Non-combustible MLI based insulation behavior under fire condition - Experimental and numerical investigation

The number of applications that demand zero-emission energy carriers, such as liquified hydrogen (LH2), is increasing worldwide. LH2 is typically transported or stored under cryogenic conditions. Storage in such conditions requires super thermal insulations which maintain very low boil-off for a prolonged time. Multi-Layer insulation (MLI) finds widespread use in cryogenic applications, designed to effectively restrict heat inleak towards cryogenic fluids. However, recent studies evidenced that exposure to high heat fluxes, such as in the event of a fire accident, can cause the thermal degradation of the insulation material, resulting in the severe collapse of its heat resistance performance. Therefore, the risk of rapid tank pressurization and its connection to the risk of BLEVE may be possible. This study proposes a numerical model to assess the performances of aluminum-based MLI materials under fire conditions. The model offers insights into the total heat transfer rate through the insulation, serving as an indicator of the deterioration's impact on overall heat transfer. The proposed numerical model is validated against experimental data obtained by a High-Temperature Thermal Vacuum Chamber test facility that reproduces fire exposure conditions. The experiments conducted in this study underscore the emergence of pressure build-up within the insulation system, which contributes to increased gas conduction. Furthermore, it demonstrates that the spacer material is not entirely damaged under simulated fire conditions. The numerical calculation also underscores the significance of the modifications in material surface emissivity due to the deterioration process. The innovative approach proposed in this study thus paves the way for the development of improved tools aiming at the stationary and mobile cryogenic tanks behavior (e.g., LNG, LOX, LN2, and LH2) in fire accident scenarios. The model developed may, in perspective, be integrated into both CFD and lumped models for the calculation of the time to failure of cryogenic equipment under external fires. Therefore, this study offers valuable insights to improve the safety of processes and equipment for the storage of cryogenic fluids, thereby supporting emergency response planning in case of fire accidents.