In general, multilayer insulation (MLI) systems are most commonly used in on-board or small stationary LH2 storage tanks to reduce heat leaks, while perlite insulation systems are most commonly used in large LH2 storage tanks. Both insulation systems require high vacuum levels below 1x10-4 torr. For high vacuum storage tanks, insulation materials are only a small fraction of the total cost. The other manufacturing cost at a high vacuum vessel is much higher than the insulation materials. In order to make cost-effective and robust insulation systems, new insulation systems using combination of conventional insulations and new composite insulation at soft vacuum levels have been proposed. The new systems are expected to have similar thermal performance to conventional insulation system at high vacuum levels and low cost due to requirement of soft vacuum.

The new insulation systems have been tested at boundary temperatures between 77K and 300K in a laboratory. The tested novel materials consist of aerogel composite blanket, layered composite blanket with fiber glass paper and fumed silica dispersion, and layered composite blanket with polyester fabric and fumed silica dispersion. The conventional insulation is MLI. Since test conditions are not the same ones as LH2 storage, it is necessary to examine thermal performance using these novel insulation systems with boundary temperature between 20K and 300K.

The present paper investigates thermal performance for these novel insulation systems at soft vacuum levels through computer simulations. General equations of thermal conductivities for these tested insulation materials were developed first. The equations are a function of temperatures and pressures. Then the models were validated against measured data. As long as the models provide high confidence, the models were applied to LH2 storage conditions and a parametric study was performed. A parametric list consists of following insulation systems at different vacuum levels: • Conventional insulations • Novel insulations • Combination of conventional and novel insulation • Combination of different novel insulations

Simulation results show that there is no benefit using combination of different insulation materials at a certain vacuum level, because there insulations require different vacuum levels to make the best thermal performance, unless a vacuum level may be varied during storage.