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Experimental analysis of local mass transfer in packed beds

CHEMICAL ENGINEERING SCIENCE 2001年第1期56卷 121-132页

作者： Guo, G Thompson, KE Louisiana State Univ Dept Chem Engn Baton Rouge LA 70803 USA

The mass transfer behavior from single spheres within random packings was examined in order to quantify the effects of local structure and hydrodynamics on mass transfer. Results show that in the sphere packs studied. structural differences at the pore scale cause the local Peclet number to vary by more than an order of magnitude and the exponent in the Sherwood versus Peclet number relationship to vary between approximately 0.3 and 0.7, both as a function of location within the packing. These combined effects cause at least a two-fold variation in local mass transfer rates and significant differences in the sensitivity of local mass transfer rates to changes in the overall flowrate to the bed. Two distributed parameters are introduced to quantify these effects, which collapse mass transfer data onto a single curve relating the local Sherwood number to a local Peclet number. The physical significance of these parameters is discussed, which aids in our understanding of fundamental behavior in disordered systems. Finally, we show how this information is used to calculate a spatially averaged mass transfer coefficient for dispersed interfaces under conditions where the total mass transfer rate for these interfaces does not reflect average behavior for the bed. (C) 2001 Elsevier Science Ltd. All rights reserved.

关键词： packed bed porous media mass transfer dissolution convective transport distributed parameter

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SPECTRAL CHARACTERIZATION OF TISSUES MICROSTRUCTURE BY ULTRASOUNDS - A STOCHASTIC APPROACH

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IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL 1990年第5期37卷 448-456页

作者： LANDINI, L VERRAZZANI, L UNIV PISA INST ELECTR & TELECOMMUNI-56100 PISAITALY

A model of the echo formation process from tissues is suggested, in order to relate microstructural features to ultrasonic spectral signatures. The tissue is modeled as a collection of ideal randomly distributed scatterers, filtered by a time-invariant system representing the measurement apparatus and the average properties of the scattering medium, to obtain the backscattered signal. The gamma distribution has been assumed to describe the process, because it offers a flexible approach to approximating the parametric regularity of the scatterers. According to the model the spectral characteristics of the backscattered signal are strictly correlated with the spatial architecture and can be related to the gamma distribution parameters, i.e. interdistance and order. The model has been tested by simulating practical situations, in order to prove its validity and to test the procedure for estimating model parameters from actual data. The correspondence of experimental results obtained from tissues of different degrees of regularity with the simulated results confirms the effectiveness of the model for tissue characterization studies.

关键词： average performance tissue characterization Ultrasonic Waves model parameters stochastic approach measurement apparatus Time invariant systems distributed parameter Gamma Distribution order

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An online fault-locating scheme for EHV/UHV transmission lines

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IET GENERATION TRANSMISSION & DISTRIBUTION 2008年第6期2卷 789-799页

作者： Xu, Z. Y. Jiao, S. H. Ran, L. Du, Z. Q. Tsinghua Univ Dept Elect Engn Beijing 100084 Peoples R China Beijing Sifang Automat Co Ltd Beijing 100085 Peoples R China Univ Durham Sci Labs Sch Engn Durham DH1 3LE England

The authors describe the principle of an online fault-locating scheme using the voltage and current synchronously sampled from both ends of a long EHV/UHV transmission line. This is based on a distributed parameter model of the line. Steady-state transmission line equations are used to construct a fault-locating function, with the effect of distributed capacitive current taken into account. Application is extended to practical situations where in-line shunt reactors are present for compensation. The fault-locating scheme is insensitive to fault path resistance, fault inception angle, load current and source impedance. Test results verify the high accuracy and speed of the scheme for different types of faults.

关键词： Scheme Power cables Stuck at faults current capacity Source impedance Shunt reactors Transmission Lines distributed parameter

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Recent activities in the field of thermal hydraulic researches

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JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY 2014年第10期51卷 1311-1313页

作者： Liu, Qiusheng Morooka, Shinichi Kobe Univ Dept Marine Engn Kobe Hyogo 657 Japan Waseda Univ Shinjuku Ku Tokyo Japan

In the field of thermal hydraulics, substantial progress has been made in research on single and two-phase heat transfer. Grid-enhanced convection heat transfer has been studied [1,2]. Moon et al. [1] performed an experimental study in a 6 × 6 rod bundle to investigate the effects of spacer grids on the single-phase convection heat transfer enhancement. The experimental data showed that the Reynolds number has a significant impact on the heat transfer enhancement only when the Reynolds numbers are lower than about 10,000. They suggested more systematic experiments should be performed using various spacer rids with large blockage ratios at low Reynolds numbers, considering an early phase of the re-flood conditions. Miller et al. [2] reported a two-phase dispersed droplet flow investigation of the grid-enhanced heat transfer augmentation using a 7 x 7 rod bundle heat transfer facility. It was found that a second-stage augmentation occurs under wet grid conditions at a distance of 10 diameters downstream of the grid. This second-stage augmentation was not observed under dry-grid conditions, nor was it observed in single-phase steam cooling tests [2]. Schlegel et al. [3] performed extensive experiments in pipes with diameters up to 0.304 m to collect area-averaged void fraction data using electrical impedance void meters for the purpose of remedying an inability of current drift-flux models to accurately predict the void fraction in churn-turbulent flows in large diameter pipes. They obtained a distribution parameter modified for churn-turbulent flows. It has been evaluated through comparison of the void fraction predicted by the drift-flux model and the measured void fraction.

关键词： thermal hydraulics substantial progress two-phase Heat convection TWO-PHASE Diameter FUEL ELEMENT CLUSTERS Heat exchange intensification void ratio distributed parameter thermohydraulics LARGE DIAMETER PIPE

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Global distribution of the residual ozonosphere field based on TOMS satellite data 1979-1992

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DOKLADY EARTH SCIENCES 2007年第4期414卷 582-586页

作者： Steblova, R. S. Russian Acad Sci Inst Terr Magnetism Ionosphere & Radio Wave P Troitsk 142092 Moscow Oblast Russia

The residual ozone field (ROF), i.e., the global distribution of the totalozone content (TOC) after subtracting the contribution of calm solar energy, was constructed. Onlythe experimental Total Ozone Mapping Spectrometer (TOMS) Nimbus 7 data (1978-1993) were used in [1,2]. In order to suppress temporal variations, the daily TOC values were first averaged over a 1 -yrperiod for each year of the TOMS data and then averaged over the entire 14-year period. Annual andgeneral charts of TOC were plotted. For each version, the global mean TOC meridional profile wasplotted by averaging meridional profiles. Differences between the meridional TOC distribution inthis chart and the global mean meridional distribution of this parameter make up elements of theROF. The ROF value is expressed in Dobson units (DU) with a sign. It is positive if the TOC value atthe current point exceeds the global mean value at the same latitude and is negative if therelation is the opposite. The ROF charts clearly demonstrate the following global division of theEarth's surface into two regions with the distribution of ROF elements of only one sign. Theexistence of anomalies confined to one field of the same type is a regional peculiarity. The onlydistortion is a negative anomaly over North America located in the positive ROF region. The ROFmorphology is stable.

关键词： Total Ozone Mapping Spectrometer Earth surface Ozone Layer TOC (total organic carbon) distributed parameter

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Influence of the void fraction profile on the distribution parameter C₀ for a bubbly gas-liquid flow in a horizontal round pipe

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NUCLEAR ENGINEERING AND DESIGN 2008年第4期238卷 1155-1158页

作者： Haoues, L. Ekhnovitch, A. Teyssedou, A. Ecole Polytech Inst Genie Nucl Dept Genie Phys Montreal PQ H3C 3A7 Canada

This paper presents the results of a numerical experiment on the influence of the void fraction profile on the distribution parameter C-0 in a horizontal bubbly two-phase flow. It was shown that for non-symmetric void fraction profiles, which occur normally in horizontal flows, the distribution parameter may be less than 1. In this case, the ratio of the volumetric flow quality P to the average void fraction (a can also be less than 1. (C) 2007 Elsevier B.V. All rights reserved.

关键词： liquid flow Sparkling wine Horizon void ratio distributed parameter circular tubes

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Hydrodynamics and structure of two-phase flow in the bubbling regime in small-diameter tubes

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Thermal Engineering 2006年第4期53卷 325-329页

作者： Omar, Kh. Pokhvalov, Yu.E. Commission on Atomic Energy Subscriber's Box 6091 Damascus Syria Moscow Engineering Physics Institute Kashirskoe sh. 31 Moscow 115409 Russia

Experimental data on the true gas void fraction in a vertical tube under the bubbling flow regime are presented. A generalization of these data on the basis of the drift flow model of Zuber with the distribution parameter C0= 1.2 and the weighted average gas velocity u2j= 0.16 m/s is given. The results of assessing the parameters of the downcoming flow of the fluid in the near wall zone are shown. © Nauka/Interperiodica 2006.

关键词： Experimental data fluid flow BUBBLE FLOW void ratio Hydrodynamics Bubbling distributed parameter flow regime TWO PHASE FLOW Standpipes

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VERTICAL MOTION DIAGNOSTICS RELATED TO Q-VECTORS, AND THE REORGANIZATION OF A COLD FRONTAL SYSTEM

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METEOROLOGY AND ATMOSPHERIC PHYSICS 1988年第2期39卷 65-73页

作者： TAPP, RG 1. Bureau of Meteorology Research Centre Gr-O Box 1289K 3001 Melbourne Australia

Estimates of vertical motion obtained by explicit solution of the quasi-geostrophic omega equation expressed in terms of Q-vectors (Hoskins et al., 1978) were compared with qualitative estimates based on the divergence of Q-vectors. The horizontal distributions of each were broadly similar, but differed in their detail. At any level, the relative magnitudes of centres of vertical motion varied between the parameters. The precise locations of the main centres also differed. Greater differences existed in the vertical distributions of the parameters. The divergence ofQ andF _Q of Hoskins et al. (1978) both reached maximum values in upper levels, whereas peak values of ω occurred in middle levels. A vertical distribution similar to ω was achieved ifF _Q was divided by a stability parameter. The diagnosed vertical velocities appeared consistent with the restructuring of a summertime cold front as it crossed waters south of Australia.

关键词： Diagnosis divergence Reorganisation Explicit Solution Divergence Divergence vertical motion cold front maximum value divergence Vertical distribution distributed parameter

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From conservation laws to wave propagation and back -dynamics and control in combined heat/electricity generation

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IFAC-PapersOnLine 2015年第11 11期48卷 402-407页

作者： Râsvan, Vladimir Department of Automatic Control University of Craiova 13 A.I.Cuza str. CraiovaRO-200585 Romania

Starting from some pioneering papers in distributed parameter control systems for steam turbines and their auxiliaries, a bilinear model for steam turbines with steam extraction and “long” steam pipes was elaborated and the feedback control synthesis has been performed using a suitable control Liapunov functional of quadratic type, both for distributed parameters systems and their lumped parameter approximation. The synthesized control ensures global stabilization of the steady state solution. It has been observed much later that the linearized steam wave propagation equations underlying the model were in fact a simplified linearized version of the conservation laws of the isentropic flow. Following this remark and bearing in mind the recent advances in the control of the systems described by conservation laws, the model of the combined heat electricity generation is re-written as a system which is linear in control; consequently the feedback stabilization also requires re-examination. © 2015

关键词： distributed parameter control systems Control system synthesis Feedback Linearization Physical properties Stabilization Steam Steam turbines Wave propagation Conservation law distributed parameter Electricity generation Feedback stabilization Liapunov functionals Lumped parameter approximation Steady state solution Wave propagation equations

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Distribution parameters and form-factors in quasi-one-dimensional modeling of nonequilibrium two-phase flows

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Thermal Engineering 2004年第7期51卷 566-577页

作者： Kornienko, Yu.N. pl. Bondarenko 1 Obninsk Kaluga Oblast 249033 Russia

Generalized formulations and an improved method are presented for constructing analytical local and integral (quasi-one-dimensional) closure relationships for the distribution parameters and form-factors for wall friction and heat and mass transfer. This method accounts for the nonuniformity of spatial two-phase flows in tubes, annular channels, and fuel rod assemblies.

关键词： Wall friction heat and mass transfer distributed parameter nonuniformity form factors Nonequilibrium

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