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排序方式: 共有13条查询结果,搜索用时 31 毫秒
1.
A real-time neutron radiography (RTNR) system and a high speed X-ray computed tomography (X-CT) system are compared for measurement of two-phase flow. Each system is used to determine the flow regime, and the void fraction distribution in a vertical annulus flow channel with particular attention on the temporal resolution of the systems and the time behaviour of the two-phase flow. The annulus flow channel is operated as a bubble column and measurements obtained for gas flow rates from 0.0 to 30.0 l/min. Both the RTNR and the X-CT systems show that the two-dimensional void fraction distribution can be obtained. The X-CT system is shown to have a superior temporal resolution capable of resolving the void fraction distribution in an (r,θ) plane in 4.0 ms. The RTNR system is shown to obtain void fraction distribution in a (r,z) plane in 33.0 ms. Void fraction distribution for bubbly flow and slug flow is determined.  相似文献
2.
Eye observation was used to evaluate the segregation degree of asphalt pavement, which was not much creditable. To the asphalt pavement, road surface texture measuring method which has appeared recently can identify gradational segregation; but it can’t reflect the influence of the temperature segregation. However, using infrared temperature detector to evaluate the segregation must be taken during paving, which brings much inconvenience. In this paper, measuring the air voids distribution using non-nuclear density gauge to evaluate asphalt pavement segregation was introduced. Result shows that this method can directly reflect the comprehensive results of the two types of segregation in a high efficient and accurate way. Moreover, using the sketch map of segregation area can help to analyze the segregation reason visually.  相似文献
3.
Asphalt concrete is the most widely used material for building the surface layer of pavements. It is a porous material that consists of a non-uniform arrangement of asphalt binder, aggregate particles and air voids. One of the primary factors controlling pavement performance is the fluid flow characteristics within the surface asphalt concrete layer.

This paper focuses on the numerical simulation of fluid flow in the three-dimensional (3-D) microstructure of asphalt concrete, and the calculation of permeability from the flow field. The asphalt concrete microstructure was captured using the non-destructive X-ray computed tomography (CT) technique. X-ray CT images were processed in order to identify and retain interconnected air voids and eliminate isolated voids. This image processing enhanced the efficiency of the model as it does not have to solve for flow in isolated voids that do not contribute to fluid flow. The X-ray CT images were analyzed and the results were used to determine the relationship between air void distribution and permeability directional distribution or anisotropy.

The computed permeability values were found to have good correlation with the experimental measurements. The major and minor principal directions of the permeability tensor were found to correspond to the horizontal and vertical directions, respectively. The results indicated that the non-uniform spatial distribution of air voids created more open flow paths in the horizontal directional than the vertical direction, and hence was the much higher permeability in the horizontal directions.  相似文献

4.
This paper is concerned with the prediction of the void fraction distribution in two-phase bubbly flows in fuel rod bundles. Special attention has been devoted to the phenomena which govern the void fraction distribution in the lateral direction of a channel. A two-fluid model of two-phase flow has been formulated and implemented into a commercial computational fluid dynamics (CFD) code. The model has been used for the prediction of the void distribution in three different channels: a circular channel (inside diameter (ID), 34.5 mm) with a single heated rod of 13.9 mm outside diameter (OD), and circular channels (ID, 71 mm) with six heated rods (13.8 and 13.9 mm OD each). The predicted axial and lateral avoid fraction distributions in subcooled and bulk boiling regions have been area averaged in three lateral zones and compared with experimental data: in all cases, satisfactory agreement between the predictions and measurements has been obtained.  相似文献
5.
王小军  陈炳德  黄彦平  孙奇 《化工学报》2007,58(6):1353-1358
采用计算流体动力学(CFD)程序CFX4.4对加热上升管内过冷流动沸腾工况下气水两相流动局部两相流参数(空泡份额和汽泡尺寸)进行了数值模拟。对数值差分方法、相关模型(界面力和气泡诱导的紊流)和汽泡尺寸进行了敏感性分析。空泡份额分布计算结果与实验结果比较表明,在低空泡份额工况下,两者符合较好,在高空泡份额工况下两者存在一定偏差,并且气相速度和汽泡尺寸的计算结果不理想。计算结果与实验结果之间的差异说明程序模型对于加热上升管内过冷流动沸腾模拟并不完善,建立更为合理的汽泡尺寸模型,考虑汽泡的合并和撕裂是必要的。  相似文献
6.
为研究型煤制备工艺与性能之间的关系,以指导生产工艺优化,利用单偏光显微镜及数字图像处理技术对不同黏结剂添加量和成型压力下制备的型煤空隙总体特征,以及水平方向与垂直方向上空隙分布特征进行研究,深入分析了空隙直径、位置及定向程度等特征。研究结果表明:不同黏结剂添加量及成型压力制备的型煤中空隙率差别较大;型煤水平方向与垂直方向上空隙率不同,水平方向上空隙直径较为集中;型煤空隙分布不均匀,定向程度差;型煤空隙从表面到内部有增大趋势。  相似文献
7.
This paper addresses bubbly flow modeling within Venturi tubes and nozzles using the two-fluid model. The effects of non-drag forces as virtual mass and the so-called “transversal forces” such as lift and wall lubrication are investigated in the context of the two-fluid model. As expected, the transversal forces have an important influence on void distribution as long as the virtual mass affects the pressure drop along the contraction, which is the main parameter for the flow rate measurement. Models for the virtual mass and lift forces were implemented via user routines in commercial computational fluid dynamics (CFD) software, as the models embedded within these packages, specifically for virtual mass, were found not to be adequate for the purpose of this study. The models are validated against results from the literature and pressure drop measurements along a Venturi tube, developed in this work. Additionally, some experimental visualizations were used to make a qualitative comparison with predicted void distribution.  相似文献
8.
建立了微重力下相变蓄热容器的仿真计算模型,根据蓄热容器内凝固过程的仿真结果建立了更加符合实际的空穴分布模型,对相变蓄热过程进行了仿真计算。对比分析了该文空穴模型与忽略空穴、简单空穴模型对应的仿真结果,证明空穴分布形式对于蓄热容器内的相变蓄热过程的显著影响。通过建立更加真实的空穴分布模型提高了相变蓄热过程仿真计算的准确性,对蓄热容器的设计改进具有积极的指导意义。  相似文献
9.
The oxidation of iron in dry and wet O2 at 400-600 °C has been re-investigated using gravimetry, SEM/EDX, XRD and FIB. In the presence of O2, water vapour accelerates iron oxidation at 500 and 600 °C. At 400 and 500 °C the magnetite layer is duplex and exposure to water vapour results in the formation of blades on top of a fine-grained hematite layer. At 600 °C it results in a surface without needles and blades. The increased oxidation rate at 500 and 600 °C is attributed to a smaller grain size in the hematite layer resulting in faster ion transport.  相似文献
10.
The pore space of mono-sized spherical particle systems of increasing density is characterized by Delaunay empty spheres. Periodic packings of densities ranging from 0.57 up to 0.70 are generated numerically by symmetric vibration. The Voronoi diagrams of these packings are then computed with an algorithm based on the research of Delaunay empty spheres. The voids distribution and the tortuosity of packings as a function of density are studied. As the density increases, the voids distribution becomes more narrow. For partly ordered packings of high density, the voids distribution presents two peaks corresponding to the size of Delaunay empty spheres of perturbed fcc or hcp packings. The tortuosity of disordered packings decreases slowly with density. However, when the system becomes partly ordered, a large increase in tortuosity is observed.  相似文献
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