Tuning hydrogen boil-off via inert gas insulation purge in a vapor cooled shielded fuel tank

Abstract

Vapor cooled polymer composite tanks for liquid hydrogen are a newopportunity for light weight power-system integration into unmanned aerial vehicles. Vapor shielding has the ancillary benefit of pre-conditioning the hydrogen for use by a fuel cell. However, the mass flow rate required by a fuel cell should be matched by the natural boil-off rate of the tank. With limited ability to vary insulation thicknesses, the challenge becomes satisfying the fuel cell consumption in UAVs at different mass flow rates when at varying stages of flight from take-off, cruise, and landing. This paper provides experimental measurements of mass flow rate of hydrogen from the tank considering batch purging with helium or argon in the vapor cool shielded insulation layer. A 5-shell vapor cooled shielded tank is used with two layers of insulation including aerogel, helium or argon, and two vapor channels. A more complete understanding of system-level thermal conductance is determined by mass flow of hydrogen leaving the tank during hypothetical flight.