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A gas–solid circulating fluidized bed heat exchanger is designed and built to investigate the particle collision behavior and heat transfer performance under different operating parameters, such as air flow rate, heat flux, and particle type. Air, Polyoxymethylene (POM) and three sizes of glass beads (GB) are selected as working media. Time-domain and frequency-domain analyses are conducted for the collision acceleration signals. The results show that adding solid particles can enhance heat transfer and increase pressure drop of system. The heat transfer enhancing factor reaches up to 33.4%, and the maximum pressure drop ratio is no more than 15.7%. The frequency distribution range of pure gas phase collisions is 0–1000 Hz, and the solid phase plays a dominant role in the collision of gas–solid two-phase flow, distributed between 2000 and 25,000 Hz. The signal power increases with the increase in air flow rate. The heat transfer enhancing factor of POM particles decreases with the increase in air flow rate, but those of GB particles first increases and then decreases. The signal power of POM particles is generally greater than those of GB particles. The heat transfer enhancing factor of POM particles is obviously higher than those of GB particles, especially at low air flow rate. The pressure drop ratio fluctuates with the increase in air flow rate, and generally increases with the increase in heat flux. The drop ratio of the POM particles is higher than those of the GB particles. [Display omitted] • Circulating fluidized bed technology is applied to gas-phase heat transfer process. • Particle collision behavior and heat transfer performance are investigated. • Effects of air flow rate, heat flux and particle type are discussed. • Signal power generally increases with the increase in air flow rate and particle size. • Adding solid particles can enhance heat transfer and increase pressure drop. [ABSTRACT FROM AUTHOR]

Gas-solid two-phase flow characteristics in a 90° bend within a pneumatic conveying system are critical for design and performance optimization, impacting conveying efficiency and system safety. Electrical Capacitance Volumetric Tomography (ECVT) and Computational Fluid Dynamics (CFD) simulations were employed in this study to investigate the flow characteristics in the bend. The ECVT system for bends was validated through static tests. A setup with a 36 mm inner diameter was constructed for high-speed 3D imaging of 0.9 mm quartz particles. Flow patterns, solid-phase concentration, particle velocity spectra, and mass flow rate were analyzed under various gas velocities. The Euler-Lagrange method and SST K-ω model were used to simulate particle flow and pipe wall erosion numerically. Results indicate diverse flow patterns across different gas velocities, where moderate turbulence enhances efficiency and limits erosion. This study offers an experimental basis for predicting and controlling particle motion, providing scientific guidance for optimizing pneumatic systems. [Display omitted] • 3D imaging of a 90° bend was achieved using a 32-electrode ECVT sensor. • Solid concentration, particle velocity, and mass flow rate were analyzed. • Turbulence effect of particle flow in a 90° bend was investigated experimentally. • Euler-Lagrange and SST K-ω models validated experiments and assessed wall erosion. [ABSTRACT FROM AUTHOR]

This study was conducted for parameter sensitivity analysis of an eco-friendly fire-fighting device, the sand-ejecting fire extinguisher, by means of experiments and CFD-DEM coupling simulations. The paper presents a total of nine impeller design schemes. Simulations were carried out to reproduce the sand ejection process with each scheme. The results show that the gas flow field has an effect on the ejection process under the windless environment, so the sand ejection characteristic analyses are based on DEM calculations. The phenomenon that a greater number of blades could provide longer ejection distance is also found in the simulation process. Radial and forward schemes may be more suitable for gas-station fires while backward schemes not because of the sand accumulation character. The CFD-DEM calculation shows that increasing the sand mass flow could extend the ejection distance but is more susceptible to ambient wind. [Display omitted] • Gas phase has a little effect on the simulation results in windless environment. • A greater number of blades, a longer ejection distance. • Increasing the sand mass flow could extent the ejection distance. [ABSTRACT FROM AUTHOR]

In the process of particle–fluid flow, solid particles are easily deposited in pipes, which leads to collisions and abrasion, especially in pipelines with grooves. Therefore, some structural components are always designed above the groove to improve particle trajectories inside the groove in the pipeline. In the present study, the deposition of particles was analyzed in detail by means of experimental visualization, and Computational Fluid Dynamics and Discrete Element Method model (CFD-DEM) methods were used to investigate the motion and deposition of particles when both grooves and baffles are designed in the pipeline system. Finally, the effect of the baffle width on the deposition of particles in the groove was studied. The results show that the baffle width has a slight effect on the mass of particles deposited in the groove after the number of particles there stabilizes, but when the width of baffle is the same as that of the groove, the time it takes the particles to reach this stable state is shortest. [Display omitted] • Particle deposition in the pipe from particle–fluid flow was analyzed in detail. • CFD-DEM method was used to study gas–particle flow and particle deposition. • Motion characteristics of particles were analyzed. • Baffle affects the characteristics of particle motion in the pipe with grooves. [ABSTRACT FROM AUTHOR]

Gas–solid two-phase flow and water vaporization processes tend to have a significant impact on the efficiency of flue gas desulfurization with a powder-particle spouted bed. According to the numerical results obtained in this study, the 2D spouted bed developed a classic three-area flow, and the 3D spouted bed entered into a bubbling-like state. The gas and particles flowed in the opposite direction at the junction of the cone and cylinder. The water vaporization rate was higher at the junction of the spout area and the annulus area, lower at the center of the spout area, and the lowest in the annulus area of the 3D spouted bed. Furthermore, it was found that a larger gas velocity, a higher liquid temperature, and a lower gas humidity leads to a higher water vaporization process. [Display omitted] • CFD completed the simulation of water vaporization process in a three-dimensional PPSB. • The main area where water vaporization occurs was the junction between the injection area and the annulus area. • In-depth study of the effect of operating parameters on the rate of water vaporization. [ABSTRACT FROM AUTHOR]

Erosion has been recognized as one of the major threats for industries involving multiphase transportation pipelines. Within the last decades, effective parameters on wear pattern have been identified. As a result, the (famous) V-shaped erosion profile has been detected for the pipes' elbow section. In this study, CFD is employed to investigate the erosion mechanism on the square duct elbows. A novel erosion pattern has been observed for square ducts in comparison with the pipes. The impact of several parameters (particle and flow velocity, secondary flow, turbulent intensity, particle streamline) has been inspected as well. It has been led to the conclusion that the erosion rate of square ducts is lower than common pipes, especially when either higher flow velocities or bigger particles size are employed. Unlabelled Image • Observation of novel ER pattern (none-uniform and uniform velvet) for square ducts • Fully interpretation of ER pattern only from the force behavior on particle • Identification of reason between different ER profiles in square and circular ducts • Investigation of effective parameters on ER pattern in all test cases [ABSTRACT FROM AUTHOR]

The measurement signal from the inner flush-mounted electrostatic sensor includes both induced charge signal and transferred charge signal. The extraction of induced charge signal from the mixed signals is of great significance to the solid phase velocity measurement. In this paper, a method of extracting induced charge signal based on the waveform characteristic in time domain is proposed. In the calibration experiment of the belt-style electrostatic velocity measurement rig, the mean absolute percentage error and the mean relative standard deviation (1.30%/1.01%) are lower than the direct cross-correlation method (4.81%/5.71%) and the Empirical Mode Decomposition (EMD-based) method (2.55%/2.38%), moreover, the average signal-to-noise ratio (SNR) of the proposed method is the greatest. In the experiment of gas-solid two-phase flow rig, the average correlation coefficient and the mean relative standard deviation are 0.77 and 2.46%, which are better than the direct cross-correlation (0.48/2.87%) and the Discrete Wavelet Transform (DWT) (0.74/2.69%). Unlabelled Image • A new method of extracting electrostatic induced charge signal is proposed. • The time domain characteristic of induced charge signal is utilized. • Correlation coefficient of autocorrelation function is better at screening the IMF. • The proposed method improves the quality of particle velocity measurement. [ABSTRACT FROM AUTHOR]

The ventilations of pressure cylinders is a widely used practice in coal mine roadways in China. It has been determined that the velocities of the ventilations will directly affect the diffusion of the dust particles which reduce the visibility of road-header drivers, and also tend to slowdown operating efficiency. In this study, a CFD-DPM method was adopted in order to examine the airflow flow and dust pollution behaviors in coal mine roadways under various ventilation velocities. The results showed that airflow fields could be divided into disordered regions of airflow flow fast and chaos; recirculation regions, where there were dust backflow; and stable regions, from the heading faces to the exits of the coal mine roadways. The airflow were observed to carry the dust particles along the roadway wall away from the pressure cylinders from the disordered regions into the recirculation regions due to the blocks caused by the road-headers. It was observed that the dust migration had slowed down in the areas behind the road-headers due to the sudden decreases in the airflow velocities. Then, major amounts of dust particles were carried by airflow into the stable regions. The remaining dust was carried to the exits of the pressure cylinders as a result of the dust backflow. As a result, areas of approximately 5 m behind of the road-headers, as well as the areas near the exits of the pressure cylinders, contained high dust concentrations. The dust concentrations near the exits of the pressure cylinders into which the dust particles had been attracted due to the strong entrainment effects, were found to increase with increasing of the ventilation velocities. However, this had only occurred when ventilation velocities had exceeded 17 m/s. Image 1 • Dust dispersions under different ventilation velocities were studied. • Turbulent regions, backflow regions and stable regions. • There was airflow and dust refluxing from the behind the road-header. • High dust area existed when ventilation velocities exceeded 17 m/s. [ABSTRACT FROM AUTHOR]

In-line measurement of the mass flow rate of solids in pneumatic conveying pipelines is essential for the efficient and optimized operation of many industrial processes. This paper presents a comparative study of using induced and transferred charges from non-intrusive electrodes exposed to the particle flow for mass flow rate measurement. A novel signal conditioning circuit, which consists of a current sense amplifier and a charge amplifier, is designed to convert the induced and transferred charges into two separate voltage signals. Empirical measurement models that relate the particle velocity, the root-mean-square (r.m.s) magnitude of the induced charge signal and the slope of the transferred charge signal to the mass flow rate are proposed. Experiments were undertaken using electrodes of different widths and under different mass flow rate and particle velocity conditions. Results obtained show that both the r.m.s magnitude of the induced charge signal and the slope of the transferred charge signal increase with the mass flow rate and the velocity of particles. In general, the measurement results using the induced and transferred charges from either the narrow or the wide electrode are similar. However, the method based on the transferred charge is less reliable due to confined sensing area and electrode charging by particles adhered to the electrode surface. Unlabelled Image • The induced and transferred charges from electrostatic electrodes are measured. • Models are established for solids' mass flow rate measurement using both charges. • The relative errors using both charges from narrow or wide electrodes are similar. • Measurement based on the transferred charge is less reliable. [ABSTRACT FROM AUTHOR]

Abstract In order to study the hydrodynamics characteristics of gas-solid two-phase flow in the two-stage series riser, a filtered two-fluid model considering filter size, filtered solids volume fraction and slip velocity is used. Comparing to simulated results from different drag models including the filtered model, Gidaspow model and Wen-Yu model, the results from the filtered model are in better agreement with the experimental data of Zhu et al. Also, the details comparison of flow behaviors of particles between the two-stage series riser and typical riser are conducted. The enlarged section in the bottom for a two-stage series riser can strengthen the back-mixing of particles and gas-solid interaction. Simulation results reveal that the solids volume fraction displays the typical S-type distribution with an increase of solids mass rate, but the gap is declined along the bed height. The distributions of solids volume fraction, axial velocity and residence time are investigated by analyzing the simulated results at the different geometry of enlarged zone at the bottom of a two-stage series riser. Graphical abstract Unlabelled Image Highlights • Flow behavior of particles is simulated using the filtered model. • The impact of different drag models on simulated results is tested. • By changing the geometry of the first zone, the distribution of particles is obtained. • The effect of solids mass rate on flow behavior of particles is analyzed. [ABSTRACT FROM AUTHOR]

Abstract It is known that high-concentrations of dust threaten the health of road-header drivers in fully mechanized excavation faces. The regulation of the gas-solid two-phase flow in fully mechanized excavation faces is a key scientific issue for dust prevention and treatment. In this research study, a real fully mechanized excavation face was taken as the physical model. Then, a CFD-DPM method was adopted to model the gas-particle two-phase flow around a driver in a mine roadway. The results showed that there were two counter directional airflow paths on the heading face which formed three vortices, the centers of which were located in the front left, left and middle sections of the road-header, respectively, in the fully mechanized excavation face. The driver was located at the intersection of the three airflow paths. For example, the position of the driver was within the vortices from the left, front-right and rear of the road-header, respectively. The aforementioned airflows carried dust to the space around the driver through three path types including from the heading face, along the roadway floor left of the road-header, and by refluxing from the rear of the road-header. The dust concentration in front of the driver was observed to increase with a fluctuating growth trend. Also, the dust concentraion to the rear of the driver displayed stepped increases. Finally, the dust concentration which had refluxed from the rear of the driver was determined to be highest and was observed to be three times higher than the dust concentration which originated from the heading face. This study's simulation results were verified by the results of the field measurements. Graphical abstract Unlabelled Image Highlights • Gas-particle two-phase flow model of an excavation face was established. • Dust distribution around road-header drivers in an excavation face was studied. • The driver was located at the intersection of the three airflow paths. • There was dust refluxing from the rear of the road-header. • Dust concentration refluxed from driver rear was determined to be highest. [ABSTRACT FROM AUTHOR]

Directed energy deposition (DED) offers an unprecedentedly convenient and efficient additive manufacturing approach for novel alloy design. As a critical component of the novel DED system, a powder mixer plays an important role in the stable and uniform mixing of different powders. In this work, the coaxial-jet dome powder mixer (CDPM) was designed based on the convergent-jet cone powder mixer (CCPM). In order to explore a reliable multi-powder mixing mechanism, the gas-solid two-phase flow state in the mixing chamber was simulated by the large eddy simulation and discrete particle model (LES-DPM) method. In addition, the powder delivery stability and mixing uniformity of the mixer were characterized by curve fitting and image processing methods. Finally, CDPM avoids the generation of ineffective vortices that occurred in the mixing chamber. In addition, deposition experiments show that the powder mixer can ensure the uniform distribution of multiple elements in the local forming zone. [Display omitted] • Additive manufacturing gives more freedom to design multi-powder mixer. • The synchronization of atomization and mixing enables the powder to mix fully. • Vortex mixing mechanism links structural details to multi-powder mixing effects. • The well-designed mixing chamber avoids the generation of invalid vortex. • High-speed photography results reveal effective vortex mixing principle. [ABSTRACT FROM AUTHOR]

Mass flow rate measurement of pneumatically conveyed particles is desirable for the optimal control of many industrial processes. The unpredicted variation of moisture content in particles affects the accuracy of mass flow measurement of particles in enclosed pipelines using electrostatic electrodes. In this study, the characteristics of measured electrostatic signals from particle flow under different flow conditions are analysed to study the effect of moisture content on the mass flow rate measurement. The measurement principle of ring-shaped electrostatic electrodes, the effects of moisture content on electrification of solid particles, and the experimental setup used in the study are presented. Two types of electrostatic electrodes with different axial widths and structure are adopted to measure the electrostatic signals of nonporous glass beads and porous activated carbon powder on the vertical pipeline of a 74 mm bore gas–solid two-phase flow test rig under various moisture content, mass flow rate and conveying velocity conditions. The experimental results indicate that the amplitude and frequency characteristics of the electrostatic signals change with the moisture content. The deviation of mass flow measurement that caused by the variation of moisture content is analysed, and a recalibration process is demonstrated to be effective for the improvement of measurement accuracy. [ABSTRACT FROM AUTHOR]

Due to the low leaching rate of heavy metals and high energy utilization, the plasma melting furnace is widely used in the harmless treatment of waste incineration. In this paper, the gas-solid two-phase flow in the plasma melting furnace was numerically modelled by means of Euler-Lagrange approach. Conclusions can be drawn that the raw fly ash should be pelletized in order to successfully participate in the melting reaction and effectively avoid the collisional erosion with the graphite cathode. The velocity and temperature fields in the furnace showed asymmetry due to the interaction between the flue gas and slag particles. The heat-up degree of fly ash was much greater than that of SiO 2 particle while the speed discrepancy was small. The average temperature of slag particles in the effective melting region was relatively higher, which is more beneficial to the melting reaction. In addition, three evaluation indicators were established to analyze the distribution of slag particles on the bath surface. The mass proportions of different slag particles in the effective melting region were >40%, the maximum value of their radial distribution can be obtained in the radius range of 0.9–1.0 m, and the mass ratios of fly ash and SiO 2 particles in the same radius domain were overall closer to that of entering the furnace. Finally, the collisional erosion effect of slag particles on the graphite cathode was discussed in detail. [Display omitted] • Particle flow in the plasma melting furnace is studied by Euler-Lagrange approach. • Fly ash pelletizing facilitates melting reaction and avoids collisional erosion. • Distribution of particles on bath surface can be evaluated by three key indicators. • High portion of particles in the effective melting region benefits melting reaction. [ABSTRACT FROM AUTHOR]

Wet particle fluidization is commonly applied in some industries such as catalytic cracking, pharmaceutical manufacturing, mineral processing, food drying, etc. Understanding the within fluidization characteristics is important for the scale-up, design and optimization of industrial process. This article reviews the recent studies on fluidization characteristics of wet particles in fluidized beds and spouted beds. Both physical experiment and numerical simulation results are included. For physical experiments, the focus is on the development of new measurement methods and the resulting findings. For numerical simulations, the focus is especially on the development of the discrete element method (DEM) which can lead to new insights for wet particle fluidization at particle scale. Finally, challenges and needs for future research on wet particle fluidization are discussed. [Display omitted] [ABSTRACT FROM AUTHOR]

Erosion of particles in elbows mounted in series is a detriment in the course of natural gas transmission. The flow and erosion characteristics of π-shaped pipelines were investigated via coupling the computational fluid dynamics (CFD) and the discrete phase model (DPM) method. The effect of pipe orientation on particle erosion was mainly studied. Spiral and asymmetrical trajectories of particles were observed from the second elbow to the downstream straight pipe of the fourth elbow in the non-coplanar π-shaped pipelines. The integral erosion rate of the first elbow increased by 0.35%, and it grew by 72.49% and 87.48% in the second and fourth elbows in non-coplanar structures, respectively, while the integral erosion rate of the third elbow reduced by 32.94%. In the actual transportation of natural gas, it is necessary to make local thickening treatment of the second and fourth elbow of the non-coplanar π-shaped pipelines. [Display omitted] • A swirling effect was discovered in non-coplanar structures. • Spiral and asymmetrical particle trajectories were generated. • Integral erosion degree of fourth elbow increased by 87.48% due to swirling effect. • The erosion rate increased exponentially with the increase of velocity. [ABSTRACT FROM AUTHOR]

The high-speed particle image velocimetry is applied to measure the particle velocities of a horizontal self-exited gas-solid two-phase pipe flow with soft fins at the air velocity of the minimum pressure drop. The detailed particle dynamics of using fins' cases are analyzed and compared with a conventional non-fin case. It is found that the particle accelerating process is delayed in the acceleration regime and the vertical particle velocity is decreased near the top part of fully-developed regime due to the effect of fins' oscillations. The continuous wavelet transform of axial particle fluctuation velocity suggests that the fins make the particle motions fall into a lower frequency range in the acceleration regime. In the fully-developed regime, the dominating frequencies of large-scale particle flows are decreased and the streaks appearing in the range of high frequency are weakened by using fins. The energy distributions of proper orthogonal decomposition (POD) modes indicate that the relative energy of POD mode1 is increased by using fins in both acceleration and fully-developed regimes, and the dominance is significantly enhanced by using fins in the fully-developed regime. The auto-correlation coefficients and central frequencies of POD modes exhibit that the dominating large-scale particle motion is enhanced by using fins, correspondingly, small-scale particle motion is suppressed. [Display omitted] • The particle velocity of a horizontal self-exited gas-solid two-phase pipe flow is measured at minimum air velocity by PIV. • POD and continuous wavelet transform is adopted to analyze the particle fluctuation velocities. • The dominating frequencies of large-scale particle flows are decreased. • The streaks appears in the range of high frequency are weakened by using fins. • The dominance of POD mode 1 is significantly enhanced by using fins in the fully-developed regime. [ABSTRACT FROM AUTHOR]

The purpose of this study is to apply the oscillation flow induced by a combination of a circular cylinder and non-uniform soft fins to gas–solid two-phase flows to reduce the transport gas velocity and power consumption in a horizontal pipe. In order to evaluate the oscillation flow, several different sizes of square and circular cylinders are used to combine four pieces of soft fins with non-uniform lengths, which are mounted on the horizontal central plane in front of the particle supply. The test pipe comprises a horizontal acrylic pipe with a length of 5 m and an inside diameter of 80 mm. Spherical polyethylene particles with an average diameter of 2.3 mm and density of 978 kg/m3 were used as the test particles. The average gas velocity was 9–16 m/s, and the solid mass flow rate was 0.11–0.51 kg/s. It is found that the combination of a circular cylinder or square cylinder of L = 10 mm with non-uniform soft fins causes the lowest pressure drop and highest velocity fluctuation in the oscillation flow based on single-phase flow (gas only) measurement. Compared to conventional gas–solid two-phase flows, the reduction in the minimum transport velocity, pressure drop, power consumption, and additional pressure drop were obtained using a combination of a circular cylinder with non-uniform soft fins. This combination provides the highest reduction rates in the minimum conveying velocity and an additional pressure drop by approximately 10.0% and 34.1%, respectively. Based on particle image velocimetry measurements, the time-mean particle velocity and particle fluctuating velocity of a circular cylinder with non-uniform soft fins were higher than those of conventional flows near the bottom part of the pipe, thus easily accelerating and suspending particles near the pipe bottom, even at lower gas velocities. [Display omitted] • A combination of a circular cylinder and soft fins was used to induce the oscillation flow. • The oscillation flow was applied to gas-solid two-phase flow for energy-saving conveying. • The pressure drop, minimum velocity, and power consumption are reduced. • The particle velocity and fluctuating velocity were high near the bottom part of the pipe. [ABSTRACT FROM AUTHOR]

A Lagrangian algebraic slip mixture model (LASMM) has been employed to study gas-solid two-phase flows. In this model the slip velocity between gas and solid particles was derived from Lagrangian form. Hence the accelerations of various forces on the particle were considered through the single solid particle Lagrangian movement equation. Owing to the governing equations of LASMM based on Euler equations, this model therefore realized the connection between Eulerian model and Lagrangian model. Through the comparisons of the numerical simulations to the experiments and two-fluid models, this model was validated. [ABSTRACT FROM AUTHOR]

Abstract: This paper is concerned with the generation of the Acoustic Emission (AE) from particulate flow and an investigation of the potential of implementing AE for flow parameters, namely the solid mass flow rate, particle velocity and size, monitoring. A series of experiments has been conducted to gather AE signals from a laboratory scale single flow-loop pneumatic conveying system. Initially, AE sensors were attached to two steel meshes which were placed with a fixed axial distance in the pipeline to study the generation of the AE and subsequently the possibility of using those generated AE to determine particle velocity in the pipeline. Particle velocities measured from this approach were compared with theoretical predictions. The results indicated that this approach could measure the mean particle velocity with reasonable accuracy. The generation of AE on five different sensor mounting locations was also studied. The results showed that sensors mounted on all those locations were able to respond to changes in the flow parameters. However, only two sensor locations (outer bend and Mesh) were chosen for further investigation. The final experimental results indicated that the AE features, namely Root-Mean-Square (RMS) and energy of the AE, are related to the changes in the flow parameters and good correlations were found. Good correlations between the RMS and energy of the AE with the momentum and kinetic energy of the particles, respectively, were also found. Overall, the studies indicated that features of AE have great potential in gas–solid two phase flow parameter monitoring. However, the studies also show that the applicability of the AE techniques to measure solid mass flow rates in practice would require tedious calibration. [Copyright &y& Elsevier]

Pneumatically conveyed particles are commonly responsible for triggering the erosion process by impacts on the wall. Elbows with hemispherical protrusions had been proposed to mitigate erosion. Numerical simulations were carried out using the experimentally verified CFD-DPM method. The continuous impact of particles and secondary flow made the erosion scar on the extrados surface appear as an ellipse with v. For a single row of protrusions, a small arrangement angle and a large protrusion radius is more effective in improving the erosion resistance of the elbow. When θ = 30° and r = D /6, the maximum erosion rate could be reduced by up to 36.59%. The multiple rows of protrusions further mitigated the erosion of the elbow and can reduce the maximum erosion rate by 39.09% at most, but it will cause greater flow resistance. • Protrusions can reduce the maximum erosion rate by 39.09% at most. • Multiple rows of protrusions have a better effect but greater flow resistance. • Protrusions can disperse particle flow, form vortex, and inhibit secondary flow. • A large protrusion radius r and a small position θ are better choices. [ABSTRACT FROM AUTHOR]

CFD simulations are performed based on a three-dimensional upper respiratory tract (URT) model combined through Computerized Tomography (CT). A gas-solid two-phase flow model based on the Euler-Lagrange (E -L) method is used to analyze the gas-solid flow in the URT, and the van der Waals force among particles is considered. Simulated results show that most of the particles in the URT deposit on the entrance of the nasal cavity, the back wall of the throat, and the front wall of the exit. The flow velocities at these positions are relatively high, while the number of particles deposited in the vortex area is very small. Deposition of particles increases with the increase of particle size at the entrance of the nasal cavity and the throat. Small particles mostly deposit on the front wall of the throat. Compared with big particles, small particles are easier to flow toward the lower respiratory tract (LRT). Sediment distribution map of different sizes' particles. [Display omitted] • Increasing the inspiratory flow rate can increase the particle aggregation. • Bigger particles tend to concentrate in the URT before the throat. • Smaller particles are more dispersed in the URT and likely to deposit in the tail of the URT. • Particle deposition and escape are related to the particle size, inhalation flow rate and flow field structure. [ABSTRACT FROM AUTHOR]

Abstract: The present work focuses on developing a new comprehensive correlation for better prediction of the solids concentration in the fully developed region of co-current upward gas–solid flow in circulating fluidized bed (CFB) risers. Systematic experiments were carried out in two risers (15.1 m and 10.5 m high with the same 0.1 m i.d.) with FCC and sand particles. The results obtained from about 200 sets of operating conditions show that the average solids concentration in the fully developed region is more than just a function of the corresponding terminal solids concentration, as most previous correlations are based on. Operating conditions, particle properties and riser diameters also have significant effects on the solids concentrations in the fully developed region of CFB risers. Based on our experimental data and those reported in the open literature from CFB risers up to 0.4 m in diameter and 27 m in height with superficial gas velocities and solids circulation rates up to 11.5 m/s and 685 kg/m2·s, a new empirical correlation for predicting the average solids concentrations in the fully developed region of CFB risers is proposed. The correlation works well for a wide range of operating conditions, particle properties and riser diameters. [Copyright &y& Elsevier]

Abstract: To investigate solids concentration in the fully developed region of co-current downward gas–solid flow, actual solids concentrations were measured in a circulating fluidized bed (CFB) downer with 9.3 m in height and 0.1 m in diameter using a fiber optical probe. The results obtained from this work and in the literature show that the average solids concentration in the fully developed region of the CFB downers is not only a function of the corresponding terminal solids concentration, but the operating conditions and particle properties also have influences on the average solids concentration in the fully developed region of the CFB downers. Particle diameter and density affect the solids concentrations differently under different operating conditions. Downer diameters almost have no influence on the solids concentrations. By taking into account the effects of operating conditions, particle properties and downer diameters, an empirical correlation to predict the solids concentrations in the fully developed region of CFB downers is proposed. The predictions of the correlation are in good agreement with the experimental data of this work and in the literature. [Copyright &y& Elsevier]

Abstract: Particle rotation plays an important role on several aspects in gas–solid two-phase flow. However, it has not been paid much attention due to a lack of appropriate measurement methods. An attempt has been made in the present paper on the experimental study of particle rotation characteristics in a cold pilot-scale Circulating Fluidized Bed (CFB) riser, by using a high-speed digital imaging measurement system. It is found that one can measure rotation speeds manually for particles with special speckles on their surfaces or irregular shapes by observing particle image sequences. A dual-frequency imaging method was presented to enlarge the maximal measurable rotation speed at finite frame frequency and the measured rotation speeds are validated theoretically. Furthermore, particle rotation characteristics in a cross-section in upper dilute-phase zone were analyzed statistically. The results show that the average particle rotation speed is about 300 rev/s with the top speed of 2000 rev/s, when the superficial gas velocity U g, external solids mass flux G s and average particle diameter are 5 m/s, 1.5 kg/(m2 s) and 0.5 mm, separately. The average particle rotation speed near the wall area is higher than that in the center area at the testing cross-section. Those particles, with either smaller size or higher radial component of translational speed, may have higher average rotation speed. The average rotation speed of irregular particles is apparently higher than that of the spherical ones. [Copyright &y& Elsevier]

Abstract: Numerical simulations for gas–solid two-phase flows were conducted for an experimental coating booth and an industrial coating booth to study the effect of the coating powder size on the performance of the coating process. To optimize coating parameters, simulations were conducted for different coating parameters, such as the size of the coating part, the distance between the coating part and the spray gun, the air flow rate and particle flow rate from the spray gun, the position of the pattern adjust sleeve of the spray gun, and the electrostatic field, in order to increase the coating process efficiency and coating quality. In numerical simulations, the air flow field is obtained by solving three-dimensional Navier–Stokes equations with standard κ–ɛ turbulence model and non-equilibrium wall function. The second phase, the coating powder, consists of spherical particles and is dispersed in the continuous phase, the air. In addition to solving transport equations for the air, the trajectories of the particles are calculated by solving the particle motion equations using Lagrangian method. It is assumed that the particle–particle interaction can be neglected due to low particle volume fraction in coating systems. The electrostatic field is predicted by solving the Laplace equation. [Copyright &y& Elsevier]

A numerical parametric study was performed on the influence of various physical aspects over the hydrodynamics of gas–solid two-phase flow in the riser of a circulating fluidized bed (CFB). The addressed features were the solid phase viscosity, the gas–solid interface momentum transfer correlations, and the coordinate system. An Eulerian continuum formulation was applied for both phases. The resulting two-fluid model and numerical procedure followed a version of the MICEFLOW code. The simulation results are compared to available experimental data. The effects of the concerning features on the flow behavior are shown, mainly regarding cluster evolution. The flow frequency fluctuations typical to CFB risers were observed. It was also observed that for high values of solid phase viscosity there is an accumulation of solids near the outlet forming large clusters. When those clusters fall down, the instantaneous cross-sectional average solid mass velocity becomes negative. For inviscid solid phase, no cluster formation is observed. The results show the incorrectness of assuming symmetry boundary condition at the axis of the riser when cylindrical coordinates are used. Quite different results were obtained for different correlations for gas–solid interface momentum transfer. Finally, a comparison is presented of predictions from the Illinois Institute of Technology (IIT) hydrodynamic models A and B. [Copyright &y& Elsevier]

In order to reveal the unsteady features of gas–solid two-phase flow in both Fourier and physical spaces, the wavelet multi-resolution analysis was first employed to analyze the experimental data of the wall pressure–time signal. Then the definitions of the wavelet multi-resolution root mean square (RMS), skewness factor and probability density function (PDF) were developed and were applied to the statistical analysis of gas–solid two-phase flow in the frequency space. From the random-like pressure fluctuations, the fluctuating pressure components due to the dispersed suspension flow and the dune flow can be extracted based on the wavelet multi-resolution analysis over a time–frequency plane. It was found that the larger gas velocity results in the larger RMS pressure component at the higher frequency, while the lower gas velocity results in the larger RMS pressure component at the lower frequency. At a low velocity, the wavelet multi-resolution probability density function shifted to a unimodel from a bimodel distribution when increasing the frequency. In the acceleration region the pressure fluctuation components of the higher frequency deviated from the Gaussian-type fluctuation and resulted in the larger negative convectional skewness factor. [Copyright &y& Elsevier]