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Description
For the next-generation of aircraft, cryogenic liquid hydrogen (LH2) is a front-running option for serving as propulsion fuel due to its high gravimetric energy density. However, significant advances in terms of LH2 storage and distribution need to be established to have LH2 as a viable option of aircraft propulsion fuel. Advanced thermal management of an LH2 tank is crucial, since boil-off can result in significant loss of aircraft flight range. To reveal the thermal behaviour of the LH2 tank during operation, in this paper, we present the thermal modelling performed in the COCOLIH2T-project. A generalised thermal model has been set up, usable for any LH2 tank size. With this model, tank operation modes like cold refuelling, warm refuelling, defuelling, and dormancy are simulated. The core of the simulation model is based on the pressure-enthalpy characteristics of parahydrogen, simulating the LH2 stored in the inner tank as a single node. The main thermal insulation of the LH2 tank architecture considered is a vacuum insulation with MLI used as radiation barrier between outer and inner tank. Furthermore, the thermal connections between outer tank and inner tank have been characterized thermally.
For the refuelling model, the thermal masses of the composite structure, MLI, and inner-to-outer-tank spacers were accounted for. A boiling characteristic was determined to simulate the interaction between the liquid/vapour-mixture of H2 with the composite inner tank. The Leidenfrost effect significantly affects this boiling behaviour at the wall, and therefore has a strong effect on the thermal cooldown time of the inner tank during the warm refuelling process.
The tank internal pressure was analysed, such that during defuelling operation, the pressure inside the tank remains within practical bounds, i.e. not too high due to structural integrity, and not too low to sustain outflow of LH2 towards a low-pressure sink. The pressure can be elevated by supplying ambient temperature, high pressure GH2 to the inner tank.
Additional simulations on the behaviour of LH2 have been carried out, revealing the effects of boil-off and sloshing on the transient thermal management of the tank.
The models presented in this paper serve as general models for the purpose of revealing the thermal behaviour of a vacuum- and MLI-insulated LH2 tank. For the COCOLIH2T project specifically, the design considered has an inner tank volume of 1100 L, with a heat leak budget of 40 W. The simulation models enable this tank design to progress towards a TRL4 demonstration of the LH2 tank in a ground-based test rig. The TRL4 demonstration will eventually serve as the final milestone of the project.
| Submitters Country | Netherlands |
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