配风方式对超低挥发分碳基燃料NO_x排放特性的影响

针对超低挥发分碳基燃料热解半焦,在30 kW预热燃烧试验台上研究不同二次风动量和通入方式对预热燃烧特性和NO_x生成特性的影响。结果表明,随着二次风动量逐渐增加,神木半焦的燃烧效率呈先升高再降低的趋势,NO_x排放量呈先减小再增大的趋势,适当提高二次风动量,可以提高燃烧效率同时减少NO_x排放;不同二次风射流方式对NO_x排放浓度影响较大;采用30°偏角的斜射流方式通入二次风时,燃烧室内平均温度比采用直射流时高约100℃。采用直射流和30°偏角的斜射流方式最终NO_x排放质量浓度分别为99. 7、152. 3 mg/m~3(6%O_2)。     

循环流化床锅炉内颗粒速度分布的实验研究

为了研究操作参数对循环流化床锅炉内颗粒速度分布的影响,在冷态模型装置上使用PV6A型颗粒速度光纤测量仪、毕托管对循环流化床锅炉炉膛内的颗粒速度进行了测量与分析。结果表明:在流化风速为2.57 m/s、循环质量流率为0.58 kg/(m2.s)、一次风量为2 300 m3/h、二次风量为1 500 m3/h时,循环流化床锅炉炉膛内颗粒浓度分布、压降、流化状态、质量循环都达到一个较稳定的水平,呈现典型的环核分布特征。     

改进型漩流燃烧器技术在在E JI-670-13.8-545 тK锅炉中的应用

改进型旋流燃烧器.根据牡丹江第二发电厂入炉煤质灰分高、挥发分适中的特点,为确保一次风出喷口后形成较大的回流区,实现低负荷稳燃性能,在一次风喷口内侧加装稳燃齿并将=:次风旋流器由原位置向炉膛方向适当推进.经计算设计为:(1)扩流锥占一次风流通面积百分比为:40~50%,一次风扩流锥优化角度α;一次风稳燃齿数6个,一次风扩口优化角度B:(2)二次风叶片数16,::次风扩口角度lO度,叶片遮盖度1.5,二次风叶片倾角64度.(3)为延长二次风旋转射流在炉膛内的长度,二次风旋流器由原位置向炉膛适当推进.由于入炉煤质灰份较大,一次风侧部件磨损问题尤为突出.本次改造方案采用的耐热和防磨措施如下:(1)据相关资料:磨损速率与含粉气流流速成三次方关系,含粉气流流速对磨损影响极大.在保证稳定燃烧的情况下,为减轻磨损,燃烧器一次风速选用较低的21.9 m/s,低于一次风管道流速28.5 m/s:(2)适当减小冲击角,优化设计一次风扩流锥防磨环角度;(3)燃烧器喷口采用特殊性能的耐热合金钢,其耐热温度达1250℃.扩流锥所在位置距炉膛较近,必须具有良好的耐热耐磨特性.材料选用耐热抗磨铸钢,900℃时,HRC≥26.     

基于计算流体动力学的颗粒磨蚀管道弯头研究

为了探究气-固两相流中颗粒对管道弯头的磨蚀机理,采用计算流体动力学软件对90°弯头进行磨蚀模拟研究。结果表明:颗粒在弯头内的轨迹是先汇聚、后发散的过程,弯头壁面上颗粒汇集程度最大的位置也是磨蚀最严重的地方;随着气流速度与颗粒粒径的改变,最大磨蚀点分布在与x=0坐标面夹角为70~90°的截面之间,并且分布在z=0平面的一侧;最大磨蚀率与颗粒流量成正比;在颗粒质量流量为0.1 kg/s的条件下,当颗粒粒径小于45μm时,气流速度对最大磨蚀率影响不大,当颗粒粒径大于45μm时,最大磨蚀率与气流速度接近二次多项式关系;当气流速度为20 m/s时,粒径介于45~75μm的颗粒的磨蚀率最大,而且颗粒流量越大,这种趋势越明显。     

改进型漩流燃烧器技术在在ЕЛ-670-13．8-545тК锅炉中的应用

改进型旋流燃烧器。根据牡丹江第二发电厂入炉煤质灰分高、挥发分适中的特点，为确保一次风出喷口后形成较大的回流区，实现低负荷稳燃性能，在一次风喷口内侧加装稳燃齿并将二次风旋流器由原位置向炉膛方向适当推进。经计算设计为：（1）扩流锥占一次风流通面积百分比为：40～50％，一次风扩流锥优化角度α，一次风稳燃齿数6个，一次风扩口优化角度β：（2）二次风叶片数16，二次风扩口角度10度，叶片遮盖度1．5，二次风叶片倾角64度。（3）为延长二次风旋转射流在炉膛内的长度，二次风旋流器由原位置向炉膛适当推进。由于入炉煤质灰份较大，一次风侧部件磨损问题尤为突出。本次改造方案采用的耐热和防磨措施如下：（1）据相关资料：磨损速率与含粉气流流速成三次方关系，含粉气流流速对磨损影响极大。在保证稳定燃烧的情况下，为减轻磨损，燃烧器一次风速选用较低的21．9m／S，低于一次风管道流速28．5m／s：（2）适当减小冲击角，优化设计一次风扩流锥防磨环角度：（3）燃烧器喷口采用特殊性能的耐热合金钢，其耐热温度达1250℃。扩流锥所在位置距炉膛较近，必须具有良好的耐热耐磨特性。材料选用耐热抗磨铸钢，900℃时，HRC≥26。[     

四角切向燃烧锅炉燃烧器区空气立场的对炉内工况影响

[摘要]四角切圆燃烧方式的传统做法是使一、二次风射流在炉内同向正切或反切于同一假想圆,形成一股一、二次风旋转上升的气流。但在实际运行中,由于炉膛出口处的气流存在残余旋转,从而造成了水平烟道两侧烟气的温度场和速度场分布不均,过热器的热偏差较大,甚至引起爆管,若假想切圆直径过大,则火焰太靠近炉墙,易引起水冷壁结渣和燃烧器烧损变形;若假想切圆直径过小,则着火不稳定,炉内气流扰动强度差,而且还不利于燃料的燃尽。     

卧式冷藏柜送风角度对风幕影响的模拟及分析

冷藏柜是食品冷链的关键环节,冷藏柜内的食品要频繁地与周围环境进行热质交换,因此也是食品冷链中食品变质和能源消耗较为严重的环节。大量的试验已经表明送风角度影响冷藏柜风幕的性能,且存在最佳送风角度。本文采用数值模拟的方法研究不同送风角度下冷藏柜内的温度分布和速度分布。模拟结果表明:送风角度为-5°时,射流能够形成较为完好的风幕,截面平均温度较低,送回风温差较小,柜内温度分布较为均匀稳定。     

CAARC标准高层建筑模型风致效应及背风侧流场特性研究

通过风洞测压试验、PIV试验和动力响应计算,对比分析0°和90°风向下,CAARC模型围护结构风压、模型背风侧流场特性及主体结构风振响应。①对比了模型立面风压分布及整体风力,两种风向下,模型表面风压分布的较大差异存在于侧风面。相比于0°风向,90°风向下模型整体阻力和升力较小,但整体扭矩较大。②直观展现了模型背风侧的流场特性。两种风向下,模型后部水平面内均出现尾流涡对;竖直面内的显著旋涡仅出现在0°风向。相比而言,0°风向下,尾流涡对尺寸较大,逆向流速较高,周围流体横风向运动剧烈。③给出了模型顶部位移和加速度随折减风速变化的拟合方程,两种风向下,模型顶部顺风向响应与折减风速的2～2.6次幂成正比;横风向响应与折减风速的3～3.5次幂成正比。相比而言,90°风向下,模型顶部横风向位移和加速度随折减风速的增幅分别为0°风向下的2倍和2.6倍。     

聚能锥角对线性聚能爆破致裂岩体效果的影响

为研究不同聚能锥角下线性聚能爆破致裂岩体效果,在巷道岩壁开展了5种聚能锥角(40°、50°、60°、70°、80°)下的聚能爆破和岩体损伤测试试验,数值模拟了不同聚能锥角形成的聚能射流。结果表明:线性聚能爆破定向致裂岩体效果显著,聚能方向损伤增量显著大于非聚能方向;聚能锥角为40°时致裂岩体效果最好,最大损伤增量达0.93,裂纹扩展深度和长度较大,50°、60°、70°和80°聚能锥角时,最大损伤增量、射流压力、射流长度、射流头部速度、射流尾部速度等均随聚能锥角的增大而减小,致裂岩体效果逐渐减弱。     

半正方形罩线型切割器的数值模拟研究

半正方形药型罩也可以看作两个楔角90°楔形药型罩相对排列在一起而演化出的一种线型聚能装药结构。应用LS-DYNA非线性有限元软件完成了爆炸载荷下半正方形罩线性切割器形成射流过程的数值模拟。结果表明,半正方形罩线性切割器能形成一股片状扇形聚能射流;半正方形罩线型切割器形成射流存在一个初始射流二次汇聚的过程,二次汇聚形成的射流速度比一次汇聚射流速度提高了33%以上;半正方形罩线型切割器形成射流速度要明显高于普通线型切割器;随药型罩厚度的增加,半正方形罩线型切割器形成射流速度降低。     

一种新型燃用煤粉工业锅炉燃烧器流场特性研究

针对一种新型的燃用煤粉工业锅炉燃烧器,利用计算流体力学软件,通过改变一、二次风速及内二次风旋流强度以及钝体流通阻塞率等参数,模拟燃烧器出口附近流场分布,研究不同参数下回流区大小及回流量的变化,分析流场的湍流强度分布.结果表明,回流区长度与内二次风速、内二次风旋流强度及钝体阻塞率成正比,与一次风速成反比.回流量总体上随着内二次风旋流强度、内二次风速、一次风速的增加而增大;改变钝体阻塞率,则有较复杂的变化.湍流强度沿径向呈先增后减的变化,沿轴向则在某个截面后不断衰减.     

Note on axis-symmetric jet mixing of compressible dusty fluid

Summary Laminar jet mixing of a compressible dusty fluid issuing from a circular opening has been considered. Assuming that the jet mixing is under full expansion, the governing equations have been linearised and solved by successively using Hankel and Laplace transform techniques. Numerical computations of the integrals giving velocity, temperature and density of both the fluid and particle phase have been made to discuss results. The increase in the concentration of dust particles results in width of the jet is greater for compressible flow. The compressible dusty jet does not cool as fast as a compressible jet of clear fluid. The particle concentration decreases along the axial direction but increases towards the free jet boundary.     

A NUMERICAL SIMULATION OF SWIRLING FLOW PNEUMATIC CONVEYING IN A HORIZONTAL PIPELINE

A numerical simulation for swirling and axial flow pneumatic conveying in a horizontal pipe was carried out with a Eulerian approach for the gas phase and a stochastic Lagrangian approach for particle phase, where particle-particle and particle-wall collisions were taken into consideration. The k-ε turbulence model is used to characterize the time and length scales of the gas-phase turbulence. Models are proposed for predicting the particle source and additional pressure loss. The numerical results are presented for polyethylene pellets of 3.1 mm diameter conveyed through a pipeline of 13 m in length with an inner diameter of 80 mm, solid mass flow rate was 0.084 kg/s, and gas velocity was varied from 10 m/s to 18 m/s. The particle flow patterns, the particle concentration and the particle velocity, and additional pressure loss were obtained. It is found that the particle velocity and concentration has almost same value along flow direction in swirling flow pneumatic conveying. The profile of particle concentration for swirling flow pneumatic conveying exhibits symmetric distribution towards the centerline and the higher particle concentration appears in neighbor of wall in the acceleration region. At downstream, the uniform profile of particle concentration is observed. The particle velocity profile, on the other hand, is uniform for both swirling and axial flow pneumatic conveying. A comparison of the calculations with the measured data shows a good agreement within an average error of less than 15 percent.     

A NUMERICAL SIMULATION OF SWIRLING FLOW PNEUMATIC CONVEYING IN A HORIZONTAL PIPELINE

ABSTRACT

A numerical simulation for swirling and axial flow pneumatic conveying in a horizontal pipe was carried out with a Eulerian approach for the gas phase and a stochastic Lagrangian approach for particle phase, where particle-particle and particle-wall collisions were taken into consideration. The k-? turbulence model is used to characterize the time and length scales of the gas-phase turbulence. Models are proposed for predicting the particle source and additional pressure loss. The numerical results are presented for polyethylene pellets of 3.1 mm diameter conveyed through a pipeline of 13 m in length with an inner diameter of 80 mm, solid mass flow rate was 0.084 kg/s, and gas velocity was varied from 10 m/s to 18 m/s. The particle flow patterns, the particle concentration and the particle velocity, and additional pressure loss were obtained. It is found that the particle velocity and concentration has almost same value along flow direction in swirling flow pneumatic conveying. The profile of particle concentration for swirling flow pneumatic conveying exhibits symmetric distribution towards the centerline and the higher particle concentration appears in neighbor of wall in the acceleration region. At downstream, the uniform profile of particle concentration is observed. The particle velocity profile, on the other hand, is uniform for both swirling and axial flow pneumatic conveying. A comparison of the calculations with the measured data shows a good agreement within an average error of less than 15 percent.     

掺杂稀土氧化物的ZnO-Bi2O3系压敏陶瓷中的"软心"

研究了掺杂Ce2O3和Gd2O3对ZnO—Bi2O3系压敏陶瓷电气性能的影响，发现大尺寸试样的内层电位梯度明显低于表层，即表现出“软心”特征．“软心”导致试样平均电位梯度随着试样几何尺寸的增大而下降．沿轴向晶粒尺寸没有明显的差异．根据沿轴向截取的等厚薄片的电流与温度的关系，发现表层的晶界势垒高度比内层的高．这种晶界势垒高度的非均匀分布可能与添加稀土氧化物后造成的氧元素分布不均匀有关．     

“Studies of the Effect of Compaction force on Displacement of Large Compacts Formed from Direct Compression Matrices”

Large compacts (3.93 cm x 4 cm) formed from commercial direct compression bases have been prepared by hydraulic compression and then loaded in axial compression when removed from the die.

Avicel and Sta-Rx formed compacts resistant to shear, and failure in free axial compression was due to induced tensile stresses both radial and circumferential. Paracetamol DC, a direct compression form of paracetamol, behaved as a brittle solid and split axially along its length. Emdex and Encompress formed compacts weak in shear and failed along double shear cones at low axial loading.

Emdex gave force v displacement plots for both axial and radial displacement which suggests that it flows plastically at low loads insufficient to cause failure. The other compacts behaved as elastic solids at low axial loadings.

A method was devised to compare radial pressure at various points along the axial length of the compacts when they were formed or recompressed in the die. Although easily ejeeted, compacts of Avicel and Sta-Rx were the best transmitters of radial pressure. Emdex and Encompress compacts were both difficult to eject. It is suggested that this is due to shear failure and and rebonding along the shear cones demonstrated infreeaxial compression.     

嵌套式螺杆挤出机的固相温度分布

介绍了一种新型嵌套式螺杆挤出机。在考虑离心力和物料可压缩性条件下,通过非等温模型求解了新型螺杆挤出机内外螺杆固相界面温度沿螺杆轴向和槽深方向的分布。计算结果表明,内外螺杆的固相界面温度沿轴向均按近似指数函数的规律增加,一直到固相界面温度达到熔点并出现熔膜为止,内螺杆固体输送段的长度大于外螺杆。机筒温度较高时可缩短固体输送段的长度,但不利于固体输送段压力梯度的建立。热量沿内外螺杆槽深方向传入固体床的深度都只有在15%~20%槽深的范围。     

轴向磁场对硅单晶Czochralski生长过程的影响

利用有限元方法对炉内的传递过程进行了全局数值模拟,假定熔体和气相中的流动都为准稳态轴对称层流,熔体为不可压缩流体,Cz炉外壁温度维持恒定,模拟磁场强度范围为(0～0.3)T,研究了用Czochralski(Cz)法生长单晶硅轴向磁场对熔体流动和氧传输过程的影响.结果表明:轴向磁场可有效地抑制熔体内的流动,但增大加热器功率和结晶界面处晶体内的轴向温度梯度;对于常规Cz炉,轴向磁场可增大结晶界面平均氧浓度,而对于具有气体导板的Cz炉,则会减小结晶界面平均氧浓度.     

一种适用于煤粉工业锅炉燃烧器的冷态流场特性研究

利用试验和数值模拟的方法对一种适用于煤粉工业锅炉燃烧器的冷态流场特性进行了研究.结果表明,回流区的长度随内二次风旋流强度的增大而明显增大,随钝体阻塞率的减小而缩短;燃烧器回流区内的回流速度随一次风风速的增加略有降低,随内二次风旋流强度的增加而增大,随钝体阻塞率的增加呈先增大后减小的趋势.试验结果为该燃烧器的设计和热态试验提供了一定的指导.     

An Experimental Technique for the Analysis of Slug Flows in Pneumatic Pipelines Using Pressure Measurements

An experimental technique has been developed to measure the flow characteristics of slugs in dense phase pneumatic conveying using pressure measurements. This method is based on the unique characteristics of slug flows in pipes, i.e., an axial pressure fluctuation along the pipeline and a pressure difference in the radial direction at the back of a slug. Standard differential pressure transducers were used in this study and the influence of the finite response time of these transducers was considered. Experiments were conducted over a range of gas-solids flow conditions and experimental data were analyzed to describe the behavior of solids slugs through pipes. The calculated slug velocity and length using axial pressure measurements were confirmed by video recordings, and the synthesis between axial and radial pressure signals showed reasonable agreement in flow pattern analysis. This relatively simple measuring technique has been found effective in detecting solids slugs traveling through horizontal pipes and will distinguish various flow regimes. It provides a useful and easily applied tool for system optimizing and benchmarking in industrial applications.