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A computational study of the role of particle size standard deviation on the collision frequency in differential settling

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International Journal of Sediment Research 2013年第1期28卷 34-45页

作者： c.HEILIGER N.B.KAYE f.Y.TESTIK civil Engineering Clemson UniversityClemsonSC29634USA

The results of a simple computational model for differential settling are presented illustrating the significant role that particle size distribution plays in collision frequency and sedimentation rate of particles in a quiescent environment. The model tracks a large number of particles（order 10;） with log-normally distributed diameters,as they settle at their Stokes settling *** collisions are detected and result in larger particles that fall more rapidly.A number of simplifying assumptions are made in the model in order to avoid empirical correlations for phenomena such as collision efficiency and particle *** simplifying assumptions were needed to isolate and quantify the role of the particle size *** concentration profiles indicate that,even in the absence of collisions, the standard deviation（σ;） of the particle size strongly influences the bulk mass settling rate as,for largerσ;, more mass is concentrated in larger,faster falling *** collision frequency is also a strong function ofσ;. for a given mass concentration the collision frequency first increases linearly with increasingσ;as greater variation in particle size leads to greater variation in particle velocity,and shorter times for particles to catch each *** largerσ;more mass is concentrated in larger particles,so,for a given mass concentration,there are fewer particles per unit volume,increasing the mean distance between the particles and reducing the collision *** implications of these results for sedimentation measurement using optical attenuation techniques are discussed.

关键词： Settling Sediment size distribution Sediment collision frequency coefficient of variation

A review of friction stir welding of steels： Tool, material flow, microstructure, and properties

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Journal of Materials Science & Technology 2018年第1期34卷 39-57页

作者： f.c. Liu Y. Hovanski M.P. Miles c.D. Sorensen T.W. Nelson Department of Mechanical Engineering Brigham Young University Provo UT 84602. USA Manufacturing Engineering Technology Brigham Young University Provo UT 84602 USA

considerable progress has been achieved in friction stir welding （fSW） of steels in every aspect of tool fab- rication, microstructure control and properties evaluation in the past two decades. With the development of reliable welding tools and precise control systems, fSW of steels has reached a new level of technical maturity. High-quality, long welds can be produced in many engineering steels. compared to traditional fusion welding, fSW exhibits unique advantages producing joints with better properties. As a result of active control of the welding temperature and/or cooling rate, fSW has the capability of fabricating steel joints with excellent toughness and strength. for example, unfavorable phase transformations that usu- ally occur during traditional welding can be avoided and favorable phase fractions in advanced steels can be maintained in the weld zone thus avoiding the typical property degradations associated with fusion welding. If phase transformations do occur during fSW of thick steels, optimization of microstructure and properties can be attained by controlling the heat input and post-weld cooling rate.

关键词： Joining Stainless steels carbon steels High strength low alloy (HSLA) steels Advanced high strength steels (AHSS) Oxide dispersion strengthened (ODS) steels

Drying of pasty and granular materials in mechanically and conventional spouted beds

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Particuology 2019年第1期17卷 176-183页

作者： Robson c. Sousa Maria c. ferreira Haritz Altzibar fábio B. freire José T. freire Rural and chemical Engineering Department Federal University of Espirito SantoAlegreES. Brazil chemical Engineering Department Federal University of Sao CarlosSao CarlosSPBrazil chemical Engineering Department University of Basque CountryBilbaoSpain

A contactor vessel was built to operate as either a mechanically or a conventional spouted bed for the purpose of analyzing the drying of pasty and granular materials under comparable conditions in both configurations. A classical conical–cylindrical spouted bed with a 60° conical base and an air inlet central orifice was modified to enable the switch by introducing in the vessel’s center an open helicoidal conveyor screw placed above the air inlet orifice. This screw is removable and conveniently returns the bed to its conventional spouted configuration. Experiments on drying solutions (calcium carbonate suspensions and skimmed milk) and granular materials (porous alumina particles) were performed for various bed parameter settings. The spouting pressure drop, outlet air temperature, and relative humidity were measured over time under different conditions. Mechanical agitation is proved effective in drying diluted carbonate calcium liquid suspensions and coarse porous alumina particles at an air velocity approximately 50% lower in comparison to drying in a conventional spouted bed. The conventional spouted bed performed better at drying liquid skimmed milk as the mechanical agitation combined with the axial inlet air flow is not effective in mitigating sticking and powder agglomeration in the bed when handling pastes of complex composition. Introducing mechanical agitation in the designed setup broadens the operating range of a conventional spouted bed with axial air flow in the inlet.

关键词： characteristic curve Drying kinetic Spouted-bed dynamics Mechanical agitation Alumina particles Paste drying

coupling sensor observation services and web processing services for online geoprocessing in water dam monitoring

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International Journal of Digital Earth 2018年第1期11卷 64-78页

作者： c.Stasch B.Pross B.Gräler c.Malewski c.förster S.Jirka 52°North GmbH Martin-Luther-King-WegMünsterGermany Wupperverband Untere LichtenplatzerWuppertalGermany

Novel sensor technologies are rapidly *** enable a monitoring and modelling of our environment in a level of detail that was not possible a few years ***,while the raw data produced by these sensors are useful to get a first overview,it usually needs to be post-processed and integrated with other data or models in different *** this paper,we present an approach for integrating several geoprocessing components in the TaMIS water dam monitoring system developed with the Wupperverband,a regional waterbody authority in *** approach relies upon the OGc Web Processing Service and is tightly coupled with Sensor Observation Service instances running at the *** implementing the standardized XML-based interface,lightweight REST APIs have been developed to ease the integration with thin Web clients and other Web-based *** this standards-based approach,new processing facilities can be easily integrated and coupled with different observation data sources.

关键词： Geoprocessing sensor web spatial data infrastructure water monitoring dam monitoring

Infuence of elemental composition in environmental impacts of steel

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Journal of Iron and Steel Research International 2020年第5期27卷 598-607页

作者： E.Batuecas c.Mayo R.Diaz f.J.Perez Thermal and fluid Engineering Department Carlos III University of Madrid28911 LeganesMadridSpain chemical and Materials Engineering Department Complutense University of Madrid28040 MadridSpain Technical Sciences and Engineering UDIMA University28400 Collado VillalbaMadridSpain。

The environmental behavior of four steels was *** the operation phase of concentrating solar power plants,steels withstand high temperature because of its contact with molten ***,choosing the steel type for the molten salt tanks remains a great *** the cold tank,carbon steel is usually used although an approach with low chromium content steel is being studied for these ***,in high temperature applications,such as hot store tank,austenitic stainless steel is the most frequent ***,ferritic steel is being considered as a promising material in these *** many researchers studied the steel technical properties without considering their environmental damages,this work aimed to introduce the environmental aspects into the material choice by using the life cycle assessment *** one hand,the results showed the environmental adequacy of carbon steel against low chromium content *** the other hand,the results obtained in those steels suitable in high temperature application revealed signifcant environmental benefts from the ferritic steel instead of the austenitic steel.

关键词： Renewable energy concentrating solar power Life cycle assessment Molten salt ferritic steel Austenitic steel

Kinetics and mechanistic investigation of epoxide/cO2 cycloaddition by a synergistic catalytic effect of pyrrolidinopyridinium iodide and zinc halides

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Journal of Energy chemistry 2019年第10期28卷 35-42页

作者： Abdul Rehman Valentine c. Eze M.f.M.Gunam Resul Adam Harvey School of Engineering Merz CourtNewcastle UniversityNewcastle Upon Tyne NE1 7RUUK Department of chemical and Polymer Engineering University of Engineering and Technology LahoreFaisalabad CampusPakistan

formation of styrene carbonate (Sc) by the cycloaddition of cO2 to styrene oxide (SO) catalysed by pyrrolidinopyridinium iodide (PPI) in combination with zinc halides (Zncl2, ZnBr2 and ZnI2) was investigated. complete conversion of the SO to Sc was achieved in 3 h with 100% selectivity using 1/0.5 molar (PPI/ZnI2) catalyst ratio under mild reaction conditions i.e., 100℃ and 10 bar cO2 pressure. The synergistic effect of ZnI2 and PPI resulted in more than 7-fold increase in reaction rate than using PPI alone. The cycloaddition reaction demonstrated the first-order dependence with respect to the epoxide, cO2 and catalyst concentrations. Moreover, the kinetic and thermodynamic activation parameters of Sc formation were determined using the Arrhenius and Eyring equations. The positive values of △H(42.8 kJ mol^-1) and △G(102.3 kJ mol^-1) revealed endergonic and chemically controlled nature of the reaction, whereas the large negative values of △S(-159.4 J mol^-1 K^-1) indicate a highly ordered activated complex at the transition state. The activation energy for Sc formation catalyzed by PPI alone was found to be 73.2 kJ mol^-1 over a temperature range of 100-140℃, which was reduced to 46.1 kJ mol^-1 when using PPI in combination with ZnI2 as a binary catalyst. Based on the kinetic study, a synergistic acid-based reaction mechanism was proposed.

关键词： cycloaddition cO2 utilization cyclic carbonates Homogeneous catalysis Activation energy

filling the Disaster Data Gap:Lessons from cataloging Singapore’s Past Disasters

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International Journal of Disaster Risk Science 2021年第2期12卷 188-204页

作者： Yolanda c.Lin feroz Khan Susanna f.Jenkins David Lallemant Department of Geography and Environmental Studies University of New MexicoAlbuquerqueNM87131USA Asian School of the Environment Nanyang Technological UniversitySingapore639798Singapore Earth Observatory of Singapore Singapore639798Singapore Disaster Resilience Leadership Academy Tulane UniversityNew OrleansLA70112USA

International disaster databases and catalogs provide a baseline for researchers,governments,communities,and organizations to understand the risk of a particular place,analyze broader trends in disaster risk,and justify investments in *** because Singapore is routinely identified as one of the safest countries in the world,Singapore’s past disasters have not been studied extensively with few events captured in major global databases such as *** this article,we fill the disaster data gap for postwar Singapore(1950–2020)using specified metrics through an archival search,review of literature,and analysis of secondary *** present four key lessons from cataloging these ***,we expand Singapore’s disaster catalog to 39 events in this time period and quantify the extent of this data ***,we identify the mitigating actions that have followed past events that contribute to Singapore’s present-day ***,we discuss how these past events uncover continuities among vulnerability bearers in ***,we identify limitations of a disaster catalog when considering future *** expanding the disaster catalog,this case study of Singapore supports the need for comprehensive understanding of past disasters in order to examine current and future disaster resilience.

关键词： catalog Database Data gap Disasters Resilience Singapore

Analytical　Study　on　Impingement　Heat　Transfer　with　Single－Phase　free－Surface　circular　Liquid　Jets

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Journal of Thermal Science 1996年第4期5卷 271-277页

作者： c.f.Ma T.Masuoka 等 BeijingPolytechnicUniversity Beijing100022China KyushuInstituteofTechnology Kitakyushu804Japan

An analytical research was conducted to study heat transfer from horizontal surfaces to normally impinging circular jets under arbitrary-heat-flux conditions. The laminar thermal and hydraulic boundary layers were divided into five regions of flow. General expressions of heat transfer coefficients were obtained in all the four regions of stagnation and wall jet zones before the hydraulic jump.

关键词： jet impingement connective heat transfer boundary layer theory.

Local convective Heat Transfer from Small Heaters to Impinging Submerged Axisymmetric Jets of Seven coolants with Prandtl Number Ranging from 0.7 to 348

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Journal of Thermal Science 1997年第4期6卷 286-297页

作者： H.Sun c.f.Ma 等 DepartmentofThermalScience＆Engineering BeijingPolytechnicUniversityBeijing100022China DepartmentofT

Using seven working fluids, a systematic experimental study was performed to investigate the local convective heat transfer from vertical heaters to impinging circular submerged jets in the range of Reynolds number between 1.17 ×102 and 3.69 × 104 with the emphasis placed on the examination of Prandtl number dependence. Heat transfer coefficiellts at the stagnation point were collected and correlated with the plate held within and beyond the potential core. Radial distribution of the local heat transfer coefficient was measured with five test liquids. Based on the measured profiles of the local heat transfer, a correlation was developed to cover the entire range of the radial distance. Besides the presellt data, the correlations developed in this work were also compared with a large quantity of available data of circular air jets. General agreement was observed between the air data and the correlat ions.

关键词： forced convection jets Prandtl number