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利用液氮制冷技术制取液氮样品,以二级轻气炮为加载工具,对液氮样品进行平面冲击压缩,实验测量了液氮10-60Gpa一次冲击Hugoniot数据。实验结果显示,33Gpa以上氮的冲击波速度一粒子速度关系式与低压段有明显差别,表现为氮的压缩系数增大。经理论计算和分析,可以认为液氮在冲击压力33Gpa以上,液氮体系会发生分子离解相变。  相似文献
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液氮过冷流动沸腾广泛见于各种低温换热设备中.采用双流体模型分析液氮过冷流动沸腾, 需要为模型提供适当的封闭方程, 用于描述汽液两相间质量、动量以及能量的传输过程, 封闭方程的合理性直接决定了双流体模型的准确性. 将液氮流动沸腾通道划分为近壁区和主流区, 分别介绍液氮核态沸腾壁面上的传热传质机理模型, 以及两相流程内汽液之间的相互作用的相间传输模型, 建立液氮流动沸腾过程适用的双流体模型, 并分析了对模型预测能力具有显著影响的因素, 指出存在的问题和解决方案.  相似文献
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The flow boiling patterns of liquid nitrogen in a vertical mini-tube with an inner diameter of 1.931 mm are visualized with a high-speed digital camera. The superficial gas and liquid velocities are in the ranges of 0.01–26.5 m/s and 0.01–1.2 m/s, respectively. Four typical flow patterns, namely, bubbly, slug, churn and annular flow are observed. Some interesting scenes about the entrainment and liquid droplet deposition in the churn and annular flow, and the flow reversal with the indication of negative pressure drop, are also presented. Based on the visualization, the two-phase flow regime maps are obtained. Compared with the flow regime maps for gas–water flow in tubes with similar hydraulic diameters, the region of slug flow in the present study reduces significantly. Correspondingly, the transition boundary from the bubbly flow to slug flow shifts to higher superficial gas velocity, and that of churn to annular flow moves to lower superficial gas velocity. Moreover, time-averaged void fraction is calculated by quantitative image-digitizing technique and compared with various prediction models. Finally, three kinds of oscillations with long-period and large-amplitude are found, possible explanation for the oscillations is given by comparing the instantaneous flow images with the data of pressure, mass flux and temperature recorded synchronously.  相似文献
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为分析液氮注入对含水煤层裂隙疲劳增扩的影响,分别取干燥煤样、50%水饱和煤样和100%水饱和煤样,在室内开展了周期疲劳液氮浸泡试验,利用激光显微镜和声波测试仪测试液氮作用前后煤样表面裂隙结构和波速的变化.结果表明:1)经过液氮浸泡后,干燥煤样裂隙扩展效果不明显,10个浸泡周期后煤样仍完整;2)含水煤样的裂隙主要在垂直节理方向发生扩展;3)饱水程度越高,煤样裂隙扩展越显著;4)饱水程度越高,煤样液氮浸泡破坏所需的浸泡周期越短.煤样的饱水程度对液氮致裂效果影响显著.  相似文献
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