Bed Of Particles Research Articles

Microrollers flow uphill as granular media

Pour sand into a container and only the grains near the top surface move. The collective motion associated with the translational and rotational energy of the grains in a thin flowing layer is quickly dissipated as friction through multibody interactions. Alternatively, consider what will happen to a bed of particles if one applies a torque to each individual particle. In this paper, we demonstrate an experimental system where torque is applied at the constituent level through a rotating magnetic field in a dense bed of microrollers. The net result is the grains roll uphill, forming a heap with a negative angle of repose. Two different regimes have been identified related to the degree of mobility or fluidisation of the particles in the bulk. Velocimetry of the near surface flowing layer reveals the collective motion of these responsive particles scales in a similar way to flowing bulk granular flows. A simple granular model that includes cohesion accurately predicts the apparent negative coefficient of friction. In contrast to the response of active or responsive particles that mimic thermodynamic principles, this system results in macroscopic collective behavior that has the kinematics of a purely dissipative granular system.

Prediction of effective thermal conductivity of packed beds of polyhedral particles

In packed beds, particle shape influences the heat transfer considering different particle-particle contacts and pore morphology. This paper extends a predictive model for effective thermal conductivity, the Zehner, Bauer and Schlünder (ZBS) model for various shapes. Thus, real structures were studied parallel with numerically generated packings and thermal simulations were performed in FEM solver. ZBS model parameters, porosity, shape factor and interparticle contact area ratio were derived. FEM and ZBS results were compared over a wide range of particle-to-gas conductivity ratios. ZBS model predicted well for lower conductivity particles with the newly introduced sphericity term. In the mid-range of particle conductivity, the results are shape factor sensitive, model predicts well with experimental validation. New correlations were built for ZBS model parameters, extending the model for irregular, non-spherical particles. Prospectively, particle-particle heat transfer coefficients for the discrete element method (DEM) can be derived from the effective thermal conductivity of such particles.

Experimental and numerical investigation of bimodal particle distributions for enhanced thermal conductivity in particle based concentrating solar power applications

Ceramic-based solid particles have recently attracted substantial interest as a thermal transport medium in high-temperature energy storage and thermal energy conversion systems due to their ability to operate at high temperatures (>1000 °C). This is especially useful in the concentrating solar power (CSP) industry where solid particles are utilized as heat transfer and energy storage media. Thermal conductivity of particles in CSP is critically important to the overall heat transfer that occurs within a heat exchanger. A low-cost and effective method to increase the thermal conductivity of a particle bed is by reducing its porosity by employing 2 differently sized particles. This is done in this work by examining several large particle volume fractions for the binary particle mixture of HSP 16/30–40/70. The thermal conductivity can be increased further by applying a load to the particles. At lower temperatures (20 to 300 °C), previous work has demonstrated a binary particle distribution has superior thermal conductivity. In this paper, the thermal conductivities of binary particle distributions under pressure loading are explored at ambient temperatures revealing enhanced thermal conductivity. Furthermore, high temperature (from 300 to 700 °C) analysis of binary particle distributions are also explored with results being that monodispersed distributions yield higher thermal conductivities due to enhanced surface radiation in larger particles. A bimodal distribution increases packed bed thermal conductivity only up to around ∼ 375 °C at which monodisperse distributions with larger particles yield the highest thermal conductivities. These results are compared to existing models (such as the widely used ZBS model) to demonstrate that the current models don’t adequately predict the impact of porosity on thermal conductivity, particularly at higher temperatures where radiation becomes the dominant heat transfer mechanism.

Role of surface morphology in bed particle layer formation on quartz bed particles in fluidized bed combustion of woody biomass

The influence of quartz bed particle surface morphology on the bed particle layer and crack layer formation process in fluidized bed combustion of woody biomass was investigated in this work. Bed material samples were collected at different sampling times from the startup with a fresh bed in industrial scale bubbling fluidized bed (BFB) and circulating fluidized bed (CFB) boilers, both utilizing woody biomass. X-ray microtomography (XMT) and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM/EDS) were employed to characterize bed particle layers and crack layers in the samples. Results showed that there is a noticeable difference between the bed layer characteristics over the so-called “concave” and “convex”-shaped morphologies on the bed particle surface with respect to layer formation. The concave areas are mainly covered with a thin inner layer, whilst the convex display a comparably thick inner layer and an outer layer. In addition, 3D images of the particles revealed that the crack layers mainly originate from concave areas where the particle is less protected by an outer bed particle layer in conjunction with cracks in the inner layer.

Re-concentration of coking middling particles in a liquid-solid fluidized bed: Fluidization characteristics and density segregation

The re-enrichment of coking middling particles is an important way to realize the efficient utilization of coal resources. In this study, by combining numerical simulation and experimental method, the density segregation process and mechanism of coking middling particles in a liquid-solid fluidized bed are studied. The results show that the density segregation process of coking middling particles is mainly divided into the falling outer ring at the sidewall and the rising inner ring. Herein, the ash distribution variance of coking middling particles also shows a changing trend of first increasing and then decreasing with the values increase of operating parameter. Further, after the separation process in the fluidized bed, the cleaned coal product with a yield of 42.77 and an ash content of 8.69% is enriched from 1 to 3 mm coking middling coal (ash content of 28.2%), indicating that coking middling particles are separated efficiently in the liquid-solid fluidized bed.

Study of mixing characteristics of boiler slag in hexagonal cold slag tube

The slag cooler is an important auxiliary machine of the boiler. Taking the high-temperature ash particles in the hexagonal slag cooling tube as the research object, based on the EDEM discrete element method, a particle-particle contact model is established, and the mixing index and difference function are used as the mixing evaluation index, in-depth analysis of the impact of different filling rates on the mixing of high-temperature ash particles. The results show that as the filling rate decreases, the time for ash particles to reach stable mixing becomes shorter, and the time for particles to reach stable mixing under different filling rates is 22 seconds, 28 seconds, and 34 seconds, respectively. The smaller the filling rate, the smaller the fluctuation range of the difference function R and S values, therefore, the better the mixing effect of the particles in the material bed.

CFD Simulation of Air-Glass Beads Fluidized Bed Hydrodynamics

The hydrodynamic behaviour of air-glass beads bubbling fluidized bed reactor containing spherical glass beads is numerically studied, using OpenFoam v7 CFD software. Both Gidaspow and Syamlal-O'Brien drag models are used to calculate momentum exchange coefficients. Simulation predictions of pressure loss, bed expansion rate, and air volume fraction parameters were compared and validated using data, existing in the literature obtained experimentally and performed by other numerical softwares. Pressure loss and rate of bed expansion were calculated with relative root mean square error (RMSE) equal to 0.65 and 0.095 respectively; Syamlal-O'Brien model is considered more accurate than Gidaspow model. Hence, numerical model reliability developed on OpenFoam was also proved. The hydrodynamic aspect study of the fluidized bed reactor was then performed, to analyse the impact of inlet air velocity (U) on particles motion. It was revealed that with U increment, air and glass beads axial velocities increase in the reactor centre and decrease in the sidewalls. Thus, a greater particle bed expansion is induced and the solid particles accumulated highly on the reactor sidewalls. In general, with the increase of U, the solid volume fraction decreases from 0.63 to 0.58 observed at 0.065 m/s and 0.51 m/s, respectively.

Efficient Chimeric Antigen Receptor T-Cell Generation Starting with Leukoreduction System Chambers of Thrombocyte Apheresis Sets

Introduction: Primary human blood cells represent an essential model system to study physiology and disease. However, human blood is a limited resource. During healthy donor plateletpheresis, the leukoreduction system chamber (LRSC) reduces the leukocyte amount within the subsequent platelet concentrate through saturated, fluidized, particle bed filtration technology. Normally, the LRSC is discarded after apheresis is completed. Compared to peripheral blood, LRSC yields 10-fold mononuclear cell concentration. Methods: To explore if those retained leukocytes are attractive for research purposes, we isolated CD3+ T cells from the usually discarded LRSCs via density gradient centrifugation in order to manufacture CD19-targeted chimeric antigen receptor (CAR) T cells. Results: Immunophenotypic characterization revealed viable and normal CD4+ and CD8+ T-cell populations within LRSC, with low CD19+ B cell counts. Magnetic-activated cell sorting (MACS) purified CD3+ T cells were transduced with CD19 CAR-encoding lentiviral self-inactivating vectors using concentrated viral supernatants. Robust CD19 CAR cell surface expression on transduced T cells was confirmed by flow cytometry. CD19 CAR T cells were further enriched through anti-CAR MACS, yielding 80% CAR+ T-cell populations. In vitro CAR T cell expansion to clinically relevant numbers was achieved. To prove functionality, CAR T cells were co-incubated with the human CD19+ B cell precursor leukemia cell line Nalm6. Compared to unmodified T cells, CD19 CAR T cells effectively eradicated Nalm6 cells. Conclusion: Taken together, we can show that lymphocytes isolated from LRSCs of plateletpheresis sets can be efficiently used for the generation of functional CAR T cells for experimental purposes.

High temperature CO2 capture in lithium orthosilicate packed fluidized bed: Gamma ray densitometry based numerical model and its experimental validation

BackgroundLithium orthosilicate (Li4SiO4) is steadily emerging as the default solid sorbent for high temperature CO2 capture in industrial settings. Li4SiO4 is also one the few materials qualified to serve as both catalyst and sorbent in sorption enhanced steam reforming process for high purity carbon neutral H2 production. Application of packed fluidization technique to enhance CO2 uptake in packed bed of pure Li4SiO4 particles has not been reported until now. MethodsGamma ray densitometry (GRD) technique is employed to non-intrusively obtain average voidage of Li4SiO4 packed fluidized bed as a function of operating time and axial bed coordinate. Based on the experimental results of GRD technique, a numerical model is developed to obtain the transient cross-sectional profiles of internal bed temperature and gas phase CO2 concentration as high temperature carbonation of Li4SiO4 progresses in packed fluidized bed. The numerical model is validated using experimentally obtained internal bed temperature and breakthrough curves. Temporal variation of bed effective thermal conductivity has been evaluated from model temperature profiles. FindingsIt was observed that the time averaged effective thermal conductivity and net solid weight gain of packed fluidized bed is around 1.7–2.3 and 1.1–1.3 times that of unary packed bed respectively at specified process parameters for high temperature CO2 capture.

Investigation of SiC formation on the graphite surface by CO-H2-SiO gas

FINEX process, which utilizes hydrogen (H2) as a part of reductants, has emerged as an environmentally sustainable ironmaking process to meet the upcoming carbon-neutral era. In the H2-enriched atmosphere, local slag holdup in the carbonaceous particle bed may increase due to the increased melting temperature of slags by the rapid reduction of iron oxide and the resulting lower wettability of the carbonaceous materials by liquid slag. In-situ SiC formation on the carbon surface gains much attention as a method to reduce the slag holdup. In this study, as a fundamental study, we investigated the SiC formation on the surface of a graphite substrate under a CO-H2-SiO gas environment at 1873 K. It was found that as the partial pressure of H2 increased, the penetration depth of a SiC layer formed on the graphite surface increased, and the surface roughness became enhanced. A reaction rate analysis revealed that the H2-CO gas mixture accelerated the SiC formation on the graphite surface compared to the N2-CO gas mixture. This effect was attributed to the high bimolecular diffusivity of H2-CO. Our results demonstrate that under a CO-H2-SiO gas environment, the fast diffusion of H2 gas through micropores in the graphite significantly enhances the formation of SiC on the graphite surface. The results obtained in this study show that the acceleration of SiC formation under an H2-enriched atmosphere would improve the wettability of molten slag and reduce the slag holdup in the FINEX process.

Enhancing molten tin methane pyrolysis performance for hydrogen and carbon production in a hybrid solar/electric bubbling reactor

Methane pyrolysis in liquid metals is a worth-developing process for CO2-free hydrogen production. This study investigates methane pyrolysis in molten tin and highlights the impact of several parameters on methane conversion (XCH4) in a novel hybrid solar/electric bubbling reactor. Temperature (1200–1300 °C), total inlet gas flow rate (Q0 = 0.25–0.5 NL/min), melt height (Him = 60-120-235 mm) and hybridization are addressed. Increasing the temperature from 1200 °C to 1300 °C (Q0 = 0.25 NL/min and Him = 120 mm) improves XCH4 (32% vs. 69%). Increasing Q0 from 0.25 to 0.5 NL/min (T = 1200 °C and Him = 120 mm) reduces XCH4 (19% vs. 9%). Doubling the melt height (Him from 60 to 120 mm) increases the residence time of bubbles, which increases XCH4 (7% vs. 19%). A customized sparger is also tested and shows little effect, probably because the holes are relatively large (1 mm diameter). An immersed bed of steel particles (0.2–0.4 mm diameter) instead shows improved results (XCH4 = 32%) at a relatively low temperature (1100 °C). Continuous reactor operation at 1300 °C without clogging is also confirmed. Analysis of carbon accumulated at melt surface during molten media methane pyrolysis reveals a tin-containing sheet-like structure.

Characterizing bubble behavior in a pseudo‐2D fluidized bed of wet particles

AbstractBy applying digital image analysis on the bubble characteristics in a two dimensional wet‐particle fluidized‐bed, we report two‐stage evolution of bubble characteristics with increasing liquid content. In the first stage, bubble number and uniformity of bubble fraction increase, while bubble average diameter and aspect ratio decrease. In the second stage, these characteristics shift toward an opposite direction. This two‐stage evolution of bubble characteristics are analogous to that of reducing particle size in dry‐particle fluidization, and the fluidizing properties of particles shifts from Geldart Group B to Group A and then to Group C. Furthermore, liquid addition causes a continuous decrease of bubble fraction and bubble flow rate. This is different from dry‐particle fluidization, in which reducing particle size causes an increase trend. An explanation for this difference is that liquid addition increases the equivalent size of agglomerates in wet‐particle fluidization, which is opposite to the effect of reducing particle size.

Development and combustion characteristics of microwave plasma-assisted fluidized bed combustor

A novel waste treatment method that can efficiently decompose waste, suppress by-product generation, and operate at a low cost is urgently required. Herein, a microwave plasma-assisted combustor was developed and its combustion characteristics were investigated for application in solid waste treatment. The experimental conditions for obtaining good states of fluidization, mixing, and plasma formation were examined prior to the combustion experiments. Subsequently, the optimal experimental conditions, such as the filling amount of bed particles, bed particle diameter, microwave irradiation position, and microwave output, required for good combustion were achieved. Combustion experiments based on these conditions revealed that a good fluidization state is required to obtain a good combustion state in this device, although the combustion condition does not necessarily depend on the system pressure at each O2 flow rate. Comparison of the conditions with similar fluidization states at O2 flow rates of 1–4 L/min revealed a maximum fuel conversion ratio at 4 L/min owing to the combustion promotion caused by increased O2 partial pressure. The fuel did not remain in the fluidized bed combustor after the combustion experiments.

Combustion characteristics of millimeter-sized aluminum particles in fluidized bed

Al is an attractive alternative fuel, but it has very low combustion efficiency because of the dense Al2O3 layer that formed during combustion. This layer blocks O2 diffusion, which hinders Al combustion. To solve this problem, many methods have been adopted, such as nano/μm-sized particles, alloys, additives. But these methods are expensive, complicated and unfeasible for large-scale production. In this study, a method that adopts fluidized bed has been proposed. The fluidized bed has attrition characteristics, which may destroy the oxide layer during combustion. A fluidized bed reactor was used to investigate the combustion characteristics of Al particles. The results indicate that the combustible particle size can increase to 0.5 mm with the help of fluidization, and the combustion efficiency can be increased by about three times. The combustion mode of millimeter-sized Al particles in fluidized bed is layer-by-layer combustion, but the agglomeration still exists and hinders the complete combustion.

Comprehensive study on parabolic trough solar receiver-reactors via a novel efficient optical-thermal-chemical model of catalyst packed bed characteristics

The catalyst packed bed structure plays an important role in the promising solar-driven catalyst packed bed based thermochemical hydrogen production systems. However, corresponding accurate yet efficient numerical methods for characterizing and optimizing the catalyst packed bed structure as well as the whole complex solar-driven thermochemical process is still urgently needed. In this paper, a novel three-dimensional comprehensive model is proposed for the hydrogen production of methanol steam reforming reaction (MSRR) in parabolic trough solar receiver-reactors (PTSRR). A relatively realistic porosity distribution obtained by the discrete element method was combined with the optical-thermal-chemical coupling model. The proposed model was validated, proved to improve the accuracy of numerical predictions in a more efficient way. Moreover, it was effectively applied to tune the overall energy flow of the complex optical-thermal-chemical process of PTSRR-MSRRs for better performance, by optimizing the catalyst packed bed structure in aspects of catalyst sizes and packing methods. The results revealed that single packed beds of larger catalyst particles show better performance within the selected catalyst size range. The radial layered packing method of larger particle-to-particle diameter ratios can bring higher energy conversion efficiency and lower flow resistance, as compared to the single packing method and fully mixed packing method. This study could provide an efficient numerical modelling method and significant guidance for other similar solar-driven thermochemical applications of catalyst packed beds.

CFD-DEM coupled simulation of fluidized beds with improved lumped formulation for heat transfer

PurposeThis paper aims to present a novel approach for computing particle temperatures in simulations coupling computational fluid dynamics (CFD) and discrete element method (DEM) to predict flow and heat transfer in fluidized beds of thermally thick spherical particles.Design/methodology/approachAn improved lumped formulation based on Hermite-type approximations for integrals to relate surface temperature to average temperature and surface heat flux is used to overcome the limitations of classical lumped models. The model is validated through comparisons with analytical solutions for a convectively cooled sphere and experimental data for a fixed particle bed. The coupled CFD-DEM model is then applied to simulate a Geldart D bubbling fluidized bed, comparing the results to those obtained using the classical lumped model.FindingsThe validation cases demonstrate that ignoring internal thermal resistance can significantly impact the temperature in cases where the Biot number is greater than 0.1. The results for the fixed bed case clearly demonstrate that the proposed method yields significantly improved outcomes compared to the classical model. The fluidized bed results show that surface temperature can deviate considerably from the average temperature, underscoring the importance of accurately accounting for surface temperature in convective heat transfer predictions and surface processes.Originality/valueThe proposed approach offers a physically more consistent simulation without imposing a significant increase in computational cost. The improved lumped formulation can be easily and inexpensively integrated into a typical DEM solver workflow to predict heat transfer for spherical particles, with important implications for various industrial applications.

Intruder trajectory tracking in a three-dimensional vibration-driven granular system: Unveiling the mechanism of the Brazil nut effect

We employ a Hall-effect magnetic sensor array to accurately track the trajectory of a single magnetic sphere, referred to as the “intruder,” within a three-dimensional vibro-fluidized granular bed to unravel the underlying physical mechanism governing the motion of the intruder. Within the acceleration range of 3.5 g ≥ Γ ≥ 1.5 g, we find that, regardless of the intruder’s initial position, it consistently reaches the same equilibrium depth when the vibration acceleration (Γ) and frequency (ω) are fixed. For Γ ≤ 2.5 g, the equilibrium position lies on the surface of the granular bed, while for Γ > 2.5 g, it shifts below the surface. Additionally, intruders with different densities exhibit varying equilibrium depths, with higher density resulting in a deeper equilibrium position. To understand the mechanism behind the intruder’s upward or downward motion, we measure its rising or sinking velocities under different vibration parameters. Our findings demonstrate that the rising velocity of the intruder, under varying vibration accelerations (Γ) and frequencies (ω), can be collapsed using the ratio Γ/ω, while the sinking velocity remains unaffected by the vibration strength. This confirms that the upward motion of the larger sphere, associated with the Brazil nut effect, primarily arises from the void-filling mechanism of the bed particles. Furthermore, our experiments reveal that the presence of convection within the bed particles has minimal impact on the motion of the intruder.

An investigation of the aeration proportion effect at the supply and recycle chambers on the optimal operation point of the U-type loop seal and the maximum solid circulation rate in a fluidized bed reactor

A loop seal is used to control a solid circulation rate and loop seal aeration ratios at the supply and recycle chambers are another factor that affects its efficiency and circulating behaviors of solid particles in a fluidized bed reactor. This research aimed to find the proper aeration proportion and operation point of the loop seal that affected the highest solid circulation rate. A riser used in the experiment had a cross-sectional area of 100 × 100 mm2 and 4500 mm height above a distributor plate. A U-type loop seal was constructed by a supply chamber and a recycle chamber with the same cross-sectional area. A horizontal passage of 50 mm length was connected with both chambers. The sand was a bed particle with an average diameter of 320 μm. The loop seal aerations were fed at the bottom of the supply and recycle chambers. It was found that the loop seal could not operate with supply-aeration flow rate percentages (PQS) of 0% and 100%. The PQS of about 73% gave the maximum solid circulation rate and was an optimal operation point at which air supplied at the supply chamber started bypassing into the recycle chamber.

CFD-DEM Simulation of Fast Fluidization of Fine Particles in a Micro Riser

In recent years, the discrete element method (DEM) has gradually been applied to the traditional fluidization simulation of fine particles in a micro fluidized bed (MFB). The application of DEM in the simulating fast fluidization of fine particles in MFB has not yet received attention. This article presents a drag model that relies on the surrounding environment of particles, namely the particle circumstance-dependent drag model or PCDD model. Fast fluidization in an MFB of fine particles is simulated using DEM based on the PCDD model. Simulations indicate that the local structure in an MFB exhibits particle aggregation, which is a natural property of fast fluidization, forming a structure where a continuous dilute phase and dispersed concentrated phase coexist. There exists a strong effect of solid back-mixing in an MFB, leading to relatively low outlet solid flux. The gas back-mixing effect is, however, not so distinct. The axial porosity shows a monotonically increasing distribution with the bed height but does not strictly follow the single exponential distribution. The solid volume fraction at the bottom of the bed is significantly lower than the correlated value in CFB. The axial heterogeneous distribution of the cross-sectional average porosity in the lower half of the bed is also weakened. The radial porosity shows a higher distribution pattern in the central region and a lower one in the sidewall region.

Wet fluidization characterization of potash particles in a pulsation-assisted fluidized bed

In order to improve fluidization behavior, pulsed airflow was employed to break agglomeration and eliminate channeling in a fluidized bed with wet potash particles. The effects of pulsation frequency, pulsed air to continuous flow ratio (r), and inlet relative humidity of the air on bubbling behavior were investigated via an electrical capacitance tomography system. A frequency of 1.0 Hz and an r of 0.33 with 0.1 s opening time were found to be the optimum condition, leading to the lowest minimum fluidization velocity (umf) and generation of homogeneous bubbles in size and shape. A new theoretical model was developed to predict the umf of wet particles in a fluidized bed by considering both the liquid bridge force and resonant force resulting from the pulsation. Average absolute deviation percentage values between the predicted umf and the experimental data were 13.8 and 20.7 for the dry and wet particles, respectively, indicating good agreement.