AP1000设计基准事故试验热冲击过程数值模拟

针对AP1000核电厂安全级设备鉴定设计基准事故(DBA)模拟试验第1s热冲击过程,构建了过热蒸汽由储汽罐充入试验仓的模型.利用Fluent流体计算软件对瞬态热冲击过程进行了数值模拟,得到试验系统内气体温度、压力、流速、组分质量分数瞬态变化过程及其空间分布状态.结果表明:超音速蒸汽射流进入试验仓,经挡板减速并改变方向,与仓内空气混合,同时压缩空气,使仓内介质温度和压力快速上升并达到要求值;试验仓内瞬态压力分布均匀,但温度分布取决于蒸汽的流动,随着蒸汽不断充满试验仓,1s后仓内温度分布趋于均匀;储汽罐释放高温高压过热蒸汽充入试验仓的工艺可以满足DBA试验第1s热冲击试验要求.     

超临界水氧化后生活垃圾中元素的迁移规律

采用超临界水氧化处理垃圾的方式,对生活垃圾中C、N、S元素的迁移规律进行了研究.结果表明:随着温度的升高,气相产物碳收率增加,固相产物碳收率降低,液相产物碳收率基本稳定;NO、NO2、NH3及HCN产气氮收率均接近0,有一部分N元素转化为N2O气体;有5%~30%的硫元素以硫酸盐的形式存在于液相中,几乎不产生SO2、SO3气体.同时,添加活性炭既能促进氧化反应又可降低N2O气体的生成.     

惰性气体对爆燃火焰淬熄的影响

对高速爆燃火焰在He与N2作用下在圆管内的淬熄进行了数值模拟,分析了当可燃气体活性与圆管直径不同时惰性气体对淬熄的影响.结果表明,He的淬熄性能大大优于N2,火焰在圆管内的淬熄长度随着可燃气体活性的增强而增大,活性较高的可燃气体火焰在N2中不容易被淬熄.对肯尼斯层流扩散火焰的淬熄模型方程进行了修正,得出了在爆燃条件下圆管的临界淬熄直径正比于惰性气体热扩散率的1/3次方的结果.     

玉米秆在流化床中燃烧特性的初步研究

对玉米秆与弱酸性床料的混合流化特性进行了研究,结果表明,长度为20～50mm玉米秆与一定粒径分布的床料,当质量配比为1%,流化数N=3～6时,能较均匀地混合流化,但N>6后,混合的均匀度有所下降.根据热重试验结果可以看出玉米秆着火温度低,挥发份析出速度快,并容易燃尽.在0.2MWth流化床试验台上研究发现,当N>6时,玉米秆和床料分层严重,密相区温度在820℃以下,当N=3～6时,密相区温度能达到设计要求,说明冷态试验结果能够指导热态运行,玉米秆流化床燃烧时流化风速不能太大.经过24h热态试验后,床料没有出现烧结现象,利用XRF技术分析发现玉米秆灰中碱金属含量较高,高温对流受热面的沾灰可能性较大.     

循环流化床提升段径向气体混合的试验研究

在3种规模的循环流化床(CFB)冷态试验台上对提升段稀相区径向气体混合规律进行了试验研究.3种试验台提升段净高均为4.Om,截面尺寸分别是内径O.19 m的圆管、O.3m×0.3m的方截面和0.25 m×0.5 m的矩形截面.以dp=120μm,ρ=2 400kg/m3的砂作为试验床料,CO2作为示踪气体,对影响气体混合的因素如表观流化速度Ug、颗粒浓度、提升段尺寸等进行了试验研究.发现颗粒的存在减缓了气体横向混合的速度,但颗粒对气体横向混合的影响不是单向的.对一定风速,存在一个颗粒浓度转折点,小于此浓度时D,随颗粒浓度的增加而减小,大于此浓度Dr随颗粒浓度的增加而增加.在本试验中此转折点浓度为8～1O kg/m3,应为气固流型的转折点.提升段直径Dt对Dr影响很大,结合前人研究结果,Dr随Dt呈线性增加,但更确切的关系确定有待进一步数据积累.与颗粒浓度和提升段直径相比,气体流化速度对Dt的影响很小.     

流型对循环流化床径向气体混合影响的试验研究

在提升段净高为4.0 m、内径0.19 m的循环流化床冷态试验台上进行了快速床和气力输送两种流型中径向气体混合的试验研究,试验用物料为河沙,d_p=120 μm,真实密度ρ_s=2 400 kg/m~3.试验台颗粒循环流率(G_s)和流化风速(U_g)可独立控制,根据床层上、下部压力梯度随流化风速的变化关系判断快速流态化的存在区域.采用柱塞流模型,用CO_2作为示踪气体进行3种风速下的径向气体混合试验,得出了快速床和气力输送两种流型中气体径向扩散系数Dr随颗粒浓度变化的趋势.研究发现,在气力输送流型中Dr随颗粒浓度增加而减小,在快速床流型中Dr随颗粒浓度增加而增大.结合固体颗粒在不同流型中的存在状态解释了流型对Dr的不同影响作用.     

流化床燃烧棉秆的混合特性及床料的选择

在0.2 MW热功率的试验台上进行了燃烧试验,研究了棉秆长度、床料粒径、配比和流化速度对混合均匀程度的影响.试验结果表明:①长度10～100 mm特别是50 mm左右的棉秆,与φ0.6～1 mm床料能均匀地混合.当床料重量比为2%,在流化数为3～7时,能均匀地混合流化;但流化数大于7时,混合的均匀度稍有降低,棉秆与床料的配比对混合也有影响.②棉秆流化床燃烧宜选择弱酸性床料,不会出现烧结现象而影响床料的正常流化.     

基于槽式聚光反射装置的太阳集热器件性能实验研究

利用槽式太阳能聚光反射装置,对两种太阳能真空管集热器和CHAPS平板集热器进行了以水为流动工质的性能试验,实测系统热效率及温度.对真空管进行了为N2流动工质的实验.实验表明,以水为工质时,采用聚光式太阳能真空管及CHAPS平板集热器,系统具有较好的热转换效率,达70%～80%.当水流量低于0.0046kg/s时,水容易加热至沸腾状态.用真空管对N2进行加热,可使气体温度达450～500℃,但加热气体时的热效率较低,在32%以下.     

Ti2AlNb合金铸锭化学成分均匀性熔炼工艺研究

采用真空自耗电弧炉熔炼设备,研究了传统添加纯铝铌板熔炼工艺、添加Al-Nb中间合金改进工艺、采取氩气可控充入、冷却水温措施优化工艺Ti2AlNb基合金铸锭的均匀性.通过对三种工艺Ti2AlNb铸锭的不同截面化学成分及杂质元素的测定试验,结果表明:传统工艺易出现Nb元素偏析,添加Al-Nb中间合金工艺易出现Al元素挥发,...     

开式脉动热管传热极限的试验研究

在由内径分别为1 mm和2 mm的细铜管弯曲而成的2组40弯头开式回路脉动热管试验装置上,采用R123为工作介质,定性分析了充液率及加热方式对传热极限的影响,并将试验值与Katpradit传热极限关联式的计算值进行了比较,结果表明:随着充液率的提高,传热极限先增大而后减小,存在一个最佳充液率(约50%);在3种加热方式中,垂直底部加热有助于脉动热管取得较大的传热极限值,而垂直项部加热则对应较小的传热极限值.通过对Katpradit传热极限关联式进行适当修正,得到了新的试验关联式.     

等温容器内多孔介质强化导热研究

等温容器是在充放气过程中容器内温度基本保持不变的一种特殊容器,在气动系统中有着广泛的应用.为强化放气过程中容器壁向内部的导热,以容器截面为研究对象,对内部铜丝的分布进行了探讨.在细铜丝填充密度一定的情况下,基于多孔介质模型,以容器截面导热热阻最小为目标,优化出两层和三层变密度填充下金属丝的分布.其热阻与均匀填充时相比,分别减少了37.63%和43.70%.研究结果表明,通过改变等温容器内细铜丝的分布可以强化容器壁向内部的导热.     

Melting evaluation of a thermal energy storage unit with partially filled metal foam*

This paper introduces a novel strategy on enhancing melting heat transfer for a shell-and-tube unit by partially filling porous foam. A series of filling ratios for metal foam are studied regarding thermal energy charging performance. A two-dimensional axial-symmetric model is established and verified by comparing of temperature with experimental data, obtaining satisfactory agreement between the two methods. The characteristics of the melting process such as melting fraction, temperature response and uniformity, heat storage and velocity field are analyzed in detail. The results show that the appropriate reduction of the metal foam filling ratio in the upper part can significantly promote the heat storage process due to mainly the enhanced natural convection effect. By comparing 17 cases with different filling ratios, an optimal filling ratio of 0.89 is recommended to achieve a 10.5% higher heat storage efficiency than the one with fully filled condition. The temperature uniformity first increases and then decreases with metal foam filling ratios. The best temperature uniformity is achieved for the filling ratio of 0.95. The case with a filling ratio of 0.89 possesses the shortest energy charging time at the expense of reducing the temperature uniformity. Compared with the fully filled metal foam, a better energy storage process was achieved with less metal foam material.     

Characteristics of heat transfer and temperature rise of hydrogen during rapid hydrogen filling at high pressure

An experiment has been done to measure the rise in temperature of a gas during filling a tank at high pressure. The experimental condition is that filling gases are nitrogen and hydrogen at a pressure of 5 to 35 MPa and at a filling mass of G=45 to 324 g/min for hydrogen. The temperatures are measured either horizontally or vertically at five positions in the tank. It is found that heat loss transferred from compressed gas to the tank wall has a significant effect on the rise in the filled gas temperature. The heat transfer coefficient is estimated after the end of filling and is about α_h=270 W/(m²K) for the hydrogen at 35 MPa. A theoretical procedure is proposed to calculate the temperature increase of the gas on a basis of assumption that the gas temperature in the tank is uniform at any time, and the heat transfer coefficient is given. The calculation shows that the temperature is in reasonable agreement with the measured temperatures by assuming α_h=500 W/(m²K) during the filling of hydrogen at 35 MPa, although the estimated heat loss after the end of filling becomes larger than the actual one. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(1): 13–27, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20140     

球磨机中颗粒混合运动的数值模拟

针对球磨机在火电厂应用广泛而对其内部颗粒混合运动的信息了解甚少的现状,采用离散元法直接跟踪球磨机内的每一个颗粒,考虑其所受重力、摩擦力和碰撞阻力的联合作用,建立了颗粒的三维动力学模型,对球磨机中颗粒复杂混合运动的全过程进行了数值模拟,并着重探讨了颗粒大小、颗粒密度及颗粒粒度不均等关键参数对球磨机中颗粒混合运动特性的影响.结果表明,随着球磨机的转动,球磨机内各区域的颗粒均逐渐混合均匀,但球磨机内不同区域颗粒混合的均匀程度不同.相同填充率条件下,小颗粒混合达到均匀的时间较长;相同粒径条件下,密度较大的颗粒其混合达到均匀的时间也较长.颗粒粒度不均时,随着球磨机的转动,颗粒出现分层现象.     

A novel batch-type hydrogen transmitting system using metal hydrides

In the case of transporting hydrogen by means of metal hydrides, a key problem is to reduce the weight of the portable container filled with metal hydrides. The paper describes a novel batch-type hydrogen transmitting system characterized by a portable light container filled with metal hydrides, which is not pressure-proof but only mechanically durable. Hydriding is performed by setting the portable light container in a fixed pressure-proof vessel and admitting hydrogen and nitrogen inside and outside the portable container, respectively, while adjusting the pressure difference between both gases to be zero. Using this system, 2.9 Nm³ of hydrogen can be stored in 14.3 kg of the total mass of the solid constituents including 3.5 kg of Mg-10% Ni alloy. The portable container contains twice as much hydrogen per unit weight and volume as a conventional compressed gas cylinder. Due to the advanced design of this portable container, the optimum hydrogen content could be around 5 wt % based upon the total mass of the container.     

Experimental study of the start-up of a fuel cell stack for backup power application

The transient response of proton exchange membrane fuel cells during start-up is an important issue for backup power systems which require a very short start-up time in order to limit the use of batteries during a blackout. The start-up procedure of a ten cells stack was studied: in the first stage the cathode channel initially filled with nitrogen was supplied with oxygen in open circuit then in the second stage it was connected to the load. The influences of the current time-profile (step or ramp), the cell voltage at the connection and the gas flow rates on the voltage variation were investigated. It was found that the voltage value during the filling of the cathode is not sufficient to determine which fraction of the cathode was filled with oxygen. In most cases, high oxygen flow rates allow reducing the start-up time of the stack. Furthermore, for fixed current density and stoichiometric coefficients it was found that a minimum start-up time exits. The analysis of transient response to current steps showed that around 70% of the maximum electrical power was available less than 2 s after the beginning of the start-up procedure.     

Charging strategy through analysis of charging influence factors of ultra-light hydrogen storage with polyethylene terephthalate liner

A lightweight type 4 vessel with a polyethylene terephthalate (PET) liner is analyzed. The derived heat transfer coefficients between the gas and wall are applied, and a parametric study is performed. An optimized charging strategy is also developed. Firstly, when the injected hydrogen temperature decreases, the charging time increases, and the charged gas temperature decreases. Secondly, the higher the ambient temperature, the shorter the charging time, and the higher the charged gas temperature. Thirdly, the larger the mass flow rate, the shorter the charging time, and the higher charged gas temperature. Fourthly, as the initial pressure inside the vessel increases, the charging time shortens, and the charged gas temperature decreases. Fifthly, using the formulated charging strategy, during summer, the charged gas temperature decreases by approximately 9 °C. In winter, the charging time is reduced by approximately 58 s. The results provide important information of temperature control for ensuring vessel safety.     

A case study of a hydride container performance applying non dimensional parameters

Many efforts have been done so far to understand sorption dynamics of hydride containers for hydrogen storage. Particularly, there are many articles in literature where experimental results for different hydride systems and container set-ups were successfully simulated using basically the same group of models. This fact is the base of a previous work where we defined a series of non dimensional parameters which may be used to estimate absorption time of hydride containers.In this work we compare estimated absorption times with experimental outcomes for a prototype hydride container. We performed non dimensional analysis of our finned container prototype at two scales, i.e.: overall or macroscopic container scale and pore or microscopic scale. We discuss about this simplified model approach that allows estimating, with few parameters, the reaction time of a complex-geometry prototype.The prototype container was designed according to the results of a numerical optimization that maximized the amount of hydrogen absorbed for a 3 min charging period. Experimental results indicate good agreement between estimated and experimental absorption time, making the non dimensional method a useful tool at preliminary stages of hydride container design.     

Mixing with time dependent natural convection

Chaotic mixing inside a two dimensional cavity can be achieved with time dependent natural convection if the motion of a fluid is generated by imposing alternating hot and cold wall temperatures. With this set up no moving walls are required to mix the fluid inside the container. In this comment we illustrate this idea by numerically solving the governing equations of natural convection in a two dimensional square cavity with sections of its upper and lower horizontal walls cooled and heated in a periodic manner. These conditions generate a vortex of time dependent intensity that moves its center in a closed loop around the geometrical center of the container. The mixing properties of the flow are illustrated by Lagrangian tracking of a collection of points originally located in a line.     

管袋充填高含粘量泥浆的高效脱水方法

针对土工管袋充填高含粘量泥浆时脱水固结慢的问题,通过室内试验研究了土颗粒沉淀规律及充填土料含粘量、管袋袋布等效孔径、管袋袋壁的拍打扰动等对脱水效率的影响,开发出一种管袋充填高含粘量泥浆时高效脱水的施工方法,即对于粘粒含量达到20%的充填泥浆,以低于30%的浓度进行充灌有利于粗细土颗粒分离;管袋顶部排水面采用大等效孔径的编织布制作,并在充灌后静止20min待粗颗粒基本沉淀结束后以时间间隔小于1min的频率均匀拍打袋壁,可以使处于悬浮状态的粘粒和部分粉粒在短时间内排出管袋。利用该方法充灌后10h管袋底部孔隙水压力消散程度可达到75%,可以继续上层管袋的充灌。