Soot formation characteristics in a pulverized coal flame formed in a swirling flow

To understand the soot formation characteristics in a pulverized coal flame with a swirling flow, simultaneous imaging of Mie scattering of coal particles and laser induced incandescence (LII) of soot were performed in this study. The pulverized coal flame was stabilized by a hydrogen diffusion pilot flame. The characteristic structures of soot formation in the pulverized coal flame with a swirling flow were analyzed based on a comparison of the experimental results and two-dimensional numerical simulation in the mixing region of coal particles and the oxidizer. The interactions between coal particle clouds and soot formation are discussed in detail. The results clearly show that the averaged radial dispersions of scattering signals from coal particles and of the LII signals from soot are overlapped. The overlapping region appeared nearby the nozzle exit due to the turbulent mixing and the high temperature region formed by swirl-induced recirculation flow. This overlapping region radially expands with increasing the height from the burner. Additionally, the characteristic areas of soot formation were observed in the results of simultaneous imaging of Mie scattering and LII. These areas are 1) streaky soot formation areas around the particle clouds, 2) soot formation areas inside of the particle clouds and 3) soot formation areas around the large coal particles.     

流量控制电磁阀的小流量特性分析

介绍可调无级输出流量控制电磁阀在小流量输出区域的输出原理与特性。通过改变小流量区域的流道几何结构,改变电磁阀小流量区域的流量性能。     

旋进漩涡流量调节装置流量调节特性研究

采用实验方法,对旋进漩涡流量计-锥形阀组合式流量调节装置的流量测量与调节特性,进行了研究.首先在有无锥形阀情况下,对旋进漩涡流量计的输出特性进行了测试,发现无论上游有无锥形阀,所测得压力信号的脉动频率与流量之间均呈现良好的线性关系,且同一流量时,锥形阀的存在引起的压力脉动频率变化小于5%.测量结果说明,在这种组合式的流量调节装置中,旋进漩涡流量计能够正常工作.装置的流量调节特性测试中,在进口压力为0.11～0.23MPa、阀芯行程0～8mm的范围内,测量了流量的变化情况.结果发现,进口压力不变时,流量随着开度的增大而增大,流量与开度之间呈线性关系;当进口压力增大时,通过的流量也增大;反之亦然.     

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.     

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.     

Electronic expansion valve mass flow rate prediction based on dimensionless correlation and ANN model

Refrigerant mass flow rate through electronic expansion valve (EEV) makes significant sense for refrigeration system intelligent control and energy conservation. Objectives of this study were to present experimental data of R134a mass flow rate through EEV and to develop models for EEV mass flow rate prediction via two approaches: dimensionless correlation based on Buckingham π-theorem and artificial neural network (ANN) model based on dimensionless parameters. The database utilized for model training and test was comprised of our experimental data and data available in open literatures including R22, R407C, R410A and R134a. Compared with three existing dimensionless correlations, the proposed dimensionless correlation and ANN model demonstrated higher accuracy. The proposed dimensionless correlation gave mean relative error (MRE) of 6.60%, relative mean square error of (RMSE) 12.05 kg h⁻¹ and correlation coefficient (R²) of 0.9810. The ANN model with the configuration of 8-6-1 showed MRE, RMSE and R² of 3.97%, 7.59 kg h⁻¹ and 0.9924, respectively.     

模拟海深条件下提升阀流动特性的实验研究

水压传动技术应用于深海环境可以直接从海洋中吸水加压，高压水作功之后可以直接排入海洋，不需要水箱和回水管道，大大简化了系统，具有独特的优势。然而，在深海作业时，液压元件的工况同陆地相比有较大的差异，海深压力相当于在元件出口加了一个背压。文中用背压来模拟海水压力，对以水作介质时背压对提升阀口流量特性的影响进行了实验研究。研究结果表明，背压使得流量饱和更容易发生；有背压时的流量系数比没有背压时的流量系数大；当阀芯和阀座有叠合时，背压对阀口流量特性的影响比阀芯和阀座没有叠合时的影响大。     

A Numerical Simulation of Swirling Flow Pneumatic Conveying in a Vertical Pipeline

A numerical prediction for the axial and swirling pneumatic conveying in a vertical pipe was performed based on an Eulerian approach for the gas and a stochastic Lagrangian approach for the particles, where κ – ? turbulence model, the model of particle-particle and particle-wall collisions, was adopted. The numerical results are presented for polyethylene pellets of 3.2mm diameter conveyed through a pipeline of 12m in height with an inner diameter of 80mm. The initial swirl number was 0.0 and 0.68, the mean gas velocity varied from 11 to 17m/s, and the solid mass flow rate was 0.03 and 0.084 kg/s. From the numerical analysis, the swirl decay of the swirling gas-solid flow was found to be rapid in the acceleration region and approached the clean swirling flow in a fully developed region. The turbulent kinetic energy and energy dissipation rates of the swirling gas-solid flow increased near the wall and reduced in other regions. The comparison of predicted values with measured data showed a good agreement.     

超临界CO_2在电子膨胀阀内流动特性的数值分析

建立了超临界CO_2通过电子膨胀阀(EEV)降压过程的二维计算模型,采用均相流模型对超临界CO_2通过EEV的两相流动过程进行了数值模拟。结果表明超临界CO_2进入膨胀阀后,沿着工质的流动方向,其状态参数在开始变化不大,在接近阀芯最下端的部分,各状态参数开始剧烈变化。越靠近膨胀阀对称中心,CO_2压力越大,接近壁面处的压力最小。工质的流速最大的位置位于阀芯尖端,可达到179 m/s。CO_2工质流过阀芯尖端流阻最大处时,CO_2的压力急剧降低,两相间的质量传递率急剧增加,CO_2发生相变。随着EEV内CO_2压力的降低,CO_2气体份额持续增大,气体份额大小值与压力大小成反相关。     

Wavelet Multi-Resolution Cross-Correlation Analysis of Swirling Gas-Solid Flow in a Horizontal Pipe

A wavelet multi-resolution cross-correlation analysis was developed and applied to experimental pressure-time signals in order to analyze the characteristics of swirling gas-solid flow in both Fourier and physical spaces. The experiment was carried out in a horizontal pipe with a length of 7.5 m and an inner diameter of 76 mm. The initial swirl number based on the total inflow was varied from 0.0 to 0.61, the mean gas velocity was varied from 6 to 28 m/s, and the solid mass flow rate was varied from 0.08 to 0.5. From the wavelet multi-resolution correlation analysis of the fluctuating pressure in the range of low air velocity, the characteristics of swirling gas-solid two-phase flows were extracted at various frequencies. Much stronger correlations were found in the range of low frequency, which implied periodic motion of dunes and sliding clusters. Additionally, it was revealed that the motion of a large cluster sliding flow contains two smaller clusters and the moving velocities of dunes were 1 m/s and 2 m/s, respectively. However, no correlation existed at smaller scales of correlation features, which indicated heterogeneous suspension flow.     

Wavelet Multi-Resolution Cross-Correlation Analysis of Swirling Gas-Solid Flow in a Horizontal Pipe

A wavelet multi-resolution cross-correlation analysis was developed and applied to experimental pressure-time signals in order to analyze the characteristics of swirling gas-solid flow in both Fourier and physical spaces. The experiment was carried out in a horizontal pipe with a length of 7.5 m and an inner diameter of 76 mm. The initial swirl number based on the total inflow was varied from 0.0 to 0.61, the mean gas velocity was varied from 6 to 28 m/s, and the solid mass flow rate was varied from 0.08 to 0.5. From the wavelet multi-resolution correlation analysis of the fluctuating pressure in the range of low air velocity, the characteristics of swirling gas-solid two-phase flows were extracted at various frequencies. Much stronger correlations were found in the range of low frequency, which implied periodic motion of dunes and sliding clusters. Additionally, it was revealed that the motion of a large cluster sliding flow contains two smaller clusters and the moving velocities of dunes were 1 m/s and 2 m/s, respectively. However, no correlation existed at smaller scales of correlation features, which indicated heterogeneous suspension flow.     

主给水调节阀节流窗口周向设计及其对流动特性的影响

安装于核电站二回路的主给水调节阀通过控制给水流量来调节蒸汽发生器内的水位高度,因此主给水调节阀的流动特性影响着核电站的运行安全与效率.首先,提出了无量纲的节流窗口周向布置不平衡度δ,进行主给水调节阀节流窗口周向设计;其次,利用经网格无关性与流量实验验证的数值模拟方法分析了阀内流场的速度和压力分布特性;最后,探讨了节流窗...     

煤化工专用控制阀多相流流场特性研究

针对煤化工专用控制阀易磨损失效的问题,提出基于数值模拟的阀内流场分析方法.今基于可实现k-ε(Realizable k-ε)双方程湍流模型,通过有限元分析法(finite element analysis,FEA),对控制阀的多相流流场中的湍流特征进行数值模拟研究,得到湍流流场内的压力、速度的分布,并结合Preston磨削经验公式,得到控制阀内最易磨损的区域,从而为后续控制阀的结构优化设计及表面强化打下了基础.     

Nonintrusive Monitoring of Slug Sequence and Flow Stability in Dense-Phase Pneumatic Conveying

This article presents three sensing methods developed for the nonintrusive monitoring of important flow parameters in dense-phase pneumatic conveying. With the optical measurement system, images of the flow are acquired and an image analysis is used to determine the sequence, length, and velocity of slugs for given materials and operating conditions. The conveying parameters of interest are also monitored with a capacitive sensor by means of exploiting electrical properties of the flowing media. The charge-based measurement system uses a field meter to determine the electric field strength caused by charged particles and provides information about the sequence and regularity of the moving slugs. The noninvasive principle of all three methods avoids concerns about particle contact effects (e.g., wear of the measurement equipment or interference with the flow). All three prototype sensors have been tested under slug flow conditions. A comparison of the three sensing methods against key requirements in pneumatic conveying reveals that capacitive sensing seems to be best suited for reliable flow determination in slug flow.     

Nonintrusive Monitoring of Slug Sequence and Flow Stability in Dense-Phase Pneumatic Conveying

This article presents three sensing methods developed for the nonintrusive monitoring of important flow parameters in dense-phase pneumatic conveying. With the optical measurement system, images of the flow are acquired and an image analysis is used to determine the sequence, length, and velocity of slugs for given materials and operating conditions. The conveying parameters of interest are also monitored with a capacitive sensor by means of exploiting electrical properties of the flowing media. The charge-based measurement system uses a field meter to determine the electric field strength caused by charged particles and provides information about the sequence and regularity of the moving slugs. The noninvasive principle of all three methods avoids concerns about particle contact effects (e.g., wear of the measurement equipment or interference with the flow). All three prototype sensors have been tested under slug flow conditions. A comparison of the three sensing methods against key requirements in pneumatic conveying reveals that capacitive sensing seems to be best suited for reliable flow determination in slug flow.     

On the gas flow rate through a Mach disk in an underexpanded jet

An air jet with an excess static pressure at a regime of escape into quiescent air is considered. The range of Mach number variation is 1–3, and that of the inefficiency ratio 1–1000. An analysis has been made on the basis of the well-known experimental-calculated approximation dependences for stationary expanding flows. We solve the inverse problem where the parameters at the nozzle exit and the geometric characteristics of the initial section of the jet are known and it is required to find the remaining quantities corresponding to them. In the present analysis, this is the rate of flow through a central discontinuity and the integral characteristic of the magnitude of the total pressure loss. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 82, No. 2, pp. 320–325, March–April, 2009.     

Segregation patterns and characteristics differences of superfine pulverized coal ground by three pulverizing systems

Comminution methods and segregation of coal powder are key factors affecting the characteristics of superfine pulverized coal. However, there are few articles available in this issue. In this paper, three representative pulverizing systems with diverse grinding patterns and gathering methods are selected to prepare superfine powder using the same raw coal. Afterwards, element analysis, approximate analysis, maceral determinations, surface area measurement and XPS tests are performed successively. The segregation tendencies and its influences on the coal powder are compared and discussed among three groups. Data of similar sizes in three groups receive special attentions. Based on the experiments, it is found that at the same conditions, vitrinite is easier to gain thorough crushing compared with inertinite. Due to the smaller sizes, vitrinite and ashes are prone to escape from the cyclone separator. Due to the high density, inertinite and ashes are apt to accumulate in the lower part of the coal pile. The maceral segregation imposes greater influences on the C-containing functional groups on the surfaces than the mechanochemical effects. The significances of this paper lie in figuring out the influences of grinding methods on properties and segregation patterns of superfine pulverized coal, which provide valuable references for industrial applications of this technology.     

流式细胞仪样品流速及聚焦流测量方法研究

为提高流式细胞仪的探测分辨率和数据检测的稳定性,需要精确控制样品流速,并分析样品流速和鞘液流速对样品聚焦流的影响,可通过样品聚焦流直径和样品聚焦流在流动室流道中的相对位置来评价样品的聚焦状况。利用蠕动泵运动特点,设计了一种平均流量称重法测量样品流速的方法,并与微流量传感器测量结果作比较;采用最小二乘法线性拟合蠕动泵的控制电压和样品流速之间的函数关系,并采用显微成像法直接测量和分析样品流速和鞘液流速对样品聚焦流直径、偏离流动室流道中心线的距离的影响。实验结果显示,采用平均流量称重法与微流量传感器测得的样品流速的线性相关系数高达0.982 8;蠕动泵的样品流速与其控制电压的线性相关系数高于0.99,说明利用该线性关系可以实现样品流速的精确控制;采用的显微成像法能快速方便地测得样品聚焦流的直径及位置,为流式细胞仪样品流速、鞘液流速的调控以及液流器件组装精度的测试提供了指导方法。     

流速和管径对热力特性的影响

论述了低温系统绝热性能和流阻特性对液流温度的影响,推导了液流温升及最优流速公式,分析了流速和管径与液流温升的关系,提出了确定流速和管径的方法。