Bubbling to Jetting Transition during Argon Injection in Molten Steel

Bubbling to Jetting Transition is of the outmost importance in metallurgical processes given that the flow regime influences the refining rates, the refractory erosion, and the blockage of injection nozzles. Bubbling to jetting transition during subsonic bottom injection of argon in molten steel is studied here. The effect of the molten steel height, the injection velocity, the nozzle diameter, and the molten steel viscosity on the jet height and the bubbling to jetting transition is numerically analyzed using Computational Fluid Dynamics. Five subsonic argon injection velocities are considered: 5, 25, 50, 100 and 150 m/s. Three values of the metal height are taken into account, namely 1.5 m, 2 m and 2.5 m. Besides, three values of the nozzle diameters are considered: 0.001 m, 0.005 m and 0.01 m. Finally, three values of the molten steel viscosity are supposed: 0.0067, 0.1 and 1 kg/(m·s). It is observed that for the argon-molten steel system, the bubbling to jetting transition occurs for an injection velocity less than 25 m/s and that for the range of viscosities considered, the molten steel viscosity does not exert significant influence on the jet height and the bubbling to jetting transition. Due to the jet instability at subsonic velocities, a second transition, namely jetting to bubbling, is appreciated.

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.

Re-Densification Effect of Pressure-Injected Peptide-Hyaluronic Acid Combination on Male Androgenic Alopecia

Introduction: Mechanism of male androgenic alopecia (MAGA) is complex and leads to an excessive hair shedding and decreased hair density. Oral, topical, and injectable autologous treatments demonstrate ability to stimulate hair re-growth, but the response is suboptimal or plateaus off. Synthetic combination of the peptide complex and hyaluronic acid (P-HA) demonstrated hair regrowth in alopecia patients. Electronically-operated pneumatic injections (EPI) generate micro-trauma in the dermis and under wound-healing conditions may enhance regeneration effect of P-HA. Methods: Subjects seeking improvement of their male pattern hair loss (Hamilton-Norwood type 2-4) received the P-HA treatments through EPI. The course included 4 treatments every two weeks over the 8-week period. In 6 months, the hair growth was assessed comparative to baseline by global clinical photography and digital phototrichograms. The treatment safety and tolerability were documented through the whole study period. Results: Twelve men (30-45 years old) completed the treatment course with high tolerability and without adverse events. Post-treatment assessment of the previously bald areas showed improved coverage on the clinical photographs. The phototrichograms demonstrated statistically significant increase in terminal hair density by 36%, cumulative hair thickness by 37%, and follicular units by 20%;all contributing to a 38% increase in cumulated hair density (all p Conclusion: Electronic pneumatic injections are well tolerated and can be safely used for the needle-free administration of the peptide-hyaluronic acid combination in MAGA therapy. We achieved significant hair re-densification in the balding scalp. The exact role of the EPI-induced impact in the hair re-growth mechanism remains to be ascertained. .

Adaptability research of hydrofoil surface water injection on cavitation suppression

To study the effectiveness of hydrofoil surface water injection on cavitation suppression,the unsteady cavitation flow field around the NACA0066 hydrofoil at attack angle of 6°was simulated by the modified RNG k-εturbulence model combined with the full-cavitation model.The structure of cavitation flow field and the hydrodynamic performance of hydrofoil were analyzed at the cavitation number of 0.85,0.70,0.55,respectively.The results show that barriered by the jet,the momentum of the reentrant jet was reduced;The development of cavitation and the strength of cavity shedding were weakened to some extent.Cavitation suppression effect was very obvious in the cavitation conditions with the cavitation number of 0.7 and above when the injection position was at 37% chord length from the hydrofoil leading edge and the jet-flow ratio kept 0.3.Time-averaged lift and drag coefficient were reduced,and the lift-drag ratio increased in water injection conditions.

冲压发动机燃烧室超声速来流横向喷雾轨迹预测模型及动态特性分析研究

为探究超声速来流下圆柱横向射流轨迹及喷雾动态特性,在宽来流马赫数(Ma=1.50,2.02,3.09)条件下开展了不同喷嘴直径与喷注压力的煤油喷雾试验,通过纹影系统捕捉射流图像并进行外边界拟合与频谱分析。建立了考虑射流前激波效应的穿透深度预测模型,最大与平均相对误差较先前的预测模型分别下降约36%和19.1%。通过快速傅里叶变换分析,发现喷雾所受扰动以低频波为主,同时伴有时间特征较为复杂的波动。本征正交分解分析结果证明,喷雾表面同时存在高低频扰动,但低频波占据主导地位,高频波能量较低可被忽略,对应了快速傅里叶变换分析结果;低频波频率与来流有效韦伯数有关,有效韦伯数增大会使波长减小,当喷雾前端的来流速度差别较小时,频率就会增大。

基于射流补水的水泵水轮机S特性改善研究

针对水泵水轮机的“S”特性提出了在导叶顶盖位置无叶区处加装注水管的解决方案,并模拟了注水管安装在不同位置时的“S”特性曲线,分析了加装注水管后转轮区域内流线及转轮各叶道流量的分布规律。结果表明,于导叶顶盖加装注水管可以有效改善转轮内部流动,减轻转轮和导叶内部流动的相互影响,减小叶道涡的尺寸,同时有效缓解了转轮各叶道流量分布不均的现象。在注水管处于无叶区中段和活动导叶附近时,对“S”特性的改善效果明显。

木塑复合材料3DP设备微滴喷射过程仿真及关键参数研究

【目的】以自主研发的木塑复合材料三维打印与胶黏(3DP)微滴喷射系统为基础,开展紫外线固化黏结剂(UV胶)微滴喷射过程的研究,优化喷射系统工艺参数和阀体结构参数,为木塑复合材料3DP工艺液滴铺展渗透研究提供数据支撑。【方法】对喷射阀撞针的位移特征、UV胶的流变特性进行测定分析,确定了影响木塑复合材料3DP设备微滴喷射过程的喷射参数。采用有限元法对微滴喷射过程进行仿真,分析了微滴喷射过程中UV胶在喷嘴处速度、压力和质量流率的变化特征,获得了喷射参数对微滴喷射过程的影响规律。选取撞针速度、喷嘴直径、供胶压力为自变量,以液滴成形质量和主液滴速度为评价指标,开展仿真试验求解优化参数组。【结果】单因素试验得到了撞针速度0.3~0.9 m·s^(−1),喷嘴直径0.10~0.20 mm,供胶压力0.1~0.3 MPa,阀座锥角120°~130°的合理喷射参数范围。正交试验得到了喷嘴直径是影响液滴质量的显著因素,供胶压力是影响液滴速度的显著因素,并获得最优的喷射参数组合为喷嘴直径0.10 mm,撞针速度0.9 m·s^(−1),供胶压力0.1 MPa、阀座锥角130°。【结论】建立了基于木塑复合材料3DP微滴喷射过程的VOF有限元模型,完成了喷射参数对微滴喷射影响的研究,获得了最优的喷射参数组合。

基于射流点火和气道喷水技术的缸内直喷汽油机稀薄燃烧特性研究

在一台4缸涡轮增压汽油机的基础上,增加预燃室和进气道喷水系统,在最佳油耗工况附近(转速2500 r/min,平均有效压力为0.8~1.2 MPa)开展了试验,研究和分析了汽油机稀薄燃烧特性,以及射流点火和进气道喷水技术对稀薄燃烧性能的影响。结果表明,稀薄燃烧可以将有效热效率从当量燃烧的39.5%提高到42.4%左右,但是当过量空气系数超过1.4以后,燃烧稳定性和碳氢排放变差。采用射流点火技术可以将稳定燃烧的过量空气系数拓展到1.7以上,热效率增加至43.0%以上,燃烧持续期最大缩短37.6%,循环波动不超过1.3%。在此基础上增加进气道喷水,对于平均有效压力在1.1 MPa以上的负荷,抑制爆震效果明显,喷水脉宽达到4 ms时,爆震限制的燃烧重心可以提前到活塞上止点后8°左右,同时最大热效率超过44%,循环波动不超过3%;但是对于平均有效压力低于1.1 MPa的负荷,爆震现象不严重,喷水反而会降低燃烧速率和热效率,同时燃烧稳定性和未燃碳氢排放也随之恶化。

Experiments on Gas Jet in the Wendelstein 7-AS Stellarator

Wendelstein 7-AS (W7-AS) pertains to an advanced helical stellarator. A new fuelling method, the supersonic molecular beam injection (SMBI, named Gas Jet in Germany) system was installed in W7-AS in May 2001 as a cooperation research item co-supported by the National Nature Science Foundation of China and the Max-Planck Institute of Plasma Physics, Garching, Germany. The experiments of the gas jet with hydrogen or deuterium on W7-AS were implemented. The experimental results exhibit the following features such as high fuelling efficiency, stable high-density plasmas and reduction of the recycling fluxes from the vessel wall during injection. These crucial points show that the new fuelling method can be applied to long and stable discharges.

Analyzing of mixing performance determination factors for the structure of radial multiple jets-in-crossflow

The radial multiple jets-in-crossflow mixing structure(RMJCMS) is extensively used in industrial manufacture. In this research, the effects of thickness of injection ring on mixing performance and factors influencing the mixing performance of RMJCMS were discussed based on the results of computational fluid dynamics. The simulation results showed that the dimensionless mixing distance, with the increase of the thickness of injection ring, drops from 1.1 to 0.18 first and then increases to 0.27 while the uniformity of flux monotonously improves, manifesting that the consistency of flux is not the single element determining the mixing performance. Analyzing the simulation results, a conclusion was drawn that the consistency of flux, penetration mode and interaction among injection flows which can be altered by adjusting the thickness of injection ring, determine the mixing performance of RMJCMS jointly. That is to say, in RMJCMS an injection ring with a suitable thickness can realize the function of injection and rectification simultaneously, which not only improves the mixing performance but also reduces the complexity of RMJCMS as well.

Study of the expansion characteristics of a pulsed plasma jet in air

In the background of electrothermal-chemical （ETC） emission,an investigation has been conducted on the characteristics of a freely expanding pulsed plasma jet in air.The evolutionary process of the plasma jet is experimentally investigated using a piezoelectric pressure sensor and a digital high-speed video system.The variation relation in the extended volume,axial displacement and radial displacement of the pulsed plasma jet in atmosphere with time under different discharge voltages and jet breaking pressures is obtained.Based on experiments,a two-dimensional axisymmetric unsteady model is established to analyze the characteristics of the two-phase interface and the variation of flow-field parameters resulting from a pulsed plasma jet into air at a pressure of 1.5-3.5 MPa under three nozzle diameters （3 mm,4 mm and 5 ram,respectively）.The images of the plasma jet reveal a changing shape process,from a quasiellipsoid to a conical head and an elongated cylindrical tail.The axial displacement of the jet is always larger than that along the radial direction.The extended volume reveals a single peak distribution with time.Compared to the experiment,the numerical simulation agrees well with the experimental data.The parameters of the jet field mutate at the nozzle exit with a decrease in the parameter pulse near the nozzle,and become more and more gradual and close to environmental parameters.Increasing the injection pressure and nozzle diameter can increase the parameters of the flow field such as the expansion volume of the pulsed plasma jet,the size of the Mach disk and the pressure.In addition,the turbulent mixing in the expansion process is also enhanced.

双直喷型柴油JCCI模式的参数优化数值模拟

针对双直喷型柴油射流控制压燃模式,利用三维数值模拟结合优化算法,分析了预喷正时、射流正时、初始温度、初始压力和预喷射能量比等参数对发动机燃烧与排放性能的影响.计算结果表明,射流正时可以有效控制着火相位和燃烧相位,预喷正时主要影响预混合气燃烧后期.当燃烧相位在6~8°CA ATDC区间时,发动机经济性最佳.射流正时和预喷正时均较晚时,燃烧呈现两阶段高温放热过程,整体燃烧速率大于射流正时与预喷正时均较早的单阶段高温放热过程,因此等效燃油消耗率下降6.80 g/(kW·h).

超临界状态下RP-3航空燃料射流的数值模拟研究

为了研究高超声速飞行器主动冷却系统中的航空燃料喷射及其影响,对超临界状态下RP-3航空燃料的平孔喷嘴射流进行数值模拟,首先利用Fluent软件进行计算流体动力学(CFD)分析,然后使用多相混合物模型模拟空化两相流,最后采用全空化模型来预测高温条件下燃料的饱和蒸气压对空化产生的机理和影响——当入口压力(P_(in))高达4 MPa时,分析在不同环境压力(P_(∞))下,温度为333~543 K的航空燃料射流。结果发现:随着燃料温度的升高,饱和蒸气压升高,喷嘴喉部空化和出口闪蒸逐渐发生;随着环境压力的降低,压降增大导致喷嘴内的质量流量增大,喷嘴内的流动逐渐从单相流过渡到空化两相流。

基于喷孔布置及喷射参数协调控制的双直喷发动机燃烧及碳烟排放特性研究

通过建立三维计算流体力学(computational fluid dynamic,CFD)柴油/天然气双直喷模型耦合多组分混合物简化化学动力学机理及现象学碳烟模型,模拟研究了天然气射流中心轴线与水平方向夹角α、天然气喷射持续期(natural gas injection duration,NID)的协调作用对柴油微引高压直喷天然气发动机燃烧过程及碳烟生成、氧化过程的影响。结果表明:缩短NID可提高扩散火焰的传播速度,增加燃烧区域的化学反应速率,且最高燃烧压力、峰值放热率、最大压力升高率(maximum pressure rise rate,MPRR)、指示热效率(indicated thermal efficiency,ITE)升高;随NID缩短,A_(4)、C_(2)H_(2)消耗反应速率增加,OH生成峰值增加,碳烟生成降低而氧化增强。增大α促进了大尺度涡旋结构的生成,降低了进入挤气区域的燃料比例,同时利于ITE的改善;较短的NID下,增大α后最高燃烧压力、峰值放热率提升明显;α增大至20°可显著降低A_(4)、C_(2)H_(2)生成峰值,抑制碳烟成核及表面生长反应,降低碳烟生成。综合考虑最高燃烧压力、ITE、MPRR及碳烟排放,确定两个优化方案分别为:α=15°&NID=16.5°及α=20°&NID=21.5°。

驱动压力调节对可控型射流注射系统性能的影响

为探究驱动压力调制对可控型射流注射系统动力学特征及注射性能的影响,利用高精度射流冲击测试平台及高速摄影装置,分析射流冲击变化特征及扩散特征,并结合离体组织注射试验结果探究驱动压力调制机理。研究结果表明,通过驱动压力切换可以达到可控型射流注射系统高、低两段式射流速度的要求,且通过控制驱动压力可以实现对射流注射系统的冲击特征及扩散特征进行控制。不同喷射剂量工况均存在较优驱动压力组合,典型大剂量注射工况1.0 mL的最优驱动压力组合为(1.00—0.25) MPa,通过驱动压力调制可以进一步提高可控型射流注射系统的注射性能。

中高渗疏松砂岩水力喷射压裂水动力封隔特性

为确定海上疏松砂岩高渗透条件下水力喷射孔内流体增压特性是否满足岩石定点起裂条件,采用了计算流体力学方法,基于达西定律推导出速度与渗透率关系方程,建立了考虑岩石孔眼边界高渗条件下水力喷射孔眼内流体动力学模型,实验验证模型可靠,得出了地层渗透率、喷嘴压降、环空围压等关键参数对孔内流体增压的影响规律。结果表明,疏松砂岩高渗透性是降低其水力喷射压裂水动力封隔能力的关键因素,孔内流体增压值随储层渗透率升高呈现非线性递减;喷嘴压降与孔内流体增压值呈线性增加关系,但孔内流体增压值的增长斜率随储层渗透率升高而降低;环空围压对孔内流体增压值无显著影响;敏感性分析表明,影响孔内流体增压的参数排序:储层渗透率>喷嘴压降>环空围压。研究结果可为海上水力喷射压裂水力学参数优化设计提供理论依据。

喷嘴长度对射流式施肥器性能影响的数值研究

为强化施肥器的吸肥性能,提出采用计算流体力学手段研究喷嘴长度对射流式施肥器吸肥性能的影响。建立不可压缩多相流模型,基于该模型研究喷嘴长度对射流式施肥器的吸肥性能的影响,并对其影响机制进行调查分析。研究结果表明:喷嘴长度对射流式施肥器的吸肥性能有显著影响,当喷嘴长度过长时,施肥器的吸肥量增长受限,吸肥性能降低。不同进出口压差条件下,喷嘴长度为L施肥器的吸肥浓度、进口流量比和吸肥效率这几个指标也均为最低;且当进出口压差为1.0 MPa时,喷嘴长度较小的施肥器的吸肥量均比喷嘴长度为L时的吸肥量大10%以上。通过对施肥器内部流场进行分析得到,施肥器内部负压分布是影响吸肥性能的关键,而较大的喷嘴长度则会限制吸肥腔内部的负压分布面积导致更加剧烈的空化现象,进而影响其相应的吸肥性能。

基于水射流引射与干雾降尘技术的新型孔口除尘装置研发

为有效控制煤矿井下干式钻孔作业的粉尘污染问题,在分析干式钻孔产尘扩散特性的基础上,结合水射流负压引射与干雾降尘技术优势,设计研发了新型干式钻孔孔口除尘装置。通过理论分析与实验室试验研究了该装置各组件的具体结构和主要性能参数,并在杨柳煤矿顺层孔钻场开展了现场试验,实测了该装置的除尘效果。结果表明:新型孔口除尘装置由孔口集尘装置、水射流负压引射装置、干雾降尘装置三部分组成,分别具备尘源密闭、抽吸粉尘、捕集外溢粉尘等功能。水射流负压引射装置的工作水流量、抽吸量及引射系数均随工作水压的增大呈线性增大。气压0.70 MPa、水压0.18 MPa为单个干雾喷头的最佳工况参数,当干雾发生器挂载15个干雾喷头、干雾降尘装置距孔口1.2 m时,可实现对孔口全部漏尘点的雾场覆盖。新型孔口除尘装置现场应用后,钻机下风侧6 m和20m的全尘除尘率分别达到了88.9%和87.5%,取得了显著的除尘效果。

高压旋喷灌浆加固超深富水砂层试验研究

穿沁隧洞工程检修井位于强透水砂层中,该工程竖井防渗十分重要,竖井开挖前需要对井底和洞口进行高压旋喷灌浆加固。为了检验高压旋喷灌浆加固超深透水砂层的防渗效果,确定合适的施工工法、桩位布置和工艺参数,分别采用双高压三管法和MJS工法开展现场喷射试验研究。现场试验及检测结果显示,两种工法均可用于深度超过40 m透水砂层的防渗加固。采用双高压三管法时灌浆压力不宜小于40 MPa,喷嘴的提升速度和转速宜分别为5 cm/min、5 r/min,成桩直径宜为1 m,连续防渗体的桩间距宜控制在0.6~0.8 m。采用MJS工法时灌浆压力不宜小于40 MPa,喷嘴的提升速度和转速宜分别为2.5 cm/min、3 r/min,成桩直径可达到2 m,连续防渗体的桩间距宜为1.5 m。二者相比,MJS工法具有成桩直径大、施工效率高等优点,对于超深地层的高压旋喷灌浆加固可优先选用。