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Evaluation of flow regime of turbidity currents entering Dez Reservoir using extended shallow water model

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Water Science and Engineering 2014年第3期7卷 267-276页

作者： Valery Ivanovich ELFIMOV Hamid KHAKZAD Division of Civil Engineering Peoples' Friendship University of Russia

In this study, the performance of the extended shallow water model （ESWM） in evaluation of the flow regime of turbidity currents entering the Dez Reservoir was investigated. The continuity equations for fluid and particles and the Navier-Stokes equations govern the entire flow of turbidity currents. The shallow water equations governing the flow of the depositing phase of turbidity currents are derived from these equations. A case study was conducted on the flow regime of turbidity currents entering the Dez Reservoir in Iran from January 2002 to July 2003. Facing a serious sedimentation problem, the dead storage of the Dez Reservoir will be full in the coming 10 years, and the inflowing water in the hydropower conduit system is now becoming turbid. Based on the values of the dimensionless friction number （ Nf ≤1 ） and dimensionless entrainment number （ NE≤ 1 ） of turbidity currents, and the coefficient of determination between the observed and predicted deposit depths （R2 = 0.86） for the flow regime of negligible friction and negligible entrainment （NFNE）, the flow regime of turbidity currents coming into the Dez Reservoir is considered to be NFNE. The results suggest that the ESWM is an appropriate approach for evaluation of the flow regime of turbidity currents in dam reservoirs where the characteristics of turbidity currents, such as the deposit depth, must be evaluated.

关键词： flow regime turbidity current Dez Reservoir extended shallow water model Navier-Stokes equations

Hydrodynamic characteristics of a rectangular gas-driven inverse liquid-solid fluidized bed

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Particuology 2023年第7期78卷 86-96页

作者： Yicheng Deng Keying Ma jaqi Huang Yuanyuan Shao Jesse Zhu School of Chemical Engineering and Technology Tianjin UniversityTianjin300072China Department of Chemical and Biochemical Engineering Western UniversityLondonOntarioN6A3K7Canada Institute of Shaoxing Tianjin UniversityZhejiang312300China Nottingham Ningbo China Beacons of Excellence Research and Innovation Institute The University of Nottingham Ningbo ChinaNingboZhejiang.315100China

The hydrodynamic characteristics of a rectangular gas-driven inverse liquid-solid fluidized bed(GDFB)using particles of different diameters and densities were investigated in detail.Rising gas bubbles cause a liquid upflow in the riser portion,enabling a liquid downflow that causes an inverse fluidization in the downer portion.Four flow regimes(fixed bed regime,initial fluidization regime,complete fluidization regime,and circulating fluidization regime)and three transition gas velocities(initial fluidization gas velocity,minimum fluidization gas velocity,and circulating fluidization gas velocity)were identified via visual observation and by monitoring the variations in the pressure drop.The axial local bed voidage(e)of the downer first decreases and then increases with the increase of the gas velocity.Both the liquid circulation velocity and the average particle velocity inside the downer increase with the increase of the gas velocity in the riser,but decrease with the particle loading.An empirical formula was proposed to successfully predict the Richardson-Zaki index“n”,and the predicted e obtained from this formula has a±5%relative error when compared with the experimental e.

关键词： Gas-driven Inverse fluidized bed flow regime Average particle velocity Liquid circulation velocity Bed voidage

CFD simulation of flow and mixing characteristics in a stirred tank agitated by improved disc turbines

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Chinese Journal of Chemical Engineering 2022年第10期50卷 95-107页

作者： Zhuotai Jia Lele Xu Xiaoxia Duan Zai-Sha Mao Qinghua Zhang Chao Yang CAS Key Laboratory of Green Process and Engineering Institute of Process EngineeringChinese Academy of SciencesBeijing 100190China School of Chemical Engineering University of Chinese Academy of SciencesBeijing 100049China School of Chemical Engineering Nanjing Tech UniversityNanjing 211816China

To reduce the power consumption and improve the mixing performance in stirred tanks,two improved disc turbines namely swept-back parabolic disc turbine(SPDT)and staggered fan-shaped parabolic disc turbine(SFPDT)are developed.After validation of computational fluid dynamics(CFD)model with experimental results,CFD simulations are carried out to study the flow pattern,mean velocity,power consumption,pumping capacity and mixing efficiency of the improved and traditional impellers in a dished-bottom tank under turbulent flow conditions,The results indicate that compared with the commonly used parabolic disc turbine(PDT),the power number of proposed SPDT and SFPDT impellers is reduced by 43%and 12%,and the pumping efficiency is increased by 68%and 13%,respectively.Furthermore,under the same power consumption(0-700 W·m^(-3)),the mixing performance of both SPDT and SFPDT is also superior to that of Rushton turbine and PDT.

关键词： flow regime Mixing time Stirred vessel Computational fluiddynamics Improved discturbine

Hydrodynamics of a bubble-induced inverse fluidized bed reactor with a nanobubble tray

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Particuology 2023年第2期73卷 8-16页

作者： Yicheng Deng Keying Ma Yuanyuan Shao Jesse Zhu School of Chemical Engineering and Technology Tianjin UniversityTianjin300072China Department of Chemical and Biochemical Engineering The University of Western OntarioLondonOntarioN6A 3K7Canada Institute of Shaoxing Tianjin UniversityZhejiang312300China

This paper reports on the hydrodynamics of a bubble-induced inverse fluidized bed reactor,using a nanobubble tray gas distributor,where solid particles are fluidized only by an upward gas flow.Increasing the gas velocity,the fixed layer of particles initially packed at the top of the liquid starts to move downwards,due to the rise of bubbles in this system,and then gradually expands downwards until fully suspended.The axial local pressure drops and standard deviation were examined to delineate the flow regime comprehensively under different superficial gas velocities.Four flow regimes(fixed bed regime,initial fluidization regime,expanded regime,and post-homogeneous regime)were observed and three transitional gas velocities(the initial fluidization velocity,minimum fluidization velocity,and homogeneous fluidization velocity)were identified to demarcate the flow regime.Three correlations were developed for the three transitional velocities.As the fine bubbles generated from the nanobubble tray gas distributor are well distributed in the entire column,the bed expansion process of the particles is relatively steady.

关键词： Bubble-induced Inverse fluidized bed Pressure drop flow regime Bed expansion ratio Standard deviation

Investigation on gas–solid flow regimes in a novel multistage fluidized bed

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Chinese Journal of Chemical Engineering 2022年第6期35卷 21-30页

作者： Gongpeng Wu Yan He College of Electromechanical Engineering Qingdao University of Science and TechnologyQingdao 266061China

Gas–solid flow regime in a novel multistage circulating fluidized bed is investigated in this study.Pressure fluctuations are first sampled from gas–solid flow systems and then are analyzed through frequency and time–frequency domain methods including power spectrum and Hilbert–Huang transform.According to the flow characteristics obtained from pressure fluctuations,it is found that the gas–solid motions in the multistage circulating fluidized bed exhibit two dominant motion peaks in low and high frequencies.Moreover,gas-cluster motions become intensive for the multistage circulating fluidized bed in comparison with the fast bed.Unlike the traditional methods,the fuzzy C-means clustering method is introduced to objectively identify flow regime in the multistage circulating fluidized bed on the basis of the flow characteristics extracted from bubbling,turbulent,fast,and multistage fluidized beds.The identification accuracy of fuzzy C-means clustering method is first verified.The identification results show that the flow regime in the multistage circulating fluidized bed is in the scope of fast flow regime under examined conditions.Moreover,the results indicate that the consistency of flow regime between two enlarged sections exists.In addition,the transition onset of fast flow regime in the multistage circulating fluidized bed is higher than that in the fast bed.

关键词： Multistage riser Pressure fluctuation flow regime Fuzzy C-means clustering Hilbert-Huang

Determination of groundwater flow regimes based on the spatial non-local distribution of hydraulic gradient:Model and validation

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Journal of Hydrodynamics 2022年第2期34卷 299-307页

作者： Xiu-xuan Wang Jia-zhong Qian Lei Ma Qian-kun Luo Guan-qun Zhou School of Resources and Environmental Engineering Hefei University of TechnologyHefei230009China

The groundwater flow in natural aquifers can change from the Darcy flow to the non-Darcian flow due to a variety of causes,such as the increase of the Reynolds number in the highly permeable media or the decrease of the hydraulic gradient below a threshold in the low-permeability media,while the representative flow regime cannot be reliably determined using the traditional criteria.To address this challenge,this paper proposes a new term called the equivalent hydraulic gradient(EHG)by generalizing the differential form of the Darcy’s law using a spatial integral of the upstream hydraulic head.The nonlocal spatial variation of the hydraulic head difference between upstream and downstream zones is assumed to be the potential cause of the transition of the groundwater flow regimes.This assumption is analogous to the common assumption used for quantifying the anomalous pollutant transport in the geological media.Applications of this idea show that the EHG concept could distinguish three main flow regimes,namely the Super-Darcy flow,the Darcy flow,and the Sub-Darcy flow,although the Super-Darcy flow regime is rarely observed in the laboratory column flow experiments.Results of this study therefore shed lights on the interpretation of the fundamental dynamics of the groundwater moving in various heterogeneous aquifers,and may lead to the rebuilding of the hydrodynamics of the surface water,the groundwater,and the soil.

关键词： Hydraulic head distribution spatially non-local effect flow regime Forchheimer number Reynolds number

Identification of flow regimes and determination of the boundaries for magnetized fluidized bed with Geldart-B particles

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Particuology 2022年第12期71卷 75-89页

作者： Quanhong Zhu Hengjun Gai Hongbing Song Meng Xiao Tingting Huang Weikang Hao College of Chemical Engineering Qingdao University of Science and TechnologyQingdao 266042China College of Chemical Engineering Hebei University of TechnologyTianjin 300401China Qingdao Institute of Bioenergy and Bioprocess Technology Chinese Academy of SciencesQingdao 266101China

The magnetized fluidized bed(MFB)with Geldart-B particles exhibits many distinct flow regimes depend-ing on the magnetic field intensity(H)and gas velocity(U_(g)).The identification of these regimes was reviewed for the MFB with magnetizable particles and that with binary admixture of magnetizable and nonmagnetizable particles.Meanwhile,methods for determining the boundaries between two adjacent flow regimes were clarified.The MFB state was found to depend not only on H and Ug but also on their application sequence(i.e.,operation mode)within certain operating zones.The dependence feature arose from that the MFB therein could have different equilibrium states for the same combination of H and Ug.Furthermore,such a polymorphic characteristic of the MFB was revealed to result from the internal friction among the particles that were in unfluidized/packed state.Many of the MFB states were demon-strated to be in metastable equilibrium.Nevertheless,they differed significantly from the metastates well-known in the discipline of physical chemistry,such as supercooling and superheated.In fact,they belonged to the amorphous/glass state.This review will deepen our hydrodynamic understanding of the MFB and further promote its commercial application in the chemical and biochemical industries.

关键词： Magnetized fluidized bed flow regime Boundary Polymorphic Internal friction Amorphous

Local solids flow structure in a countercurrent liquid-upward and solids-downward fluidized bed(CCLSFB)system

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Particuology 2023年第5期76卷 13-22页

作者： Enming Zhang Keying Ma Yuanyuan Shao Jesse Zhu School of Chemical Engineering and Technology Tianjin UniversityTianjin300072China Department of Chemical&Biochemical Engineering Western UniversityLondonOntarioN6A 3K7Canada Institute of Shaoxing Tianjin UniversityZhejiang312300China

The local solids holdup and local particle velocity in a Countercurrent Liquid-upward and Solids-downward Fluidized Bed(CCLSFB)were investigated in details using optical fiber probes with two different models in a Plexiglas column of 1.5 m in height and 7.0 cm in inner diameter.A new flow regime map including fluidized bed,transition,and flooding regimes was established.The axial solids holdup distribution is almost uniform at low liquid velocity and/or solids flowrate and becomes less uniform with higher solids holdup at the top of the column after the operating liquid velocity is reaching the flooding velocity.The radial solids holdup profile is also nearly flat with a slightly lower solids holdup in the near-wall region at low liquid velocity and solids flowrate but becomes nonuniform as the operating liquid velocity approaches the flooding velocity.Two equations were also proposed to correlate radial local solids holdups.The descending particle velocity in CCLSFB increases with the decrease of the liquid velocity and the increase of the solids flowrate.A generally uniform particle velocity distribution was found in the axial direction,as well as in the radial direction except for a small decrease near the wall.These results on the local solids flow structure would provide basic information and theoretical supports for the design and industrial application of CCLSFB.

关键词： Countercurrent liquid-solid fluidized bed flow regime Optical fiber probe Solids holdup Particle velocity

Characterizations of gas-liquid interface distribution and slug evolution in a vertical pipe

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Petroleum Science 2023年第5期20卷 3157-3171页

作者： Hai-Yang Yu Qiang Xu Ye-Qi Cao Bo Huang Han-Xuan Wang Lie-Jin Guo State Key Laboratory of Multiphase flow in Power Engineering Xi'an Jiaotong UniversityXi’an710049ShaanxiChina

Large vertical pipes are key structures connecting subsea wells to offshore platforms.However,existing studies mainly focus on small vertical pipes.In a vertical acrylic pipe with 80 mm inner diameter and 11 m height,a high-speed camera was used to visually research the influences of pipe diameters,liquid properties and inlet effect on air-water co-flow characteristic.Different flow regime maps of vertical pipes(diameters are in the range of 50e189 mm)were compared and the critical gas velocity of the transition boundary from bubble to slug flow tended to increase with the increase of diameters at D≥80 mm.Drift-flux models were established in different flow regimes and liquid properties have a significant effect on drift coefficients of bubble flow and slug flow(void fraction a≤0.4).The influence of inlet turbulent effect on the gas-liquid interface distribution gradually weakened and disappeared from the pipe base to 85D,where the flow was fully developed.Slug frequency has a trend of increase first and then decrease with the gas Weber numbers increasing at low liquid superficial velocities(J_(L)≤0.31 m/s).And on the basis of this law,a new slug frequency correlation was proposed.It was found that there was an exponential relationship between the ratio of lengths of Taylor bubble to slug and the void fraction.

关键词： Void fraction flow regime Drift coefficien Slug frequency Taylor bubble length