聚氨酯-丙烯酸酯柔性壁的减阻性能

采用种子乳液聚合法和物理共混交联法制备了以水为溶剂的聚氨酯-聚丙烯酸乙酯(PU/PEA)乳液和聚氨酯-聚丙烯酸丁酯(PU/PBA)乳液柔性壁。该乳液不仅环保,而且强度高,弹性好,粘接性优良。小型水洞平板阻力测试结果表明,PU/PEA复合乳液有一定的减阻作用,水流速度高时减阻率也高,流速为3.0 m/s时达到8.8,PU/PEA(40/60)复合乳液涂层在0.5~3 m/s的速度范围内平均减阻率达到5%;粒子图像速度测试给出了在相同雷诺数下柔性壁与铝板的平均摩擦阻力系数的比较以及计算得到的减阻率。结果表明,PBA/PU和P(BA-EA)/PU的减阻效果差不多,平均约5.3%,而PBA/PU-MMA低速减阻,高速不减阻。PU/PBA混合乳液涂层在0.5 m/s和1 m/s的流速下减阻率分别为7%和4%。     

探头局部扰流对超声流量计测量结果影响

插入式探头安装方式会对超声流量计内部流场产生扰动,进而影响测量结果。在高压空气流量标准装置上对DN100 mm和DN200 mm的气体超声流量计进行标定,结果显示探头局部扰流对超声流量计会产生负向误差,管道口径越小,局部扰流引入的误差越大。DN100 mm超声流量计在3～27 m/s的流速范围内的测量误差在–1.5%～–3%之间,而DN200 mm的超声流量计在1.4～13 m/s的流速范围内的测量误差在–1.2%～–2.1%之间。分析不同压力、不同流速下探头局部扰流对超声流量计测量结果的影响规律,并基于流速和测量误差对实验结果进行曲线拟合,提供了拟合曲线的数学模型。     

空调器用换热器的换热量衰减率测试方法

为了快速评估空调器用换热器长期运行后的换热量衰减情况,本文提出一套通过测试换热器加速积尘前后的换热量来预测其换热量衰减率的测试方法。该测试方法中,采用负反馈模式精确调节换热器迎风面的粉尘浓度,能够在加速积尘时间内维持换热器迎风面粉尘浓度的稳定性;通过对加速积尘循环空间与换热量测试风道进行一体化设计,能够在不需要移机时实现加速积尘与换热量测试之间的切换。在入口空气温度为45℃、流速为1. 5 m/s,入口水温为21℃、流速为0. 5 m/s的工况下对该测试方法的可靠性和一致性进行了验证,结果表明:换热器迎风面粉尘浓度能够稳定维持在目标浓度120 mg/m3,波动范围在±20%内;对4种具有不同结构的换热器样件进行了多次换热量衰减率测试,其换热量衰减率相对偏差均在±10%之内,表明该测试方法具有较好的一致性。     

流体绕流不同方向振动圆柱换热特性数值分析

基于Fluent动网格及UDF编程技术对二维流场中振动圆柱的换热特性进行了研究,分析了来流速度及圆柱振动方向对其换热特性的影响。数值计算结果表明,相比于静止圆柱换热,当圆柱的最大振动速度远大于来流速度时,其振动强化传热效果显著;随着流速的增大,振动圆柱的强化传热效果降低,当流速为圆柱最大振动速度的4倍时,圆柱传热效果仅增强1.2%。另外,对相等流速下的圆柱沿不同方向的振动换热特性研究表明,振动方向对圆柱强化换热的影响不显著。     

用LDV测量液体管道流速分布的研究

设计了一个用LDV测量圆管流场分布的专用装置,保证入射、出射光线穿过圆管轴心且对称分布;测得了不同流量下DN100管径内的水流速分布曲线;比较了不同位置经典理论模型的流速计算值与实测值的误差。结果表明DN100mm管道在1.0～5.0m/s的流速范围内非边界区域流速测量误差不超过0.15m/s。     

微风仪检定装置研制成功

国家气象局科教司最近召开的“微风仪检定装置验收鉴定会”通过了工作段流场气流品质好,均匀性优于1%,稳定性优于2%的微风仪检定装置(低流速风洞)的技术鉴定。该风洞结构合理,所采取的测试手段先进,在0.1～2m/s 范围内达到国际先进水平。     

脉冲喷吹清灰过程的喷吹气流偏斜影响

为评估喷吹气流偏斜现象对滤筒清灰性能的影响,分别以喷孔式喷口和喷嘴式喷口为研究对象,应用脉冲喷吹实验平台并结合纹影法研究喷吹气流偏斜影响;采用纹影法获取喷口高速气流流场影响区域,对比不同型式和不同孔径的喷口对气流偏斜的影响;采用侧壁压力峰值作为评价指标,测试不同喷口型式的偏斜现象对侧壁压力峰值的影响。结果表明:喷口气流偏斜现象与喷吹压力、喷口孔径成正相关关系,喷吹压力由0.3 MPa升高至0.5 MPa,气流核心区的最大速度由249 m/s增大至381 m/s,水平方向分速度由66 m/s增大至79 m/s,气流偏斜影响区域增大;喷嘴式喷口可以避免脉冲喷吹气流发生偏斜现象,并会增大滤筒侧壁中上部区域的压力峰值,同时改善滤筒侧壁压力峰值分布的均匀性。     

静水拖曳法电磁流速仪校准方法

利用搭建的高精度静水拖曳法流速标准装置,对JFE公司ACM3-RS电磁流速仪的流速测量能力进行了实验研究。考察了该流速仪的零点特性,以拖车车速为标准测试了不同速度下流速仪的示值误差,并分析了不同入水深度对测量结果的影响。实验结果表明,流速低于1600mm/s时该流速仪具有良好的线性和重复性,示值误差能够优于2%或5m/s,在流速更高时需重新标定;该流速仪存在明显的零点漂移现象,实际应用中需及时修正;淹没深度对流速仪测量结果有明显影响,建议应用前考虑实际淹没深度进行校准。     

铅铋共晶合金的流动速度对CLAM钢腐蚀行为的影响

为了研究中国低活化马氏体(CLAM)钢在不同相对流速铅铋共晶合金(LBE)中的腐蚀行为,本研究对CLAM钢在550℃不同流动速度(0 m/s、1. 70 m/s、2. 98 m/s、3. 69 m/s、4. 77 m/s)的液态LBE中进行了500 h的腐蚀试验。试验后分别对腐蚀试样表面进行SEM、XRD检测以及对试样截面进行SEM-EDS和面扫描检测。结果表明,经过500 h腐蚀试验后的试样表面均形成双层结构的氧化层,外氧化层由Fe_3O_4组成,内氧化层由(Fe,Cr)_3O_4组成。在LBE相对流速从0 m/s增大到2. 98 m/s的过程中,试样表面氧化层的厚度逐渐增大,这是由于相对流速的增大提高了Fe元素的溶解速率和O元素的扩散迁移速率,进而导致试样表面发生严重的氧化腐蚀。而当LBE相对流速从2. 98 m/s继续增大到4. 77 m/s时,CLAM钢表面的氧化层厚度逐渐减小,这是由于随着LBE相对流速的进一步增大,试样表面冲蚀腐蚀程度逐渐加重,外氧化层厚度因遭受一定程度的剥落而急剧减小,进而使得试样表面总氧化层的厚度逐渐减小。本研究结果为未来ADS嬗变系统的实际应用提供了数据支持和参考。     

水流作用下双圆柱墩混凝土梁桥的动力响应实测与数值模拟

西藏达林大桥为一座7跨桥面连续的混凝土梁桥,下部结构采用双圆柱桥墩。2018年7月,在水流作用下达林大桥桥墩及桥面出现了显著的顺桥向振动。该文报道了水流作用下大桥的动力响应实测与数值模拟研究。实测表明:桥梁顺桥向振动表现为桥梁一阶纵向模态为主的拍振,横桥向为随机微振动;顺桥向最大加速度约为0.08 m/s2,梁端最大位移约为1.56 mm。基于一阶纵向振动模态参数,将双圆柱墩梁桥简化为单自由振动体系,在2 m/s~10 m/s流速范围内(折减流速U_r=1.69~8.45、雷诺数Re=2.6×106~1.3×107)进行了二维流固耦合数值模拟,得到了桥墩双圆柱升阻力系数以及不同结构阻尼比时的涡振响应。并对桥墩振型与水流流速剖面等三维效应进行修正,得到了墩顶位移随流速变化的关系。结果表明:上游柱尾流对下游柱的脉动涡激升力有显著增强作用,在3 m/s~6 m/s流速范围内双圆柱桥墩出现了涡激振动。在考虑三维修正后,ζ=0.01工况下墩顶位移数值模拟结果与实测值较为吻合。随着阻尼比ζ的增加,涡振最大振幅变小,锁定区间基本不变。     

Pressure drop reduction phenomenon of slush nitrogen flow in a horizontal pipe

Cryogenic slush fluids, such as slush hydrogen and slush nitrogen, are two-phase single-component fluids containing solid particles in a liquid. Their density and refrigerant capacity are greater than those of a liquid-state fluid alone. Owing to these advantages, there are high expectations for use of slush fluids in various applications such as a clean-energy fuel, fuel for space-planes to improve the efficiency of transportation and storage, and as a refrigerant for high-temperature superconducting power machines. Experimental tests were performed with slush nitrogen to obtain the frictional pressure drop flowing in a horizontal pipe with an inner diameter of 15 mm and a length of 400 mm. The primary objective of the study was to investigate the pressure drop reduction phenomenon according to changes in velocity and solid fraction. The pressure drop correlation between the friction factor and the Reynolds number was obtained, and an empirical correlation between them was derived. The flow pattern for slush nitrogen inside a pipe and the behavior of solid particles were observed using a high-speed video camera and the PIV method. From the experimental results, the pressure drop reduction phenomenon emerged clearly when the flow velocity was higher than 3.6 m/s and the flow pattern of solid particles inside the pipe was pseudo-homogeneous.     

Fluidization of lactose carrier powders through normally directed airflow: The effect of recirculation and particle size

This study investigates the fluidization of lactose carriers from a powder bed subjected to a normal force in a channel flow using high-speed imaging, particle image velocimetry (PIV), and high-speed, long-distance microscopy (HS-LDM). Pharmaceutical lactose carriers (LH200 and SV010) with different cohesiveness and fines percentages were examined in this study. Airflow velocities in the range of 1.4 m/s and 7m/s were tested, corresponding to flow rates ranging from 20 to 100 L/min. The use of HS-LDM in tandem with PIV has enabled measurement of the slip factor between particles and conveying airflow as well as metrics that help to identify dose homogeneity as a function of location in the channel flow. The results indicate a lower slip ratio and a larger change in powder particle size bands percentages along with channel height in the region near the powder bed, because of flow recirculation and higher velocity fluctuation observed in that region.     

Pressure drop of slush nitrogen flow in converging–diverging pipes and corrugated pipes

Cryogenic slush fluids such as slush hydrogen and slush nitrogen are solid–liquid, two-phase fluids. As a functional thermal fluid, there are high expectations for use of slush fluids in various applications such as fuels for spacecraft engines, clean-energy fuels to improve the efficiency of transportation and storage, and as refrigerants for high-temperature superconducting equipment. Experimental flow tests were performed using slush nitrogen to elucidate pressure-drop characteristics of converging–diverging (C–D) pipes and corrugated pipes. In experimental results regarding pressure drop in two different types of C–D Pipes, i.e., a long-throated pipe and a short-throated pipe, each having an inner diameter of 15 mm, pressure drop for slush nitrogen in the long-throated pipe at a flow velocity of over 1.3 m/s increased by a maximum of 50–60% as compared to that for liquid nitrogen, while the increase was about 4 times as compared to slush nitrogen in the short-throated pipe. At a flow velocity of over 1.5 m/s in the short-throated pipe, pressure drop reduction became apparent, and it was confirmed that the decrease in pressure drop compared to liquid nitrogen was a maximum of 40–50%. In the case of two different types of corrugated pipes with an inner diameter of either 12 mm or 15 mm, a pressure-drop reduction was confirmed at a flow velocity of over 2 m/s, and reached a maximum value of 37% at 30 wt.% compared to liquid nitrogen. The greater the solid fractions, the smaller the pipe friction factor became, and the pipe friction factor at the same solid fraction showed a constant value regardless of the Reynolds number. From the observation of the solid particles’ behavior using a high-speed video camera and the PIV method, the pressure-drop reduction mechanisms for both C–D and corrugated pipes were demonstrated.     

Temperature and velocity measurement fields of fluids using a schlieren system

This paper proposes a combined method for two-dimensional temperature and velocity measurements in liquid and gas flow using a schlieren system. Temperature measurements are made by relating the intensity level of each pixel in a schlieren image to the corresponding knife-edge position measured at the exit focal plane of the schlieren system. The same schlieren images were also used to measure the velocity of the fluid flow. The measurement is made by using particle image velocimetry (PIV). The PIV software used in this work analyzes motion between consecutive schlieren frames to obtain velocity fields. The proposed technique was applied to measure the temperature and velocity fields in the natural convection of water provoked by a heated rectangular plate.     

Application of particle image velocimetry for measuring He II thermal counterflow jets

The particle image velocimetry (PIV) technique was successfully applied for measuring the velocity of a He II thermal counterflow jet. Neutrally buoyant hydrogen-deuterium solid particles were used as tracer particles for PIV measurement. In the application, the normal component velocity was measured. The jet velocity profile and spatial decay of the jet velocity were compared with those of turbulent round jets of ordinary viscous fluids. The velocity measured near the jet nozzle exit was compared with the theoretical prediction for the normal component flow velocity.     

First retrieval of vertical profiles of turbulence characteristics and horizontal wind velocity from solar transmission measurements at 212 and 405 GHz

We report on the investigation and successful application of vertical profiling of the structure parameter C2m and of the outer scale L0 of absorption fluctuations and of the horizontal wind velocity (vector) during daytime by the analysis of solar transmission measurements. The method is relatively simple and straightforward so that the presented (or a similar) technique could be used in the routine remote sensing of daytime C2m, L0, and wind profiles. It requires multiple beams pointing in different directions at the Sun. The retrieved profiles are consistent with the current knowledge of atmospheric physics. Simultaneous in situ wind velocity measurements agree with the retrieved wind velocity in the lowest 100 m above ground within the measurement uncertainties of less than +/-2 m/s. The derived values of C2m at 200 m above ground are in good agreement (within a factor of 1.5) with the findings of an earlier investigation at the same test site. Finally, it is shown that irradiance fluctuations of millimeter and submillimeter waves are dominantly affected by humidity fluctuations, even at a dry and elevated site.     

CFD simulation and optimization of the flow field in horizontal turbo air classifiers

This paper mainly presents a numerical study of the gas flow in horizontal turbo air classifiers. The effect of the air-inlet direction on the performance of classifier was also investigated through powder classification experiments. The simulated results show that the vertical vortex is the dominant flow in conical part of the classifier and there exists the horizontal vortex in the classifying chamber. The tangential velocity profile resembles a Rankine vortex inside the rotor cage. The vertical vortex intensity increases with increasing the inlet air velocity, while the rotor cage speed has limited effect on the control of gas pathlines in the classifying chamber. Horizontal turbo air classifiers are divided into four quadrants according to the air-inlet direction. For classifiers in quadrants I and III, a double-layer flow with opposite directions generates around the rotor cage which causes a secondary vortex. The secondary vortex is eliminated and the airflow becomes uniform in the classifier that belongs to quadrant Π or IV. The experimental results with fluidized catalytic cracking catalysts and fly ash demonstrate that cut sizes of this classifier decrease averagely by 5 μm and 2.2 μm respectively, and the classification accuracy increases by 7.5–10.3%.     

Modeling the structure of fulleranes and their endohedral complexes involving small molecules with nontrivial topological properties

'In' and 'out' isomers of perhydrogenated fullerenes and endohedral fullerene complexes have only recently been incorporated into the realm of topological chemistry. The 'in' isomers are, until now, purely hypothetical while for the latter group mostly studied are the complexes with metal ions that can be obtained during the fullerenes manufacturing. Much more difficult to obtain are the complexes with small molecules buried inside fullerene cages produced by laborious synthesis involving opening the cage, inserting the guest into it, and closing the cage chemically. This complicated procedure has only recently been accomplished for a hydrogen molecule put in the C60. Two H2 molecules inside the opened C70 cage and H2O in the opened C60 have been also reported recently. Model calculations, when carefully applied, allow one to predict the possibility of obtaining endohedral fullerene complexes with small molecules and 'in' isomers of perhydrogenated fullerenes. However, such systems are too large to be reliably handled by quantum calculations. Interestingly, such a simple method as molecular mechanics seems much more trustworthy.     

计及气流影响的小长径比插入管消声器声学特性的实验研究

在管内平均气流流速10 m/s~100 m/s范围内,对长径比L/D=0.6的插入管型抗性消声器内部和外部声学特性进行了实验研究。探讨了气流流速大小和消声器结构参数的变化对插入管消声器声学特性的影响,并结合腔内气流涡模态和尾管声学模态对小长径比插入管消声器的声学特性机理进行了分析。实验及理论分析表明,气流流速对消声器内外声学特性均有明显的影响。与消声器静态特性不同的是,在有气流情况下必须计及腔体内上游插入管气流喷射引发的涡模态。计及气流影响的小长径比插入管消声器声学特性与消声器腔内气流再生噪声的涡模态和消声器尾管的声学模态关系密切,而与消声器空腔本体声学模态无关。