Hydrogen as an energy source is a promising solution for sustainable andCO2-neutral mobility. The storage of hydrogen as a fuel is an important basis for this. High-pressure tanks are already being used in some applications and are being continuously developed further. For aerospace applications, the storage of hydrogen in liquid form (LH2) is an interesting solution due to its high energy density .
The development and use of storage systems for liquid hydrogen in aircraft is associated with a variety of challenges. A key requirement for such hydrogen storage systems is to be as lightweight as possible. Carbon fiber-reinforced plastics (CFRP) are an obvious choice here. However, their material behavior at such low temperatures (-252 °C!) has not yet been sufficiently researched. The effects of thermal expansion in particular make a robust design difficult. The tank structures and their supply connections must be leak-proof under all filling and temperature conditions and over the entire service life of the structure. Furthermore, suitable production technologies for these materials with sufficient industrial maturity are required and may still need to be developed. These and other requirements and aspects influence each other. This makes the development process complex, time-consuming and expensive.
Structure
To speed up the development process, our institute has developed several test technologies along the test pyramid. One of these is the half-tank test, which enables testing under realistic conditions. This test rig thus offers a generic test option for developing analysis methods and verifying new structural concepts. The test setup is based on a half tank, or half tank for short, with a diameter of 400 mm and an arbitrary dome contour. The object of investigation is precisely this dome area and a length of 200 mm into the cylindrical area. The half-tank test specimens are clamped in a pressure vessel designed for pressures of up to 20 bar and a possible bursting of the tank. The clamping seals the half tank to the container wall and thus separates the tank volume from the outside atmosphere. A displacement body inside the half tank efficiently reduces the required test volume. Cooling channels, a heat shield and baffle plates ensure that the thermal boundary conditions are maintained. Several pipe connections allow both the setting of vacuum conditions in the tank and the printing of the tank. The volume of the half tank can be filled with either gases (nitrogen, hydrogen, helium, etc.) or cryogenic liquids (liquid nitrogen, liquid hydrogen). At the same time, the concept enables the use of various sensors. Windows in the tank wall of the test stand allow visual inspection of the half-tank test specimen.
Main areas of investigation
One focus of the investigations is the measurement of the permeation or leakage behavior of the half-tank system. Internal pressurization with helium while maintaining a vacuum on the outside makes it possible to determine how much helium flows through the tank wall. Such tests can be carried out for various systems. For example, new production or joining technologies can be researched close to the application and the corresponding leakage properties measured. Load conditions can also be varied as a result of different thermal conditions and different pressure levels. A comprehensive sensor system measures the temperature distribution and deformations. The test stand is also designed for a possible bursting of the half tank and thus also allows the investigation of damage mechanisms and the associated influence on the leakage behavior. The possibility of filling the half-tank with liquid hydrogen represents a realistic test scenario. The results form an excellent experimental basis for investigating the behavior of such tanks and for validating simulations of the aforementioned load scenarios.
