An investigation of carbon nanotube jet grinding

Since their observation in 1976 and 1991, carbon nanotubes (CNTs) have generated much interest due to their properties and potential applications. CNTs are tubular carbon molecules with remarkable mechanical, electrical, chemical and thermal properties, which make them useful in various applications. Industries producing CNTs via the fluidized bed chemical vapor deposition technique face challenges related to the size of CNT bundles. The two main challenges are agglomeration and agglomerate size distribution control. A solution to these challenges involves the use of jet mills to grind the CNT agglomerates. The goal of this study was to determine whether the nanotubes could be ground with air jets using a commercial jet mill and apply a two-parameter model to describe the grinding process. The present study has indicated that air-jet grinding of CNTs is feasible with a typical commercial jet mill. This paper presents the effect of operational parameters on the arithmetic mean diameter of the ground product. Sonic velocity through the grinding nozzles was required to obtain reasonable grinding rates and relatively narrow particle size distributions. This occurs at high air to solids feedrate ratios. Additionally, a simple attrition model can describe the grinding process in the spiral jet mill.     

立式罐冷却管喷水孔堵塞的原因及解决办法

在油库检查中发现,立式罐冷却喷水环管的喷水孔经常堵塞,堵塞的主要原因是水中含有杂质,喷水环管上没有装放空阀,喷水环管内壁有毛刺和喷水孔易锈蚀。根据堵塞原因找出对应的解决办法,并进一步说明了采用膜式喷头的好处。     

Engineering Model of a Nonisobaric Heavily Laden Gas‐Particle Jet

An axisymmetrical model of a rapid nonisobaric heavily laden gas‐particle jet is developed. The model is based on the general functions for both axial and radial pressure distributions, which were discovered by a numerical study of rapid gas‐particle jets by the CFD code. The model equations were solved analytically. The results obtained by the model developed are in good agreement with those computed by the CFD code for a wide range of flow parameters.     

磁流变阻尼器内部流体动能的能量采集

为了构建自供能式磁流变阻尼器内部实时状态监测传感系统,本文介绍了一种针对磁流变阻尼器内部流体能的能量采集装置。该装置被安装于磁流变阻尼器活塞顶端并为检测阻尼器内部工作参数的无线传感模块1供电。根据能量守恒定律,推导出磁流变阻尼器中磁流变液流动能的理论模型。通过实验测试分析了在不同的外界激励下能量采集装置的工作情况,证明了采集的电能随着活塞的运动频率增加而增加,而与磁流变阻尼器的磁流变特性没有明显的关系。测试表明利用此装置能较好的采集到来自于磁流变阻尼器内部流体流动产生的能量,为无线传感模块供电。     

Surface characterization of 6H-SiC (0001) substrates in indentation and abrasive machining

Surface characterization of 6H-SiC (0001) substrates in indentation and abrasive machining was carried out to investigate microfracture, residual damage, and surface roughness associated with material removal and surface generation. Brittle versus plastic deformation was studied using Vickers indention and nano-indentation. To characterize the abrasive machining response, the 6H-SiC (0001) substrates were ground using diamond wheels with grit sizes of 25, 15 and 7 μm, and then polished with diamond suspensions of 3 and 0.05 μm. It is found that in indentation, there was a scale effect for brittle versus plastic deformation in 6H-SiC substrates. Also, in grinding, the scales of fracture and surface roughness of the substrates decreased with a decrease in diamond grit size. However, in polishing, a reduction in grit size of diamond suspensions gave no significant improvement in surface roughness. Furthermore, the results showed that fracture-free 6H-SiC (0001) surfaces were generated in polishing with the existence of the residual crystal defects, which were associated with the origin of defects in single crystal growth.     

Experimental determination of gas holdup and volumetric mass transfer coefficient in a jet bubbling reactor

The hydrodynamics and mass transfer characteristics of a lab-scale jet bubbling reactor(JBR) including the gas holdup, volumetric mass transfer coefficient and specific interfacial area were assessed experimentally investigating the influence of temperature, p H and superficial gas velocity. The reactor diameter and height were 11 and 30 cm,respectively. It was equipped with a single sparger, operating at atmospheric pressure, 20 and 40℃, and two p H values of 3 and 6. The height of the liquid was 23 cm, while the superficial gas velocity changed within 0.010–0.040 m·s~(-1) range. Experiments were conducted with pure oxygen as the gas phase and saturated lime solution as the liquid phase. The liquid-side volumetric mass transfer coefficient was determined under unsteady-state oxygen absorption in a saturated lime solution. The gas holdup was calculated based on the liquid height change, while the specific interfacial area was obtained by a physical method based on the bubble size distribution(BSD) in different superficial gas velocities. The results indicated that at the same temperature but different p H, the gas holdup variation was negligible, while the liquid-side volumetric mass transfer coefficient at the p H value of 6 was higher than that at the p H = 3. At a constant p H but different temperatures, the gas holdup and the liquid-side volumetric mass transfer coefficients at 40℃ were higher than that of the same at 20℃. A reasonable and appropriate estimation of the liquid-side volumetric mass transfer coefficient(kla) in a pilot-scale JBR was provided which can be applied to the design and scale-up of JBRs.     

Artificial neural network approaches on composition-property relationships of jet fuels based on GC-MS

The relationships of composition-properties of 80 jet fuels concerning chemical compositions and several specification properties including density, flashpoint, freezing point, aniline point and net heat of combustion were studied. The chemical compositions of the jet fuels were determined by GC-MS, and grouped into eight classes of hydrocarbon compounds, including n-paraffins, isoparaffins, monocyclopraffins, dicyclopraffins, alkylbenzens, naphthalenes, tetralins, hydroaromatics. Several quantitative composition-property relationships were developed with three artificial neural network (ANN) approaches, including single-layer feedforward neural network (SLFNN), multiple layer feedforward neural network (MLFNN) and general regressed neural network (GRNN). It was found that SLFNNs are adequate to predict density, freezing point and net heat of combustion, while MLFNNs produce better results as far as the flash point and aniline point prediction are concerned. Comparisons with the multiple linear regression (MLR) correlations reported and the standard ASTM methods showed that ANN approaches of composition-property relationships are significant improvement on MLR correlations, and are comparable to the standard ASTM methods.     

喷射电沉积块体纳米晶Co-Ni合金工艺的研究

利用扫描电子显微镜（SEM），能谱仪（EDS）及X射线衍射（XRD）等分析方法研究了工艺参数对电解液喷射电沉积法制备块体纳米晶Co-Ni合金沉积层成分及结构的影响。结果表明；在本实验条件下，随电解液喷射速度的增加，沉积层中钴含量增加，而晶粒尺寸减小；随电解液温度的升高，沉积层中钴含量减小到一定值后增大，晶粒尺寸呈相反的趋势。沉积层的表面形貌为胞状结构。     

BUBBLE MEASUREMENTS IN A GAS-LIQUID JET

Measurements have been carried out in the developing and fully developed regions of a free, axisymmetric, isothermal, air-water, bubbly jet. Three experiments have been conducted at a fixed jet-exit Reynolds number and gas superficial velocity using three different bubble injector assemblies producing bubbles of moderately different average sizes and size distributions. The volume fraction of the bubbly jet flow examined in this study is low and the resulting dispersed flow is dilute. A one-component Phase-Doppler Velocimetry system has been employed to measure bubble size and velocity non-intrusively. Visual data collected simultaneously with the light-scattering measurements were analyzed with the aid of image processing and used to verify the trends portrayed by the light-scattering measurements and to determine average bubble size. Our measurements show that, even in the dilute flow examined here, differences in initial bubble-size and size distribution can influence the RMS velocity fluctuations of the bubbles, particularly in the jet development region. The average bubble velocities are less sensitive. Evidence that the development pattern of the jet near the exit is affected by the presence of the bubbles is also presented. Near the exit of the jet, bubbles are shown to be ejected laterally outside the jet due to the significant lift force caused by the high velocity gradient in the axisymmetric shear layer. The observed sensitivity of the bubble flow to size-related parameters and initial conditions in this dilute case, indicates that discrepancies in previous measurements of dispersed, bubbly flows could be attributed to different size characteristics and/or initial conditions.     

火箭发动机自由射流噪声模拟过程

准确仿真火箭发动机的自由射流噪声,是保证火箭稳定发射的关键手段.火箭发射过程中的自由射流噪声主要由发动机流场中的燃烧噪声、内部障碍物周围的流动噪声、管壁的摩擦噪声等单极子声源所产生的复合噪声叠加而成,噪声在方向上的特征较为复杂.传统的Reynolds-averaged Navier-Stokes方法仅仅得到了时均的流场,无法预测自由射流的方向性,导致对噪声的仿真效果不好.提出采用大涡仿真与FW-H表面积分法相结合对火箭发动机的流场与噪声远场进行仿真,使用大涡仿真与Mohring声类比相结合,对噪声的方向性进行预测,克服传统方法存在的弊端,完成噪声仿真过程.仿真结果显示:流场吻合很好,声场中低频声压级吻合较好,高频声压级略低于测定值,测点的综合声压级误差较小.