Flame Structure of a Jet Flame with Penetration of Side Micro-jets

In this paper, an innovative jet lifted flame with side micro-jets has been proposed and its effects on the flame structure have also been investigated. Due to the changes of the initial combustion conditions, mixing and aerodynamics which resulted from the perturbation of the side micro-jets, such a lifted jet flame has different flame structure compared with the common premixed flame. Results demonstrate that use of the micro-jets can control, to a certain extent, the flame structure, including the flame length, lift-off distance and blow-off limit. With the same fuel and air flow rate, the flame length with the side micro-jets will decrease about 5%-40% as the air volume ratio a increases from 58%-76%. Compared with the common diffusion flame, the jet flame with the side micro-jets demonstrates to be easier to be a momentum-dominated flame. The flame length with 2 micro-jets is about 5% less than with 6 micro-jets under the same fuel and air flow rate. With the same a, the fewer number of the controlled jets lead to the flame with relatively shorter length, not easier to be blown off and higher NOx emission. With certain fuel flow rate, the critical air volume ratio is largest for the flame with 3 micro-jets, which is more difficult to be blown off than the cases with 2, 4 or 6 micro-jets.

Fabrication and characterization of mussel-inspired layer-by-layer assembled CL-20-based energetic films via micro-jet printing

Three-dimensional(3D)micro-jet printing is a droplet deposition technique based on liquid-phase materials.To improve the deposition density and performance of energetic films with micro/nanoscale on an energetic chip,polydopamine(PDA)was utilized as a linker bridge to induce the in-situ self-assembly of CL-20-based energetic film via 3D micro-jet printing.The self-assembly was extensively characterized by confocal laser scanning microscopy(CLSM),SEM,power-XRD,XPS,and DSC.The performance of the self-assembled film was verified by the mechanical properties and detonation properties,and a possible self-assembly mechanism in the layer-by-layer micro-jet printing process was proposed.The results indicated PDA-induced self-assembly enhanced the physical entanglement between the binders and energetic crystal,reduced the porosity from 15.87%to 11.28%,and improved the elastic modulus and the detonation performance of the CL-20-based energetic film.This work proposes a novel and promising energetic film design and fabrication strategy to enhance the interaction between the energetic composite layers in the micro-jet printing process.

A non-monotonic blow-off limit of micro-jet methane diffusion flame at different tube-wall thicknesses

In order to provide guideline for choosing a suitable tube-wall thickness(d)for the micro-jet methane diffusion flame,the effect of tube-wall thickness on the blow-off limit is investigated via numerical simulation in the present work.The results show that the blow-off limit of micro-jet methane diffusion flame firstly increases and then decreases with the increase of tube-wall thickness.Subsequently,the underlying mechanisms responsible for the above non-monotonic blow-off limit are discussed in terms of the flow filed,strain effect and conjugate heat exchange.The analysis indicates that the flow field is insignificant for the non-monotonic blow-off limit.A smaller strain effect can induce the increase of the blow-off limit fromd=0.1 to 0.2 mm,and a worse heat recirculation effect can induce the decrease of the blow-off limit fromd=0.2 to 0.4 mm.The non-monotonic blow-off limit is mainly determined by the heat loss of flame to the tube-wall and the performance of tube-wall on preheating unburned fuel.The smallest heat loss of flame to the tube-wall and the best performance of tube-wall on preheating unburned fuel result in the largest blow-off limit atd=0.2 mm.Therefore,a moderate tube-wall thickness is more suitable to manufacture the micro-jet burner.

A Voice Coil Powered Controllable Micro-Jet Injection System

A medical device of micro-jet injection for drug delivery is described in this paper. The device is powered by a Lorentz force driver (or voice coil motor, VCM) and is able to perform pulsed injection through controlling the direction of the current passing through the device. The driving force and the resulting injection pressure are also controllable through control of the current intensity of the VCM. A physical model was established by combining the existing jet injection model with the relationship of the driving force obtained from a finite-element-method (FEM) analysis, and was verified by experimental measurements. The numerical calculation of the physical model reveals the relationship between the injection pressure and the current intensity of VCM under system conditions. In normal cases, the injection dose can be varied. Thus the relationship between the current intensity of VCM and the dose value was numerically obtained under the condition for the maximum injection pressure to be above a threshold value. These results can be used for optimization of the device.

Effect of Thermal Conductivity of Tube-Wall on Blow-Off Limit of a Micro-Jet Methane Diffusion Flame

The operating range of the flow rate or flow velocity for the micro-jet flame is quite wide,which can be used as the heat source.In order to optimize the micro-jet tube combustor in terms of the solid material,the present paper numerically investigates the impact of thermal conductivity(λs)on the operating limit of micro-jet flame.Unexpectedly,the non-monotonic blow-off limits with the increase ofλs is found,and the corresponding generation mechanisms are analyzed in terms of the thermal coupling effect,flow field,and strain effect.At first,the lower preheating temperature of the fuel and larger heat loss amount to the environment lead to a larger blow-off limit at a largerλs.After that,the smaller local flow velocity in the vicinity of flame root and smaller strain effect slightly increase the blow-off limit with the continuously increasingλs.Therefore,it is deduced that the applied performance of micro-jet combustor with a smaller thermal conductivity is better in terms of the blow-off limit.

The Enhanced Measurements of Laser Micro-jet Processing

In the paper, the enhanced measurements of the laser micro-jet processing are discussed. In fact, within pure water breakdown threshold of laser, the less focal which focused with the appropriate focusing lens and the small nozzle of water chamber enhance the laser power density ,at the same time, the laser beam transport in the wave guided water with the proper total reflection angle. The laser power which depended on the properties of the diameter, the coupling water chamber and the coupling efficiency of the micro-jet and laser beam expect of the properties of laser.

微氧射流技术在慢性伤口患者中的应用

目的:探讨微氧射流技术在慢性伤口患者中的应用效果。方法:选取2022年11月1日~2023年10月31日收治的60例慢性伤口患者作为研究对象,采用随机数字表法分为研究组和对照组各30例,对照组接受常规换药处理,研究组在对照组基础上接受微氧射流技术;比较两组愈合疗效、住院情况、生活质量[采用健康调查简表(SF-36)]、细菌阳性率。结果:研究组创面愈合总有效率高于对照组(P<0.05);研究组换药消耗时间、伤口愈合时间、换药次数、创面深度均低于对照组(P<0.01);干预后,两组SF-36评分均高于干预前(P<0.05),且研究组高于对照组(P<0.01);研究组铜绿假单菌、大肠杆菌、金黄色葡萄球菌及其他菌总阳性率低于对照组(P<0.05)。结论:微氧射流技术能改善慢性伤口患者愈合情况,抑制细菌繁殖,降低细菌阳性率,提高创面愈合疗效和患者生活质量。

自激振荡射流微通道换热特性及热力学分析

该文对自激振荡射流微通道内流体换热性能进行模拟研究,结果表明在不同入口质量流量(1.0~6.0 g/s)条件下,自激振荡器内高压区域的移动造成了微通道散热器内射流的偏转,形成射流周期性循环摆动的同时强化了流体区域的扰动。此外,经对比分析后发现相较射流微通道内流体区域其冲击范围更广,因此其均温性能也优于射流微通道。与此同时,该文运用热力学原理分析评价自激振荡技术对射流微通道内流体流动换热性能的影响,发现自激振荡器所产生的振荡射流可以减小射流微通道内流体对流换热过程中的不可逆损失,其热能传输效率高达到98.48%。

微磨料气射流加工结构化拓扑鱼鳞表面的实验研究

为了在脆性难加工材料上制备结构化鱼鳞表面,首先提取了鱼鳞表面的拓扑特征,建立了鱼鳞单元的表面模型,并基于鱼鳞模型进行搭接,得到结构化鱼鳞表面;然后根据微磨料气射流加工原理,分析了气射流加工拓扑鱼鳞实验的可行性与影响结构化鱼鳞表面形貌的重要工艺参数;最后采用单因素实验法对重要加工参数进行实验分析,得到了较好的拓扑鱼鳞表面单元,并以此进行排布得到结构化表面。研究结果表明,微磨料气射流加工结构化拓扑鱼鳞表面较为合理的工艺参数组合是加工时间为10 s、气射流加工压力为0.5 MPa、靶距离为10 mm以及射流角度为30°,在此工艺条件下,鱼鳞表面的形态和尺寸可能会受到一定的影响,但鱼鳞表面的拓扑属性保持不变。

强激光加载下铝、锡微喷特性实验研究

基于皮秒激光驱动的高能X射线源具有微焦点、高亮度和高分辨的优良特性,已成为研究金属材料微层裂和微喷射现象的热门诊断方法之一。锡因其熔点较低而成为微喷研究熔化影响的首选材料,铝由于熔点相对较高,不易发生冲击或卸载熔化形成液滴喷射,因此,铝微喷实验研究结果相对较少。基于“星光-III”激光装置的纳秒加载源和皮秒束诊断源,发展了皮秒激光驱动高能X射线背光照相技术,研究了表面含V型几何缺陷的金属锡、铝微喷特性,通过延时控制,获取了两种典型金属微喷射过程的高分辨物理图像,得到了喷射物质的形态分布、平均速度和面密度分布等重要信息。采用SPH方法对实验结果进行了数值模拟分析,揭示了实验中喷射物的形成机理以及高速喷射物质的来源。

射流清洗对微灌过滤器滤网清洗效果及损伤研究

为探究射流清洗技术在农业微灌过滤器清洗过程中的应用,开展射流清洗试验研究,分析入射压力、喷嘴口径、喷嘴扩散角度等3个参数对微灌过滤器滤网清洗效果及表面损伤程度的影响规律.试验结果表明:清洗效果随入射压力、喷嘴口径、喷嘴扩散角度的增大而提升,但提升幅度不断减小;滤网表面损伤程度随入射压力、喷嘴口径的增大而增大,随喷嘴扩散角度的增大而减小,其幅度逐渐减小;通过方差分析可知,射流参数对清洗效果影响程度从大到小依次为喷嘴口径、入射压力、喷嘴扩散角度,对滤网表面损伤影响程度从大到小依次为喷嘴口径、喷嘴扩散角度、入射压力;通过TOPSIS综合评价得到最佳射流参数组合为入射压力0.3 MPa,喷嘴口径3 mm,喷嘴扩散角度80°.

微磨料气射流加工技术研究现状与展望

微磨料射流加工技术是一种基于高能流体的磨粒冲蚀磨损加工技术,已广泛应用于难加工材料、复杂三维型面、光滑表面的加工。为进一步提高磨料射流加工过程中的精准控形控性能力,国内外学者开展了诸多基础加工理论与工艺探索等方面的研究工作。本文在概述磨料射流加工技术发展的基础上,全面总结了国内外学者在微磨料气射流加工(MAJM)技术中的微磨料气射流束发散效应及其抑制策略、材料力学性能对材料冲蚀去除模式的影响、材料冲蚀加工过程磨料嵌入抑制策略、微结构冲蚀加工几何特征等方面的主要研究成果,并对微磨料射流加工技术的难点与发展趋势进行了展望。

磁场辅助场致射流微细放电加工研究

场致射流放电加工方法利用高压电场诱导形成的微细射流与工件间放电来蚀除材料。虽无电极损耗,但微细射流的柔性较大且易受外界干扰,导致放电分散性和随机性较强,因此难以对其进行精准控制。为此,设计了一种四极性磁场施加装置,通过磁场对离子束的约束作用控制射流,并分析了磁场的作用机理,研究了磁场约束对场致射流放电加工的蚀坑宽度、深度及表面粗糙度的影响规律。结果表明,随着磁感应强度的增大,放电蚀坑的最大深度和表面粗糙度值都减小;磁场散焦方向上蚀坑的宽度增加,而聚焦方向上蚀坑的宽度减小,同时放电时的极间距离也减小。经试验验证,所提出的磁场辅助场致射流放电加工方法适用于具有沟槽类型特征的部件加工。

基于离子液射流定域电沉积的微镍柱成形研究

为提高定域电沉积三维金属微结构的加工效率和质量,采用离子液射流定域电沉积方式制备直径50~100μm、高度450~500μm的微镍柱,探究了工艺参数对沉积速率、微镍柱直径和微观形貌的影响。结果表明,在选定的参数范围内,微镍柱直径和沉积速率随着电压的增大同时增大,占空比对微镍柱沉积速率的影响高于对平均直径的影响,而脉冲频率对于微镍柱沉积速率影响不大。通过体式显微镜观察微镍柱微观形貌呈尖端效应,表明在阳极尖端半径对应区域和离子液射流范围内的共有区域具有电沉积定域性和优先性。合理控制阳极运动轨迹,调节参数为极间电压4.4 V、占空比50%、脉冲频率10 kHz时,可获得轮廓平直、表面致密的直径为61μm微镍柱。

静电溶吹微纳无机纤维制备技术及其应用进展

静电纺丝技术存在生产效率低和对高黏纺丝溶液限制大等问题,阻碍了高性能无机纤维的大规模产业化进程,而静电溶吹技术基于静电力与气流力的耦合作用,可助力微纳纤维的高产高质。为推广静电溶吹纺丝技术并为微纳无机纤维生产提供理论和实践依据,综述了该技术的基础研究,包括原理和先进设备;具体分析了该技术生产无机纤维的影响因素,尤其明晰了产业化的可控工艺;总结了目前国内外静电溶吹技术制备无机纤维的应用进展,通过与其它纺丝技术的对比阐明了静电溶吹技术目前存在的优势和挑战,并指出协同提升纤维质量和产量、赋予纤维结构/功能多样化以及研发多孔轻质无机纤维和超细无机纱线是该技术未来的重要发展方向。

船用微引燃甲醇发动机喷油器参数对燃烧和排放特性的影响

[目的]为改善大功率船用发动机燃烧、性能及排放,采用柴油微喷引燃甲醇喷射方式,研究发动机缸内燃烧和排放特性。[方法]基于一台大缸径船用ACD320中速柴油机,建立柴油微喷引燃甲醇发动机三维仿真模型,研究喷油器参数(喷孔数与甲醇喷雾夹角γ)对大缸径船用甲醇发动机燃烧性能与排放特性的影响。[结果]研究结果表明:随着喷孔数的增加,缸内甲醇雾化效果较好,使缸内工质混合较充分,CA50提前,燃烧持续期缩短,获得了较高的指示热效率和较好的燃油消耗率,并有助于降低碳烟排放,但会导致NO_(x)排放量升高。但随着甲醇喷雾夹角的增大,指示热效率增大,能够获得较好的燃油经济性和较低碳烟排放量。当甲醇喷雾夹角位于柴油喷雾夹角时(γ>60°),缸内火焰传播速度较快,指示热效率较大,燃料燃烧较充分,获得碳烟最低排放量和最优燃油消耗率。[结论]分析结果可为发动机喷油器布置提供了理论依据。

基于微型泵和颗粒阻塞的通用柔性微夹钳设计

针对自动化分拣系统中夹持装置很难实现微型化的问题,提出并制备一种通用柔性微夹钳。研究利用电共轭流体产生的射流和颗粒材料产生的堵塞实现柔性抓取的工作原理。微夹钳的整体结构包括1个带有电共轭流体射流发生器的微型泵和1个小型颗粒阻塞夹持器。通过调节微型泵中薄膜中的气压,颗粒阻塞夹持器可以迅速抓取各种尺寸和形状的物体。通过弹性膜的变形分析,推导出微夹钳数学模型并验证其抓取性能。最后,制备的微夹钳原型的外径为14 mm,总长度为40 mm,末端直径为10 mm。研究结果表明:选取二乙二醇丁醚醋酸酯作为工作液时,在颗粒材料填充率为50%且电压为4 kV的条件下,微夹钳的最大抓取力为93 mN,可在0.6 s内迅速完成多种形状精密件的抓取。

纳米流体微射流耦合微肋通道热沉传热特性研究

聚光太阳能电池工作时产生的热量对其有一定的消极影响,散热装置作为聚光太阳能电池工作过程中的必要装置,对于保证聚光条件下太阳能电池长期安全稳定高效运行有重要作用,采用纳米流体对其进行冷却是一种行之有效的途径。文中构建了一种微射流耦合微肋通道热沉,以纳米流体作为冷却介质,采用数值模拟和实验研究相结合的方法对热沉湍流传热和流动特性进行研究。通过数值模拟分别对SiC、Al_(2)O_(3)、SiO_(2)、TiO_(2)纳米流体与水作为冷却介质的冷却效果进行对比研究,最终选用其中冷却性能最好的SiC-W纳米流体进行实验,实验测试表明,SiC-W纳米流体相较于水有如下优势:导热系数增加约10.2%,平均传热系数增加约6.7%,且增加压损不超过水的1%。由此展现了SiC-W纳米流体优越的传热性能和应用价值。

椰子油火龙果汁纳米乳液冻干果粉的制备及其结构表征

联合真空冷冻干燥技术与动态超高压微射流技术制备椰子油火龙果汁纳米乳液冻干果粉,通过单因素试验及响应面法优化制备工艺条件,并对果粉理化性质及结构进行表征。结果表明:最佳制备工艺条件为以乳液质量为基准,椰子油添加量4.17%、皂角提取物添加量3.22 mg/100 g,在动态超高压微射流100 MPa下处理3次,所得冻干果粉中椰子油包埋率为61.21%±0.69%,溶解性为88.14%±0.91%。扫描电镜结果显示,果粉结构为片层块状结构,附着有单个球状细小颗粒。红外光谱结果表明,冻干果粉可有效包埋椰子油,减缓油脂氧化。差示量热扫描结果显示,冻干果粉具有良好的耐热性。

微气泡型管式气液接触器的气液两相流动特性研究

与常用气液鼓泡塔相比,管式气液接触器通过在管道空间内产生的均匀气泡状高分散体系强化气液传质过程,具有含气率高、能耗低和维护简单等优点。自主设计研制了带文丘里射流气泡发生器的微气泡型管式气液接触器;利用计算流体动力学(CFD)数值模拟和室内实验相结合的方法,对其所涉及的成泡机理、气泡粒径分布特性等进行了系统研究。结果表明,采用体积分数法(VOF)模型耦合RNG k-ε湍流模型可模拟分析微气泡型管式气液接触器内成泡机理和气泡形态;在文丘里射流气泡发生器的扩张段内可将大气泡剪切破碎成微气泡,且微气泡均匀稳定;气泡粒径随液体流量的增大而减小,在液体流量为14.0 L/min、气体流量为最大自然吸气量、柱体长度为800 mm时气泡粒径最小(76.5μm);气泡粒径随气体流量的增大而增大,在气体流量为1.5 L/min、液体流量为8.0 L/min、柱体长度为800 mm时气泡粒径最小(86.7μm);气泡粒径随柱体长度的增大呈现先降低后基本不变的趋势,当柱体长度大于800 mm时,其对气泡粒径的影响较小。