Experiments for cryogenic fuel handling require a wide range of instruments with sensors in order to capture all the relevant physical quantities and effects. The aim is to obtain a detailed and empirical insight into temperature distribution, phase transitions (liquid-gas), fill levels and free liquid surfaces, as well as sloshing. This also enables a comparison to be made with computer simulations (CFD, Computational Fluid Dynamics) and for the computer code used to be validated.
The Department of Transport and Propulsion Systems is therefore also responsible for the testing of new sensor principles in cryogenic liquids. In collaboration with universities and industrial partners, the following topics are being researched:
Tests are conducted in liquid nitrogen (LN2) at -196 °C, as well as liquid hydrogen (LH2) at -252 °C.
Glass fibre sensors enable the 'distributed' gathering of temperature fields. With a single fibre, a variety of measuring points can be carried out, such as the temperature distribution found for example in a cryo-holder filled with hydrogen. Sensors based on Rayleigh backscattering and fibre Bragg gratings are used in this process.
View through an optical glass fibre bundle of a foil heater in liquid nitrogen.
Optical glass fibre bundles provide an insight into experiment tanks without the need for an access window or camera in the holder. The image is transferred by approximately 105 bundled optical fibres. The bundle and its field of view can be easily positioned prior to the cooling down process.
Mittels Elektrischer Kapazitätstomographie und Ultraschalltomographie werden Gasblasen, Gasströme sowie Füllstände in der kryogenen Flüssigkeit quantitativ erfasst.
Using electrical capacitance tomography and ultrasonic tomography, gas bubbles, gas flow and fill levels can be quantified in the cryogenic liquid.
DLR is leading some of the work that is carried out as part of the ESA TRP project, CryoSense (Advanced Measurement Technologies for Cryogenic Flows in Reduced Gravity), in collaboration with its partners ISAT (Institute of Sensor and Actuator Technology at Coburg University) www.isat-coburg.de/, the Chair of Measurement and Control Technology at Universität Bayreuth http://www.mrt.uni-bayreuth.de/de/index.html, as well as Airbus Defence and Space.