Understanding the physical phenomena that occur inside heat exchangers for liquefaction of hydrogen.

Liquid hydrogen is an attractive solution for long-range distribution. The largest barriers for implementing large-scale hydrogen liquefaction plants are currently their high energy consumption and cost. The heat exchangers are among the most important equipment in these plants. It has been shown that it may be beneficial to use a mixture of helium-neon ("Nelium") as refrigerant in the cryogenic cooling cycle, because this gives the possibility to utilize highly efficient turbocompressor equipment. In this work, we discuss the physical phenomena that are expected to occur inside cryogenic heat exchangers if Nelium is used as refrigerant for low temperature cooling and liquefaction of hydrogen. We present a detailed heat exchanger model for a simple heat exchanger geometry and study phenomena such as nonequilibrium ortho-para conversion, possible solid-formation of neon and boiling/condensation of Nelium at the lowest temperatures. We elaborate how the physical phenomena can be exploited in the design of more energy- and spaceefficient heat exchanger equipment for hydrogen liquefaction processes.

液氢（liquid hydrogen）是实现长距离输送的极具吸引力的技术方案。当前，制约大规模氢气液化工厂规模化落地的核心瓶颈在于其高昂的能耗与成本。换热器（heat exchanger）是此类工厂中最为关键的核心设备之一。已有研究表明，在低温制冷循环中采用氦氖混合工质（Nelium）作为制冷剂具备显著优势，因其可适配高效涡轮压缩机设备的使用需求。本研究探讨了采用Nelium作为制冷剂开展氢气低温冷却与液化时，低温换热器（cryogenic heat exchanger）内部可能出现的各类物理现象。我们针对一种简化的换热器几何构型搭建了精细化的换热器模型，并对多种关键物理现象展开研究，包括非平衡态正氢-仲氢转化、氖的固相析出，以及极低温下Nelium的沸腾与冷凝过程。最后，我们详细阐释了如何利用上述物理现象，为氢气液化流程设计出更节能、更紧凑的高性能换热器设备。