Experiments on two-phase flow in hydraulic jump on pebbled rough bed:Part 1–Turbulence properties and particle chord time and length

This study reported and discussed turbulence characteristics,such as turbulence intensity,correlation time scales,and advective length scales.The characteristic air–water time scale,including the particle chord time and length and their probability density functions(PDFs),was investigated.The results demonstrated that turbulence intensity was relatively greater on a rough bed in the roller length,whereas further downstream,the decay rate was higher.In addition,the relationship between turbulence intensity and dimensionless bubble count rate reflected an increase in turbulence intensity associated with the number of entrained particles.Triple decomposition analysis(TDA)was performed to determine the contributions of slow and fast turbulent components.The TDA results indicated that,regardless of bed type and inflow conditions,the sum of the band-pass(T'_(u))and high-pass(T″_(u))filtered turbulence intensities was equal to the turbulence intensity of the raw signal data(T_(u)).T″_(u) highlighted a higher turbulence intensity and larger vorticities on the rough bed for an identical inflow Froude number.Additional TDA results were presented in terms of the interfacial velocity,auto-and cross-correlation time scales,and longitudinal advection length scale,with the effects of low-and high-frequency signal components on each highlighted parameter.The analysis of the air chord time indicated an increase in the proportion of small bubbles moving downstream.The second part of this research focused on the basic properties of particle grouping and clustering.

Experiments on two-phase flow in hydraulic jump on pebbled rough bed:Part 2–Bubble clustering

A survey on bubble clustering in air–water flow processes may provide significant insights into turbulent two-phaseflow.These processes have been studied in plunging jets,dropshafts,and hydraulic jumps on a smooth bed.As a first attempt,this study examined the bubble clustering process in hydraulic jumps on a pebbled rough bed using experimental data for 1.70<Fr_(1)<2.84(with Fr_(1) denoting the inflow Froude number).The basic properties of particle grouping and clustering,including the number of clusters,the dimensionless number of clusters per second,the percentage of clustered bubbles,and the number of bubbles per cluster,were analyzed based on two criteria.For both criteria,the maximum cluster count rate was greater on the rough bed than on the smooth bed,suggesting greater interactions between turbulence and bubbly flow on the rough bed.The results were consistent with the longitudinal distribution of the interfacial velocity using one of the criteria.In addition,the clustering process was analyzed using a different approach:the interparticle arrival time of bubbles.The comparison showed that the bubbly flow structure had a greater density of bubbles per unitflux on the rough bed than on the smooth bed.Bed roughness was the dominant parameter close to the jump toe.Further downstream,Fr_(1) predominated.Thus,the rate of bubble density decreased more rapidly for the hydraulic jump with the lowest Fr_(1).

纳米级PEBBLE传感器研究进展

介绍了纳米量级 PEBBLE 传感器的特点、制备方法、当前的应用及发展趋势,重点阐述了基于对细胞内氧成分探测的比例参量 PEBBLE 传感器。

Current Status of the Fabrication of Li_4SiO_4and Beryllium Pebbles for CN HCCB TBM in SWIP

Tritium breeder and neutron multiplier as functional materials play an important role not only in ITER test blanket module （TBM） but also in fusion reactor. The paper describes the status of the fabrication of the two materials in Southwestern Institute of Physics （SWIP）. Li4SiO4 pebbles were fabricated by melt-spraying method. Most of the pebbles with the diazneter of 1.0 mm are well spherically shaped. The properties of the pebbles have been investigated. The results show that the pebbles produced by this method have a high density of 93% TD （theoretical density）. It was also found that the open/closed porosity will be decreased after thermal treatment, but the average crush load will be increased to 7 N. The rotating electrode process （REP） has been adopted to produce beryllium pebble for impurity control and mass production. The pebbles with the diameter of 1.0 mm were produced by REP. The beryllium pebbles produced by REP look almost perfectly spherical with a very smooth surface and a high density of 98% TD. The test results indicate that REP method has excellent prospects for the fabrication of beryllium pebbles and the attractiveness of their properties.

The Shandong Shidao Bay 200 MWe High-Temperature Gas-Cooled Reactor Pebble-Bed Module(HTR-PM)Demonstration Power Plant:An Engineering and Technological Innovation

After the first concrete was poured on December 9,2012 at the Shidao Bay site in Rongcheng,Shandong Province,China,the construction of the reactor building for the world’s first high-temperature gascooled reactor pebble-bed module(HTR-PM)demonstration power plant was completed in June,2015.Installation of the main equipment then began,and the power plant is currently progressing well toward connecting to the grid at the end of 2017.The thermal power of a single HTR-PM reactor module is 250 MWth,the helium temperatures at the reactor core inlet/outlet are 250/750℃,and a steam of 13.25 MPa/567℃ is produced at the steam generator outlet.Two HTR-PM reactor modules are connected to a steam turbine to form a 210 MWe nuclear power plant.Due to China’s industrial capability,we were able to overcome great difficulties,manufacture first-of-a-kind equipment,and realize series major technological innovations.We have achieved successful results in many aspects,including planning and implementing R&D,establishing an industrial partnership,manufacturing equipment,fuel production,licensing,site preparation,and balancing safety and economics;these obtained experiences may also be referenced by the global nuclear community.

Study of heat transfer by using DEM–CFD method in a randomly packed pebble-bed reactor

The pebble-bed reactor is one of the most promising designs for the nuclear energy industry. In this paper,a discrete element method-computational fluid dynamics(DEM-CFD) approach that includes thermal conduction, radiation, and natural convection mechanisms was proposed to simulate the thermal-fluid phenomena after the failure of forced circulation cooling system in a pebble-bed core. The whole large-scale packed bed was created using the DEM technique, and the calculated radial porosity of the bed was validated with empirical correlations reported by researchers. To reduce computational costs, a segment of the bed was extracted, which served as a good representative of the large-scale packed bed for CFD calculation. The temperature distributions simulated with two different fluids in this DEM-CFD approach were in good agreement with SANA experimental data. The influence of the natural convection mechanism on heat transfer must be taken into account for coolants with strong convective capacity. The proposed DEM-CFD methodology offers a computationally efficient and widely applied method for understanding the heat transfer process in a pebble-bed core. The method can also be easily extended to assess the passive safety features of newly designed fluoride-salt-cooled pebble-bed reactors.

Thermal-Hydraulic System Study of the Helium Cooled Pebble Bed (HCPB) Test Blanket Module (TBM) for ITER Using System Code RELAP5

The HCPB concept has been a European DEMO reference concept for nearly one decade. Detailed thermal-hydraulic study on the control behavior of the whole system is one of the important parts of this development. The thermal-hydraulic effect of the TBM-combined cooling circuit during a cyclic operation in ITER has been studied using the system code RELAP5. The RELAP5 is based on an one-dimensional, transient two-fluid model for the flow of a two-phase steam-water mixture that can contain noncondensable components like Helium. The RELAP5models are modified to take the cyclic operation of the circulator, heat, exchanger, bypass, valves etc in to account. A sequence of operational phases is investigated, starting from the cold state through the heating phase that brings the system to a stand-by condition, followed by typical power cycles applied in ITER. The results show that the implemented control mechanisms keep the inlet temperature to the TBM and the total mass flow rate at the required values through all phases.

美国佛罗里达pebble磷矿浮选流程试验

本文对美国佛罗里达pebble磷矿进行了浮选流程试验,试验采用了3种流程,即硅浮选—镁浮选流程,镁浮选—硅浮选流程和镁浮选—脱泥—硅浮选流程。试验结果表明:镁浮选—脱泥—硅浮选流程得到的精矿不但质量较好,而且有较高的P2O5回收率,其综合精矿P2O5品位为30.45%,MgO质量分数为0.98%,P2O5回收率为80.13%。镁浮选—脱泥—硅浮选流程具有流程及药剂制度简单,药剂用量少,试验指标高等优点,是美国佛罗里达pebble磷矿综合利用的有效方法。

Modeling of Fuel Elements Cycling System in Pebble Bed Reactor Based on Timed Places Control Petri Nets

Pebble bed reactors use cycling scheme of spherical fuel elements relying on fuel elements cycling system (FECS). The structure and control logic of FECS are very complex. Each control link has strict requirements on time and sequence. This increases the difficulties of description and analysis. In this paper, timed places control Petri nets (TPCPN) is applied for the modeling of FECS. On this basis the simulation of two important processes, namely uploading fuel elements into the core for the first time and emptying the core is finished by simulation software Arena. The results show that as TPCPN is able to describe different kinds of logic relationship and has time properties and control properties, it’s very suitable for the modeling and analysis of FECS.

Effects of vibration conditions,spatial confinement and friction on mixing and segregation characteristics of mixed pebble beds for CFETR WCCB blanket

This paper presents the study of the dynamic characteristics of confined mixed pebble beds with different friction under different vibration conditions using the discrete element method.Theλsegre-gation index is used to quantify the degree of particle mixing or segregation.The percolation,convection and diffusion mechanisms are responsible for the segregation patterns of the mixed pebble.The results show the degree of segregation can be suppressed by decreasing the vibration acceleration or free space height below a threshold.Further simulation reveals the threshold of vibration acceleration or free space height both are related to the bed height increment which determines the strength of the percolation mechanism.In addition,the strength of percolation and convection becomes weaker by decreasing the friction of particles and walls,which makes the pebbled bed remains in a mixed state under vibration.These findings are significant to clarify the main factors behind the three segregation mechanisms and hence provide solutions to retaining the mixed state of the Li2TiO3&Be12Ti mixed pebble bed.

Smart passive gait retraining intervention via pebbles for reducing peakplantar pressure: Short-term results

Recently, there has been a growing interest in gait retraining to alter the gait parameters of different populations.In these gait retraining, peak plantar pressure (PPP) was considered as an important parameter of the footbiomechanics. It has been found that high PPP correlates to the common foot deformities including pes planus/cavus. However, previous studies utilized excessive electronics in gait retraining, which is challenging toimplement daily especially when device cleaning, flexibility and portability are considered. Therefore, this studyinvestigated feasibility of a novel unpowered gait retraining for reducing high PPP. Twelve potential participantsidentified for investigation through a baseline PPP evaluation with Novel Pedar-x system. Participants received asingle session for the gait retraining with pebbles in the form of rigid spherical inserts (RSI) placed in locations ofhigh PPP inside the deformable insole. This provides tactile cues alerting the participants to alter their gait toreduce excess PPP. The PPP values were tracked in weekly follow-up sessions for 6 weeks. The results demonstrated that participants responded to RSI altering their gait to reduce PPP and maximum force by 14% and 10.5%after six weeks respectively. This study is valuable for physicians in reducing PPP when non-electronics arerequired.

Pebble模糊有穷自动机和传递闭包逻辑

定义了Lukasiewicz逻辑下的一阶有界传递闭包逻辑,并且给出了模糊有穷自动机的一阶有界传递闭包逻辑;另外,我们还介绍了两类模糊有穷自动机:Nested模糊有穷自动机和Pebble模糊有穷自动机,并且证得这两类模糊自动机都可以由一阶有界传递闭包逻辑来刻画,因此它们并没有提升模糊自动机的语言识别能力;进而得到本文的主要结论:在Lukasiewicz逻辑下,模糊单体二阶逻辑与Lukasiewicz逻辑下的一阶有界传递闭包逻辑之间等价,且模糊自动机所识别的语言与Pebble模糊有穷自动机识别的语言是等价的。

Effects of coefficient of friction and coefficient of restitution on static packing characteristics of polydisperse spherical pebble bed

The effects of the coefficient of friction and coefficient of restitution on the static packing characteristics of a polydisperse spherical pebble bed are numerically investigated using the discrete element method.Several important static packing characteristics under different coefficients of friction and restitution are presented and discussed.The results show that the coefficients of friction and restitution impose opposite effects on the packing heights and global packing factor.Neither the coefficient of friction nor restitution affected the oscillation width of the wall,whereas their effects are primarily reflected in the oscillation amplitude of the radial local packing factor and the axial local packing factor distribution at the top of the pebble bed.In both the contact force distribution and coordination number distribution,a left-shifted phenomenon appearing as the coefficient of friction occurred,and only the magnitude of the maximum frequency is affected when the coefficient of restitution changed from 0.1 to 0.9.In all simulation cases,the effects of the coefficients of friction and restitution are similar to that of cross-impact.

Lower time limit on the UHPM rock exhumation: Discovery of eclogite pebbles in the Late Jurassic conglomerates from the northern foot of the Dabie Mountains, eastern China

Eclogite pebbles are first discovered in late Jurassic conglomerates of the Fenghuangtai Formation from the northern foot of the Dabie Mountains, eastern China. The eclogite shows relatively strong retrograde metamor-phism. The major remnant minerals are garnet, phengite, quartz, rutile, clinozoisite, fingerprint(or worm)-form sym-plectite and pseudomorphic enclosure of coesite in garnet. End-member components of the garnet mainly made up of grossular (27.7%-37.8%), almandinc (45.5%-49.0%) and pyrope (12.3%-25.7%). End-member components of the pyrope is less than 30%, i.e. equivalent to C type eclogite. Si-cations of the phengite are 3.44-3.54 p.f.u. (taking O=11as standard). It is estimated that the pressures are 2.5-3.2 GPa, the temperatures are 600-900℃. Discovery of the eclogite pebbles in the late Jurassic conglomerates from the northern foot of the Dabie Mountains suggests that the HP-UHP metamorphic rocks of the Dabie Mountains, which were formed in Triassic, had been exposed to the surface in

Smart Pebble鹅卵石

Smart Pebble鹅卵石,来自于韩国设计品牌designMAXX,采用新兴的铂固化硅橡胶(Platinum silicone),它拥有高度的可塑性,平滑不会刮伤高贵的笔电、手机,中空设计犹如吸盘一般。

Pebble Dumplings

Ingredients:Polished glutinous rice powder, yellow cheese powder,cocoa powder, and red bean paste or other for stuffing.Method:1. Mix the rice powder with cheese and cocoa powdersrespectively, add in water and roll a yellow dough and abrown dough; prepare another pure rice

圈的中间图pebbling数和Graham猜想

图G的一个pebbling移动是从一个顶点移走2个pebble,而把其中的1个pebble移到与其相邻的一个顶点上.图G的pebbling数f(G)是最小的正整数n,使得不论n个pebble如何放置在G的顶点上,总可以通过一系列的pebbling移动,把1个pebble移到图G的任意一个顶点上.图G的中间图M(G)就是在G的每一条边上插入一个新点,再把G上相邻边上的新点用一条边连接起来的图.对于任意两个连通图G和H,Graham猜测f(G×H)≤f(G)f(H).首先研究了圈的中间图的pebbling数,然后讨论了一些圈的中间图满足Graham猜想.

广义友谊图乘积上的Graham pebbling猜想

连通图G的pebbling数f(G)是最小的正整数n,使得不管n个pebble如何放置在G的顶点上,总可以通过一系列的pebbling移动把一个pebble移到图G的任意一个顶点上.Graham猜测对于任意的连通图G和H有f(G×H)≤f(G)f(H).文中证明了当H为友谊图或广义友谊图,G是一个具有2-pebbling性质的图时,Graham猜想成立.作为一个推论,文中也证明了当G和H是友谊图或广义友谊图时,Graham猜想成立.

几类二部图的pebbling数

Chung定义了图G上的一个pebbling移动是从一个顶点移走两个pebble而把其中的一个移到与其相邻的一个顶点上.连通图G的pebbling数f(G)是最小的正整数n,使得不管n个pebble如何放置在G的顶点上,总可以通过一系列的pebbling移动把一个pebble移到G的任意一个顶点上.Graham猜测对于任意的连通图G和H有f(G×H)≤f(G)f(H).作者们验证了三类二部图的2-pebbling性质以及当H为此类二部图,G为一个2-pebbling性质的图时,Graham猜想成立.

关于正则二部图的Pebbling数

图G的pebbling数f(G)是最小的正整数n,使得不管n个pebble如何放置在G的顶点上,总可以通过一系列的pebbling移动把一个pebble移到图G的任意一个顶点上,其中图G的一个pebbling移动是从一个顶点移走2个pebble,而把其中的一个移到与其相邻的一个顶点上.证明了具有2m个顶点的k-正则二部图的Pebbling数为2m,其中k≥「(m+1)/2﹁.