等离子-熔化极气体保护焊电弧特性研究现状

等离子-熔化极气体保护焊的电弧形态和熔滴过渡方式直接关系到焊缝质量,采用不同的电极连接形式,如直流正接、直流反接,电弧形态及熔滴过渡方式均不同;主要介绍了目前等离子-熔化极气体保护焊在采用不同的电极连接形式下,不同的电弧形态和熔滴过渡方式,以及电弧成分组成和温度分布;通过对熔化极等离子弧静特性等方面的研究发现,熔化极电流的大小不是由焊丝与工件间的电压决定的,而是由导电嘴与焊丝端部处的等离子弧电位差决定的,并决定电流的方向.     

不同参数下MIG焊电弧光谱波动特点

熔化极惰性气体保护焊(MIG)过程中,熔滴过渡、弧长波动等会引起辐射的剧烈变化,其变化规律对于焊接质量检测具有重要意义.文中通过采集不同参数下的MIG焊电弧光谱分布,研究其在焊接过程中的变化规律;并结合该参数下熔滴过渡特征,基于电弧物理理论,对典型参数下光谱波动的规律进行物理解释.结果表明,不同参数下电弧光谱的分布和变化规律不同,具有各自的光谱分布特征;在MIG焊接过程中,由于熔滴过渡会造成光谱信息的规律波动,但在过渡的不同时间段,光谱信号在不同谱段(紫外区、可见光区、近红外区)的变化规律存在较大差异.     

Steady‐state behavior of liquid fuel hydrazine decomposition in packed bed

A general theoretical model is presented to analyze the steady‐state decomposition process of liquid monopropellants in packed beds for thruster systems. Additionally, an experiment studying the decomposition of liquid hydrazine in a packed bed is used to validate this model. The liquid droplet evaporation rate is determined through calculating the gas‐liquid mass transfer for the mixture temperatures lower than the liquid propellant boiling point and solving the gas‐liquid or liquid‐solid heat transfer equations at the temperature exceeding the boiling point. The process of liquid propellant decomposition in packed beds are simulated based on the Naive–Stokes equation for the mixture model integrated with the developed liquid evaporation rate, in which both the heterogeneous catalytic reaction coupled with the diffusion of reactants in the pore of catalyst, and the homogenous decomposition reactions are considered. The calculated results for the axial distribution of the temperature are in good agreement with the experimental data. © 2014 American Institute of Chemical Engineers AIChE J, 61: 1064–1080, 2015     

Magnetic ionic liquid‐water Janus droplets: Preparation,structure and morphology adjustment and magnetic manipulation

Surfactant‐free magnetic ionic liquid (MIL)‐water Janus microdroplets with adjustable structures and morphologies are prepared in capillary‐based microfluidic devices. Their morphologies (e.g., sizes, curvatures of the interfaces, and structures from Janus to core/shell) can be adjusted in a wide range by changing the flow rate ratio of water to MIL, adding different mass fractions of polyethylene glycol in water, and using soybean oil rather than liquid paraffin as the continuous phase. MIL‐water‐MIL ternary Janus magnetic microdroplets with adjustable symmetric and asymmetric structures are also prepared. These Janus microdroplets can be manipulated by magnetic attraction, leading to easy formation of water‐MIL‐water, MIL‐water‐oil, necklace‐structured MIL‐water alternative Janus droplets as well as more complex Janus droplets, such as MIL‐CO₂‐in‐water and MIL‐water‐water droplets. Such preparation strategy is simple and can be applied in fields like pharmaceuticals, multi‐drug chemotherapies, and catalysis with expensive materials. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4115–4123, 2017     

Study of the drying behavior of high load multiphase droplets in an acoustic levitator at high temperature conditions

Experimental data on the drying behavior of suspension droplets is limited, despite its importance in industrial applications for material processing, chemical or the food industry involving spray dryers. This fact is particularly significant for high load and temperature conditions, as found in such industrial applications. In this work, the drying behavior of acoustically levitated multiphase droplets has been experimentally investigated. The acoustic tube levitator has been modified in order to allow experiments to be performed at high temperature conditions. The flow rate, temperature and relative humidity of this air stream can be controlled by an air conditioning system. A CMOS camera and a back-light illumination system are used to measure the droplet cross-sectional area and vertical position of the droplet during the drying process. The experiments have been performed using water–glass particle suspensions. The glass particles have a mean particle size and relative density of 13 μm and 2.5, respectively. The effect of the air temperature (60 °C<T<120 °C), initial volume of the droplet (0.05 μl<V₀<0.7 μl), initial solid mass load (0.01<Y_S<0.5) and relative humidity of the air (0.05<HR<0.45) on the mean porosity of the grain, first drying period duration and liquid evaporation rate has been analyzed by means of a parametric screening matrix and also by means of a central composite design (CCD) experimental design. The most important parameters to be considered for the porosity and the drying behavior in the range of variables analyzed are the initial solid mass load and the initial droplet volume. The relative humidity of the air exerts a moderate influence on the drying behavior of the droplet and the temperature has only a very low impact on the mean porosity. In addition, particular attention should be given to the drying behavior of small droplets, which result in a very low mean porosity values for high solid mass loads. The CCD confirms that the initial droplet volume, the solid mass load and their interaction exert significant influence on the three responses.     

高速电弧喷涂3Cr13钢雾化粒子温度和飞行速度数值模拟

用二相流流体动力学和空气动力学理论建立了高速电弧喷涂雾化粒子温度和飞行速度的数学模型,通过引入高速电弧喷涂工艺过程的送丝速度、丝材直径、喷涂电流、电压和雾化气体压力等工艺参数,与雾化微滴温度、飞行速度和粒度分布建立联系,揭示了高速电弧喷涂工艺参数对雾化过程微滴物理特性的影响。数值分析结果表明,3Cr13钢微滴速度在实际喷涂距离范围内变化不大;粒度对微滴初始温度有较大影响;不同粒度微滴的过热度在1 320～2 090 K之间,电阻项对微滴过热度的贡献最大;微滴强烈过热是电弧喷涂材料损耗的主要原因之一。所建立的模型的数值模拟结果与试验结果吻合较好。模拟计算的高速电弧喷涂技术喷涂3Cr13钢的质均粒度和实测的相吻合,但粒度分布特征不同。     

间隙对GMAW立焊熔滴过渡的影响及温度场特性

采用高速摄像采集系统对间隙存在及变化时GMAW摆动电弧立向上焊焊接过程中的熔滴过渡行为实时图像进行采集,分析了熔滴过渡行为对电弧质量和焊接过程的影响,结合电弧质量分析仪采集的焊接电流、电弧电压概率曲线图对试验结果加以验证和补充解释,最后通过有限元数值模拟技术对GMAW立向上焊接过程数值模型进行建立,并对瞬态焊接温度场进行验证和分析. 结果表明,随着间隙的出现及尺寸的增加(0 ~ 4 mm范围内),GMAW立向上焊熔滴过渡形式由短路过渡向特殊的滴状过渡发展,模拟结果说明GMAW立向上焊热影响区具有较大的温度梯度特性.     

飞机过冷大水滴结冰探测器设计及试验

为捕获飞机过冷大水滴(SLD)结冰,设计了一种由前梭、凹槽和后梭连接而组成的SLD探测器.通过对该探测器几何结构的参数化、FENSAP-ICE软件的结冰数值模拟和结冰试验验证,确定了该探测器较优的结构参数.在常规的液滴下,SLD探测器的前梭结冰而后梭不结冰;在SLD 下,探测器的前梭、后梭均结冰,据此可捕捉和区分SLD结冰.作为关键技术之一,该SLD探测器的设计有利于解决飞机SLD结冰探测难题.     

微型直接甲醇燃料电池若干关键技术进展

在介绍微型直接甲醇燃料电池（μDMFC）工作原理的基础上,探讨了其流场板结构、流场板工艺和材料、物料管理和封装技术等关键问题。分析比较了不同结构的流场板对μDMFC性能的影响,介绍了微流场板加工的难点和流场板材料的特殊性,讨论了μDMFC物料管理方式及其进展,综述了μDMFC封装的难点和研究现状。     

铝合金Plasma-GMAW-P复合焊接电弧特性及熔滴过渡行为

研究了Plasma-GMAW复合焊接过程中的电弧特性以及熔滴过渡行为。结果表明,不同电流的等离子弧通过改变GMAW电弧的导电以及受力状态来影响GMAW电弧形态以及熔滴过渡行为。等离子弧电流较小时,GMAW电弧的等离子流效应对GMAW电弧形态影响显著,基值时期的GMAW电弧基本沿焊丝轴线燃弧,峰值时期由于在焊接方向上同时受到方向相反的2个力而被压缩,熔滴所受的等离子流力以及等离子流力垂直向下的分力因此增加,对熔滴过渡的促进作用增强,熔滴更易从焊丝脱落。等离子弧电流增加,氛围中金属蒸气增多,电荷流效应对GMAW电弧的影响增强,基值时期GMAW电弧偏向等离子弧方向燃弧,由于焊接电弧存在热惯性,MIG电弧在峰值时仍偏向等离子弧,熔滴所受等离子流力垂直向下的分力因此减小,熔滴脱离焊丝的时间增加。