Performance of Vacuum Insulations for Use in Liquid Hydrogen Systems Under Steady State and Loss of Vacuum Conditions

Reduction of global carbon emissions is pivotal to the future health of the planet. Renewable resources allow for many sectors to be decarbonized if there is a reliable means to store excess energy. Transportation via aviation and freight remains one of the most challenging sectors to decarbonize as the large weight and long charge times associated with battery electric become prohibitive to existing operations. Hydrogen production via electrolysis can provide a renewable grid with storage and a clean fuel that overcomes the key weight and fuel time limitations. Liquid hydrogen, stored at 20 K, offers an 800 times increase in density compared to gaseous hydrogen, allowing comparable volumetric energies to be achieved relative to traditional fossil fuels. Liquid hydrogen is most commonly stored in double-walled vacuum-evacuated vessels to reduce heat leak. To further mitigate heat leak due to radiation or gas conduction, filler insulations can be utilized. However, the performance of these insulations at temperatures below 77 K is unknow for both steady-state operation and loss of vacuum scenarios. In this work, the complete design, construction, and testing of an effective conductivity experiment utilizing a guarded cryocooler approach enables the measurement of effective conductivity for glass microbubbles, aerogel, multi-layer-insulation (MLI), and vacuum only with an accuracy of ±0. 11 mW/ (m-K). Measurements were collected under high vacuum conditions and a cold boundary temperature ranging from room temperature down to 20 K. At 20 K it was found that MLI had the best performance at 0. 26 mW/ (m-K), Followed by glass microbubbles at 0. 52 mW/ (m-K), Vacuum only at 0. 85 mW/ (m-K), and aerogel at 1. 34 mW/ (m-K). In addition, loss of vacuum scenarios were simulated, providing peak heat fluxes experienced with each insulation utilizing both nitrogen gas and calibrated air. Peak heat fluxes were found with vacuum only of 2880 W/m² and 2176 W/m² using nitrogen gas and air respectively. From the calibrated air tests it was found that oxygen was concentrated up to 54% in cold insulation. The results from this work enables prediction of liquid hydrogen boil-off characteristics under steady state and loss-of-vacuum scenarios as well as concentrated oxygen considerations.