A comparison between powder flow property testers

In this work, three different shear testers-the Jenike shear cell tester, the Schulze ring shear tester, and the Brookfield powder flow tester-were compared in terms of the raw shear stress time series, yield loci points, angle of internal friction, cohesion, and unconfined yield strength. The three different powders of dolomitic lime, calcium lactate, and calcium carbonate were used for these comparisons. These three powders were characterized into different flowability classes using the ]enike classification, wherein dolomitic lime falls into the cohesive range, calcium lactate falls into the free-flowing range, and calcium carbonate falls into the very cohesive range. Results showed that the best agreement between the testers was found with moderately cohesive powders such as dolomitic lime. Furthermore, the free-flowing material tends to produce more consistent data between the three testers in terms of shear stresses and yield loci. It should be noted that the pre-shear data of free-flowing powder obtained by the Jenike shear cell must be appropriately interpreted. The largest differences between the testers are found with calcium carbonate, which is a highly compressible powder. The ways in which a high powder compressibility can differently affect the results obtained with the different testers were discussed.

Study on Test Methods for Flow Ability of Superfine Powder Extinguishing Agent

According to the physical and chemical characteristics of superfine powder extinguishing agent,three test methods are selected to measure the flow ability.By studying and comparing various test methods,apparatus and conditions,the optimum method and conditions to test flow property of superfine powder extinguishing agent are confirmed.

Sn60Pb40 solder powders produced by the planar flow casting atomization process

Conventional planar flow casting(PFC) is one of rapid solidification processes for the fabrication of microcrystalline or amorphous ribbons.Based on the conventional PFC process,the planar flow casting atomization(PFCA) process has been developed,which is a new rapid solidification process for the production of metal powder directly from alloy melts.A prototype experimental apparatus was designed and manufactured.With the apparatus,Sn60Pb40 alloy solder powders were prepared,and the effects of the main technological parameters on the powder size distribution and morphology were experimentally studied.The experimental investigations indicate that the metal powders produced by the PFCA process can be classified by velocity;and fine spherical tin-lead alloy solder powders can be fabricated by adjusting the technical parameters.The new PFCA process has such features as high productivity and efficiency,low energy consumption,simple operation,short technological process,and large gross yield.

CFD Simulation of the Flow Field Inside Screw Powder Feeder

A screw powder feeder is an important device for industrial applications. There are many parameters which affect the performance of the screw powder feeder, such as the shapes of the helical screw impeller, the number of screw pitches, etc. This paper presents an analysis of a gas-solid two-phase through screw powder feeder by using a commercial Computational Fluid Dynamics（CFD） code, Fluent. The K-ε model is used to simulate gas flow. Particle trajectory is obtained by the use of a discrete phase model. The results show the effects of gas velocity and panicle size on the transportation performance.

RH底喷粉精炼过程数值模拟研究

RH真空槽底喷粉精炼将脱硫粉剂直接喷入钢液,冶金反应程度高,终点元素含量稳定,能够完成高品质钢的炉外精炼任务。对RH底喷粉过程进行数值模拟研究,探究底喷粉过程的粉剂行为及对钢液流场的影响规律,优化喷嘴布置方案,旨在推动该技术的工业化应用。研究结果表明,180°喷嘴布置方案(即下降管侧喷吹,简称方案2)的钢液环流量比0°喷嘴布置方案(即上升管侧喷吹,简称方案1)增加1.8 t/min(增量比例为1.4%);方案2的钢包最下端钢液粉剂浓度比方案1高0.2~0.9 kg/m^(3)(增量比例为6.7%~81.8%);方案2条件下,钢包内钢液流动死区的粉剂浓度随喷嘴布置高度的降低而降低。结合粉剂收得率,确定方案2喷嘴布置高度为300 mm,此时粉剂收得率较方案1提升2.59%。

容弹内片状无烟煤粉喷射掺混特性实验研究

粉末在容弹以及发动机燃烧室内的掺混状态对粉末爆轰特性有较大的影响,因此亟须对粉末在有限空间内的喷射掺混特性展开研究。搭建了一套透明的容弹系统,通过高速摄影监测系统,对片状煤粉在容弹内的喷射掺混过程进行观测,并对高速摄影拍摄图片进行后处理,分析煤粉在容弹内的喷射掺混变化规律。针对煤粉喷射掺混图像建立了一种灰度值标准差曲率分析方法,研究发现标准差曲率趋于0的初始时刻为煤粉掺混均匀最佳时刻,可以选取为最佳点火时间点,且该方法所选取的时刻与逐帧分析高速摄影图像所选取的时刻吻合。在煤粉浓度为120 g/m^(3),210 g/m^(3),300 g/m^(3)下,依次展开煤粉喷射掺混实验,并应用此灰度图像标准差曲率分析方法进行分析。实验结果表明:保持煤粉浓度一致时,掺混均匀性最佳时间随喷粉时长的增长而逐渐缩短,点火时刻提前;保持喷粉时长一致时,掺混均匀性最佳时间随供粉浓度的增长而延长,点火时刻延后。

径向进气式涡流空气分级机的流场特性与颗粒分级性能数值模拟

设计了一种径向进气式涡流空气分级机,采用Fluent软件对分级机内流场进行了数值模拟,探讨了转笼转速、进气速度和进气位置对流场的影响。结果表明:气流在分级腔体内并不是垂直上升,而是以一定倾斜角度在腔体内形成环形气流,环形气流方向与转笼转向相同;分级腔内气流为两个方向的双流层,主气流方向与转笼转向保持一致;随着转笼转速的增加,气流主体的方向不变,腔体左侧的对冲气流消失,腔体内形成的环形气流增强,但转笼下侧的二次涡流增大;不同进气速度对分级腔及转笼不同区域的切向速度具有不同的影响;进气位置的不同,分级腔内气流的流动相差较大,进气口位于转笼轴线同侧时的气流较进气口位于转笼轴线两侧时的气流更容易受到转笼的影响,进气位置对转笼周围流场分布的影响较小。采用响应面法对空气分级机的操作参数进行了优化,各参数对分割粒径影响的大小顺序为:转笼转速>进料速度>进气速度,优化的参数为转笼转速4483 r/min、进气速度15.6 m/s、进料速度9.71 kg/h,在该条件下分割粒径的预测值为40.5μm。

颗粒注射速度对铝粉/空气两相旋转爆轰波的影响

为研究颗粒注射速度对非预混铝粉/空气旋转爆轰波传播特性的影响,通过采用离散相模型、具有有限速率动力学/扩散表面燃烧模型的一步表面反应、多步可逆气相分解反应以及考虑未完全燃烧颗粒的挥发,对注射温度为300 K的铝颗粒和来流总温为900 K的高温空气进行二维数值模拟研究。研究结果表明:由于入口附近颗粒注射速度低于空气的注射速度,空气三角区和颗粒三角区无法完全重合;当颗粒注射速度从1 m/s增加到100 m/s时,爆轰波的速度和温度先减小后增加;颗粒和空气在注入燃烧室时存在较大的温度差异,导致爆轰波不稳定传播;颗粒注射速度为70 m/s时,爆轰波的稳定性最好。

沙美特罗替卡松联合经鼻高流量湿化氧疗治疗AECOPD并Ⅱ型呼吸衰竭的临床疗效

目的探讨沙美特罗替卡松联合经鼻高流量湿化氧疗(HFNC)治疗慢性阻塞性肺疾病急性发作(AECOPD)并Ⅱ型呼吸衰竭的临床疗效。方法选取2021年1月—2022年8月南方医科大学南方医院白云分院收治的AECOPD并Ⅱ型呼吸衰竭患者共110例,随机分为观察组和对照组,每组55例。对照组给予HFNC治疗,观察组给予沙美特罗替卡松联合HFNC治疗。比较两组肺功能指标[第1秒用力呼气容量(FEV 1)、用力肺活量(FVC)、FEV 1/FVC]、血气分析指标[pH值、血氧饱和度(SaO 2)、氧分压(PaO 2)、二氧化碳分压(PaCO 2)]、炎症指标[白介素-17(IL-17)、超敏C反应蛋白(hs-CRP)、圣乔治呼吸问卷(SGRQ)评分、改良英国医学研究委员会呼吸困难量表(mMRC)评分]及临床疗效。结果治疗后,观察组肺功能指标优于对照组(P<0.05)。观察组pH值、SaO 2、PaO 2较对照组增高,PaCO 2较对照组降低(P<0.05)。观察组血清hs-CRP、IL-17水平较对照组降低(P<0.05)。观察组SGRQ及mMRC评分较对照组降低(P<0.05)。观察组患者的临床疗效优于对照组(P<0.05)。结论沙美特罗替卡松联合HFNC治疗能够改善AECOPD并Ⅱ型呼吸衰竭患者肺功能、呼吸功能及血气分析指标,抑制机体炎症反应。

Analysis of the Agglomeration of Powder in a Coaxial Powder Feeding Nozzle Used for Laser Energy Deposition

To improve the agglomeration of powder in a coaxial powder feeding nozzle used in the frame of a laser energy deposition technique,the influence of several parameters must be carefully assessed.In the present study the problem is addressed by means of numerical simulations based on a DEM-CFD(Discrete Element Method and Discrete Element Method)coupled model.The influence of the powder flow concentration,powder flow focal length and the amount of powder at the nozzle outlet on the rate of convergence of the powder flow is considered.The role played by the nozzle outlet width,the angle between the inner and outer walls and the powder incident angle in determining the powder flow concentration is also considered.The results show that,with increasing of nozzle outlet width,the powder flow concentration per unit volume at the nozzle focal point undergoes a non-monotonic behaviour(it first increases and then decreases).When the nozzle outlet widthδis 1.00 mm,the powder flow concentration at the focal point is maximal and the powder flow convergence can be considered optimal.By increasing the angle between the inner and outer walls,the powder flow concentration related to the upper focus decreases,the focus diameter increases and the powder flow aggregation worsens.The powder flow concentration increases first and then decreases with increasing incident angle.When the incident angleθis 30°,the powder flow exhibits the best agglomeration properties.When the outlet width is smaller,the angle between the inner and outer walls is larger,and when the incident angle is set at 30°,the powder flow concentration of the coaxial nozzle can be effectively improved.

基于Flow3D软件对激光熔覆工艺过程的仿真研究

为了更好的了解工艺参数对激光熔覆过程的影响,本研究采用高斯面热源模型,通过Flow3D软件对激光与氮化硼复合粉末涂层的相互作用过程中温度场的分布以及涂层的演变过程进行了数值仿真模拟,结果表明当激光功率P=660W、扫描速度V=0.14m/s、光斑直径D=12μm时,单道熔覆层的成形效果最好。并根据最佳单道熔覆参数,以理论计算的搭接率设为模拟中的激光扫描间距进行双道搭接实验,得到最佳激光扫描间距为d=30μm,此时成形效果最佳,且无明显搭接痕迹。本研究探讨了不同工艺参数对熔覆层的影响,可为后续激光加工方法与技术的发展提供理论支撑。

激光内送粉变姿态熔覆非水平熔池流场的数值模拟

目的提高激光内送粉变姿态熔覆层成形质量,对变姿态熔覆时非水平熔池流场随基板倾斜角的演变规律进行研究。方法首先,利用FLUENT软件中离散相模型对喷嘴流场进行模拟,获取粉末频次的分布规律。其次,采用流体体积法耦合熔化/凝固模型对熔池流场进行计算。通过施加质量源项引入同步送粉,施加能量源项模拟激光热输入,选取姿态角为30°、60°、90°进行计算,对熔池流场及熔覆层界面进行追踪分析。最后,基于激光内送粉熔覆工艺进行实验测定。结果粉斑内粉末量呈“中间均匀,两端密集”的分布规律。熔池流动为“双环流”分布特征,但流动方向受重力影响,产生偏转。取3种姿态角计算时间同为0.3 s时,熔池中心处流体的偏转角分别为2°、4°、6°,并且随着倾斜角的增大,熔覆层高度分别增加了0.28%、0.83%、1.45%,熔覆层宽度减小了1.19%、1.28%、1.73%,熔覆层顶点偏移量增大到48.08、86.54、105.76μm。最后结合实验测定,数值计算与实验结果一致。结论Marangoni应力使得激光内送粉熔覆熔池流体产生由中心向边界流动的“双环流”分布特征,非水平熔池流动方向受重力影响产生偏转。随着基板倾斜角增大,熔覆层截面高度增加、宽度降低、顶点偏移量增加。为提高不便摆平非水平基面的激光内送粉变姿态熔覆再制造成形质量提供了指导。

粉末燃料典型流化装置流量调节对流化的影响

粉末燃料供应系统是实现粉末冲压发动机流量调节的最关键技术,供应系统的优劣直接影响发动机性能,也是需要解决的主要问题之一。本文运用欧拉连续介质方法对粉末燃料典型流化装置流量调节对流化的影响进行研究,探究流量调节过程中等固气比调节对流化的影响,分析粉末在存储罐、流化区域、出口管路上的分布规律。通过分析等固气比调节的输出粉末质量流量变化规律、粉末分布、罐体气相压降判断粉末流化效果的优劣,进而完成粉末燃料典型流化装置流量调节对流化影响的研究。结果表明,随着输入粉末质量流量的增大,粉末供应到达稳定供应状态的时长逐渐减小;输入粉末平均质量流通量在12732.4~16976.5 kg/(m2·s)的设计工况,到达稳定供应状态需要的时间短,是较为理想的输入粉末质量流量的设计工况;粉末燃料供应系统为欠阻尼系统,供应系统开机后推力增加的过程中,阻尼振荡频率随着输出粉末质量流量的增大而增大;在到达稳定前,流化区域形成的旋流影响范围先增大再变小后保持稳定(或者消失),旋流具有稳定粉末供应的作用。

扶元散加减联合门冬胰岛素治疗糖尿病肾病患者的临床效果及对其血清炎性因子水平及肾血流的影响

目的探讨扶元散加减联合门冬胰岛素治疗糖尿病肾病的临床效果。方法72例糖尿病肾病患者随机分为两组,对照组给予门冬胰岛素治疗,观察组给予扶元散加减联合门冬胰岛素治疗,比较两组的治疗效果、血清炎性因子水平和肾血流指标。结果治疗后,观察组的总有效率高于对照组,血清TNF-α、IL-6、CRP水平均低于对照组,EDV、PSV均高于对照组,PI低于对照组(P<0.05)。结论扶元散加减联合门冬胰岛素治疗糖尿病肾病可明显改善患者的血清炎性因子水平,促进肾血流恢复。

易流型辅助胶凝材料的制备及其对混凝土性能的影响

基于四川地区的锂渣、钛矿渣、磷渣3种固体废弃物,开展固废基易流型混凝土掺合料的研究。通过与各种掺合料多元体系复配获得了性能优异的易流型掺合料,并系统研究了该辅助胶凝材料对混凝土工作性能、力学性能及耐久性能的影响。结果表明,磷渣粉、钛矿渣粉和石灰石粉复掺替代粉煤灰时,混凝土浆体的屈服应力有小幅下降,扩展度普遍大于550 mm,工作性能得到优化;改性锂渣粉、钛矿渣粉和石灰石粉复掺替代矿粉时,在锂渣粉掺量不高时,混凝土工作性能和力学性能较优,但锂渣粉掺量过大时会增大混凝土塑性黏度,掺量建议不超过胶凝材料的10%。

Selective laser sintering mechanism of polymer-coated molybdenum powder

A type of polymer-coated molybdenum powder used in selective laser sintering technology was prepared by coating polymer on molybdenum particles and frozen grinding techniques, with the maximum particle diameter of 71 μm. The laser sintering experiments of polymer-coated molybdenum powder were conducted by using the self-developed selective laser sintering machine (HLRP-350I). The method of microscopic analysis was used to investigate the dynamic laser sintering process of polymer-coated molybdenum powder. Based on the study, the laser sintering mechanisms of polymer-coated molybdenum powder were presented. It is found that the mechanism is viscous flow when the laser sintering temperature is between 100 ℃ and 160 ℃, which can be described by a two-sphere model; and the mechanism is melting /solidification when the temperature is above 160 ℃.

The Review of Powder Coatings

With the environmental regulations becoming more stringent and awareness of consumers increasing to protect environment, an urgent problem is to reduce the use of volatile organic compounds (VOCs). Powder coating is a kind of solid powder coating without any solvent. Due to its excellent application performance and environment-friendly, it is widely used in the field of metal coating, especially appliances of offices and home. In recent years, the use of powder coatings has been developed very fast and the requirements of functional powder coatings are also gradually strengthened. According to resin of the film forming, powder coatings can be divided into two types: thermosetting powder coatings and thermoplastic powder coatings. Each kind of powder coatings has its own advantages and disadvantages, and they will be applied in different fields. In order to improve the properties of powder coatings, there are many reports and studies about them. The compositions of powder coatings were extruded, crushed and screened to gain powder of coating. The powder always was stored at room temperature. The powder coatings often operated by two kinds which were electrostatic spraying method and fluidized bed dipping method. After that, the powder was heated to melt and cure. Finally, a smooth bright permanent film on articles was formed to achieve the purpose of decoration and corrosion. The process flow preparation of powder coatings always separated into dry process production and wet process production. The development courses of powder coatings about resins, pigments and fillers are summarized. The future development trends of powder coatings are illustrated.

THEORETICAL DISCUSSION ON UNSTEADY FLOW OF FLUID DURING METAL ATOMIZATION

The expressions of fluid velocity under several conditions during gas atomization according to the unsteady flow mechanics are propsed, and the basic ways to maintain the stability of fluid flow is analyzed

立式粉体干燥器中不同粒径湿颗粒流动特性研究

为了研究立式粉体干燥器内不同粒径聚甲醛颗粒流动特性,采用CFD-DEM模型耦合液桥力模块的方法,分析了含水率和颗粒粒径对聚甲醛颗粒流动特性的影响,并验证了该分析方法的正确性。研究结果表明:基于量纲分析法,结合已有实验数据拟合得出平均颗粒速度的经验关联式,计算值与实验值的最大误差为25.13%,可以较好地描述干燥单元内的平均颗粒速度变化。截面平均固含率随着颗粒直径的增大而降低,干燥单元内固含率在轴向和径向分布上分别呈现“上浓下稀”、“边壁高近流体低”的特点。当颗粒直径d_(p)<2 mm且含水率V_(lb)≥0.1%时,容易造成干燥单元入口堵塞,并且干燥单元内固含率剧减。截面平均颗粒速度随着轴向高度和颗粒直径的增大而增大,从边壁区到近流体区域的局部颗粒速度逐渐减小。当颗粒直径相同时,湿颗粒比干颗粒的颗粒速度小;当颗粒直径超过临界值2 mm时,随着含水率的增高,颗粒速度略微减小,颗粒平均停留时间和固含率总体上有所增加。

Treatment of perianal infection in acute leukemia hematopoietic stem celltransplantation with Xiongzhen ointment mixed with furacilin powder

目的：探讨应用熊珍软膏加呋喃西林粉对急性髓系白血病M2a型造血干细胞移植患者肛周进行护理的效果观察.方法：以我院一例急性髓系白血病M2a型造血干细胞移植患者为研究对象,采用护理病历报告方法,记录熊珍软膏加呋喃西林粉对该例患者在造血干细胞移植期间进行肛周护理的方法及效果.结果：给予熊珍软膏加呋喃西林粉治疗后,患者在移植过程中未出现明显的肛周感染,于24天完成移植顺利转入过渡病房.结论：在层流室的肛周护理中增加熊珍软膏加呋喃西林粉的涂抹可减少肛周感染的发生.