Two-Phase Flow Instabilities in Liquid Hydrogen Flow Systems

Autonomous vehicles (AVs) require a large amount of power for propulsion and computing. Liquid hydrogen (LH2) in conjunction with high-efficiency fuel cells is a potential option to power AVs providing a high energy density by mass. Two-phase flow instabilities present a challenge in the flow systems that would be needed to re-fuel AVs. Pressure drop oscillations (PDO) are one of the most prevalent instability types in flow boiling systems[KM1] . For LH2 systems PDO can cause large fluctuations of system variables. Large fluctuations increase strain on systems and lead to unstable flow. Lumped-element modeling of PDO in two-phase hydrogen flow is undertaken to evaluate the instability characteristics in liquid hydrogen systems. A non-trivial consideration is the non-monotonic steady-state pressure drop in the two-phase flow regime. PDO occurring in the negative slope region of this curve is sensitive to the system components, such as an orifice. Pressure drop and mass flux phase graphs and time-domain evolutions of the system variables are generated to understand what conditions will cause PDO to occur, as well as the amplitude and frequency of the oscillations.