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21.
In recent years the requirement for the reduction of energy consumption has been increasing to solve the problems of global warming and the shortage of petroleum resources. For example, in the power generation field, as thermal power generation occupied 60% of the power generation demand, considerable improvement of the thermal efficiency is required. This paper describes the pressure drop characteristics of finned tube banks used for heat exchangers in thermal power generation that were clarified by testing serrated finned tube banks with different fin heights for improved heat transfer and conventional spiral finned tube banks with different fin heights, and an equation to predict pressure drop which is necessary for the heat exchanger design is proposed. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(3): 179–193, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20112 相似文献
22.
钢筋混凝土框架梁截面的优化确定 总被引:1,自引:0,他引:1
以梁的配筋和截面有效高度为优化设计变量 ,导出了 RC框架梁的优化配筋率和优化设计高度 ,并给出了各种荷载作用下 ,不同设防烈度和场地类别条件下的截面优化设计高度表达式 ,为设计人员提供了方便 . 相似文献
23.
Quality assessment of SRTM C- and X-band interferometric data: Implications for the retrieval of vegetation canopy height 总被引:1,自引:0,他引:1
The Shuttle Radar Topography Mission distinguished itself as the first near-global spaceborne mission to demonstrate direct sensitivity to vertical vegetation structure. Whether this sensitivity is viewed as exploitable signal or unwanted bias, a great deal of interest exists in retrieving vegetation canopy height information from the SRTM data. This study presents a comprehensive application-specific assessment of SRTM data quality, focusing on the characterization and mitigation of two primary sources of relative vertical error: uncompensated Shuttle mast motion and random phase noise. The assessment spans four test sites located in the upper Midwestern United States and examines the dependence of data quality on both frequency, i.e., C-band vs. X-band, and the number of acquired datatakes. The results indicate that the quality of SRTM data may be higher than previously thought. Novel mitigation strategies include a knowledge-based approach to sample averaging, which has the potential to reduce phase noise error by 43 to 80%. The strategies presented here are being implemented as part of an ongoing effort to produce regional- to continental-scale estimates of vegetation canopy height within the conterminous U.S. 相似文献
24.
The effect of absorber packing height on the performance of a hybrid liquid desiccant system 总被引:1,自引:0,他引:1
A hybrid system consisting of vapour compression unit, a liquid desiccant system, and a flat solar hot water collector were designed, fabricated and tested. This combination allowed for a separate control of humidity and temperature without energy penalty. Various packing heights of the absorber component were tested to determine the optimal performance of the combined unit. A 1000 mm packing height with cross-sectional area of 600×600 mm, proved to be the best height that gives promising improvements in the coefficient of performance of the vapour compression unit. 相似文献
25.
Wayne S. Walker Josef M. Kellndorfer Michael Hoppus 《Remote sensing of environment》2007,109(4):482-499
Exploiting synergies afforded by a host of recently available national-scale data sets derived from interferometric synthetic aperture radar (InSAR) and passive optical remote sensing, this paper describes the development of a novel empirical approach for the provision of regional- to continental-scale estimates of vegetation canopy height. Supported by data from the 2000 Shuttle Radar Topography Mission (SRTM), the National Elevation Dataset (NED), the LANDFIRE project, and the National Land Cover Database (NLCD) 2001, this paper describes a data fusion and modeling strategy for developing the first-ever high-resolution map of canopy height for the conterminous U.S. The approach was tested as part of a prototype study spanning some 62,000 km2 in central Utah (NLCD mapping zone 16). A mapping strategy based on object-oriented image analysis and tree-based regression techniques is employed. Empirical model development is driven by a database of height metrics obtained from an extensive field plot network administered by the USDA Forest Service-Forest Inventory and Analysis (FIA) program. Based on data from 508 FIA field plots, an average absolute height error of 2.1 m (r = 0.88) was achieved for the prototype mapping zone. 相似文献
26.
GAOHui LIYan YANGLi-ping DENGHong 《半导体光子学与技术》2005,11(2):85-88,106
Hexagonal microtube ZnO was firstly grown on single crystal p-Si (111) substrates by hydrothermal method, and fabricated Ag/n-ZnO and Au/n-ZnO Schottky junction. Schottky effective barrier heights were calculated by I-V measurement. It is confirmed that the presence of a large amount of surface states related possibly to lattice imperfections existed near the surface leads to the pinning of the surface Fermi level at 0.35 eV below the conduction-band edge. Then the fabricated Schottky barrier junctions are evaluated for their use as UV photodetectors. 相似文献
27.
28.
针对目前对高度表进行原位检测的需求,设计了一种新的高度模拟方法;该方法的实现以ARM为核心,通过高度模拟电路产生各种需要的高度电压信号,从而达到高度模拟的目的,并且无需对机载高度表进行拆装,操作简单、快捷、可靠性较高;实验结果表明,这种方法的高度模拟精度较高,具有一定的实用价值和经济效益. 相似文献
29.
Feedrate optimization and tool profile modification for the high-efficiency ball-end milling process 总被引:3,自引:2,他引:3
Jenq-Shyong By Chen Yung-Kuo Huang Mao-Son Chen 《International Journal of Machine Tools and Manufacture》2005,45(9):1070-1076
Trend in die/mold machining is to produce highly quailed surface using the high-speed hard machining with the ball-end cutter. The ball-end milling is, however, less efficiency than the flat end milling. It is important to optimize the feedrate that gives the maximum material removal rate constrained by an allowable surface roughness. The state-of-art of the CBN ball-end cutter technology allows increasing the tooth feed for high-speed and high-efficiency machining. However, because the spherical shape of the cutter can result in the scallop-liked cusps on the machined surface, the surface roughness consideration makes a feedrate limitation to the CBN cutter. In this paper, the optimization of the feedrate by considering the generated-scallop effect of the ball-end cutter has been studied. It was found that the tooth feed must be kept within one third of the path pick in order to keep the feed-interval scallop height not over the path-interval scallop height. Therefore, the potential capability of the CBN cutter for the larger tooth feed (i.e. high efficient) machining can not be fully exploited. It was found a notch-cut on the center of the ball-end cutter reduced the feed-interval cusp height, thus allowing an increased feedrate of more than 50% compared with the standard ball-end cutter. If the parameters of the notch-cut profile can be optimized, it is believed that the feedrate can be further increased. 相似文献
30.