Project Summary

The project “Liquid Hydrogen Storage and Thermal Management Systems Technology Demonstrators to Limit Liquid Hydrogen Boiloff for Hydrogen-Electric Aviation” aims to develop and demonstrate innovative technologies for storing liquid hydrogen, managing its thermal properties and performing efficient refuelling operations. This involves building systems that can safely and efficiently store and transfer liquid hydrogen in an airport environment by managing the boiloff challenge. This is a logical step towards ZeroAvia’s ultimate goal of enabling a true zero-emission propulsion technology for aviation and the innovation pioneered in the context of this project could benefit the entire multimodal hydrogen landscape.

Project Achievements

A system architecture, topology, and piping & instrumentation diagram for a hydrogen storage and filling system was developed and formalised with initial concept of operations. Flow transfer characteristics between tanks were analysed in-depth using computational fluid dynamics with Siemens StarCCM. This activity focused on resolving the flow profiles and flow rates during single-phase liquid hydrogen transfer in a straight horizontal precooled pipe with steady turbulent K-Epsilon solver. The systems-level topology was further analysed with MATLAB Simscape Fluids. This activity focused on the systems-level performance analysis during two-phase liquid hydrogen transfer and modeled the tanks, pressure builder, transfer lines, and venting mechanism.

Conclusions

In comparing the CFD modelling results with the Gnielinski pressure loss correlation used in MATLAB Simscape pipe flow models, excellent agreement was found between the two. It was also found that commercially available and relatively inexpensive 1/2″ (or 12mm) transfer lines are able to provide up to 0.167 kg/s mass flow rate in precooled horizontal straight configurations. Full system modeling that included other line losses indicated that a line diameter of 1 inch is more adequate to achieve the target fill-time. Also, to maintain supply tank at 8 bar, the pressure builder needs to have the capacity to vaporize LH2 at a rate of 1.56 kg/min, which is equivalent to 19 kW of heat. These key parameters allow us to build a functional experimental facility that would help validate our models, which in turn can be used in designing LH2 refueling products that enables zero-emission aviation.

Next Steps

Several assumptions have been made during the systems level modelling and CFD modelling of this project. For example, the CFD modelling does not consider transient changes in the tank, or variation in properties. Simscape system modeling uses literature-based assumptions for pressure builder performance and 3D effects in the tank for heat transfer coefficients. Therefore, liquid hydrogen behavior in the tanks needs to be further resolved in a much more detailed CFD campaign to better predict evaporation/ recondensation in the tank to support system level predictions. At this time, the CFD results assume a straight horizontal pipe, and further work should explore the effects of expected bends, turns, and non-horizontal pipe sections in the transfer line. Through detailed tank CFD, vapour and liquid heat transfer coefficients and the effects of geometry, surface roughness, and tank sloshing, etc. can be analysed, and hence are ideal next steps. To further cement the understanding of these phenomena and the behavior of tanks, the pressure builder and the system level 1-D simulation, experimental validation should also be sought.