Cross-sectional Average Velocity Research Articles

Numerical simulation analysis and experimental verification of air flow measurement in large-diameter S-shaped pipe

Abstract The ventilation systems in nuclear power plants, hydropower plants, and other large-scale projects involve the transportation of fluids through large-scale pipelines. To achieve a more stable flow velocity distribution, the fluid needs to pass through a straight pipe section of sufficient length upon entering the pipe. Typically, this straight pipe section should be at least 15 times the inner diameter of the pipe. However, for large-diameter irregular square pipes with a diameter exceeding 1m, where the curved section is short and there are no long straight pipe sections before and after it, the flow field inside the pipe becomes complex, requiring accurate measurement of the flow rate.In this regard, a numerical simulation analysis is conducted to address this challenge. A mean velocity evaluation method based on the coefficient of variation is proposed. This method identifies multiple points within the pipe that best represent the average flow velocity, determining the insertion depth of sensors and the weight coefficients of these multiple measuring points. A calculation formula is derived, utilizing the cross-sectional average velocity as a function with the velocity values at multiple points in the flow field as independent variables. To validate the accuracy of the proposed method, flow measurement experiments are performed on a wind tunnel test bench. The calculated values obtained from the derived formula through numerical analysis are compared with the experimental results. The relative error within the full range is found to be less than 0.54%, confirming the accuracy of the formula. The research findings present a novel measurement method for airflow in large-diameter irregular square pipes and offer valuable practical insights for engineering applications.

Effects of bag characteristics and channel side slope on incipient motion of a single Geobag under river current loading

Geobag stability has not been extensively studied under river current loading. In this study, the impacts of geobag characteristics (shape, bag material, and fill ratio of sand) and channel side slope (flat and 1V:2H) on a single geobag's stability were systematically investigated in a physical model to form the solid foundation for the research of group geobags. Overall, a geobag with a higher fill ratio, combined with the more flexible cloth material, was found to be the most stable. Critical Shields parameters were estimated between 0.0018 and 0.019, and the cross-sectional averaged flow velocity at incipient motion ranged from 0.49 m/s to 1.08 m/s. A shape factor was introduced to better describe the relationship between geobag characteristics and their stability on both riverbed configurations. Both the fill ratio and the bed side slope had higher importance on the geobag's stability compared to the relative depth, bag shape, and angle of flexibility.

Effect of elasticity on the induced charge electro-osmotic mixing of viscoelastic fluids in a micromixer with a conductive cylinder

Mixing of reagents in microfluidics is critical, and currently, the focus is on Newtonian fluids, but these reagents are often viscoelastic fluids. In this study, a micromixer containing a conductive cylinder is proposed based on the principle of induced charge electro-osmosis (ICEO). The Oldroyd-B constitutive model was chosen to characterize the flow properties of viscoelastic fluids, and the Poisson–Boltzmann model was used to describe the ion distribution in the electrolyte. The impact of the elasticity number (El) of viscoelastic fluids on the mixing efficiency, velocity, and vortex in the micromixer was studied. The results show that the mixing efficiency is only 55.41% when El = 0 (Newtonian fluid), and the mixing efficiency reaches 99.08% when El = 50. As El increases from 0 to 50, the cross-sectional average velocity at 50 μm from the micromixer exit decreases from 160 to 26.1 μm/s. Furthermore, the vortices around the conductive plate generated by the ICEO phenomenon begin to fluctuate at El = 7.

Transport of non-flushable wipes in sewers and its application in sewer management

Flushing wipes into sewers has caused severe blockage issues in urban sewer systems, especially during the COVID-19 pandemic; however, the transport mechanism of wipes in sewers has not been reported. To address this knowledge gap, the transport of non-flushable wipes with different densities was systematically studied in a circular pipe. The critical shear stress and flow velocity for the incipient motion of wipes were found to increase with increasing wipe density and with decreasing relative wipe size, starting from 0.02 Pa and 0.05 m/s, respectively. Non-dimensional equations were developed for characterizing the incipient motion using two parameters: the critical Shield number and particle Froude number. The mean wipe velocity, mean ambient flow velocity, and wipe density could be well described by a power relationship. The ratio of wipe velocity to local flow velocity increased with the increase of wipe vertical position in the pipe. Different movement modes of wipes were observed and classified by using the ambient cross-sectional average velocity Ua: the sliding mode started first, followed by rolling/saltation at Ua = 0.18 m/s and suspension at Ua = 0.41 m/s. The threshold values for each mode were found to increase with increasing wipe density. Finally, the research results were applied in sewer management.

Study on Hydrodynamics of Fish-Friendly Open-Channel Flow

To elucidate the hydrodynamic characteristics of a fish-friendly open channel, a three-dimensional numerical hydrodynamic model is constructed in this study employing the Large-eddy Simulation (LES) technique. The reliability of this numerical model is thoroughly validated by incorporating periodic boundaries in the flow direction, allowing for the recurrent development of water flow within the computational domain and utilizing experimental data from a flume. The results demonstrate that the fish-friendly channel is partitioned into a high-velocity mainstream zone and a low-velocity habitat zone. The time-averaged flow velocity in the mainstream zone is approximately 2.0 times the cross-sectional average flow velocity. In the low-velocity habitat zone, the average hourly flow velocity and turbulence are at a relatively low level, rendering the zone suitable for fish habitation and the incubation of adhesive fish eggs. A significant vortex structure is present in the mixing layer at the junction of the main flow area and the habitat area, which not only markedly increases the turbulence intensity but also serves as the primary driver of momentum exchange within the open channel.

Experimental and Analytical Investigations of Wire-Partially Insulated Parallel Plate Electrode Type Electrohydrodynamic Fan

As an alternative to conventional mechanical fans, EHD fans and/or EHD gas pumps, which generate less noise, were investigated for cooling systems, such as in electronic equipment and automobiles. Wire-parallel plate electrode type EHD fans, which have greater design freedom and potential for practical application, have been suggested. This study clarifies the characteristics of a wire-partially insulated parallel plate electrode type EHD fan under DC positive applied voltage. In order to understand the characteristics of the EHD fan more deeply, visualizations of the air flow in the flow channel and the exit area were conducted by using PIV and CFD analyses. In the experiment, air at atmospheric pressure and room temperature was used as a working fluid. The experimental results for fan characteristics of the EHD fan, such as the velocity profile, cross-sectional average velocity, volumetric flow rate in the flow channel or at the exit area, power, and so on, are considered in detail. In addition, the flow visualization and the instantaneous and time-averaged velocity profiles from the PIV analysis are discussed. A comparison with the experimental results described above, and differences of flow regime for different locations, are also presented and discussed. Furthermore, a two-dimensional steady state flow simulation by means of CFD analysis was conducted and its experimental results analyzed.

An innovative method for measuring the three-dimensional water surface morphology of unsteady flow using light detection and ranging technology

High-resolution free-surface elevation measurement is challenging due to the rapid evolution of unsteady flow. In this study, using dam-break flow as an example, the applicability of a low-cost sensor, the Intel® RealSense™ L515 solid-state light detection and ranging (LiDAR) probe, for the free-surface elevation measurement was evaluated. A white inorganic pigment was added to the water to improve the water's laser reflection. A series of dam-break flow experiments were systematically conducted, including asymmetric flow with obstacles in downstream rivers. The results demonstrate that the single-point time-domain process and water surface profile as measured by the LiDAR probe showed good consistency with acoustic displacement meter measurements with uniform correction of the free-surface elevation deviation. The proposed method's advantage is that the unsteady flow's free surface can be obtained with high temporal and spatial resolution; in addition, the volume flow rate and cross-sectional average velocity can be indirectly obtained, thus providing a useful reference for measuring the free surface of unsteady flow under laboratory conditions.

Influence of orifice thickness and chamfer on broadband noise in a water circuit

An incompressible large-eddy simulation (LES) is used to predict broadband noise generation by an orifice in a water circuit. Flow conditions are chosen in order to avoid cavitation. The model’s results are compared to measured wall pressure fluctuations for three orifices: a thin sharp-square-edge orifice, a thick sharp-square-edge orifice and a thick narrower orifice with an upstream chamfer. Reynolds-averaged Navier–Stokes (RANS) and large-eddy simulations (LES) fail to reproduce the steady-flow drag coefficient of the thick sharp-edge orifice and of the upstream-chamfered orifice. Large differences are found in the steady-flow drag coefficient of different samples of the thick orifice. An edge-tone like instability is observed in the near-field pressure fluctuations of one of the thick sharp-square-edge orifices, which does not appear in the other samples and is suppressed by the upstream chamfer. However, there are only minor differences in far-field radiated sound for these thick sharp-edged orifices. A plane-wave model with acoustic source from the LES predicts the power spectral density (PSD) of the acoustic pressures within a factor 3. At low Strouhal numbers (based on the orifice diameter and the cross-sectional averaged velocity in the orifice) the thin orifice behaves similarly to the thicker strongly chamfered orifices, with thin central cylindrical section. At higher Strouhal numbers the measured and predicted acoustic-pressure fluctuations due to these orifices are two orders of magnitude lower than those of thick orifices with sharp square edges. As orifices are used for the control of the flow distribution through complex water-cooling networks, the good results for thick chamfered narrow orifices call for a further study to find shapes that minimize the sound production at constant static pressure drop.

Fiber-Concentration Distributions of Pulp Suspension Flow behind a Partition Plate Inserted in a Channel as Applied to a Papermaking Machine

This study involved an experimental investigation of the distribution of pulp fiber concentration in the region behind a partition plate with a tapered trailing-edge inserted in a convergent channel. The channel was modeled at the laboratory scale for the dispersion and rectification components of the headbox passage in a papermaking machine. For the experiments, the inlet cross-sectional average flow velocity, USUBa/SUB, of an actual pulp suspension was in the range of 0.03-3.3 m/s. The flow was visualized, and the fiber-concentration distribution was measured. Subsequently, the effects of the flow velocity on the time-averaged and fluctuating fiber-concentration distributions (CSUBa/SUB and C’, respectively) in the flow direction were examined through comparisons with those in the cases where the plate was installed in the parallel channel or had a simple rectangular edge. In the convergent channel with the tapered trailing-edge, the fiber-concentration defect behind the plate was reduced abruptly. Moreover, the uniformity of the fiber-concentration distribution at the convergence exit did not vary with the flow velocity, thereby having a low value. Overall, the fundamental observations obtained in this study can contribute to the optimization and improvement of the headbox channels of papermaking machines.

Discrete Bubble Flow in Granular Porous Media via Multiphase Computational Fluid Dynamic Simulation

The coal seam gas industry has raised public concerns about the potential risk of groundwater contamination, where gases leaked from coal seams are thought to pollute groundwater. However, the basic principles and controlling parameters for gas seepage from deep ground formations to the ground surface have not been fully understood. As a possible mechanism for gas transport in the subsurface environment, discrete bubble flow was previously investigated using laboratory experiments by Ma et al. (Water Resour. Res, 2015, 51 (6), 4359–4373). This study developed a multiphase computational fluid dynamic (CFD) model to simulate discrete bubbly flow in a two-dimensional granular porous media at the pore scale. Following the experimental setup from Ma et al. (Water Resour. Res, 2015, 51 (6), 4359–4373), a “point source” with preset bubble fluxes was specified in a simulating domain representing the flume size in the earlier experiments. There were around 7,000 granular particles within this domain to model the porous media. This numerical model was validated by conserving the gas mass in the simulating domain. The simulation results provide more physical insights into complex bubble transport behaviour in porous media through specific plume parameters. The breakthrough time of the bubble plume and the cross-sectional averaged velocity of ambient pore water flow were manifested to be proportional to the gas release rates in the logarithmic scales. Also, the bubble plume width was also observed to be proportional to the gas release rates. Moreover, the gas distribution on the top boundary could be observed. The outcomes were further tested against the scaling solutions proposed by Ma et al. (Water Resour. Res, 2015, 51 (6), 4359–4373) with disagreements. The limitations of this multiphase computational fluid dynamic model were finally discussed.

The onset of turbulence in pulsating flows in smooth pipes

Experimental study examines the structure of nominally laminar flows subjected to sinusoidal variation of flow rate in smooth pipes. An experimental setup employed for this purpose provides high stability of flow rate variation pattern and is able to reproduce flow reversal during a fraction of pulsation period. The Reynolds number based on the highest cross-section average velocity over the pulsation period is 1200. SIV technique is used to measure the instantaneous vector fields of velocity in two regimes of pulsating flow. While there is no flow reversal in the first regime, it occupies approximately 0.4 of the pulsation period in the second regime. The increase in the amplitude of high-frequency fluctuation of velocity is documented in both regimes near the pipe wall within the Stokes layer. Evolution of the shape of velocity profiles and fluctuation amplitude profiles depending on the pulsation phase is presented. Our analysis suggests that forced sinusoidal pulsation of flow rate at the considered parameters results in the onset of instability and signs of transition to turbulence in the near-wall flow in the smooth pipe. We describe possible mechanism of turbulization of the near-wall flow under the impact of forced flow rate pulsation.

Hydrodynamic and acoustic pressure fluctuations in water pipes due to an orifice: Comparison of measurements with Large Eddy Simulations

The present article investigates the turbulent wall pressure fluctuations due to flow through single-hole sharp-square-edged orifices (opening area ratios of 11%, 20% and 31%) in a water-filled pipe by means of measurements and incompressible Large Eddy Simulations (LES) for opening area ratios of 20% and 31%. The orifice plate thickness was half the orifice diameter. The static pressure measurements and simulations show that the vena-contracta factors of the orifices are dependent on Reynolds numbers, which is due to the finite thickness of the orifices. These LES simulations provide a good prediction of the near-field hydrodynamic wall pressure fluctuations, which dominate up to the first three pipe diameters downstream of the orifice. Upstream and far downstream wall pressure fluctuations are dominated by acoustic pressure fluctuations. The source of the radiated sound field was estimated from the surface integral of the fluctuations across the orifice in the LES. The sound field was calculated by implementing the sound source in a one dimensional acoustic model of the test section. The power spectrum density (PSD) of the wall pressure fluctuations for pipe Reynolds numbers varying from 4000 to 10000 collapsed when presented in dimensionless form, which uses the dynamic pressure in the orifice as reference pressure and the ratio of cross-sectional averaged orifice velocity and orifice diameter as characteristic frequency. In the inertial range of the turbulence a global decay of the pressure PSD and of the sound source show a power of the Strouhal number between −113 and −2.8. For higher frequencies the pressure fluctuations were dominated by acoustic resonances. For wider orifices the magnitude of these acoustic pressure fluctuations is predicted within a factor two by the acoustic model. For the narrowest orifice (opening ratio of 11%) the measured PSD of pressure fluctuations displays sharp peaks due to self-sustained oscillations (whistling). A simple power law of the sound source is not accurate due to the unstable hydrodynamic modes related to orifice thickness. However, using the simple model for the sound source the acoustic model predicts the acoustic pressure fluctuations reasonably well for all orifices. At low frequency one observes a peak in the PSD hydrodynamic wall-pressure fluctuations at one pipe diameter downstream of the orifice. It is probably due to an acoustically silent “edge-tone-like” sinusoidal self-sustained motion of the jet.

Effects of discharge on the velocity distribution and riverbed evolution in a meandering channel

To discuss the effects of discharge on the velocity distribution and riverbed evolution in a meandering river, a generalized meandering channel model was designed, and the instantaneous velocities and water levels in thirteen cross-sections and the digital elevations of the bed surfaces were measured. The results show that for the same discharge, the transverse water surface gradients are large at the downstream positions adjacent to the apex sections and small near the middle positions of the crossover areas. With increasing discharge, the transverse water surface gradients in the curved segments increase, the transverse underflows strengthen, and the transverse surface flows exhibit no obvious changes. If the curvature of a meandering channel is large and there are a large number of sediment particles whose incipient velocities are smaller than the transverse underflow velocities near the apex sections, then the regions between the apex-sectional convex sides and the outlets of the adjacent downstream crossover areas are prone to sediment deposition, and the frequency distributions of the bed surface elevations are positively skewed. For the same cross-section, the cross-sectional average velocity increases with increasing discharge. For the same discharge, the cross-sectional average velocities are large near the middle positions of the crossover areas and small near the apex sections. The thalweg swings randomly along the channel, but its overall trend is approximately the same as that of the flow dynamic axis. In a cross-section, the positions with large turbulent kinetic energy are located in the mainstream area, and the average turbulent kinetic energy increases with increasing discharge.

Monitoring of Yangtze River Discharge at Datong Hydrometric Station Using Acoustic Tomography Technology

To continuously monitor the discharge of the Yangtze River, two coastal acoustic tomography (CAT) systems with synchronized transmission were deployed at the Datong hydrometric station of the Yangtze River from July 2018 to January 2021. To accurately estimate the discharge of the Yangtze River, the cross-sectional averaged flow velocity and area data were estimated by establishing two empirical relationships: one between the range-averaged flow velocity measured by acoustic Doppler current profiler (ADCP) and the reciprocal travel time difference measured by CAT, and the other between the ADCP-measured cross-sectional area and the water-surface elevation (stage). Compared with the discharges directly measured by ADCP, our estimation had the root mean square error of 946 m3/s, accounting for 2.5% of the mean discharge. The discharges varied from 10,981 to 81,807 m3/s over the 2.5-years observational period, with a mean of 30,708 m3/s. The annual mean discharge was 29,163 and 34,763 m3/s in 2019 and 2020, respectively. Our monitoring successfully covered two complete flood processes, with a peak discharge of 69,744 (July 17, 2019) and 81,807 m3/s (July 13, 2020). Our study provides an innovative method to achieve accuracy and real-time monitoring of river discharges even during extreme flood events.

Two-phase flow simulations of fixed 3D oscillating water columns using OpenFOAM: A comparison of two methods for modeling quadratic power takeoff

This study examines the performance of a numerical method that introduces an artificial sink term to the Reynolds-averaged Navier Stokes equations to simulate the flow through an orifice used as a quadratic Power Takeoff (PTO) for Oscillating Water Columns (OWCs). The method replaces the quadratic PTO by an artificial Forchheimer-flow region (referred to as the artificial Forchheimer-flow method). The performance of this method was evaluated by making comparisons with the existing experimental results for two OWCs and the numerical results obtained by using air-water two-phase flow simulations of the air flow through an orifice (referred to as the orifice-flow method). The surface elevations, velocity fields and pressure fields obtained by the orifice-flow and artificial Forchheimer-flow methods are compared. To use the artificial Forchheimer-flow method, an equation for specifying the Forchheimer coefficient is provided and the sensitivity of the pneumatic efficiency to the Forchheimer coefficient is discussed. It can be concluded that the artificial Forchheimer-flow method can satisfactorily reproduce the measured pneumatic efficiency, pressure field in the air, the velocity field in the water and the cross-sectional average velocity of the air. Compared to the orifice-flow method, the artificial Forchheimer-flow method can speed up the simulation by at least 25 times.

Measuring Aqueduct of Sylvius Cerebrospinal Fluid Flow in Multiple Sclerosis Using Different Software.

Aqueduct of Sylvius (AoS) cerebrospinal fluid flow can be quantified using phase-contrast (PC) Magnetic Resonance Imaging. The software used for AoS segmentation might affect the PC-derived measures. We analyzed AoS PC data of 30 people with multiple sclerosis and 19 normal controls using three software packages, and estimated cross-sectional area (CSA), average and highest AoS velocity (Vmean and Vmax), flow rate and volume. Our aims were to assess the repeatability and reproducibility of each PC-derived measure obtained with the various software packages, including in terms of group differentiation. All the variables had good repeatability, except the average Vmean, flow rate and volume obtained with one software package. Substantial to perfect agreement was seen when evaluating the overlap between the AoS segmentations obtained with different software packages. No variable was significantly different between software packages, with the exception of Vmean diastolic peak and CSA. Vmax diastolic peak differentiated groups, regardless of the software package. In conclusion, a clinical study should preliminarily evaluate the repeatability in order to interpret its findings. Vmax seemed to be a repeatable and reproducible measure, since the pixel with its value is usually located in the center of the AoS, and is thus unlikely be affected by ROI size.

A Modified Chezy Formula for One-Dimensional Unsteady Frictional Resistance in Open Channel Flow

Abstract It has been observed in literature that for unsteady flow conditions the one-to-one relationships between flow depth, cross-sectional averaged velocity, and frictional resistance as determined from steady uniform flow cases may not be appropriate for these more complex flow systems. Thus, a general friction resistance formula needs to be modified through the addition of new descriptive terms to account for flow unsteadiness, in order to eliminate errors due to uniform and steady-flow assumptions. An extended Chezy formula incorporating both time and space partial derivatives of hydraulic parameters was developed using dimensional analysis to investigate the relationship between flow unsteadiness and friction resistance. Results show that the proposed formula performs better than the traditional Chezy formula for simulating real hydrograph cases whereby both formula coefficients are individually identified for each flood event and coefficients are predetermined using other flood events as calibration cases. Although the extended Chezy formula as well as the original Chezy formula perform worse with the increasing degree of flow unsteadiness, its results are less dramatically affected by unsteadiness intensity, thereby improving estimations of flood routing. As a result, it tends to perform much better than traditional Chezy formula for severe flood events. Under more complex conditions whereby peak flooding events may occur predominantly under unsteady flow, the extended Chezy model may provide as a valuable tool for researchers, practitioners, and water managers for assessing and predicting impacts for flooding and for the development of more appropriate mitigation strategies and more accurate risk assessments.

Estimation of natural streams longitudinal dispersion coefficient using hybrid evolutionary machine learning model

Among several indicators for river engineering sustainability, the longitudinal dispersion coefficient () is the main parameter that defines the transport of pollutants in natural streams. Accurate estimation of has been challenging for hydrologists due to the high stochasticity and non-linearity of this hydraulic-environmental parameter. This study presents a new hybrid machine learning (ML) model integrating a Gaussian Process Regression (GPR) and an evolutionary feature selection (FS) approach (i.e. Covariance Matrix Adaptation Evolution Strategy (CMAES)) to estimate in natural streams. The dataset consists of geometric and hydraulic river system parameters from 29 streams in the United States. The modeling results showed that the proposed model outperformed other models in the literature, producing more stable and accurate estimations. The FS approach evidenced the significance of the cross-sectional average flow velocity (U), channel width (B), and channel sinuosity σ to estimate the dispersion coefficient. In quantitative terms, the integrated GPR model with feature selection approach attained the minimum root mean square error () and maximum coefficient of determination (). The proposed hybrid evolutionary ML model arises as robust, flexible and reliable alternative computer aid technology for predicting the longitudinal dispersion coefficient in natural streams.

Resource assessment for hydro-kinetic turbines in Ethiopian rivers and irrigation canals

We describe resource assessment of rivers and a canal in the Upper Blue Nile Basin, Ethiopia for hydro-kinetic turbines (HKTs). Various hydrodynamics methods are coupled with hydrological methods with the aim of transforming the measured flow rate or discharge into velocity data to determine the power density (PD), the available power per square meter of vertical flow area. We estimate the PD over the length of the rivers and canal and estimate the power density variation over the months of the year. The Gumara, Gilgel-Abay, and Bahirdar-Abay rivers in the Blue Nile Basin were studied along with the Koga irrigation main canal. Historical databases of yearly, monthly, and daily averaged discharge were used. The key elements of this analysis are (i) converting discharge into velocity for PD determination, and (ii) the period over which the velocity is averaged compared to the averaging time used to determine the HKT power curve. All software used in this work is publicly available. To predict PD, ARC-GIS was used to estimate the reach length and cross-section from raster Digital Elevation Models (DEMs). The hydraulic modeling of the velocity was done using HEC-RAS software. Field measurements were conducted to validate the hydrodynamic model. The result of the study was cross-sectional area average water velocity V¯A, which used to predict the PD. To relate the time average of velocity V¯T to the power curve of a HKT a 2-minute average velocity measurement was conducted with a total of 270 samples. It is found that 25% of the Gumara river is suitable for HKTs with a maximum of 1.4 kW/m2 power can be extracted. The Gilgel-Abay river has a maximum velocity above 1 m/s and 3.4 kW/m2 power can be extracted over 32% of its length. Similarly, for Bahirdar-Abay river, over 29% of the reach length 2.6 kW/m2 power can be extracted.

Gas-solid Flow Behaviors in a Pressurized Multi-stage Circulating Fluidized Bed with Geldart Group B Particles

Abstract A comprehensive study of gas-solids flow behaviors was conducted in a novel multi-stage circulating fluidized bed (MCFB). Experiments were carried out in a cold model apparatus (a jetting fluidized bed, JFB, of 0.3 m diameter and 1.95 m tall, a riser of 0.15 m diameter and 12 m tall) at different elevated pressure, solids circulation rates and gas velocities. Geldart group B polystyrene particles of 400 μm in diameter and 1020 kg/m3 in density were used as bed materials. The characteristic of L-valve, axial and radial distributions of solids holdup were systematically tested at elevated pressures by pressure transducers with the frequency of 100 Hz and model PC6M of the optical fiber probes. Operating the L-valve at elevated pressure needs less cross-section average gas velocity compared to that at atmospheric pressure. Experimental results showed that under elevated pressure and high solids flow rate, the MCFB could more easily couple JFB with a riser, where the solids that entered could form three-level step-by-step supplement entrainment and multi-flow regimes formed. Besides, increasing operating pressure led to a higher the apparent solids holdup and local solids holdup. The local solids profiles behaved less uniform distribution at elevated pressure due to decreasing the gas velocity.