Multiphase-thermal flow simulation in a straight vacuum-insulated LH2 pipe: Cargo handling system in LH2 carrier

This study numerically evaluates the thermal performance of insulation materials suitable for liquid hydrogen (LH2) transportation in pipes within a cargo handling system (CHS) of LH2 carriers and the thermal flow characteristics of LH2 in these pipes, using a computational fluid dynamics simulation. The design parameters of the LH2 pipes are established based on cryogenic piping design regulations. A phase change model is employed to predict the onset of nucleate boiling (ONB) points, crucial for understanding the initial bubble formation and its impact on LH2 flow in the pipes. Our findings underscore the importance of accounting for local pressure variations and their influence on boiling points. The study calculates the total volume fraction of vaporized hydrogen in the designed pipe system and assesses its safety by comparing to the lower flammability limit (LFL) of gaseous hydrogen (GH2). The results indicate that the highest vaporization occurs in cases with vacuum-only insulation. The study also estimates the length of the pipe reaching the LFL. In addition, the thermal insulation performance of six different inner filling materials, combined with vacuum insulation, is assessed by comparing the heat transfer to the pipe through the inner layer of the insulation system. Remarkably, vacuum insulation paired with a multilayer Mylar net demonstrates superior thermal performance. The outcomes of this research are anticipated to provide valuable reference material for establishing safety assessment standards in future LH2 pipe designs.