中速磨煤机构件对气相场影响的数值模拟

中速磨煤机内部气相场研究对于燃煤电厂节能减排降碳具有重要意义。然而,中速磨煤机内部构件复杂且存在旋转部件,已有研究往往对磨煤机结构及运行进行简化处理,这势必影响气相场模拟的准确性。采用Realizable k-ε湍流模型,对7种不同结构及运行工况下磨煤机内部气相场开展数值模拟,进行网格无关性验证,并评价磨辊、磨碗与风环、分离器的简化处理对气相场数值模拟结果的影响。结果表明,忽略磨辊对研磨区气相场影响明显,而磨辊转速由28.62 r·min-1变化为57.24 r·min-1时,典型截面气相速度和磨煤机压力损失几乎不变;忽略磨碗与风环的转动,风环上方平均风速将被低估14.97%,磨煤机压力损失将被低估5.02%;忽略分离器部分对研磨区气相场影响很小,而对研磨区上方内锥体区域气相场影响显著,并使得典型截面气相速度误差高达4.80 m·s^(-1)。研究结果可为磨煤机内部流场准确、高效的数值模拟提供方法指导。

基于网格改进的喷动床/喷动流化床气相场数值模拟及试验

采用FLUENT软件对喷动床和喷动流化床这种严格轴对称的柱锥体进行数值模拟时,常见气相场的伪收敛或伪扩散,且出现流场不对称现象。从网格结构的角度,提出了一种采用非一致性网格并沿柱体的轴向与锥体入口尺寸相当的区域进行网络加密的改进方法。基于这种网格改进,对喷动床和喷动流化床的气相场进行了数值模拟,并在相应的试验装置上对模拟结果进行试验。结果表明,该网格改进对柱锥体有较好的通用性。

HFCVD系统中衬底温度场及气相空间场的数值分析

探讨了典型气氛中热丝辐射、气体热传导与对流、化学反应生热等因素对衬底温度的影响,建立了三维热丝辐射和二维热流耦合有限元模型,研究了各工艺参数对衬底温度场及气相空间场的影响。结果表明H2占主导地位的气氛中衬底表面的氢原子重组放热对衬底温度有较大影响,氩气气氛中原子重组放热对衬底温度影响很小;热丝温度对衬底温度的影响最大;进气口到衬底的距离及进气口气体流速对衬底附近的流场影响最大,适当提高进气口到衬底的距离有助于提高衬底附近流场均匀性,增大进气速度有助于突破热障提高衬底表面流速,但同时加剧了衬底附近流场的不均匀性。

轴承腔中考虑油滴运动的气相物理场分析

航空发动机轴承腔中考虑油滴运动的气相物理场分析是进行二次流及润滑系统设计的基础工作。因此,采用有限元数值分析的方法,研究了轴承腔中嵌入油滴运动影响条件下气相介质的速度场、温度场和压力场,并探讨了转子转速对气相介质流动速度、温度以及轴承腔连通区域压力分布的影响规律。分析结果表明:随着转子转速的增大,气相介质流动速度和温度增大,同时进气腔与回油腔之间压力差减小。此外,将考虑油滴运动的气相物理场与油滴/空气相的耦合计算方法所得结果进行对比,据此确定本文所采用研究方法的准确性及其在计算时间上的优势。

气-固两相旋转射流场稳定性研究

采用考虑悬浮固粒与气流相互作用的Marble压力耦合模型和涉及悬浮固粒容积系数与平均固粒雷诺数的修正斯托克斯阻力公式，得到了含悬浮固粒的旋转射流稳定性控制方程及相应的修正瑞利稳定性准则．通过计算，给出了不同团粒属性及气相跳跃速度下旋转射流的增长率和发展系数曲线，根据所得稳定性准则，得到了固粒属性对旋转射流稳定性影响的重要结论，文中结论为工程控制旋转射流场及后续发展提供了理论依据．

成形磨削过程中气液两相流VOF模拟与分析

在成形磨削过程中,磨削液在磨削区域的流动和分布情况是影响磨削精度的重要因素。通过对磨削区气体进行气流场模拟分析得出,砂轮表面附近存在气障层,工件表面附近存在返回流,并且气障层和返回流会对磨削液的有效供给产生阻碍作用。运用气液两相流VOF理论,通过对磨削区磨削液流场中的气液两相流模拟分析得出,不同喷射位置和喷射速度产生不同磨削效果,并提出了磨削液的最佳喷射位置和喷射速度,对提高成形磨削的质量和效率,防止磨削过程中工件的烧伤提供了重要的参考依据,同时对实现绿色制造具有重要的工程实际意义。

喷淋层运行方式对脱硫塔内气液两相运动规律和蒸发冷却过程影响的数值模拟

通过计算流体力学方法对大型脱硫塔内不同喷淋层的运行方式进行数值仿真,并和工程现场数据作对比.模拟采用欧拉-拉格朗日方法,并考虑了气液两相间的各种耦合作用,以及气相湍流速度脉动的随机特征对颗粒相的影响.主要结论如下:①各喷淋工况下,在烟气入口高度范围内,截面平均气流总速度和水平向(水平烟气方向)分速度均达到峰值后快速衰减,其中后者至底层喷淋处趋于零;截面平均垂直速度分量沿塔高方向的变化曲线几乎完全重合,且在整个烟气入口高度范围内单调线性增加;②各喷淋方案中,仅底层喷淋时塔内的气相温度场和水蒸气浓度场最不均匀,烟气出口截面的平均温度明显高于其他工况,出口截面的平均湿度也未达到饱和;而仅顶层喷淋时,上述不均匀性明显减小;③各喷淋方案(除仅底层喷淋外),截面平均气相温、湿度沿塔高方向变化曲线的极值都出现在烟气入口高度的下部1/4处;随着喷淋层数增多,温度曲线的最大值降低,湿度曲线的最低值则升高;④仅底层喷淋时的蒸发水量为4层喷淋全部开启时的4/5;而仅顶层喷淋时的蒸发水量和开启更多喷淋层时已没有明显差别.各喷淋方案中,仅顶层喷淋时的蒸发比率最高.

多元物理场CVI制备C/C复合材料过程优化

采用普通碳毡作为增强体,丙烯作为碳源气体,氢气作为稀释气体,在自制的化学气相沉积炉中使用多元物理场化学气相渗透工艺(MFCVI)制备了C/C复合材料。根据不同的工艺条件设计了一组正交实验,以最终密度和石墨化度为指标对材料的制备过程进行了优化。结果表明,在沉积控制温度650℃、丙烯分压12 kPa、总气流量为40 mL/s、总压力为20 kPa条件时,在15 h沉积时间内可以获得较好的综合性能指标。验证实验结果表明,在上述实验条件下,材料的密度达到1.70 g/cm3,石墨化度可达67.1%,密度分析结果表明,其密度分布呈现两边高中间低的特征,材料的密度分布可以满足应用要求。

气固两相湍流场纳米颗粒演变特性综述

含纳米颗粒的气固两相湍流场在包括航空等众多领域中很常见,以单体、聚集体和团聚体不同形式存在的纳米颗粒在流场中经过生成、对流、扩散、凝并、破碎等过程,其数密度、尺度、尺度分散度等将发生变化。本文就以上相关研究状况进行了回顾,说明颗粒生成是气相化学反应产生的可冷凝蒸汽物质因表面冷却、绝热膨胀或混合、湍流混合或化学过程产生的过饱和所导致;导致颗粒凝并的原因包括布朗运动、湍流剪切、速度梯度、差异沉降;颗粒的凝并取决于颗粒的尺度和流场的特性,并受初始颗粒分布及湍流扩散控制;湍流场对颗粒凝并的影响除了湍流强度的因素外,还体现在由湍流脉动所引发的颗粒数密度的脉动;颗粒凝并后形成尺度较大的团聚体容易在流场剪切和其他因素作用下发生破碎;剪切破碎是导致颗粒破碎的主要因素,有效破碎系数取决于剪切率和颗粒的体积分数;颗粒的沉降取决于颗粒尺度、形状和流体性质等因素;导致颗粒沉降的因素有重力、扩散、惯性撞击、电场和热迁移等;当存在温度梯度时,热泳力对颗粒沉降也起到重要作用。本文最后提出了有待进一步研究的若干问题。

200MW四角切向燃烧煤粉炉炉内过程的数值模拟

借助FLUENTCFD软件平台 ,应用Eulerian/Lagrangian方法 ,在 3种不同工况下 ,对2 0 0MW四角切向燃烧煤粉锅炉炉内的流动、传热及燃烧进行了数值模拟 .为减小数值伪扩散的影响 ,采用了改进网格系统的措施 .模拟结果表明 :炉内最高温度出现在燃烧器区域 ,随着炉膛高度的增加 ,温度逐渐降低 ;整个炉膛空间存在旋转流场 ,从下至上旋转强度从弱到强 ,然后再逐渐减弱 ,直到炉膛出口仍存在残余旋流 ;炉内CO、O2 和CO2 的质量浓度分布与温度分布有很大关系 ,高温区对应着高的CO质量浓度和低的O2 、CO2 质量浓度 .数值模拟结果为锅炉的运行和改造提供了参考依据 .

Microstructures and formation mechanism of headstand pyrocarbon cones developed by electromagnetic-field-assisted CVD

Novel headstand pyrocarbon cones （HPCs） with hollow structure were developed on the surfaces of pyrocarbon layers of the carbon/carbon （C/C） composites at 650-750 °C by the electromagnetic-field-assisted chemical vapor deposition in the absence of catalysts. The fine microstructures of the HPCs were characterized by high-resolution transmission electron microscopy. The results show that the textural features of the HPCs directly transfer from turbostratic structure in roots to a well-ordered high texture in stems. And the degree of high texture ordering decreases gradually from the stem to the tail of the HPCs. The formation mechanism of the HPCs was inferred as the comprehensive effect of polarization induction on electromagnetic fields and particle-filler property under disruptive discharge.

Numerical Simulation and Analysis of Gas Flow Field in Serrated Valve Column

A three-dimensional computational fluid dynamics （CFD） model for gas flow through a serrated valve tray was presented. The flow field, as well as the dry-pressure drop of the valve under the full-opening condition was simulated based on the proposed model by using FLUENT 6.0 software. Compared with the values of dry-pressure dro.p in different turbulent models, the.simulated.results using RNG κ-ε model are in reasonable agreement with experimental data, indicating that RNG κ-ε model is suitable in simulating gas flow through the serrated valve tray. Then the CFD model combining RNG κ-ε model was used to study the three-dimensional gas flow through the considered serrated valve tray. The simulated results showed that various eddies existed on the serrated valve tray, and both the eddy and the non-eddy areas were nearly equal. The existence of addendum can decrease the eddy area caused by gas passing through the lateral outlet slots. The size of eddies can be reduced by optimizing the distance between valves.

Simulation and Analysis on the Two-Phase Flow Fields in a Rotating-Stream-Tray Absorber by Using Computational Fluid Dynamics

The flow field of gas and liquid in a φ150mm rotating-stream-tray (RST) scrubber is simulated by using computational fluid dynamic (CFD) method. The sismulation is based on the two-equation RNG κ-ε turbulence model, Eulerian multiphase model, and a real-shape 3D model with a huge number of meshes. The simulation results include detailed information about velocity, pressure, volume fraction and so on. Some features of the flow field are obtained: liquid is atomized in a thin annular zone; a high velocity air zone prevents water drops at the bottom from flying towards the wall; the pressure varies sharply at the end of blades and so on. The results will be helpful for structure optimization and engineering design.

Recognition of Similar Weather Scenarios in Terminal Area Based on Contrastive Learning

In order to improve the recognition accuracy of similar weather scenarios(SWSs)in terminal area,a recognition model for SWS based on contrastive learning(SWS-CL)is proposed.Firstly,a data augmentation method is designed to improve the number and quality of weather scenarios samples according to the characteristics of convective weather images.Secondly,in the pre-trained recognition model of SWS-CL,a loss function is formulated to minimize the distance between the anchor and positive samples,and maximize the distance between the anchor and the negative samples in the latent space.Finally,the pre-trained SWS-CL model is fine-tuned with labeled samples to improve the recognition accuracy of SWS.The comparative experiments on the weather images of Guangzhou terminal area show that the proposed data augmentation method can effectively improve the quality of weather image dataset,and the proposed SWS-CL model can achieve satisfactory recognition accuracy.It is also verified that the fine-tuned SWS-CL model has obvious advantages in datasets with sparse labels.

Single Bubble Behavior in Direct Current Electric Field

The investigation on bubble behavior in electric field helps to analyze the mechanism of electric enhancement of boiling heat transfer. Experiments were performed to investigate the bubble deformation in direct current （DC） electric field with bubbles attached to the orifice. The air bubbles were slowly generated in the transformer oil pool at different orifices, so that the effect of flow on bubble shape was eliminated. The results showed that the bubbles were elongated and the departure volume decreased when the electric field was intensified. The major and minor axes, aspect ratio and departure volume increased with increasing the orifice diameter. Both the electric field and orifice size have great influence on bubble behavior. The bubble deformation was also simulated to compare with the experimental results. The numerical and experimental data qualitatively agree with each other.

Field Electron Emission from Diamond - like Carbon Films

A low turn-on field electron emission from diamond-like carbon films has been observed for the first time to author’s knowledge.Carbon films were prepared by microwave plasma chemical vapor deposition (CVD).Special pretreatment ceramic substrates were used. The characteristics of the film have been identified by using X-ray diffraction(XRD),and Raman spectrum. The field emission experiment has been performed in a vacuum chamber with a base pressure of about 10 -5 Pa. The turn-on field of 1.2 V/μm,and the current density of 1.25 mA/cm 2 at electric field of 6 V/μm were obtained.

Study on the Flow Field around Two Parallel Moving Bubbles and Interaction Between Bubbles Rising in CMC Solutions by PIV

The flow fields surrounding two parallel moving bubbles rising from two identical orifices submerged in non-Newtonian fluid of carboxymethylcellulose （CMC） solution of three different mass concentration were measured experimentally by the use of particle image velocimetry （PIV）. The influences of gas flowrate, solution mass concentration, orifice interval and the angle between two bubble centers line and vertical direction on the flow field surrounding bubbles were discussed respectively by analyzing the velocity vector, velocity contours as well as individual velocity components. The results show that the liquid velocity both in front of two bubbles and behind increases with gas flowrate duo to shear-thinning effect of previous bubbles, whereas decreases with the increase of CMC concentration due to the increase of drag force acting on bubbles. The effect of the orifice interval on the flow field around two moving bubbles becomes gradually obvious as the interval becomes closer. Moreover, two adjacent side-by-side bubbles repulse each other during rising, leading to the practical interval between them increased somewhat above the orifice interval. When the distance between bubbles is less than the orifice interval 10 mm, the interaction between two neighboring bubbles changed from mutual repellence to attraction with the decrease of the angle of the line of linking two bubble centers to the vertical direction.

THE OBJE CTIVE ANALOGUE PREDICTION MODEL FOR TROPICAL CYCLONE TRACK WITH COMPREHENSIVE ASSESSMENT OF THE ENVIRONMENT

An objective analogue prediction model for tropical cyclone (TC) track is put forward that comprehensively assesses the environmental field. With the parameters of the tropical cyclone and environmental field at initial and future time, objective analogue criteria are set up in the model. Analogous samples are recognized by comprehensive assessment to historical TC cases for similarity with multivariate criteria,using non-linear analogue indexes especially defined for the purpose. When the historical tracks are coordinateconverted and weighted with reference to analogue indexes,forecast tracks are determined. As shown in model verification and forecast experiments, the model has forecasting skill.

Relationship of tropical cyclone size change rate with size and intensity over the western North Pacific

In this study,the relationship of tropical cyclone(TC)size change rate(SCR),within 24 hours,with size,intensity,and intensity change rate(ICR)are explored over the western North Pacific.TC size is defined as the azimuthally averaged radius of gale-force wind of 17 m s−1(R17)based on the Multiplatform Tropical Cyclone Surface Winds Analysis data.The majority of SCRs are mainly distributed in the range from−20 to 80 km d−1.The correlation coefficients between SCR and size(SCR-R17),intensity,and ICR(SCR-ICR)are−0.43,−0.12,and 0.25,respectively.The sensitivity of the SCR-R17 and SCR-ICR relationships to size,intensity,and evolution stage are further examined.Results show that the SCR-R17 relationship is more sensitive to variations of size and evolution stage than that of intensity.The relationship of SCR-ICR is largely modulated by the evolution stage.The correlation coefficient of SCR-ICR can increase from 0.25 to 0.40 when only considering the lifetime stages concurrently before and after the lifetime maximum size(LMS)and lifetime maximum intensity.This demonstrates that ICR is a potential factor in predicting SCR during these evolution stages.Besides,the TC size expansion(shrinkage)is more likely to occur for TCs with smaller(larger)size and weaker(stronger)intensity.The complexity of size change during a TC's lifetime can be attributed to the fact that shrinkage or expansion could occur both before and after LMS.

Effect of the Microclimate of Underground Systems on the Occurrence of Hibernating Bats

This study investigates the microclimatic connections between underground systems and the hibernation sites of particular species of bats. The distribution of hibernating bats was analysed in five selected zones designated Ⅰ-Ⅴ. These zones have a similar relative humidity, diverse temperature ranges inside the system, as well as air flow rates. A multi-year research programme highlighted the relationships between the occurrence of hibernating bats of various species and the microclimate of these particular zones. What is of essential importance are the sites with an air flow in their zones exceeding 0.02 m·s^-1, then is temperature and humidity. The air flow determines more intensive settling of wintering bats （zones Ⅲ, Ⅳand Ⅴ）. The zone Ⅱ-tourist zone with periodic air flows and often visited by humans is the least used by hibernating bats.