Droplet impact on regular micro-grooved surfaces

We have investigated experimentally the process of a droplet impact on a regular micro-grooved surface. The target surfaces are patterned such that micro-scale spokes radiate from the center, concentric circles, and parallel lines on the polishing copper plate, using Quasi-LIGA molding technology. The dynamic behavior of water droplets impacting on these structured surfaces is examined using a high-speed camera, including the drop impact processes, the maximum spreading diameters, and the lengths and numbers of fingers at different values of Weber number. Experimental results validate that the spreading processes are arrested on all target surfaces at low velocity. Also, the experimental results at higher impact velocity demonstrate that the spreading process is conducted on the surface parallel to the micro-grooves, but is arrested in the direction perpendicular to the micro-grooves. Besides, the lengths of fingers increase observably, even when they are ejected out as tiny droplets along the groove direction, at the same time the drop recoil velocity is reduced by micro-grooves which are parallel to the spreading direction, but not by micro-grooves which are vertical to the spreading direction.

微型组合导航SIP芯片的PDN电热协同仿真与优化

随着SIP芯片逐步小型化和集成化,导致芯片对PDN的直流压降、电流密度以及系统的温升控制要求越来越高.本文通过改变载流导体的面积来改善直流压降和电流密度过高的问题,同时针对芯片温升研究通过合理优化热过孔阵列的孔径、过孔数量以及镀铜厚度来减小热阻以达到控制芯片温升的目的.仿真结果表明,增加载流导体的面积能有效降低直流压降和电流密度,且还留有很大的裕量;而热过孔阵列的合理布局能有效控制芯片温升,从而提升了芯片的功能和可靠性.

页岩气多段压裂水平井不等长裂缝定量评价方法研究

页岩气井的压裂改造效果受储层地质、岩石力学性质和地应力等多重因素综合影响,微地震监测和产液剖面测试均显示单井各段改造效果差异较大。为精细评价气井产能,需快速、准确地评价单段的改造效果,本文基于注入压降试井理论对单段压后停泵压降数据进行分析,建立页岩气压裂井不稳定渗流数学模型,获取停泵后压力和压力导数的双对数曲线,从曲线形态和解释参数对单段压裂的改造效果进行定量评价。实例应用结果表明:该方法的解释结果与微地震监测以及G函数分析结果基本吻合,验证了该方法的准确性。该方法可有效实现单段缝长的定量评价,为准确开展数值模拟提供基础,同时也为井距的优化调整提供技术支撑。

Microphysical Processes of a Stratiform Precipitation Event over Eastern China:Analysis Using Micro Rain Radar data

Data collected using the micro rain radar(MRR) situated in Jinan city, eastern China, were used to explore the altitudinal and temporal evolution of rainfall microphysical characteristics, and to analyze the bright band(BB) characteristics and hydrometeor classification. Specifically, a low-intensity and stable stratiform precipitation event that occurred from 0000 to0550 UTC 15 February 2015 and featured a BB was studied. During this event, the rainfall intensity was less than 2 mm h-1 at a height of 300 m, which was above the radar site level, so the errors caused by the vertical air motion could be ignored.The freezing height from the radiosonde matched well with the top of the BB observed by the MRR. It was also found that the number of 0.5–1 mm diameter drops showed no noticeable variation below the BB. The maximum fall velocity and the maximum gradient fall velocity(GFV) of the raindrops appeared at the bottom of the BB. Meanwhile, a method that uses the GFV and reflectivity to identify the altitude and the thickness of the BB was established, with which the MRR can provide a reliable and real-time estimation of the 0?C isotherm. The droplet fall velocity was used to classify the types of snow crystals above the BB. In the first 20 min of the selected precipitation event, graupel prevailed above the BB; and at an altitude of2000 m, graupel also dominated in the first 250 min. After 150 min, the existence of graupel and dendritic crystals with water droplets above the BB was inferred.

多组分燃料液滴高温蒸发耦合机制研究

以高挥发性的乙醇与低挥发性的加氢生物柴油和柴油构成的多组分混合燃料为研究对象,研究了单个液滴在高温下的内部蒸汽气泡动力学及蒸发特性。在恒温加热炉中,采用挂滴法结合高速显微成像技术,在773、873和973 K温度下,捕捉了加氢生物柴油-乙醇-柴油混合燃料液滴在蒸发过程中的形态变化,分析了液滴的归一化平方直径和寿命等特征。研究表明,在773 K下,蒸发过程较平稳,液滴体积均匀减小,而在973 K下,0.093 s时液滴内开始产生微小气泡并逐渐增大;在0.767 s时再次形成微小气泡,并于0.907 s时出现第2次破裂。升高环境温度有助于增加燃料液滴的蒸发速率,加剧蒸发过程中的微爆现象,一定程度上缩短了液滴的蒸发时间;蒸发过程中液滴内部的气泡增长与汽液界面的Rayleigh-Taylor不稳定性有关,且在液滴表面观察到了表面张力现象;与柴油相比,随着二元燃料中加氢生物柴油含量的增加,组分对蒸发的抑制作用更强,与二元燃料相比,三元燃料中的乙醇促进了微爆,缩短了液滴蒸发;三元燃料的液滴蒸发按序呈现乙醇主导、乙醇和柴油共同主导以及三者共同蒸发3个典型特征阶段。

Flow Properties of Ultra-Fine Bubble Mixtures Passing through Micro-Apertures

The flow properties of fine bubble mixture flows are investigated and reported. Few previous studies have focused on ultra-fine bubble (UFB) mixtures, which contain sub-micrometer sized bubbles. In this study, UFB mixtures of water and glycerol solution are passed through micro-sized slits and capillaries, and the resultant pressure drops are evaluated in comparison with those for water and aqueous glycerol alone. The experimentally measured pressure drop for slits (≤51 μm) and capillaries (≤81 μm) is less for UFB mixtures than for water and aqueous glycerol alone. This phenomenon is considered in terms of interface behavior and attributed to the electric interaction between an electric double layer and the UFBs. Furthermore, numerical observation for slip wall conditions is conducted, and the results for UFB mixtures agree with the predicted values for slip wall conditions.

Improving Radar Rainfall Estimation by Accounting for Microphysical Processes Using a Micro Rain Radar in West Africa

This study evaluates the improvement of the radar Quantitative Precipitation Estimation (QPE) by involving microphysical processes in the determination of Z-R algorithms. Within the framework of the AMMA campaign, measurements of an X-band radar (Xport), a vertical pointing Micro Rain Radar (MRR) to investigate microphysical processes and a dense network of rain gauges deployed in Northern Benin (West Africa) in 2006 and 2007 were used as support to establish such estimators and evaluate their performance compared to other estimators in the literature. By carefully considering and correcting MRR attenuation and calibration issues, the Z-R estimator developed with the contribution of microphysical processes and non-linear least-squares adjustment proves to be more efficient for quantitative rainfall estimation and produces the best statistic scores than other optimal Z-R algorithms in the literature. We also find that it gives results comparable to some polarimetric algorithms including microphysical information through DSD integrated parameter retrievals.

整体式微通道换热器的性能分析

为了提升整体式微通道换热器的整体性能,建立了整体式微通道换热器的稳态换热模型,研究了结构参数与运行参数对其的影响规律。整体式微通道换热器以R245fa为工作工质,并在实验验证模型准确性的基础上,利用该模型模拟研究了换热器风量和换热器热管间距对系统整体热阻和空气侧压降等参数的影响。研究结果表明,当微通道换热器的蒸发段风量为0.41 m^(3)/s、冷凝段风量为0.21 m^(3)/s时,换热器的系统整体热阻为0.0380 m^(2)·K/W;随着冷凝段和蒸发段循环风量的增加,微通道换热器空气侧的压降增加,整体热阻均降低;微通道换热器的整体热阻的下降趋势随着风量的增加而逐渐减弱,得出在本研究范围内,蒸发段风量取0.45 m^(3)/s、冷凝段风量取0.69 m^(3)/s为宜;随着整体式微通道换热器热管间距的增加,微通道换热器整体热阻呈上升趋势,微通道换热器在蒸发段空气侧的压降呈下降趋势。当换热器热管间距为6 mm时,微通道换热器综合性能达到最佳。研究结果对通信基站冷却设备设计及微通道换热器结构与控制参数优化设计提供了参考依据。

Cylindrical Micro-hollow Cathode Discharge at Atmospheric Pressure

The mechanism of micro-hollow cathode discharge at atmospheric pressure is investigated through simulations using two-dimensional fluid model combined with a transport model for metastable atoms.In the simulations,electric potential,electric field,particle density,and mean electron energy of the discharge are calculated.The results show that the two characteristic regions of the discharge,i.e.cathode drop and negative glow can be distinguished in the simulation.The cathode drop is characterized by strong electric field and high mean electron energy,while quasi-neutral plasma of high density and exists in the negative glow.The peak value of electron density can reach the order of 1017cm-3.The electron temperature varies from several eV to tens of eV.The influence of cathode dimension on the discharge characteristics is also investigated.

A型肉毒毒素咬肌联合微滴注射改善面下部轮廓的临床观察

目的 研究中年女性行A型肉毒毒素咬肌注射同时结合面下部以及颈部微滴注射,改善面下分面部轮廓,提升下颌缘的同时,预防口角囊袋、木偶纹出现的临床效果。方法 回顾性分析2020年1月—2021年12月就诊于空军军医大学口腔医院颌面整形科的咬肌肥大的中年女性患者临床资料。咬肌注射采用稀释浓度为40 U/ml的A型肉毒毒素分三点注射进入咬肌后,并将稀释浓度为20 U/ml的A型肉毒毒素以1.5 cm为间隔,广泛、微量注射于下面部和颈部真皮层以及真皮下层,单点注射0.6 U。术后患者于1-2个月复诊,复诊时拍摄标准照片,并进行满意度调查。第三方医生将治疗前后的标准照片进行对比,评价下面部轮廓改善的满意度,以及口角囊袋和木偶纹术前术后的差异性。结果 共纳入20例患者,均为女性,平均年龄(36±3.2)岁,随访时间1.3月。患者主观满意度90%(18/20),认为口角囊袋及木偶纹均无明显加重。1例不满意者认为治疗时疼痛较明显,不愿再次注射,1例出现颈部淤青,影响美观。所有患者均未出现口角歪斜,吞咽困难,发声困难,面瘫等并发症。结论 应用A型肉毒毒素行咬肌注射并同期进行面下部颈部的微滴注射,在改善面部轮廓的同时,避免面部松垂的出现。

甲醇柴油微乳化液滴蒸发微爆特性研究

采用挂滴法分别研究了环境温度和初始液滴体积对微乳化甲醇柴油液滴蒸发特性的影响。结果表明:随着环境温度的升高,微爆发生时刻提前,液滴寿命减小;随着初始液滴体积增大,微爆次数增多,微爆强度逐渐减小。在同等甲醇含量条件下,随着环境温度升高,小液滴(0.8μL)微爆强度逐渐减弱,液滴蒸发过程逐渐平缓,而大液滴(1.6μL)首次微爆强度逐渐增强,微爆次数逐渐增多,液滴波动蒸发逐渐显著。温度较低时小液滴更容易发生微爆,温度高时大液滴更容易发生微爆。双组分液滴蒸发过程中内部成核速率与液滴表面蒸发速率共同影响液滴微爆。

负荷对生物接触氧化修复微污染河流的影响

为考察负荷变化对于跌水曝气生物接触氧化系统修复微污染河流的影响,在重庆市高峰镇鹿山河周边建立了旁路修复系统。试验结果表明:水力停留时间由0.5 h延长至1.0 h后,系统对鹿山河中高锰酸盐指数(COD_(Mn))、氨氮(NH^(+)_(4)-N)、总氮(TN)及总磷(TP)的平均去除率显著提升,对河流的修复效果显著增强。各污染物出水浓度随进水负荷的提升而增加,两者之间具有显著的线性关系,此外,TP、NH^(+)_(4)-N的去除负荷与进水负荷近似服从对数关系。系统抗各污染物冲击负荷的能力表现为:COD_(Mn)>TP>NH^(+)_(4)-N> TN。随着跌水曝气生物接触氧化系统级数的增加,除TN外,各污染物的去除负荷均表现为一级跌水最高,二级跌水与三级跌水次之且相当;沿程出水负荷表现出逐渐降低的趋势。

不同截面形状微肋片内流动阻力特性

以去离子水为工质,实验研究了横截面形状为圆形、椭圆及菱形的叉排微肋片组成的流道内的流动阻力特性。结果表明,3种形状肋片流道内压降随流量增大而增大。受微/小尺度下层流边界层的影响,流量较低时微肋形状对流动影响较弱,椭圆形肋片与菱形肋片内压降几乎相同,而圆形截面肋片内由于流动距离较长导致流动阻力最大;当流量较大时,椭圆形肋片内压降最小。Re较小时,长短轴一致的菱形肋片内的流动阻力系数f比椭圆形肋片略低,但在Re较高时,椭圆形肋片内的f值仍然最低。研究还表明,在现有各种关联式中,只有菱形微肋片关联计算值与本实验值较吻合。

微滴溶剂萃取/低温电热蒸发ICP-AES联用新技术用于超痕量元素分析

In this paper, a novel micro drop solvent extraction technique jonied with low temperature ETV-ICP-AES for ultra trace element analysis is reported. The apparatus of micro drop solvent extraction was designed, and preliminary investigation was made for the extraction of ultra trace La by a micro drop of 0.05 mol/L PMBP-benzene(2 μL). It was found that 500-fold concentration of ultra-trace La in 1 mL solution was achieved in 0.2 mL of glass chamber by a single micro drop of PMBP-benzene suspended on the tip of a 10 μL of microsyringe. The future development of micro drop solvent extraction technique in atomic spectrometry was briefly discussed.

基于微滴喷射技术的快速铸造方法探讨

对基于微滴喷射快速成形技术直接制造铸型的方法进行了分析,该方法用于铸型制造的精度和尺度范围均较宽,成本低、能量利用率高。随着它的精度进一步提高,其在直接快速成形铸型制造中的地位和应用将进一步提高和扩大。

利用光纤液滴指纹图分析酒精溶液等液体试样

光纤微液滴分析技术以利用光学方法检测液体特征参量为目的,利用了光纤液滴指纹图与液体物理、化学特征参量的对应关系,采用光纤来监测液滴的形成、增长和下落过程,并通过计算机分析随液滴下降过程而变化的光纤液滴指纹图。在实验中利用光纤微液滴传感器测试了多种不同液体试样,尤其分析了不同浓度的乙醇溶液对应的光纤液滴指纹图。在讨论了乙醇溶液光纤液滴指纹图的特征参量后,提出了一种可以实现对乙醇溶液折射率和浓度的测试的新方法。

气动膜片式微滴喷射装置理论分析与实验研究

微滴喷射是通过产生微米级的液滴实现流体按需精确喷射沉积成形的技术。气动膜片式微滴按需喷射装置的原理是以膜片为驱动部件,以压缩气体脉冲为驱动源,通过膜片的弹性变形实现液体腔的体积变化从而产生微液滴。通过建立驱动气压与液体腔内工作压力的关系,分析腔体内液体的流动状态,从而建立气动膜片式喷射系统的数学模型,以此作为优化装置结构和控制参数的依据。此外,利用该装置完成了黏性液体的可控喷射。研究结果为喷射制造的实际应用提供了理论与实验依据。

塑料微球表面制备聚乙烯醇涂层研究进展

在聚苯乙烯(PS)-聚乙烯醇(PVA)-碳氢聚合物(CH)三层球的设计中制备PVA涂层的方法主要包括乳液微封装法、炉内成球涂层法、浸(旋)涂法、界面缩聚法及喷涂法等,前三种方法目前最为常用。总结了前三种制备PVA涂层方法的优缺点及目前的研究和制备现状。乳液微封装法适合于500μm以下小尺寸双层球的制备,具有微球成活率高、产品质量较好等优点,但制备过程受人为因素影响较大,且不易制备大直径双层球。炉内成球涂层法也适用于小尺寸双层球的制备,其制备周期短,但液滴发生器的设计苛刻,PVA层的均匀性差,且不易制得较大尺寸的双层球。浸(旋)涂法可制备1000μm以上的大直径双层球,但该方法中影响PVA涂层铺展的因素较多,得到的PVA涂层均匀性较差,且涂层很薄。

航天飞行器微重力试验技术综述

航天飞行器的液体管理问题是制约未来先进上面级、天地往返飞行器及轨道飞行器等先进飞行器推进剂利用效率以及可靠性的关键技术问题。本文针对近年来该领域的型号技术背景、主要技术问题以及相关的试验方法开展综述研究,重点分析了针对低温推进剂热管理的相关技术途径的研究进展。

定型段长度对聚合物微管精密挤出成型的影响

基于流体动力学和聚合物流变学等理论建立了三维微管精密挤出流动模型,运用有限元方法进行了数值计算,通过对口模内外熔体各物理场量的分析,研究了定型段长度对微管挤出成型的影响。研究结果表明,口模压降、剪切速率随着定型段长度、熔体流率及熔体黏度的增大而增大;挤出胀大率随着定型段长度和熔体黏度的增大而减小,但受熔体流率的影响不明显。根据研究结果,获得了一定条件下定型段的最佳长度,进行实际口模设计时,若熔体流率或熔体黏度增大,可适当减小定型段长度,但当微管壁厚增大时,应适当增加定型段长度。