检索结果-内蒙古大学图书馆

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

来源：评论

学校读者我要写书评

暂无评论

Hybrid FDTD-SPICE analysis of radiated emission from PCB with integrated circuits

Hybrid FDTD-SPICE analysis of radiated emission from PCB wit...

引用

IEEE International Symposium on Electromagnetic Compatibility

作者： Nishizawa, A Kobidze, G Tanabe, S Mitsubishi Electr Corp Adv Technol R&D Ctr Electromech Syst Dept Amagasaki Hyogo 6618661 Japan

ISBN: (纸本)0780365690

The radiated emission from ground bouncing and transmission lines have been analyzed using the Finite Difference Time Domain (FDTD) and SPICE hybrid method. This method can consider both the non-linear electric characteristics of IC and the distributed parameters of printed circuit boards (PCB). The computed results of the electric field at 3m from the PCB were validated by the measurements. The hybrid tool allows to calculate the noise spectrum and radiation pattern. Another advantage is that this method can separate the contributions of various noise sources. This analysis tool and methodology is useful to design transmission lines and power/ground planes in PCB.

关键词： radiated emission noise spectrum Integrated circuits Transmission Lines distributed parameter Noise sources Electronic circuits Power cables

来源：评论

学校读者我要写书评

暂无评论

Crosstalk for curvilinear conductors by utilising a nonuniform transmission line approach

Crosstalk for curvilinear conductors by utilising a nonunifo...

引用

10th Topical Meeting on Electrical Performance of Electronic Packaging

作者： Ye, CF Li, EP Shenn, GY Inst High Performance Comp EMC Div Singapore 116281 Singapore

A novel approach to derive nonuniform transmission line equations for curvilinear multiconductor systems by using scalar and vector potentials associated with boundary conditions is presented. Crosstalk of bent conduc... 详细信息

ISBN: (纸本)0780370244

关键词： nonuniform transmission line distributed parameter discontinuity

来源：评论

学校读者我要写书评

暂无评论

Study on refrigerant circuitry of condenser coils with exergy destruction analysis

引用

APPLIED THERMAL ENGINEERING 2000年第6期20卷 559-577页

作者： Liang, SY Wong, TN Nathan, GK Nanyang Technol Univ Sch Mech & Prod Engn Singapore 639798 Singapore

A numerical model of air-cooled condenser coils is proposed to investigate the coil performance. In this model, the properties of refrigerant and air, as well as six exergy destruction components associated with different sources of irreversibility are computed locally along the coil based on numerous control volumes. The governing equations for a control volume are presented together with a computer simulation procedure to link all the control volumes together for a coil. Using this model, the coil characteristics in heat transfer, fluid flow and exergy destruction are analyzed with an emphasis on the refrigerant circuitry investigation. The study shows that the thermal resistance of refrigerant side is comparable to that of air side and the coil performance can be improved by varying the refrigerant mass velocity along the flow path. Compared with a common coil, using a complex refrigerant circuitry that the refrigerant circuits are properly branched or joined may reduce the heat transfer area by approximately 5% in coil design. This study also shows that the quantitative analysis on the exergy destruction components gives a clear picture in the coil performance evaluation. The results show that the criterion of exergy destruction ratio conforms well to that of coil heat flux in coil performance evaluation under the specified conditions. (C) 2000 Elsevier Science Ltd. All rights reserved.

关键词： condenser coil modeling refrigerant circuitry distributed parameter exergy destruction coil performance evaluation

来源：评论

学校读者我要写书评

暂无评论

Effect of kinetic comminution parameters and classification efficiency on output during closed-circuit cement grinding, Part 2

引用

ZKG INTERNATIONAL 2000年第5期53卷 290-+页

作者： Ito, M

The simulation of closed-circuit grinding was carried out using a comminution kinetics equation containing the parameters k and n and an equation describing classification efficiency derived fi om the operational data of three representative types of classifiers. The results show that the output of finished product from the grinding plant increases the higher the efficiency of classification However the increasing rate decreases with excess-increasing classification efficiency when the fineness is expressed by the specific surface area. The throughput of ground material through the mill, which was used as an indicator of the maximum production late, increased with rising classification efficiency. Under the usual conditions of cement grinding there was a specific relationship between the parameters k (comminution kinetic parameter) and n (particle sized distribution parameter). Under these conditions, the mill output, which was controlled to give a constant specific surface area of the finished product, increased with a decrease in the parameter n.

关键词： Output Manufactured products CLOSED LOOP mill Natural Increase classification efficiency Comminution operating data distributed parameter milling SPECIFIC AREA

来源：评论

学校读者我要写书评

暂无评论

Conformational transitions of DNA induced by changing water content of the sample: A theoretical study

引用

JOURNAL OF BIOMOLECULAR STRUCTURE & DYNAMICS 2000年第5期17卷 913-920页

作者： Tolstorukov, MY Maleev, VY Kharkov State Univ Chair Mol & Appl Biophys UA-310077 Kharkov Ukraine

A semi-phenomenological model with spatially distributed parameters is suggested to describe the processes of conformational transitions induced with change of water content of wet DNA samples. It allows describing conformational dynamics of DNA molecules with heterogeneous primary structures. It has been shown that the process of cooperative conformational transition can be simulated as propagating front of a new conformation. The evolution of a conformational perturbation of DNA molecule has been described. It can collapse for finite time or occupy the whole molecule depending on the water content of the sample.

关键词： DNA Nucleic Acid Conformation Water 核酸构象水 Nucleic Acid Conformation conformational transition moisture content Theoretical Study distributed parameter DNA

来源：评论

学校读者我要写书评

暂无评论

Size distribution and chemical composition of marine aerosols: a compilation and review

引用

TELLUS SERIES B-CHEMICAL AND PHYSICAL METEOROLOGY 2000年第4期52卷 1104-1122页

作者： Heintzenberg, J Covert, DC Van Dingenen, R Inst Tropospher Res D-04318 Leipzig Germany Univ Washington Seattle WA 98195 USA Commiss European Communities Joint Res Ctr Inst Environm I-21020 Ispra VA Italy

Some 30 years of physical and chemical marine aerosol data are reviewed to derive global-size distribution parameters and inorganic particle composition on a coarse 15 degrees x 15 degrees grid. There are large gaps in geographical and seasonal coverage and chemical and physical aerosol characterisation. About 28% of the grid cells contain physical data while there are compositional data in some 60% of the cells. The size distribution data were parametrized in terms of 2 submicrometer log-normal distributions. The sparseness of the data did not allow zonal differentiation of the distributions. By segregating the chemical data according to the major aerosol sources, sea salt, dimethylsulfide, crustal material, combustion processes and other anthropogenic sources, much information on mass concentrations and contribution of natural and anthropogenic sources to the marine aerosol can be gleaned from the data base. There are significant meridional differences in the contributions of the different sources to the marine aerosol. Very clearly, we see though that the global marine surface atmosphere is polluted by anthropogenic sulfur. Only in the case of sulfur components did the coverage allow the presentation of very coarse seasonal distributions which reflect the spring blooms in the appropriate parts of the oceans. As an example of the potential value in comparing the marine aerosol data base to chemical transport models, global seasonal meridional MSA distributions were compared to modelled MSA distributions. The general good agreement in mass concentrations is encouraging while some latitudinal discrepancies warrant further investigations covering other aerosol components such as black carbon and metals.

关键词： MAJOR SYSTEM ACQUISITION chemical compounds Coverage aerosols chemical transport distributed parameter physical data Database

来源：评论

学校读者我要写书评

暂无评论

Probabilistic accident consequence uncertainty analysis of the whole program package COSYMA

引用

RADIATION PROTECTION DOSIMETRY 2000年第3期90卷 365-372页

作者： Ehrhardt, J Jones, JA Goossens, LHJ Forschungszentrum Karlsruhe Inst Kern & Energietechn D-76021 Karlsruhe Germany Natl Radiol Protect Board Didcot OX11 0RQ Oxon England Delft Univ Technol NL-2600 GB Delft Netherlands

The overall uncertainty analysis of the program package COSYMA for assessing the radiological consequences of nuclear accidents builds on the results of a series of individual uncertainty and sensitivity analyses of its submodules. A set of 186 model parameters was identified which contribute most to the uncertainties of endpoints. Probabilistic accident consequence assessments with 144 weather sequences were performed for each of 300 sample sets derived from the uncertainty distributions of these parameters by Latin hypercube sampling. The evaluation of the results provided confidence bounds for the complementary cumulative frequency distributions of endpoints for three different source terms covering a wide range of release fractions. Concluding sensitivity analyses identified the most important model parameters responsible for the uncertainties of endpoints.

关键词： model parameters Nuclear disasters Nuclear Accidents confidence Remainder of a Series Telescoping a series Accidents Uncertainty distributed parameter

来源：评论

学校读者我要写书评

暂无评论

Drop-size distribution characteristics in tropical mesoscale convective systems

引用

JOURNAL OF APPLIED METEOROLOGY 2000年第6期39卷 760-777页

作者： Cifelli, R Williams, CR Rajopadhyaya, DK Avery, SK Gage, KS May, PT Univ Maryland Baltimore Cty Joint Ctr Earth Syst Technol Baltimore MD 21228 USA Univ Colorado Cooperat Inst Res Environm Sci Boulder CO 80309 USA NOAA Aeron Lab Boulder CO 80303 USA Bur Res Meteorol Ctr Melbourne Vic Australia

Drop-size distribution characteristics were retrieved in eight tropical mesoscale convective systems (MCS) using a dual-frequency (UHF and VHF) wind profiler technique. The MCSs occurred near Darwin, Australia, during the 1993/94 wet season and were representative of the monsoon (oceanic) regime. The retrieved drop-size parameters were compared with corresponding rain gauge and disdrometer data, and it was found that there was good agreement between the measurements, lending credence to the profiler retrievals of drop-size distribution parameters. The profiler data for each MCS were partitioned into a three-tier classification scheme (i.e., convective, mixed convective-stratiform, and stratiform) based on a modified version of Williams et al. to isolate the salient microphysical characteristics in different precipitation types. The resulting analysis allowed for an examination of the drop-size distribution parameters in each category for a height range of about 2.1 km in each MCS. In general, the distributions of all of the retrieved parameters showed the most variability in convection and the least in stratiform, with the mixed convective-stratiform category usually displaying intermediate characteristics. Although there was significant overlap in the range of many of the parameter distributions, the mean profiles were distinct. In the stratiform region, there was minimal vertical structure for all of the drop-size distribution parameters. This result suggests an equilibrium between depletion (e.g., evaporation) and growth (e.g., coalescence) over the height range examined. In contrast, the convective parameter distributions showed a more complicated structure, probably as a consequence of the complex microphysical processes occurring in the convective precipitation category. Reflectivity-rainfall (Z-R) relations of the form Z = AR(B) were developed for each precipitation category as a function of height using linear regressions to the profiler retrievals of R and

关键词： drop-size distribution tropical mesoscale convective systems mesoscale convective systems (MCS) wind profiler technique Drop size distribution height profiler Category MCS gene distributed parameter

来源：评论

学校读者我要写书评

暂无评论

High gain output feedbacks for systems with distributed parameters

引用

MATHEMATICAL MODELS & METHODS IN APPLIED SCIENCES 1999年第6期9卷 933-940页

作者： Nikitin, S Nikitina, M Arizona State Univ Dept Math Tempe AZ 85283 USA

This paper deals with the high gain feedback stabilization of single input-single output (SISO) minimum-phase systems with distributed parameters. Sufficient conditions for an infinite-dimensional SISO system to be stabilized by a high gain output feedback are obtained. The results of this paper are useful for designing and tuning high gain output feedbacks in numerous industrial control applications.

关键词： Output Output feedback Feedback single input single output systems high gain distributed parameter

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：