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排序方式: 共有6046条查询结果,搜索用时 15 毫秒
61.
为了详细研究微型向心涡轮的内部流动特性,对一台自研微型涡轮发动机的涡轮进行了气动设计和全三维粘性数值模拟仿真,验证了叶片型线设计方案的可行性,得到模拟计算结果(落压比为1.91,总压绝热效率0.73,出口气流马赫数为1.2,流量13.8g/s)。研究了微型涡轮设计工况下内部的气流状态,对微尺寸下涡轮内部的流动特性及各种流动损失产生的特点及原因进行分析总结。结果表明:导向叶流道内的流动损失主要为由气体粘性引起的叶型损失;动叶流道中流动损失主要为气体在动叶前缘产生冲击形成的滞止损失与边界层损失,动叶出口叶片尾缘处形成的尾迹涡流损失。 相似文献
62.
63.
评价了国内外成品油管道技术现状和发展趋势。基于中亚、中俄跨国管道迅速发展,国内已开展中国和俄罗斯标准差异研究,但在成品油管道运行领域较少涉及,为此选取了俄罗斯有代表性的成品油管道综合性标准。该标准的先进性主要体现在以下几个方面:油品排列原则更为细化、采用工艺混油缓冲塞和限定控制初始工艺混油以减少混油、规定成品油管道最低允许流速、严格控制混油切割浓度、基于定量计算掺混比例进行混油掺混作业等。最后,针对完善我国成品油管道运行标准提出了建议。 相似文献
64.
Geetanjali Yadav Leonard A. Fabiano Lindsay Soh Julie Zimmerman Ramkrishna Sen Warren D. Seider 《American Institute of Chemical Engineers》2021,67(1):e16992
Algae-to-biodiesel processes are hindered by high costs and low energy return on investment.1,2. Herein, three foci in research improve algae-to-biodiesel processes by: (1) reducing high installation and energy costs in the CO2 sequestration, cultivation, and harvesting stages; (2) improving oil extraction and biodiesel generation; and (3) increasing utilization of the proteins in lipid-extracted biomass (e.g., for animal feed), as well as the omega-3 fatty acids for nutraceuticals and food supplements. A process is introduced that uses carbon dioxide to aid in all three of these foci. CO2 is used first in the form of microbubbles to lyse algae cell walls, releasing triglyceride oils. CO2 also aids with transesterification of these triglycerides using methanol. At low temperatures (353.15–368.15 K) and intermediate pressures (5–10 MMPa), carbon dioxide causes methanol to dissolve partially in the triglyceride phase and triglyceride to dissolve partially in the methanol phase, increasing the transesterification reaction rate. Due to the nondestructive nature of these processes, other metabolites can also be harvested providing improvements in both mass and economic efficiency with an overall sharp reduction in the modeled price of biodiesel. 相似文献
65.
Mechanical nondiscoloring and antistretching photonic crystal (PC) films, especially those with stable structure colors during deformation, have great potential applications in wearable display devices, decoration, and packaging. Here, PC films with antistretching and invariant structural colors during deformation were prepared, by combining Zn2+ coordinated elastic material and hydroxypropyl methylcellulose (HPMC) with polystyrene@silica (PS@SiO2) colloidal crystals. The PC films release energy by forming local fractures at a microscopic level during the straining process but the lattice spacing and effective refractive index of the local array do not change. According to the Bragg law, the structure color remains unchanged. The introduction of HPMC gave the PC films excellent tensile properties, and the maximum tensile strength reached 10 MPa. And after 100 times of stretching, bending and compression cycles, the structural color remained unchanged. 相似文献
66.
Taranjot Kaur Justin Nussbaum Sanboh Lee Kevin Rodriguez Nathan B. Crane Julie Harmon 《Polymer Engineering and Science》2021,61(1):221-233
Large area projection sintering (LAPS) promises to be a new method in the field of additive manufacturing. Developed in the Mechanical Engineering Department, University of South Florida, LAPS uses long exposure times over a broad area of powder to fuse into dense, reproducible materials. In contrast, LS, a common powder-based additive manufacturing, uses a focused beam of light scanned quickly over the material. Local regions of concentrated high-energy bursts of light lead to higher peak temperatures and differing cooling dynamics and overall crystallinity. The mechanical properties of laser sintered specimens suffer because of uneven particle fusion. LAPS offers the capacity to fine-tune fusion properties through enhanced thermodynamic control of the heating and cooling profiles for sintering. Further research is required to identify the relationship between LAPS build settings and part properties to enable the fabrication of custom parts with desired properties. This study examines the influence of LAPS sintering parameters on chemical structures, crystallinity, mechanical, and thermal properties of polyamide-12 specimens using powder X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, small-angle X-ray scattering, scanning electron microscopy, and microhardness testing. It was observed that higher crystallinity was imparted to specimens that were sintered for a shorter time and vice versa. 相似文献
67.
研究典型叉流式溶液除湿系统中,溶液循环流量(Gcir)、冷/热量(Qc/Qh)和系统流程对除湿/再生空气状态变化和除湿效果的影响机制。分析不同工况下空气在焓湿图中的过程曲线特征,比较各因素影响程度。结果表明,在设计条件下,当Gcir约为0.05 kg/s时,溶液除湿系统达到最佳除湿效果;当Qc、Qh比例接近,总量由29.4 kW增加至48.9 kW时,系统中除湿量由3.7 g/kg上升至5.7 g/kg;不同流程中,当冷却对象为溶液时,溶液除湿效果较好。相较于溶液除湿系统中Gcir和Qc/Qh,溶液除湿流程对空气状态变化和除湿效果的影响程度较大。空气过程曲线在各流程下具有显著特征,溶液除湿流程是影响空气状态变化和除湿效果的核心因素。 相似文献
68.
69.
镁合金化学镀镍层的结合机理 总被引:15,自引:4,他引:15
镁合金在直接化学镀前的活化处理时,表面生成一层氟化物保护膜,溶解度计算及XPS分析表明,氟化物膜在镀液中可稳定存在,用SEM,XPS,SAM考察了初始沉积Ni,镀层横截面以及开裂后的断面形貌与成分,发现在镀层与基体之间存在着氟化物,镀液成分与Ni的混杂层,这一混杂层是镀层与基体结合的最薄弱环节,镀层开裂通常首先发生在此混杂层内。 相似文献
70.
The effects of joint design on the mechanical properties of AL7075-T6 aluminum sheet were studied on the latest automated
gas-tungsten arc-welding system. Using ER5356 filler metal, full-penetration welds were made on workpieces with various included
joint angles. Testing of the mechanical properties of the joints was done in the as-welded, naturally aged, and postweld heat-treated
conditions. The results show that by using crack-resistant filler, and by selecting the proper joint design and postweld heat
treatment, strong, dependable welds can be produced on thin AL7075 sheet material. An elasticity model of the weld joint was
established to help understand the mechanical behavior of the joints. An undermatched joint design is shown to be capable
of achieving a joint strength that matches the strength of the base alloy. 相似文献