共查询到20条相似文献,搜索用时 105 毫秒
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对热声系统中交变流动的声场与流场分布进行了数值模拟,得到了热声谐振管和回热器(板叠)内的压力和速度分布及二者之间的相位关系.数值模拟表明:在谐振管内,在模拟的边界条件下,径向速度分布出现"环形效应",流动分为核心区的完全湍流流动和湍流边界层内的粘性流动;对于水力半径和粘性渗透层深度相当的热声板叠,其内速度分布逐步出现"环形效应",流动介于层流和湍流的过渡区,为过渡态流动,在流道的大部分区域压力和速度振荡的相位差趋向于π/2;对于水力半径和粘性渗透层深度之比较小的热声回热器,其内交变流动的流动特性与稳态流动的相似,速度的径向分布为抛物线形,类似于定常流动的层流速度分布. 相似文献
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开式循环热声原理研究 总被引:1,自引:0,他引:1
稳定的开发流与热声循环的振荡流进行叠加,使开环流既是过程介质又是工作介质直接参与热声循环,从而构成开式热声系统,它具有与传统热声系统不同的热声作用机理。在开发式循环热声系统中,热声板叠中的温度分布和热流分布均发生有意义的改变。开式的循环声系统具有结构简单可靠、成本低和热效率高等特点,因而具有十分广阔的热声研究与应用前景。本文主要介绍了开式循环热声系统的工作机理和其网络模型。 相似文献
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采用数值模拟和试验研究相结合的方法探究了开槽斜板对射流冲击噪声及壁面横向射流尾迹的影响,并分析了其降噪机理。试验方面,采用PIV技术和远场传声器弧阵列在半消声室内测量了冲击射流流场和声场特性,数值模拟则采用分离涡模拟方法(detached-eddy simulation,DES)和FW-H声学比拟法相结合的混合方法,数值结果与流场/声场试验测量结果吻合较好。研究发现:冲击斜板的存在增加了冲击射流流场上游方向的声辐射;所有压比下,斜板表面凹槽结构都能够明显抑制横向流动,但只在NPR>2.5时,开槽斜板才能较好的抑制冲击射流噪声;开槽斜板主要是降低2500 Hz附近的纯音幅值,对3500~4500 Hz内的多个纯音基本不产生影响,因为凹槽结构会耗散掉冲击射流滞止区内的旋涡对,但不会影响射流剪切层涡脱落频率(3750 Hz)及该频率附近的纯音;开槽斜板对横向流动的抑制效果高达46%,且不同槽宽、槽深的开槽斜板均能够有效控制冲击射流横向流动尾迹。 相似文献
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采用Ansys Workbench 15.0自带DM模块构建来流作用下的板模型,利用MESH模块划分网格,以及System Coupling模块进行流固耦合计算,验证数值模拟的可靠性,并对影响板表面声辐射频率的因素进行分析。数值模拟与分析结果表明,在来流作用下的板模型中,板表面声辐射主要由平行于来流方向的脉动压力产生,与壁面上垂直于来流方向的脉动压力、板后的大涡、板的固有频率无关;来流作用下板表面声辐射的基频与来流作用下板振动的基频、板后空腔的基频相同,是板后大涡基频的两倍;在大涡外且不在板后空腔的流场区域内,脉动压力无基频存在;在大涡模拟已经趋于统计稳定的情况下,FW-H与LES的非同步计算可以达到和同步计算一样的效果。 相似文献
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A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils. 相似文献
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Standards are the basis for production enterprises to organize production ex-factory inspection trade 《中国标准化(英文版)》2008,25(1):24-25
Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.…… 相似文献
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The end of over unit products of more than Chinese firms have passed the quality grade certification for liquor products. These products involve distilled spirits beer wine yellow wine fruit syrup wine others cover over % of the national top-branded liquor products.…… 《中国标准化(英文版)》2008,25(1):30
The end of 2007, over 200 unit products of more than 80 Chinese firms have passed the quality grade certification for liquor products. These products involve distilled spirits, beer, wine, yellow wine, fruit syrup wine and others, and cover over 80% of the national top-branded liquor products.…… 相似文献
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Surface characterization and microstructure studies are performed on chemical vapor deposited (CVD) tungsten coating. There is about 2 μm thickness diffusion layer of tungsten in the molybdenum substrate. The thermal shock test shows tungsten coating has good adhesion with molybdenum substrate, but the elements of oxygen and carbon in the tungsten coating have the bad affection to the adhesion. The result of high-temperature diffusion experiment is the diffusion rate from molybdenum substrate to tungsten coating is faster. 相似文献
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N.A. Odintsova N.V. Ageenko K.V. Kiselev N.M. Sanina E.Y. Kostetsky 《International Journal of Refrigeration》2006,29(3):387
We studied a combined effect of the cryoprotectants both of lipid and carbohydrate origin at the presence of DMSO or without it on cell viability and the RNA synthesis in the embryonic mollusc and echinoderm cell cultures obtained at different developmental stages. Cryoprotective properties of exogenous lipids correlated with their thermotropic behavior. Lipid extracts from marine hydrobiontes, which thermal transitions are characterized by relatively small part of calorimetric thermogram area lying at temperatures above 0 °C (6–18%), were found to possess a considerable cryoprotective activity. The results are discussed in relation to the prediction of the cryoprotective activity of lipid extracts for marine animal cells. In addition, it was found that marine invertebrate cells can be cryopreserved without DMSO at the presence of trehalose and lipid extracts of some marine hydrobiontes. 相似文献
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David R. Smith F. R. Fickett 《Journal of research of the National Institute of Standards and Technology》1995,100(2):119-171
Pure silver is used extensively in the preparation of high-temperature superconductor wires, tapes, films, and other configurations in which the silver not only shields the superconducting material from the surrounding materials, but also provides a degree of flexibility and strain relief, as well as stabilization and low-resistance electrical contact. Silver is relatively expensive, but at this stage of superconductor development, its unique combination of properties seems to offer the only reasonable means of achieving usable lengths of conductor. In this role, the low-temperature physical (electrical, thermal, magnetic, optical) and mechanical properties of the silver all become important. Here we present a collection of properties data extracted from the cryogenic literature and, to the extent possible, selected for reliability. 相似文献
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Fco. Javier Franco Pérez Marc Gener Moret 《Materials and Manufacturing Processes》2017,32(7-8):876-884
ABSTRACTThe production of iron in Biscay (Basque Country, Spain) has been a hallmark of this territory of the North of the Iberian Peninsula throughout its history. The Archaeology team of the Basque Country Mining Museum has spent 13 years, so far, studying the origins of this activity through the evidences left at the old pre-hydraulic iron production workshops known as mountainside ironworks (ferrerías de monte) or haizeolak. It has catalogued 170 archaeometallurgical sites of this type in Biscay, and the archeological excavation of some of them has led to the knowledge of the different stages of the production process that took place in these workshops. The team has also experimentally reproduced the work carried out in a mountainside ironworks from the High Middle Ages, and it has currently started the characterization process of this type of activity through the study of the collected materials. 相似文献
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Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß. 相似文献
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As demands about environment protection are growing up, dry cutting technology is getting more and more concerns from all over the world. Main works performed here are study on dry cutting performances and wear mechanisms of M2high-speed steel (HSS) twist drills with CrAlTiN multicomponent coatings, which was deposited using magnetron sputter ion plating system, in drilling 45 and 30CrMnSiA steel, and their comparisons to those in drilling the same steel but using monolayer CrN and commercial TiN coated drills. Drilling performances of drills are evaluated mainly through the measurements of width on outer corner flank land and the cutting forces. Results show that performances of CrAlTiN coated drills are better than those of monolayer CrN and TiN coated drills. In drilling 45 and 30CrMnSiA steel, the average tool life of the CrAlTiN coated drills are 17.2 and 11.8 times higher than those of the uncoated drills. Observing wear of the drill with scanning electronic microscope, results show that there is no crack or spallation of the CrAlTiN coatings in wear zones. Main mechanism of the wear here is adhesion. 相似文献
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TiO2 ceramic coatings with thickness of 20 μm were formed on the surface of pure titanium by micro-plasma oxidation. Their micro-structures were investigated by by using X-ray diffraction and their surface images were detected by using scan electronic microscope. There were three kinds of TiO2 coatings, pure anatase type TiO2 phase, mixed phases consisted of rutile type TiO2 phase and anatase type TiO2 phase, pure rutile type TiO2 phase. The coating surface with the pure anatase type TiO2 phase is rough, while the coating surface with the pure rutile type TiO2phase is smooth. The upper coating surface with the mixed type TiO2 phases is anatase type TiO2 structure and the subsurface of the TiO2 coating is rutile type TiO2structure. 相似文献