Research on Premixed Abrasive Jet Derusting Machine

The structure, working principles, and main technological parameters of the premajet derusting machine are introduced. Experiments were made to test the relationship among such jet parameters as working pressure, rate of water flow, abrasive weight consistency and derusting efficiency. Reasonable parameters were decided. Results prove that the derusting machine is characterized by its high derusting efficiency (as high as 20m 2/h), good derusting quality (as good as ISO8501 1 Sa 2.5), and low specific power consumption (about 0.3kW·h/m 2). Therefore it is a new type of high efficiency derusting machine.

Research on the Mechanism of Abrasive Particles Accelerated and a Cutting System of a Premixed Abrasive Jet

Forces acting on abrasive in the process of speeding up have been analyzed. Motion differential equation of abrasive in a pipeline and nozzle has been given, respectively. Mechanisms of abrasive particles accelerated in a premixed abrasive jet has been analyzed. The study shows that driven by high-pressure water, velocity of an abrasive is near to velocity of water in pipeline through the acceleration distance. In the taper section of a nozzle, water and abrasive particles are greatly accelerated at the same time. But velocity of an abrasive always lags behind velocity of water. A premixed abrasive jet cutting system has been introduced. The structure and working principles of the system have been given. The system is an assembly of abrasive screening and filling. By use of the premixed abrasive jet cutting system established, cutting experiments have been made to test the main parameters which influence the cutting performances such as working pressure, standoff and traverse velocity, and the nozzle diameter affecting cutting chink width.

Modeling of workpiece temperature suppression in high-speed dry milling of UD-CF/PEEK considering heat partition and jet heat transfer

High-performance carbon fiber-reinforced polyether-ether-ketone(CF/PEEK)has been gradually applied in aerospace and automobile applications because of its high strength-to-weight ratio and impact resistance.The drymachining requirement tends to cause the cutting temperature to surpass the glass transition temperature(Tg),leading to poor surface quality,which is the bottleneck for dry milling of CF/PEEK.Temperature suppression has become an important breakthrough in the feasibility of high-speed dry(HSD)milling of CF/PEEK.However,heat partitioning and jet heat transfer mechanisms pose strong challenges for temperature suppression analytical modeling.To address this gap,an innovative temperature suppression analytical model based on heat partitioning and jet heat transfer mechanisms is first developed for suppressing workpiece temperature via the first-time implementation of an air jet cooling process in the HSD milling of UD-CF/PEEK.Then,verification experiments of the HSD milling of UD-CF/PEEK with four fiber orientations are performed for dry and air jet cooling conditions.The chip morphologies are characterized to reveal the formation mechanism and heat-carrying capacity of the chip.The milling force model can obtain the force coefficients and the total cutting heat.The workpiece temperature increase model is validated to elucidate the machined surface temperature evolution and heat partition characteristics.On this basis,an analytical model is verified to predict the workpiece temperature of air jet cooling HSD milled with UD-CF/PEEK with a prediction accuracy greater than 90%.Compared with those under dry conditions,the machined surface temperatures for the four fiber orientations decreased by 30%–50%and were suppressed within the Tg range under air jet cooling conditions,resulting in better surface quality.This work describes a feasible process for the HSD milling of CF/PEEK.

High Speed Observation of Periodic Cavity Behavior in a Convergent-Divergent Nozzle for Cavitating Water Jet

Cloud cavitation shows an unsteady periodic tendency under a certain flow condition. In a cavitating water jet flow with cavitation clouds, the cavities or the clouds produce high impact at their collapse. In order to make clear a mechanism of the periodic cavity behavior, we experimentally examine the behavior in a transparent cylindrical convergent-divergent nozzle using a high-speed video camera. An effect of upstream pressure fluctuation due to a plunger pump is investigated from a viewpoint of unsteady behavior in a cavitating water jet. As a result, it is found that the cavitating flow has two kinds of oscillation patterns in the cavity length (cavitation cloud region). One is due to the upstream pressure fluctuation caused by the plunger pump. The other is much shorter periodic motion related to the characteristic oscillation of cavitation clouds accompanied with the shrinking (reentrant), growing and shedding motion of the clouds.

Experimental investigation on de-icing by an array of impact rod-type plasma synthetic jets

Since flight accidents due to aircraft icing occur from time to time,this paper proposes an array of impact rod-type plasma synthetic jet de-icing methods for aircraft icing problems.The impact rod-type plasma synthetic jet actuator(PSJA)is based on the traditional PSJA with an additional impact rod structure for better de-icing in the flight environment.In this work,we first optimize the ice-breaking performance of a single-impact rod-type PSJA,and then conduct an array of impact rod-type plasma synthetic jet ice-breaking experiments to investigate the relationship between crack expansion and discharge energy,ice thickness and group spacing.The results show that the impact force and impulse of a single-impact rod-type PSJA are proportional to the discharge energy,and there exists a threshold energy Qmin for a single actuator to break the ice,which is proportional to the ice thickness.Only when the discharge energy reaches above Qmin can the ice layer produce cracks,and at the same time,the maximum radial crack length produced during the ice-breaking process is proportional to the discharge energy.When the ice is broken by an array of impact rod PSJAs,the discharge energy and group spacing together determine whether the crack can be extended to the middle region of the actuator.When the group spacing is certain,increasing the energy can increase the intersection of cracks in the middle region,and the ice-fragmentation degree is increased and the ice-breaking effect is better.At the same time,the energy estimation method of ice breaking by an array of impact rod-type PSJAs is proposed according to the law when a single actuator is breaking ice.

预混预蒸发正庚烷湍流火焰结构的实验研究

采用预混伴流射流燃烧器(PPJB)研究了初始温度400 K的预蒸发正庚烷/空气混合物在薄反应区的湍流火焰结构.采用热线风速仪标定冷态湍流流场,CH-PLIF测量湍流火焰反应区结构,共振OH-PLIF测量湍流火焰结构特征.结果表明:高湍流条件下,反应区厚度在不考虑三维效应时最大厚度为层流火焰厚度的1.6倍,其可支持薄反应区理论对预蒸发液体燃料湍流火焰的适用性.火焰面褶皱比和湍流燃烧速度的增加与湍流强度的提升不匹配.通过对火焰面曲率和平均火焰面密度的分析,发现高湍流条件下,褶皱尺度、大小和数量变化不大.一方面,湍流可能会减弱非均匀扩散造成的差异;另一方面,更可能是由于对褶皱结构的不完全捕捉和对3D效果的忽视而引发对火焰褶皱的低估.

Determination of the shedding frequency of cavitation cloud in a submerged cavitation jet based on high-speed photography images

To accurately determine the shedding frequency of the cavitation cloud in a submerged cavitation jet,the spectral analysis and the proper orthogonal decomposition(POD)for high-speed photography images are performed.The spectrums of 6 different kinds of image signals(the area-averaged gray level,the line-averaged gray level,the point gray level,the cavitation length,width,and area)are calculated and compared.The line-averaged gray level is found to be optimal in determining the shedding frequency but an accurate frequency can only be obtained in the stable-frequency zone where the cavitation cloud sheds.In repeated experiments,the plateau-shape distribution of the main frequency is established with a deviation of 10.8%.A revised Reynolds number Re'is defined and the shedding frequency can be correlated to Re'by a power law when the cavitation number is less than 0.02.This relationship is validated by the experimental data in literature.The first mode of the POD characterizes the ensemble-average of the cavitation cloud while the second mode is the major part of the cavitation cloud transient components.The modes 2-5 are organized in pairs,which confirms the periodic feature of the cavitation cloud in the submerged cavitation jet.Near the nozzle exit,the modes 2-5 are symmetrically distributed in the jet shear layer.The shedding frequency of the cloud cavitation can also be precisely determined by performing the spectral analysis of the weighting coefficients of the mode 2.This paper shows that the two parameters,namely,the line-averaged gray level and the weighting coefficients of the mode 2,can be confidently used to calculate the shedding frequency of the cavitation cloud in a submerged cavitation jet.

High-speed measurement of thickness of a water film formed by a jet obliquely impinging onto a plate using an LED-induced fluorescence method

A transient thickness distribution measured with a high temporal resolution is elemental for exploring the flow characteristics and mechanism of a liquid film formed by an impinging jet.Therefore,this paper develops a high-speed Light-Emitting Diode-Induced Fluorescence(LEDIF)system based on the brightness measured directly above the liquid film.An Ultraviolet(UV)LED lamp is used to provide sufficient and continuous excitation light.Then,a system performance analysis proves that the system can continuously measure the global film thickness at a high acquisition frequency of 5000 Hz when the dye concentration is 200 mg/L.The influence of the irregularity of the excitation intensity,including the spatial non-uniformity,temporal instability,and long-term instability,on the measurement uncertainty is analyzed in detail.The analysis indicates that the system has an acceptable uncertainty of 10%.Compared with theoretical results,experimental results verify that the LEDIF system can accurately measure the global thickness of a liquid film formed by a water jet obliquely impinging onto a plate.An experimental investigation of the radial section of the raised zone demonstrates that the radial section changes from a sewing needle to an oval when the azimuth angle increases from 10°to 90°.Meanwhile,the dynamic contact angle exponentially decreases from 41.4°to 30.1°.A dynamic analysis of surface waves shows that the measured wave velocity decreases from 12 m/s to 1 m/s and the dominant frequency decreases from 1000 Hz to 10 Hz along the flow direction.

EVALUATION OF THE CUMULATIVE FORMATION OF HIGH-SPEED LIQUID JETS

This paper describes the generation of pulsed, high-speed liquid jets usingthe cumulation method. This work mainly includes (1) the design of the nozzle assembly, (2) themeasurement of the jet velocity and (3) flow visualization of the injection sequences. Thecumulation method can be briefly described as the liquid being accelerated first by the impact of amoving projectile and then further after it enters a converging section. The experimental resultsshow that the cumulation method is useful in obtaining a liquid jet with high velocity. The flowvisulization shows the roles of the Rayleigh-Tay-lor and Kelvin-Helmholtz instabilities in thebreakup of the liquid depend on the jet diameter and the downstream distance. When the liquid jetfront is far downstream from the nozzle exit, the jet is decelerated by air drag. Meanwhile, largecoherent vortex structures are formed surrounding the jet. The liquid will break up totally by theaction of these vortices. Experimental results showing the effect of the liquid volume on the jetvelocity are also included in this paper. Finally, a method for measuring the jet velocity bycutting two carbon rods is examined.

前混合磨料射流基础研究概要

加速机理和切割是磨料射流基础研究的两个重要方面。笔者介绍了磨料射流技术及磨料粒子与流体的混合方式,分析了前混合磨料粒子在管道及喷嘴内的加速机理。结果表明:在高压输送的圆形管道中,在水流速度的带动下,经过一定的加速距离,磨料粒子的速度基本接近水流速度;在喷嘴收缩段,水流速度和磨料粒子速度同时得到大幅度加速,但磨料粒子速度总是落后于水流速度。利用建立的前混合磨料射流切割系统进行了切割试验,考察工作压力、喷射靶距及横移速度等基本参数对切割性能的影响,试验表明,工作压力对切割性能影响较大,而喷射靶距及横移速度均存在最佳范围。同时对割缝宽度进行了讨论。

前混合式磨料射流清洗油管涂料的实验研究

研究结果表明，前混合式磨料射流清洗油管涂料的清洗效率随喷嘴直径的增大而增大，喷距、喷射角和颗粒直径最佳参数值分别为１５０ｍｍ、１２０℃（或６０℃）和０．８ｍｍ。

基于迭代算法的磨料颗粒加速机制研究

在前混合射流磨料加速机制研究中一般将阻力系数当作常数且忽略巴西特力的影响。针对这一问题,采用实时对比插值法分析阻力系数且考虑巴西特力对磨料加速的影响,在此基础上建立磨料运动微分方程,并通过迭代算法进行求解,较为全面、准确地阐释磨料加速机制。结果表明:在管道及喷嘴直线段内磨料受力由大到小分别为黏性阻力、巴西特力、视质量力,在喷嘴收敛段内磨料受力由大到小分别为压强梯度力、视质量力、黏性阻力、巴西特力,且全程中巴西特力都有不可忽略的影响;在喷嘴收敛段前半段磨料加速度大于液相加速度,在收敛段后半段磨料加速度略小于液相加速度,在喷嘴直线段内磨料加速趋缓。

DLN燃烧室的燃料-空气预混均匀性研究

参照国产燃机DLN燃烧室的燃料-空气预混机构,模化设计了相应的试验装置,并在冷态条件下,测量了燃料-空气的预混预均匀性,发现无论在径向还是周向的燃料分空间布都极不均匀,这对控制燃烧时的NOx排放显然是十分不利的。为此,本文进一步分析了影响预混均匀性的各种因素,指出该燃烧室的预混不均的主要原因是燃料-空气射流动量比偏小,预混长度短和燃料径向喷射不匀,并通过实验验证了上述分析,提出了改进的措施和方向。

微喷管氢气非预混射流火焰燃烧特性

采用考虑详细化学反应机理的数值计算,对空气伴流中微圆管氢气非预混射流火焰进行了研究。不同流速下火焰OH基元分布数值计算与实验结果吻合较好。结果表明:当微圆管内径保持不变时,随着燃料速度减小,火焰最高温度逐渐降低。当燃料速度接近熄灭极限速度时,火焰最高温度开始急剧下降;微圆管氢气非预混射流火焰存在最小流速对应的熄灭极限;随着管壁材料热导率降低,火焰中心轴线上的最高温度逐渐升高,喷口处壁面温度也升高;管壁材料热导率对火焰熄灭极限速度影响不显著。

射流控制柴油机预混合压缩着火相位和排放研究

为有效控制柴油机预混合压燃着火相位,提出了射流控制压燃(jet controlled compression ignition,JCCI)方法。将一台186F柴油机改装成JCCI发动机,并进行了燃烧相位控制和排放特性试验。结果表明:CA10和CA50在较大的范围内与点火定时呈线性关系,说明在JCCI发动机中可实现对预混合燃烧相位的直接控制;在试验工况下JCCI发动机的NOx排放比原机降低较多,最大降幅超过90%;碳烟排放在低负荷与原机接近,中高负荷降低了92%;CO和THC排放比原机增加较多。

磨料质量分数对预混合磨料水射流破岩效果的影响

预混合磨料水射流是突破煤矿深长钻孔内高效破煤岩技术瓶颈的有效技术,在坚硬顶板治理、沿空留巷和硬煤增透具有广泛应用前景。磨料质量分数是影响其破煤岩效果的重要因素。为明确磨料质量分数对磨料加速、分布以及冲击动能的影响,基于离散元的耦合模型(CFD-DEM模型),考虑颗粒间的摩擦、碰撞,添加颗粒相体积分数和动量源相,修正VOF多相流模型,开发用户自定义函数(UDF)通信接口,精确计算了磨料质量分数对磨料颗粒加速运动与分布的影响,准确描述了磨料粒子对水射流流场的影响。结合预混合磨料水射流破岩实验,得到了以下结论:在固定压力下,不同磨料质量分数的射流液固能量转化效率不同,导致磨料冲击动能不同。提高磨料质量分数,能够提高破煤岩效果,但存在最优值。每一压力条件下都有与之相适配的最优质量分数,此质量分数下能量转化效率最高,磨料冲击动能最大。如射流压力5 MPa时,80目(0.178 mm)石榴石最优质量分数为11%。同一质量分数下,提高射流压力可提高磨料冲击动能,但是能量转化率和利用率降低。提高压力使射流速度增加,曳力增大,但射流与磨料接触时间缩短,导致射流能量未能及时转化为磨料动能。相较于提高射流压力,适当增加磨料质量分数以提高能量转化效率和能量利用率,是达到最佳破煤岩效果的更经济低能耗的方式。

高温射流反应腔结构设计与反应规律

结合高压水射流和岩石热裂解钻井方法,提出了适用于深部硬地层的高温射流钻井新方法,即利用高速射流对岩石表面形成冲击力,同时高温流体迅速将热量传递给岩石以达到快速破岩的目的。因此高温射流发生装置对最终作用于岩石的射流性能十分重要,设计了两种高温射流燃烧反应发生装置结构(混合装置和对冲装置),利用计算流体力学模拟了常压下不同反应参数对生成的高温射流的影响,并对两种装置进行对比分析和反应规律研究。结果表明:高温的平均射流速度随着甲醇质量流量的增加而增大;气体存在滑脱效应,在满足化学反应方程的理论值的基础上,甲醇的实际质量流量应大于理论质量流量,而氧气的实际质量流量小于理论质量流量,使两者混合和燃烧更加充分,释放更多能量;在本文模型条件下,将空气质量流量控制在0.03~0.04kg/s较为合适,既可以保证反应腔内充分燃烧,又可以获得较高的射流速度;冷水质量流量与喷嘴速度呈线性正相关;在现场实际应用中,应注意控制冷水流量,以免造成射流温度过低。不同空气质量流量条件下,混合装置的射流速度和温度较优。两种装置的射流速度和温度在不同氧气浓度条件下变化规律一致,均先增大、后减小,但是在射流速度方面,对冲装置较优。在现场实际应用时可根据需要达到的射流速度和温度选择不同结构的燃烧装置,使高温射流的性能达到最优。

湍流贫燃预混射流火焰的大涡模拟

为了研究高Karlovitz(Ka)数下湍流预混火焰的驻定机制和火焰结构,采用化学热力学建表方法结合假定概率密度函数(PDF)模型,对值班预混射流火焰(PPJB)进行大涡模拟(LES)研究。选取自点火模型作为建表模型,使用假定PDF模型考虑湍流和化学反应之间的相互作用,其中假定双混合物分数的概率密度分布为Dirichlet分布,反应进度变量的概率密度分布为β分布。模拟结果表明,能较好预测PPJB火焰的温度和主要组分的分布。使用中间组分(CO和OH)的质量分数来定性描述PPJB火焰结构,结果表明高Ka数下火焰结构受到湍流涡旋的显著影响。

淹没和非淹没下前混合磨料射流切割混凝土

本文介绍了前混合磨料射流淹没和非淹没状态下切割实验系统 ,研究了两种状态下前混合磨料射流影响切割诸因素对混凝土试件切割深度的影响。结果表明 ,靶距对切割深度有显著影响 ,即随着靶距增大 ,在淹没状态下切割深度下降比非淹没状态更大 ,而压力、磨料浓度和横移速度对切割深度影响在两种状态下基本一致。

前混合水射流超细粉碎煤粒的试验研究

以山西西山煤样为原料,开发了一种适合于煤炭物性的前混合水射流超细煤粉试验装置,研究了加载压力、循环碰撞次数和浓度对超细煤粉大小及分布的影响,并利用激光粒度仪对所得超细煤粉进行了粒度分析,用ξ电位实验研究了超细煤粉颗粒悬浮体系的分散性.试验表明,采用角形喷嘴淹没水射流技术,可以在循环碰撞为3～4次、加载压力为43～50MPa的工艺条件下将料浆比为25%～35%的煤粒粉碎至d50<22.6μm,为采用前混合水射流方法粉碎煤炭制备高性能水煤浆燃料提供了理论基础和关键技术.