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Muhammad M. Rahman Jorge C. Lallave Ashok Kumar 《International Journal of Heat and Mass Transfer》2008,51(17-18):4400-4414
Conjugate heat transfer from a uniformly heated spinning solid disk of finite thickness and radius during a semi-confined liquid jet impingement from a rotating nozzle is studied. The model covers the entire fluid region including the impinging jet on a flat circular disk and flow spreading out downstream under the spinning confinement plate and free surface flow after exposure to the ambient gaseous medium. The model examines how the heat transfer is affected by adding a secondary rotational flow under semi-confined jet impingement. The solution is made under steady state and laminar conditions. The study considered various plate materials such as aluminum, copper, silver, constantan and silicon. Ammonia, water, flouroinert FC-77 and MIL-7808 oil were used as working fluids. The range of parameters covered included Reynolds number (220–900), Ekman number (7.08 × 10?5–∞), nozzle-to-target spacing (β = 0.25–1.0), disk thicknesses to nozzle diameter ratio (b/dn = 0.25–1.67), Prandtl number (1.29–124.44) and solid to fluid thermal conductivity ratio (36.91–2222). It was found that a higher Reynolds number increased local heat transfer coefficient reducing the interface temperature difference over the entire disk surface. The rotational rate also increased local heat transfer coefficient under most conditions. An engineering correlation relating the Nusselt number with other dimensionless parameters was developed for the prediction of the system performance. 相似文献
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文中介绍了常用的UPS系统供电方式,通过对各种UPS供电方式的系统效率、设备投资、容错性能、可用性、装机占地面积及承重的比较,为用户提供在不同类型的电子信息机房选择UPS系统的建议。 相似文献
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考虑旋流衰减的影响,对气液螺旋环状流的压降特性进行研究并推导出了螺旋环状流压降预测模型。定义压降旋-直比系数为气液两相螺旋环状流和气液两相直流的压降之比,以此来表征旋流衰减对压降的影响。基于量纲分析的方法对压降旋-直比系数进行分析,推导出其表达式,压降旋-直比系数依赖于Lockhart-Martinelli 参数和气相Froude数变化。最终,得出了气液两相螺旋环状流的压降预测模型。在50 mm内径的水平管内对螺旋环状流的压降特性进行了实验研究,其中气相表观流速变化范围为10~16 m/s,体积含液率(LVF)变化范围为0.6%~4.8%。通过与实验数据进行对比,压降预测模型的相对误差在±15%以内,为工程应用提供了参考。 相似文献
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气敏传感器是利用材料的气敏特性实现目标气体浓度检测的电子元器件,在生产安全、环境监测、临床医学等领域均有广泛应用。气敏材料主要分为金属氧化物半导体材料、导电聚合物(CP)材料、金属有机框架材料。导电聚合物因其成本低、易于合成,在室温下对氨气等有害气体表现出良好的响应的特点而受到广泛关注。近年来导电聚合物复合物的研究也极大地提高了导电聚合物的气敏性能。分析了导电聚合物电阻调控机理,重点介绍了近年来对氨气、二氧化氮、硫化氢等气体的导电聚合物及其复合物的气敏传感器的研究进展,简要介绍了导电高分子在甲醇、三乙胺、一氧化碳等气体检测中的研究情况,最后展望了导电聚合物在气体传感领域的应用前景。 相似文献
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作为国家法定计量检定机构,为了保障建筑工程质量,减少建筑工程事故,几何量项目组认真汇总并研究了目前检定校准需求量较大的建筑工程计量器具的共性和差异性,设计制造了一套新型工程质量检测综合校准装置。这套装置通过平直度校准主要结构、垂直度校准主要结构、厚度校准主要结构、角度校准主要结构及其辅助设计,对建筑工程质量器具实现多维度、多参数校准。从而基本涵盖了目前工程质量基础检测计量器具在几何量领域的全部校准,并且满足现有的建筑工程质量相关器具的1/3标准器精度要求,实现可靠的量值溯源和量值传递。本装置是一套创新、综合、实用的高精度计量标准。 相似文献
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论述了纤维卷尺的历史溯源和量值溯源。依据JJG5 2001《纤维卷尺、测绳检定规程》,详细论述了纤维卷尺的不确定度评定的步骤与方法,按照校准方法,数学模型,方差和传播系数,标准不确定度,合成不确定度以及扩展不确定度计算的顺序编写。并将其扩展不确定度与规程规定的最大允许误差作比较,得出此测量方法可行的结论。并提出了高精度玻璃纤维卷尺的发展方向。 相似文献
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HUO Xiaoqian XU Ying WANG Jinghan ZHANG Tao MAIMAITI Aikebaier WANG Xigang 《化工学报》2021,71(12):5506-5514
Considering the influence of swirl attenuation, the pressure drop characteristics of gas-liquid spiral annular flow are studied, and the pressure drop prediction model of spiral annular flow is deduced. The swirl-straight ratio of pressure drop is defined as the ratio of pressure drop of swirl flow to straight flow, used to characterize the effect of swirl decay on pressure drop. The expression of swirl-straight ratio of pressure drop is derived by the method of dimensional analysis, and it has a strongly dependence on Lockhart-Martinelli coefficient and gas phase Froude number. Finally, the prediction model of pressure drop for gas-liquid swirl annular flow is obtained. The pressure drop characteristics of the swirl annular flow are experimentally studied in a horizontal tube with an inner diameter of 50 mm. The range of the gas superficial velocity is 10—16 m/s and the range of the liquid volume fraction (LVF) is 0.6%—4.8%. Through comparison with experimental data, the relative error of the pressure drop prediction model is within ±15%, which provides a method reference for engineering applications. 相似文献