Experimental and Numerical Investigation of a Novel Spiral Micromixer with Sinusoidal Channel Walls

A novel spiral micromixer with sinusoidal channel walls was designed to enhance the mixing index in the low to intermediate Reynolds number range (1 < Re < 100). To analyze the fluid flow, a set of numerical simulations were performed using the finite-difference method. The microchip was fabricated from polydimethylsiloxane, employing the soft-lithography technique. The degree of mixing was increased by 99.11 % when using the proposed micromixer, compared to 59.44 % for a simple spiral micromixer. The introduced microchannel drastically reduced the mixing length, increasing the mixing index of a 0.5-loop spiral-sinusoidal microchannel compared to that of the simple spiral microchannel with 1.5 loops. The mixing index of the 3-loop mixer was higher than that of the microchannel with 1.5 loops, and its pressure drop was increased.     

冷处理和深冷处理在渗碳齿轮件中的应用

通过分析18Cr2Ni4WA和20Cr2Ni4A钢的冷处理和深冷处理工艺过程,经试验确定合理的工艺参数后应用于渗碳齿轮件的实际生产中。结果表明,冷处理和深冷处理后渗碳层表面硬度提高3~5 HRC,并可有效增加淬硬层深度。     

Effect of cavosurface angle beveling on the exposure angle of enamel prisms in different cavity sizes

The quality of the micromechanical retention between the enamel prisms exposed through acid etching and adhesive system can be influenced by the relationship between the angle of the exposed enamel prisms and the external surface/restorative material. Therefore, the aim of the present study was to determine the influence of the enamel cavosurface beveling in different cavity sizes on the angle relation between enamel prisms and the restorative material. For this research, 30 human permanent molars were used and divided into three groups according the isthmus aperture of class I cavities (1/4, 1/3, and 1/2 of the intercuspal distance). Cavosurface angle beveling was performed in each tooth buccal or palatal/lingual side, and a resin composite restoration was placed. Each restored tooth was sectioned in buccal/palatal direction followed by analysis in scanning electron microscope. Means of the angles observed between enamel prisms and the restorative material were registered and statistically analyzed by Kruskal‐Wallis test. Results showed higher mean angle values for beveled groups when comparing with the values observed in the unbeveled margins (p < .05) regardless of the isthmus aperture, being 1/4 (beveled = 48.36°; unbeveled = 20.71°), 1/3 (beveled = 39.75°; unbeveled = 29.15°), and 1/2 (beveled = 37.02°; unbeveled = 26.34°). It was also observed that in some unbeveled cavities, there were the presence of laterally exposed enamel prisms (0°), mainly in more conservative cavities. It was concluded that the presence of higher angles values occurred in the samples with beveled margins, without presence of laterally exposed enamel prisms.     

Experimental and numerical study on tube-side flow and heat transfer characteristics of superheated vapor flow in catalyst-filled LH2 spiral wound heat exchanger

High energy consumption is considered to be one of the most persistent problems in liquid hydrogen (LH₂) plants. The combination of heat exchanger and ortho-para (O–P) hydrogen conversion has attracted considerable attention as a cutting-edge technology to reduce energy consumption. The flow and heat transfer characteristics of O–P hydrogen conversion catalyst-filled spiral wound heat exchanger (SWHE) were investigated in this study in two steps. In the first step, pressure-drop experiments were performed in a tube filled with porous media. The results indicated that the pressure drop was overestimated when using Ergun's equation. Therefore, a new empirical pressure-drop correlation for a channel filled with O–P catalyst was formulated. Subsequently, a novel heat transfer model was established based on this correlation for further numerical simulations. The distributions of the temperature, pressure, and para hydrogen content in a catalyst-filled tube were determined. In addition, the influence of the flow rate on the heat exchange coefficient and outlet para hydrogen was clarified; it was found that, with an increase in the flow rate, the heat exchange coefficient increased, whereas the outlet para hydrogen content decreased. At a flow rate of 0.5 m³/h, the para hydrogen content increased by 44% after hydrogen flowed through the channel filled with the O–P catalyst. Furthermore, a prediction model for the para hydrogen content with a flow rate range of 0–1.5 m³/h was derived. This study provides promising theoretical evidence for the engineering application of SWHEs filled with O–P catalysts in large-scale hydrogen liquefaction units.     

切制锥齿轮传动的小齿轮时机床啮合参数的确定

就圆锥齿轮传动的小齿轮切制加工时,齿轮啮合参数的确定进行了原理性的论述,分析了误差形成的基本原理,提出了齿轮误差判别依据,为圆锥齿轮加工设备参数的调整,计算平面齿轮侧面坐标点和确定切齿刀头切刀分布的主要参数提供了相关的理论依据。     

基于Visual Basic开发滚简可视化CAD系统

编制了基于VB6.O开发的螺旋滚筒可视化CAD系统,系统由切削图绘制、参数计算和零部件图绘制三部分组成,并具有图形显示、数据文件存取等功能,可快速高效地实现采煤机滚筒的可视化参数设计。     

大型直齿锥齿轮的铣削加工方法

直齿锥齿轮一般要在专用机床上加工 ,但能够加工大型直齿锥齿轮的生产企业极少。在龙门铣床上铣削加工大型直齿锥齿轮方法简单易行 ,加工精度能够满足一般使用要求 ,运行平稳。     

克林根贝格螺旋锥齿轮加工和调整

克林根贝格 (Klingelnberg)齿制的螺旋锥齿轮与目前使用最为广泛的格里森 (Gleason)齿制的螺旋锥齿轮相比 ,在加工原理、加工设备和工艺方法上均有较大的区别。结合实例分析介绍了其加工、调整以及夹具的设计方法     

基于滑动率最小的渐开线圆柱齿轮传动优化设计

针对渐开线圆柱齿轮传动的设计 ,以一对齿轮副啮合的使用寿命最长为优化设计目标 ,通过调整齿轮的变位系数使齿轮传动的最大滑动率为最小以提高其传动寿命 ,并在此基础上设法使两齿轮最大滑动率相近来使其寿命达到基本一致。探讨了数学模型的建立、算法确定、计算机程序的编制 ,并结合工程实际给出了计算实例     

采用岩心钻机改装成大口径工程钻机应注意的问题

岩心钻机改装成大口径工程钻机已取得成功，但在实际使用中，圆锥齿轮经常损坏。分析了影响钻机上圆锥齿轮使用寿命的因素，并提出了改进措施。