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local flow structure FOR NON-NEWTONIAN FLUIDS IN A PERIODICALLY CORRUGATED WALL CHANNEL

JOURNAL OF ENHANCED HEAT TRANSFER 1995年第1-2期2卷 71-77页

作者： BEREIZIAT, D DEVIENNE, R LEBOUCHE, M LEMTA - CNRS URA 875 - Université de Nancy I - 2 Av. de la Foret de Haye - B.P. 160 - 54504 Vandoeuvre-les-Nancy Cedex - France LEMTA CNRS 875 et Université Henri Poincaré Vandoeuvre-les-Nancy France Laboratoire d'Energetique et de Mecanique Theorique et Appliquee Institut National Polytechnique de Lorraine Universite Henri Poincare - Nancy I 2 Avenue de la Foret de Haye BP 160 F-54504 Vandoeuvre-les-Nancy Cedex France

Experiments were carried out to characterize the local shear flow inside a periodically corrugated wall channel by use of electrochemical method giving the wall shear rate S and laser-Doppler velocimetry (LDV) for the axial velocity profiles. Both Newtonian fluids and shear-thinning viscous fluids (carboxymethyl-cellulose sodium salt (CMC) additive) are considered, flowing in a range of Reynolds numbers and generalized Reynolds numbers for non-Newtonian fluids determining the following regimes: laminar, transitional and low-Reynolds-number turbulent. Laminar flow, steady motion with a recirculating zone, transition to turbulence with unsteady vortex and three-dimensional instabilities with reducing by the onset of a developed turbulence have been detected.

关键词： FLUID MECHANIC NON-NEWTONIAN FLUID CORRUGATED CHANNEL EXPERIMENTAL STUDY flow REGIME local flow structure

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Characteristics of local flow structure with different particle properties in a gas-solid diameter-varying fluidized bed

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POWDER TECHNOLOGY 2024年 433卷

作者： Wu, Gongpeng Tong, Hongkai He, Yan Qingdao Univ Sci & Technol Coll Electromech Engn Qingdao 266061 Peoples R China 99 Songling Rd Qingdao 266061 Peoples R China

The effects of particle property on gas-solid flow in the diameter-varying riser are experimentally examined using the optical fiber probe in this research. local flow features are obtained by signal analysis method under the operating conditions of 3-7 m/s and 8-63 kg/m2s. The results show that solid holdup distribution of glass beads is wider than that of catalyst particle particles in the wall region but is narrow in the center region. Solid holdup fluctuations tend to decrease with the increase of particle density under low-concentration conditions but in-crease at high-concentration conditions. The results from power spectrum density (PSD) show that the increase in particle density strengthens the periodic flow features in the enlarged section. The motion intensity decreases at the particle level but increases at the cluster level for high-density particles. Additionally, as particle density rises, the solid concentration discrepancies between the straight section and the enlarged section widen. In contrast to the upper straight section, the effects of particle density on gas-solid flow are minimal in the enlarged section.

关键词： local flow structure Gas -solid two-phase Diameter-varying riser Signal analysis

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Measurement of water holdup in slug region of oil-gas-water intermittent flow by plug-in conductance sensors

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flow MEASUREMENT AND INSTRUMENTATION 2025年 102卷

作者： Zhai, Lusheng Meng, Xinyu Qiao, Jiawei Huang, Yukun Wang, Wenhao Tianjin Univ Sch Elect & Informat Engn Tianjin 300072 Peoples R China

The water holdup measurement in the horizontal intermittent oil-gas-water flow slug region is of great significance for understanding interfacial heat and mass transfer and revealing the mechanism of flow pattern transition. Considering the multi-scale structural characteristics of the horizontal oil-gas-water intermittent flow, two plug-in conductance sensors are designed for the water holdup measurement in the slug region. They are distributed multi-electrode conductance sensor (DMECS) and ring-electrode conductance sensor (RECS). The finite element method is employed to optimize the geometries of the sensors to enhance the sensitivity and uniformity of the detection field. Experiments are conducted in horizontal gas-water and oil-gas-water flows within a 20 mm diameter pipe. Response signals from both conductance sensors are collected. Recurrence plots are drawn based on the collected signals to demonstrate the capability to detect local flow structures. The nonuniform distribution characteristics of water holdup in the intermittent flow slug region are studied. Besides, the influence of the oil phase on the local flow structures and water holdup is further explored. Finally, the water holdup measured by the conductance sensors is compared with the wire-mesh sensor. The results indicate that the RECS can reflect the average water holdup, whilst the DMECS is sensitive to the local water holdup characteristics. Thus, the DMECS has a higher measurement resolution for small-scale oil droplets and bubbles. By comparison, the RECS demonstrates better measurement performance for the pseudo slug flow with large-scale flow structures.

关键词： Oil-gas-water three-phase flow Intermittent flow Conductance sensor Water holdup local flow structure

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Effects of temperature on local two-phase flow structure in bubbling and turbulent fluidized beds of FCC particles

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CHEMICAL ENGINEERING SCIENCE 2004年第16期59卷 3413-3422页

作者： Cui, HP Chaouki, J Ecole Polytech Dept Chem Engn Biopro Res Ctr Montreal PQ H3C 3A7 Canada

A novel high temperature optical fiber probe has been developed to study the effects of bed temperature on the local two-phase flow structure in a pilot scale fluidized bed of the FCC particles with bed temperatures ranging from 25degreesC to 420degreesC, covering both the bubbling and turbulent fluidization regimes. The results show that fluidization is enhanced and fluctuations of the local two-phase flow structure become more intense with increasing bed temperature. At constant superficial gas velocities, the averaged local particle concentration, the dense phase fraction and particle concentration in the dense phase decrease with increasing bed temperature, whereas both the frequency of the dilute/dense phase cycle and the ratio of the dilute phase duration to the dense phase duration increase. In addition, the effects of temperature on the dilute phase depend on superficial gas velocity. The conventional two-phase models fail to predict these changes of the local flow structure with temperature, which may be explained by the fact that the role of interparticle forces is neglected at different bed temperatures. Indeed, fluidization behaviors of the FCC particles tested increasingly shift from typical Geldart A towards B with increasing temperature due to a decrease of the interparticle attractive forces and a simultaneous increase of interparticle repulsive forces. (C) 2004 Elsevier Ltd. All rights reserved.

关键词： fluidization local flow structure high temperature optical fiber probe interparticle forces Geldart's classification of particles

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Three-dimensional modeling of flow-sediment transport and large-scale bank erosion process in the Lower Yangtze River

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GEOMORPHOLOGY 2025年 471卷

作者： Deng, Shanshan Xia, Junqiang Sun, Qihang Zhu, Heng Zhou, Yueyao Wuhan Univ State Key Lab Water Resources Engn & Management Wuhan 430072 Peoples R China Minist Transport Tianjin Res Inst Water Transport Engn Tianjin Peoples R China

Bank erosion in the Lower Yangtze River (LYR) develops rapidly within a few hours, resulting in a large-scale embayment. A three-dimensional model is proposed in the current research to simulate the development of such an erosion process, coupling a hydro- and sediment dynamic module with a bank erosion module, and is evaluated against the observations in a laboratory experiment and against the measurements in LYR. Analysis of the model results indicates that: (1) the model reproduces the overall expansion process of the erosion embayment and demonstrates the essential role of changing flow structure;(2)the calculated local flow structure within the embayment consists of a major planar circulation and several minor planar circulations, and the major circulation is the primary driving force for the embayment expansion, while these minor circulations probably contribute to the cease of bank erosion;(3)Varying water level in the LYR accelerates the bank erosion process in the study reach, compared with a constant water level.

关键词： Bank erosion Three-dimensional modeling local flow structure Lower Yangtze River

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structure of the flow in the near-wall gas jet injected through circular holes in a transverse trench

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THERMOPHYSICS AND AEROMECHANICS 2021年第3期28卷 307-317页

作者： Pakhomov, M. A. Terekhov, V. V. Filippov, M., V Chokhar, I. A. Sharov, K. A. Terekhov, V., I Kutateladze Inst Thermophys SB RAS Novosibirsk Russia

Results of an experimental study of the local structure of the mean and fluctuating flow in a near-wall gas jet injected through inclined cylindrical holes along a smooth surface and in the case of injection in a transverse trench are reported. The local structure of the near-wall jet is measured by means of the particle image velocimetry. Injection of the secondary near-wall air jet into the main turbulent flow leads to a significant deformation of the streamwise velocity profile of the gas in both test cases. In the case of injection through the holes in the trench, the streamwise velocity of the gas displays a noticeably smoother profile with no clearly expressed maximum behind the cross section of the transverse trench exit. The streamwise velocity of the gas in the near-wall region has a smaller value than that in the case of injection without the trench. The transverse component of the gas velocity in the case of injection without the trench is greater than the corresponding value in the case of injection through the holes in the transverse trench after the gas leaves the trench.

关键词： near-wall gas jet local flow structure experiment injection through cylindrical holes trench PIV

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flow management in nanofiltration spiral wound modules with ladder-type spacers

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JOURNAL OF MEMBRANE SCIENCE 2002年第1-2期203卷 87-102页

作者： Geraldes, V Semiao, V de Pinho, MN Univ Tecn Lisboa Dept Chem Engn Inst Super Tecn P-1049001 Lisbon Portugal Univ Tecn Lisboa Dept Mech Engn Inst Super Tecn P-1049001 Lisbon Portugal

The incompressible laminar and two-dimensional flow in narrow rectangular channels filled with ladder-type spacers that have the transverse filaments adjacent to a semi-permeable wall, was investigated in order to have insight on the feed flow in a nanofiltration (NF)/reverse osmosis (RO) spiral wound module. The study was based on numerical simulations and on experiments of flow visualisation with tracer injection and pressure drop measurements. The numerical simulations were performed assuming fully developed laminar flow quasi-periodically repeating in successive inter-filament regions. Ladder-type spacers with inter-filament distances/channel height ratios (L-f) of 1.9, 3.8 and 5.7 were investigated. The ratio (P-f) between the transverse filaments height and channel height was investigated between 0.25 and 0.75 in the numerical study and was fixed to 0.5 in the experiments. flow visualisation with tracer injection and friction factor measurements were made for the water flow in a spacer-filled rectangular channel with 2 mm height, 30 mm wide and 200 mm long, in the range of Reynolds numbers (based on the channel height and on the average inlet velocity) between 50 and 1000. These results show that for increasing inter-filament distances the transition critical Reynolds number decreases from 300 to 150. Below this critical value, the flow is observed to be laminar and two-dimensional. The numerical simulations show that the flow structures are associated to the occurrence of recirculation zones downstream each transverse filament. For low values of the Reynolds number and P-f and high values of L-f, the recirculation region does not reach the second filament, while for high values of the Reynolds number and P-f and low values of L-f the recirculation region extends from the first to the second filament. Additionally, for P-f = 0.75, a secondary recirculation region can be formed inside the main recirculation region. Each of these situations is associated to diff

关键词： spiral wound modules ladder-type spacers computational fluid dynamics local flow structure flow visualisation

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flow visualization experiment in a two-side wall heated rectangular duct for turbulence model assessment in natural convection heat transfer

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NUCLEAR ENGINEERING AND DESIGN 2019年第Jan.期341卷 284-296页

作者： Kim, Sin-Yeob Shin, Dong-Ho Kim, Chan-Soo Park, Goon-Cherl Cho, Hyoung Kyu Seoul Natl Univ Dept Energy Syst Engn 1 Gwanak Ro Seoul South Korea Korea Atom Energy Res Inst Nucl Hydrogen Reactor Technol Div 111 Daedeok Daero 989 Beon Gil Daejeon South Korea

Reactor Cavity Cooling System (RCCS) is one of the passive safety systems in Very High Temperature gas-cooled Reactor (VHTR). RCCS incorporates riser channels connected with a chimney to remove the residual heat emitted from the reactor vessel using natural circulation, and therefore, heat transfer phenomena in the RCCS riser duct is of great importance to ensure the safety of the VHTR. To enhance the understanding of heat transfer mechanism in a heated riser duct with rectangular shape, visualization of the local flow structure was conducted with an experimental facility for the natural convection heat transfer applying the Particle Image Velocimetry (PIV) method. With measured thermal boundary conditions by IR thermometry, CFD analysis was performed for the test facility using two different turbulence models. By comparing local flow structure from the experimental data and CFD calculation results, turbulence model assessment was conducted to confirm the prediction capability of the models. Experimental data show the magnitudes and locations of maximum velocity peak which is induced by buoyancy force and the anisotropic behaviors of velocity fluctuations near wall region. CFD calculations overestimate the maximum velocity near the wall compared with experimental data, and they seem to have limitations in reproducing the secondary flow observed at the corner of the test section in the experiment. The established methodology for flow visualization and the measurement strategy for thermal boundary conditions could contribute to obtain extensive experimental data and turbulence model assessment results, which would improve the understanding of the heat transfer mechanism to enhance the performance prediction capability for the passive heat removal system of the VHTR.

关键词： VHTR RCCS riser Convective heat transfer flow visualization local flow structure Buoyancy effect

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