Analytical investigation into the powder distribution and laser beam-powder flow interaction in laser direct energy deposition with a continuous coaxial nozzle

The powder distribution and interaction between the laser beam and powder flow affect the deposition quality during the process of laser direct energy deposition with a continuous coaxial nozzle. In this paper, some key analytical formulae related to the laser beam-powder flow interaction are comprehensively deduced and validated. The powder distribution formulae for different regions are first established considering the divergence angles of powder jet. The energy attenuation formulae of laser beam passing through the powder flow are derived considering the change of powder distribution from annular to circular Gaussian modes. The temperature formulae of powder particles passing through the laser beam are derived based on a proposed temperature formula with the solid-liquid phase transition, and the powder temperature is also further analyzed. These formulae are validated by published deposition examples and used to analyze the laser beam-powder flow interaction.     

Measurement and analysis of impact dynamics suitable for modelling pneumatic transport of metallic powder flow through a directed energy deposition nozzle

In blown powder directed energy deposition (DED) additive manufacturing powdered metal feedstock is pneumatically conveyed to the meltpool via a nozzle. DED nozzles have been the subject to a growing number of research efforts using computational fluid dynamics (CFD) with multiphase flows to study and optimize powder flow. However, many research papers published to date contain powder – nozzle impact dynamics behavior that is not realistic or not derived from experiments that resemble the powder conveyance process in the DED nozzle being studied. To provide a set of data representative of DED powder flow through a nozzle particle image velocimetry (PIV) experiments were conducted using 316L stainless steel metal powder and flat targets with varying surface roughness made of oxygen free copper, mild steel, P20 tool steel, 316L stainless steel, Inconel 718, and Ti-Al6-V4. Normal coefficients of restitution (COR) were calculated and compared to several analytical and empirical models in literature.     

渗透度对锯齿形尾缘喷嘴气动声学影响研究

在低马赫数条件下（Ma=0.12）,采用时间分辨TR-PIV以及远场噪声测量方法,对不同渗透度锯齿形尾缘喷嘴的气动声学特性进行实验研究。流场测量结果表明,锯齿形尾缘喷嘴缩短势核长度,增加势核内气流和周围环境气流的掺混,随渗透度的增加该趋势得到增强。远场声学测量结果表明,随着渗透度增加,锯齿形尾缘喷嘴对于噪声低频降低和高频增加的幅度都有所增强。低渗透度的锯齿形尾缘喷嘴有效降低噪声总声压级,在150°时总声压级降低达到1.3 dB,研究对于降低工厂排空噪声有现实意义。     

机械混合法改性微纳米粉体的设备设计

粉体表面改性与复合设备是实现粉体表面改性与复合技术中的一个重要环节。在研究现有微纳米粉体表面改性与复合设备结构特点的基础上,结合微纳米粉体改性与复合的工作原理,针对微纳米粉体的表面特性,提出了机械混合法改性微纳米粉体的典型设备及其设计思想。本设计的特点在于在半椭球形容器下半部的圆柱面上设有两组8个与母线成α(α>90°)角的大小喷嘴成对角布置,以利于粉体和改性剂的分散与混合。     

射流抛光喷嘴的设计

喷嘴的结构和造型决定了冲击射流的动力特性和壁面流动特性,对抛光效果有很大影响.本文提出采用锥柱型喷嘴进行射流抛光能获得较好的射流特性.分析了射流抛光过程对射流特性的要求,提出了射流抛光喷嘴的设计原则,研究了不同几何造型喷嘴的射流特性,对射流喷嘴的不同结构和几何参数对射流特性的影响进行了仿真,模拟结果表明收缩角为13°、长径比为4的锥柱型喷嘴,其射流出口断面流速分布均匀、紊动强度低和磨粒浓度分布均匀,最适合应用于射流抛光.     

智能手机交互界面设计的认知基础

目的在智能手机逐渐成为人们生活必需品的当下,根据用户的认知特点提出关于智能手机交互界面设计的建议,使智能手机更符合用户的认知习惯,提高交互效率。方法从感觉、知觉、注意及记忆四方面出发分析个体与智能手机进行交互时所涉及的认知过程。根据颜色视觉、视觉适应等感觉特点提高用户对界面信息的感觉,根据用户的知觉的加工及知觉的特性改善用户对界面信息的知觉,根据选择性注意、注意的分配特点及注意的特性促进用户对有效信息的注意,利用记忆的存储及提取的特点增加个体对界面信息的记忆及记忆的使用。结论结合用户的认知特点提出字体、图标、背景等界面因素的设计要点优化用户与智能手机交互界面的交互过程。     

浅析音速喷嘴装置中喷嘴间的相互影响

目前采用音速喷嘴作为传递标准的气体流量标准装置被国内外检测机构广泛使用。在使用时,将根据需要的流量使用单个或多个喷嘴组合。与国外音速喷嘴的实际应用相比较,国内装置在喷嘴的安装方式、结构排列和上游设计方面多有不同。在对装置进行不确定度评定时,需要考虑喷嘴间相互影响(包括数量和位置等)对流量不确定度的影响。本文基于国内两套音速喷嘴法气体流量标准装置,利用单个、多个喷嘴的组合,测得两组相近流量点下涡轮流量计仪表系数,计算出不同组合的仪表系数偏差。本文考虑了实验时各组实际体积流量差值的影响,利用曲线拟合的方法,拟合出涡轮流量计仪表系数特性曲线,给出拟合方程式。将流量不同带来的影响剔除,最终给出喷嘴间相互影响带来的偏差,两套装置得出由此影响带来的不确定度为0.02%和0.07%。因此,在对音速喷嘴装置进行不确定度分析时应考虑这一分量。此外,通过相近流量不同喷嘴的组合对流量计进行检测,可以发现和找出喷嘴的问题,也是一种装置期间核查的好办法。     

Performance Comparison of Four Waterjet Nozzles

This article presents the results of laboratory tests on four waterjet-cleaning nozzles for industrial use. The nozzles selected for the tests included standard cone-jet and fan-jet nozzles, a cavitating jet nozzle and a resonating jet nozzle. A series of cleaning and erosion tests were conducted to compare the performance of the nozzles in terms of erosion rates and jet coverage, based on the same amount of energy input. The fan-jet nozzle was extremely sensitive to small variations in standoff distance. The cavitating jet nozzle gave similar performance over a large range in standoff distance. The cavitating jet and fan-jet nozzles were more efficient at an angle of incidence of 0° and 40°, respectively. For the same settings, the cone-jet and resonating jet nozzles gave an overall poorer performance than the fan-jet and cavitating jet nozzles. The cavitating jet nozzle exhibited even better erosion rate, erosion depth, and footprint covered than the fan-jet nozzle.     

包装印刷设备的烘干风嘴分布参数规律研究

目的为了提升包装印刷设备烘干性能,针对风嘴分布进行研究。方法依据实际包装印刷设备风嘴为参考,建立风嘴分布模型并进行非结构网格划分,根据实际情况建立适用于其工况的边界条件和控制方程;控制风嘴间距和承印物距离这2个关键参数,建立风嘴分布参数与热风场性能之间的数学模型;依据所建立数学模型估算不同参数模型的烘干效果。结果根据多组仿真实验得到了风嘴间距和承印物距离等参数对热风场分布的影响,相应经验公式为v (=-0.007×L+2.568)x~(4.311/L+0.056)。风嘴间距对于烘干风嘴影响效果明显,增加风嘴间距离可以提升烘干风嘴风速和热风场的均匀性;同时发现随着承印物不断前进和风嘴作用效果的叠加,其表面风速将持续呈现上升。结论经过研究分析,掌握了不同参数下的热风场分布规律,这对指导实际生产对于烘干风嘴设计具有重要参考价值。     

The influence of cavitation on the flow characteristics of liquid nitrogen through spray nozzles: A CFD study

Spray cooling with cryogen could achieve lower temperature level than refrigerant spray. The internal flow conditions within spray nozzles have crucial impacts on the mass flow rate, particle size, spray angle and spray penetration, thereby influencing the cooling performance. In this paper, CFD simulations based on mixture model are performed to study the cavitating flow of liquid nitrogen in spray nozzles. The cavitation model is verified using the experimental results of liquid nitrogen flow over hydrofoil. The numerical models of spray nozzle are validated against the experimental data of the mass flow rate of liquid nitrogen flow through different types of nozzles including the pressure swirl nozzle and the simple convergent nozzle. The numerical studies are performed under a wide range of pressure difference and inflow temperature, and the vapor volume fraction distribution, outlet vapor quality, mass flow rate and discharge coefficient are obtained. The results show that the outlet diameter, the pressure difference, and the inflow temperature significantly influence the mass flow rate of spray nozzles. The increase of the inflow temperature leads to higher saturation pressure, higher cavitation intensity, and more vapor at nozzle outlet, which can significantly reduce mass flow rate. While the discharge coefficient is mainly determined by the inflow temperature and has little dependence on the pressure difference and outlet diameter. Based on the numerical results, correlations of discharge coefficient are proposed for pressure swirl nozzle and simple convergent nozzles, respectively, and the deviation is less than 20% for 93% of data.     

Influence of nozzle design and process parameters on surface roughness of CFRP machined by abrasive jet

Carbon fiber reinforced polymer composites find extensive applications in the areas of automotive, aircraft and aerospace, medical sciences, and electronics. Their usage in automated engineering industry needs good quality in components and excellent surface finish. The aim of this research work is to make holes on carbon fiber reinforced polymer composite material using a newly designed nozzle with and without internal thread. Surface roughness (Ra) was calculated across the depth of the machined hole. The effect of air and abrasive mixture pressure (P), stand-off distance (L), nozzle diameter (D), and abrasive size (S) on surface roughness was carried out for two different nozzles. The experimental result showed offer of good surface finish on CFRP materials from the newly designed nozzle with internal thread.     

包装印刷设备的风嘴流场分析及优化

目的对包装印刷设备风嘴附近流场区域进行数值仿真分析,并以此为依据对其进行外侧风嘴角度的优化。方法以计算流体力学为理论基础,按照实际设备烘箱结构进行模型构建、网格切分、数值计算、特征评估,分析流畅特性,并以承印物表面为依据确定最优参数范围。结果获取了风嘴至承印物之间的流场分布,并对承印物表面的温度场、速度场、压力场进行了全面评价,获取了均值、方差、极差等主要特征。结论风嘴排列结构的外侧风嘴角度对温度场、速度场、压力场分布有着明显影响,最佳角度为150°或120°附近,应避免出现在135°附近。     

气液双介质喷嘴雾化特性的影响因素研究

目的 气液双介质喷嘴的应用是烟叶加料工艺的关键因素之一,通过采用现有的模拟手段实现加料过程的高精化,为优化实验奠定基础。方法 文中以外混式双介质喷嘴为研究对象,通过构建基于DPM的数值模型,研究不同蒸汽入口压力与针阀位置对喷嘴雾化的气动性能与粒径特性的影响规律。结果 研究表明,喷嘴出口通流面积越大,气流高速区离喷嘴越近,但蒸汽与料液的速度最大值并未有较大变化,此时液滴喷射距离由远变近,喷射半角由小变大。随着蒸汽压力的增大,气流速度以及高速区长度变大,蒸汽压力为0.1 MPa时,气流速度的最大值与蒸汽压力为0.4 MPa时的相差近25%;不同压力下喷射角变化范围较小,为21.5°~23.5°;除此之外,喷雾束变集中,定向性变好,有助于控制其在烟叶表面喷射的均匀性。结论 对于较近的烟叶墙,采用较大流通截面积的喷嘴结构有利于均匀地覆盖烟叶墙,相反,对于较远的烟叶墙,则适合采用较小流通截面积的结构。适当地提高压力有利于提高料液喷洒的均匀性,减少料液的浪费,提高烟丝制备的工艺水平。     

蒸发式冷凝器喷嘴流量均匀性数值研究

喷嘴出口流量均匀性对蒸发式冷凝器的换热效果有直接影响。本文用FLUENT软件对40种不同工况下喷淋系统内的水流情况进行数值模拟,并比较和研究影响喷嘴出口流量均匀性的主要因素。结果表明,结构对称可使各喷淋管的喷嘴出口流量分布基本相同;小直径喷嘴的出口流量均匀性良好;喷嘴直径较大时,随总喷淋量的增大,喷嘴出口流量的差异也增大;加装压力平衡管后,喷嘴出口流量均匀性会提高。     

Numerical Modeling of the Thermal and Gasdynamic Structure of Plasma Flows in Electric-Arc Reactors with Three-Jet Mixing Chambers

On the basis of a three-dimensional mixing model of plasma jets, a numerical study is made of the gasdynamic and thermal structure of plasma flows in three-jet mixing chambers of several types and in cylindrical reactors with such chambers. It is shown that in cylindrical chambers (with a diameter of 5–10 cm) and in a conic chamber with an apex angle of 60° (with a base diameter of 10 cm) for diameters of plasmatron nozzles of 1–2 cm the mixing of plasma jets proceeds virtually completely in the chamber volume. Application of such chambers provides the formation of rather uniform (in cross sections) temperature fields in the channels of plasma reactors.     

二氧化碳致裂器在岩石中深孔预裂爆破中的应用研究

二氧化碳致裂器具有施工安全、操作简单等明显的优点,由于其能量释放嘴的限制,在岩石爆破中受到一定的局限。归纳分析了当今二氧化碳致裂器释放嘴结构状况,采用大型分析软件模拟分析了释放嘴,提出了喷嘴适合边坡预裂爆破的结构形式是锥形,进口宽度为40 mm,出口宽度为20 mm,长度为18 mm,收缩角约30°释放嘴优化结构形式和合理参数,喷嘴形状应为长条矩形状,沿致裂器两侧竖向线等距排列的布置,并在实际工程中试用效果良好。     

喷射成形工艺中限制型喷嘴雾化气流场的数值模拟

利用CFD技术对在粉末冶金和喷射成形工艺中广泛使用的限制型雾化喷嘴的气体流场进行了计算。结果表明在限制型喷嘴中气流的会聚角度对金属液导流管前端的压力场和气体流场有很大的影响。平行气流可以在负压的作用下会聚到轴线上。随会聚角度增加,导液管前端的压力提高,金属导液管前端的压力场由负压向正压转变,气流沿导液管轴线方向速度的最大值也随会聚角的增加而增大,气流在会聚点处的动能也随之增加。限制型喷嘴的气体流场还受到金属导液管位置的影响,随导液管的伸出可以促进负压区的形成,提高抽吸力,保证金属液的顺利流出。     

CO2两相喷嘴延迟膨胀过程机制研究

本文针对CO2引射器主动流喷嘴渐扩段3个角度0. 076°、0. 306°、0. 612°,对比了均相平衡模型、延迟平衡型、延迟平衡耦合摩擦模型的模拟结果,并与文献实验数据作对比,探讨了非平衡相变和壁面摩擦两种流动机制对相应角度下喷嘴延迟膨胀过程的主导作用。结果表明:在本研究范围内,渐扩段角度较大(θ3=0. 612°)时,均相平衡模型预测的压力分布与实验结果吻合较好;渐扩段角度处于中间值(θ2=0. 306°)时,非平衡相变成为主导机制,延迟平衡模型模拟的压力分布平均误差为11. 87%;渐扩段角度较小(θ1=0. 076°)时,壁面摩擦是导致喷嘴延迟膨胀的主要机制,延迟平衡模型耦合摩擦模型预测的压力分布平均误差为15. 10%,延迟平衡耦合摩擦模型后发现喷嘴真实喉部后移至渐扩段,延迟平衡模型预测的质量流量较均相平衡模型仅减小0. 029%~0. 270%;渐扩段角度较小(θ1=0. 076°)时,延迟平衡模型耦合摩擦模型预测的质量流量相比于均相平衡模型明显减小了9. 95%;当喷嘴渐扩角为0. 306°和0. 612°时,相比于均相平衡模型结果,延迟平衡模型耦合摩擦模型预测的质量流量分别减小了0. 31%和0. 088%。     

Effect of nozzle type on pulse-jet cleaning performance of ceramic filter tube

The dust-cleaning efficiency of the ceramic filter tube is the key factor to determine the long-term stable operation of the dust removal system, and the type of nozzle significantly influences the performance. In this study, four types of nozzles (injection hole, sudden enlargement nozzle, tubular nozzle, and induction nozzle) are used to conduct comparative experimental study on the dust-cleaning effect of the ceramic filter tube. Using the schlieren technique find that the tubular and induction nozzles can improve the deviation angle of pulse-jet airflow. The injection parameters were set as an injection pressure of 200 kPa, an injection distance of 120 mm and a pulse width of 80 ms in the experiment. Using the sidewall pressure measurement system indicates that the integrated pressure of the sudden enlargement nozzle is the largest, but the uniformity is poor. The comprehensive pressure of the sudden enlargement nozzle is increased by 64.86 %, and the non-uniformity is reduced by 28.62 % compared with those of the induction nozzle. Using the visualization filtration cycle test system implies that the degree of damage and stripping state of the dust layer are directly proportional to the sidewall pressure. Moreover, it is found that the residual pressure drop changes exponentially with the dust removal quality under different nozzle types. These conclusions can help explain the mechanism of dust stripping and provide a basis for the selection of nozzles.     

Experimental and numerical simulation of the flow in a driving module with an annular and linear double-slot nozzle

This paper presents the results of numerical and experimental studies of the flow and comparison of propulsion performance characteristics of a model of a jet engine exhaust system equipped with an annular or (equivalent in gas consumption) linear double-slot nozzle with an inner cavity and circular segment deflector in the axial section. Calculations performed for the annular nozzle and double-slot nozzle corresponding to it in geometric parameters demonstrate that a flow similar to the flow in nozzles with a central body is formed in the exhaust system. According to the data obtained, the initial turn of the flow takes place in the oblique shock wave. In the double-slot nozzle, the final turn of the flow in the direction of the thrust vector occurs in a configuration of four shock waves positioned downwards in the flow; in the annular nozzle, it is in the intense barrel shock wave. It was established that the exhaust system with an annular of the linear doubleslot nozzle develops a thrust and specific impulse that exceed the corresponding values for the sonic nozzle equivalent in gas consumption by almost a factor of 2.