling blade nozzle structure was introduced at the inlet of flue gas in the spouted bed to enhance interphase mixing and improve the desulfurization efficiency. The computational fluid dynamics (CFD) and experimental methods were used to study the gas–solid two-phase flow, water vaporization and semi-dry flue gas desulfurization processes in a spouted bed with an integral swirling blade nozzle (SB with an ISBN). It is found that the introduction of the swirling blade can significantly intensify heat and mass transfer process in spouted beds, the gas–liquid-solid temperature in the SB with an ISBN is higher than that of the conventional SB. During the desulfurization process, the desulfurization efficiency of spouted bed with an ISBN is about 85.42 %, while that of conventional SB is 76.14 %, and the desulfurization efficiency is increased by 12.2 %.