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In a cryogenic liquid medium, shock waves will be formed by the expansion of compressed gas that has been vaporized due to the injection of a large amount of energy. This may severely threaten the reliability of high- T c superconducting (HTS) apparatus. Several studies have documented the destructive forces of evaporating nitrogen produced by arc energy. However, the properties of and propagation mechanisms relating to pressure waves in liquid nitrogen have yet to be understood. The aim of this study was to clarify the evolution of pressure waves within an enclosed pipeline and reveal the effects of several factors such as the pipe size and the injected energy on the shock-wave impact using explosion dynamics simulations. The results provide evidence for the strengthening of shock waves due to multiple reflection and superposition. In addition, analysis of the pressure impulse and effective strain reveals that, in the case of moderate injected energy, the overall shape of the inside wall of the pipe will remain unchanged except at the points closest to the explosion center; in contrast, the ends of the pipeline may suffer from more severe deformation. Finally, the calculations suggest that the shock-wave impact increases almost linearly with the injected energy, and in logarithmic coordinates, the pressure is inversely proportional to the explosion distance. These findings provide a better understanding of the characteristics and propagation patterns of shock waves in liquid nitrogen, and they lay a foundation for evaluating the safety of HTS cables and energy pipelines. [ABSTRACT FROM AUTHOR]

High-temperature superconducting (HTS) power equipment and tests at present require operating temperatures higher than the liquid nitrogen (LN2). LN2 is an important cryogenic refrigerant and liquid insulation material, which is widely used in HTS equipment. Although pressurized LN2 can achieve temperatures higher than 77 K, it requires the use of sealed pressure vessels. Thus, a liquid cryogen that can offer temperatures higher than LN2 at atmospheric pressure, excellent electrical insulation performance, and high thermal conductivity has to be explored. Tetrafluoromethane (CF4) is another cryogenic refrigerant and electrical insulation material. The mixture of LN2 and liquid CF4 has excellent thermal properties. When mixed in appropriate proportions, it has a melting point of 50 K and a boiling point of 145 K. The LN2/CF4 mixture is used in the insulating layer of the superconducting energy pipeline to provide a low-temperature environment (85–100 K) for the HTS dc cable. However, the insulation characteristics of the LN2/CF4 mixture at cryogenic temperatures have not been studied, quantitatively. In this article, a test platform is developed to measure the breakdown voltage of the liquid mixture. The dc breakdown voltages of LN2/CF4 liquid mixture under varying mixing proportions are obtained at cryogenic temperature. The insulation failure probability is estimated using a two-parameter Weibull statistical method. The results reveal that the breakdown strength of the LN2/CF4 mixture is lower than that of pure LN2. As the proportion of CF4 increases, the breakdown field strength of liquid mixture first decreases and then increases. When the mole fraction of CF4 is 60%, the average breakdown strength decreases to the lowest value (14.07 kV/mm), about half of that of pure LN2 (28.26 kV/mm). The results of this article can provide a reference for the applications of LN2/CF4 liquid mixture in HTS power equipment and a scheme to expand the working temperature range of superconducting applications. [ABSTRACT FROM AUTHOR]

High Tc superconducting (HTS) DC cable is a promising solution for large-scale power transmission over long distance. However, the refrigeration system for HTS cable is indispensable but undesirable. Considering that LNG (liquid natural gas) is now one kind of clean energy that is used more and more widely, it is possible to integrate HTS cable and LNG transportation into a single pipeline, resulting in a new energy transportation system- a HTS energy pipeline. In this paper, the principle and structure of the energy pipeline are first discussed and then the basic physical properties of the HTS tapes and liquid insulation medium in the LNG temperature range are analyzed. On this basis, a 10 kV/1 kA energy pipeline is designed, fabricated and tested. [ABSTRACT FROM AUTHOR]

• The temperature distribution of an energy pipeline is simulated and tested. • A simulation model of the energy pipeline principle prototype is proposed. • The factors and laws that affected the temperature distribution are obtained. • An empirical formula to calculate the outlet temperature is achieved. Superconducting DC energy pipeline is an energy channel that simultaneously transmits electrical energy as well as the liquid fuel. It improves the efficiency of energy transmission and reduces the overall cost by cooling high-temperature superconducting DC cables with the low-temperature liquid fuel, such as liquid hydrogen, liquefied shale gas, and liquified natural gas (LNG). In order to properly design this, it is very important to know the temperature distribution along the pipeline, which is yet to be carried out by the researchers. In this paper, a 10 m energy pipeline with LNG cooling and having a concentric nested structure is simulated and tested experimentally. The simulation results of the temperature rise along the pipeline were in good agreement with the experimental results. The effect of various parameters on the pipeline temperature were also obtained. Finally, based on the theoretical equations and simulation results, an empirical formula is proposed to calculate the temperature at the outlet of the energy pipeline. [ABSTRACT FROM AUTHOR]

• Based on the requirement of integrated transportation of electricity and LNG, an effective structure with high safety and efficient heat exchange is proposed. • The HTS tape and insulation medium used in LNG temperature range are discussed. • Based on the comparison of different types of bipolar cable and pipeline, the overall design scheme of ±100 kV/1 kA superconducting DC energy pipeline with optimized comprehensive performance is given. High Tc Superconducting (HTS) DC cable is a promising solution for large-scale power transmission over long distance. However, the indispensable refrigeration system for HTS cable might be undesirable. Considering that LNG (liquid natural gas) now is one kind of clean energy that is used more widely and widely, it is possible to integrate the HTS cable and LNG transportation into an energy pipeline, resulting an acceptable new energy transportation system. In this paper, the principle and structure of the energy pipeline are discussed firstly, and then the basic physical properties of HTS tapes and liquid insulation media in LNG temperature range are analyzed. On the base as above, the general design of ±100 kV/1kA energy pipeline is made. [ABSTRACT FROM AUTHOR]