Abstract In a new high-temperature superconducting (HTS) electricity transmission system, natural convection of liquid nitrogen in the annular channel is caused by the inside wall heating and outside wall cooling. Two-dimensional numerical simulation of the natural convection is conducted using a finite volume method. The dimensionless eccentricity, e∗, in the range of −1.0 to 1.0 is considered when the Rayleigh numbers (Ra) varied from 2 × 105 to 1 × 107. A bifurcation map of flow pattern is obtained by many numerical simulations. It is found that there are three typical flow regions in the fully developed stage, i.e. steady flow, periodic flow and chaotic flow. When the Ra is relatively low, the flow is steady and uniform. As the Ra increases, the reinforced natural convection approaches a time-dependent periodic flow and further a strongly chaotic flow. Furthermore, when the e∗ is up to 0.6, a cluster of Rayleigh-Benard convection cells appears on the top of the flowing channel, and enhances the heat transfer slightly. The effect of the e∗ and Ra on the heat transfer of natural convection is analyzed quantitatively. It is demonstrated that the most suitable region for the vertical position of the HTS cable is for a dimensionless eccentricity in the range of −0.8 to −0.6 to enhance the heat transfer while guaranteeing the safety of the HTS system.

中文翻译：

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新型组合输能系统高温超导电缆冷却液氮自然对流数值研究

摘要 在新型高温超导(HTS)输电系统中，环形通道内的液氮自然对流是由内壁加热和外壁冷却引起的。自然对流的二维数值模拟是使用有限体积方法进行的。当瑞利数 (Ra) 从 2 × 105 到 1 × 107 变化时，考虑了-1.0 到 1.0 范围内的无量纲偏心率 e*。通过许多数值模拟获得了流动模式的分岔图。发现在完全发展阶段存在三个典型的流动区域，即稳定流、周期流和混沌流。当Ra相对较低时，流动稳定均匀。随着 Ra 的增加，增强的自然对流接近于时间相关的周期性流动，并进一步成为强烈的混沌流动。此外，当 e* 达到 0.6 时，流道顶部出现一组 Rayleigh-Benard 对流单元，略微增强了传热。定量分析了 e* 和 Ra 对自然对流传热的影响。结果表明，最适合高温超导电缆垂直位置的区域是-0.8 到-0.6 范围内的无量纲偏心，以增强热传递，同时保证高温超导系统的安全性。定量分析了 e* 和 Ra 对自然对流传热的影响。结果表明，最适合高温超导电缆垂直位置的区域是-0.8 到-0.6 范围内的无量纲偏心，以增强热传递，同时保证高温超导系统的安全性。定量分析了 e* 和 Ra 对自然对流传热的影响。结果表明，最适合高温超导电缆垂直位置的区域是-0.8 到-0.6 范围内的无量纲偏心，以增强热传递，同时保证高温超导系统的安全性。