Fundamentals of Liquid Hydrogen

The Phases of Hydrogen Based on Vapor Pressure and Temperature [1]

The concept of operations for a mobile application dictates the design of ground support and onboard LH2 systems. Typical key operations include conditioning, fueling, standby storage, pressure control, variable feed rates, refueling, defueling, purging, inerting, and various maintenance activities.

Cryogenic fluid management of the hydrogen temperature, pressure, and phase conditions are critical during all of these operations. Thermal environments imposed on a mobile LH2 system vary depending on the operations underway, system design, and local natural conditions.

Solar flux and surrounding air or water temperatures and velocities drive heat loads from the environment. Additional heat loads to onboard LH2 systems come from warmer structures and penetrations via thermal conduction, and surrounding temperature boundaries via noncontact thermal radiation.

Transient heat loads are also imposed by any internal heat exchangers and thermal soak back from operating fuel cells, engines, or other sources [2].

[1] Image source: Liquid Hydrogen Systems Course, 2025.
[2] Text source: Decarbonizing Mobility with Liquid Hydrogen, SAE Research Report EPR2024015, 2024.

Matt Moran is the Managing Member at Moran Innovation LLC, and previous Managing Partner at Isotherm Energy. He's been developing power and propulsion systems for more than 40 years; and first-of-a-kind gas, slush, and liquid hydrogen systems since the mid-1980s. Matt was also the Sector Manager for Energy & Materials in his last position at NASA where he worked for 31 years. He's been a cofounder in seven technology-based startups; and provided R&D and engineering support to many organizations. Matt has three patents and more than 50 publications including his online Cryogenic Fluid Management guide and Decarbonizing Mobility with Liquid Hydrogen SAE report. He has created and taught liquid hydrogen courses, webinars, and workshops to global audiences.