Simulation of the Fast Filling of Hydrogen Tanks

High pressure storage of hydrogen in tanks is a promising option to provide the necessary fuel for transportation purposes. The fill process of a high-pressure tank should be reasonably short but must be designed to avoid too high temperatures in the tank. The shorter the fill should be the higher the maximum temperature in the tank climbs. For safety reasons an upper temperature limit is included in the requirements for refillable hydrogen tanks (ISO 15869) which sets the limit for any fill optimization. It is crucial to understand the phenomena during a tank fill to stay within the safety margins. The paper describes the fast filling process of hydrogen tanks by simulations based on the Computational Fluid Dynamics (CFD) code CFX. The major result of the simulations is the local temperature distribution in the tank depending on the materials of liner and outer thermal insulation. Different material combinations (type III and IV) are investigated. Some measurements from literature are available and are used to validate the approach followed in CFX to simulate the fast filling of tanks. Validation has to be continued in future to further improve the predictability of the calculations for arbitrary geometries and material combinations. 1.0 INTRODUCTION The use of hydrogen as a fuel for passenger cars, buses or trucks requires a safe and optimized method to store a sufficient amount of hydrogen. High pressure storage of hydrogen in vehicle tanks is a promising option. Maus [1] gives a very good overview on most aspects of pros and cons of different tank materials and the experimental investigation including modeling of the high pressure storage of hydrogen. The development of a predictable model to calculate the fill process of a high pressure tank occupies a large part of the work of Maus. Dicken and Mérida [2] describe the setup and results of CFD simulations of some fill experiments they carried out. They demonstrate that the knowledge of the spatial temperature distribution during compression is very important to identify the available margin from a maximum allowable temperature in the tank. In practical applications a single representative probe in the tank has to replace the spatial field of temperatures. A typical task for a model is to find the location where the single probe is close to the mean temperature in the tank. The purpose of this work is to validate a hydrogen tank model developed for the code CFD code CFX against data available from literature and to perform parametric studies. The model may be later used to contribute to the design of new fill experiments at the institute.