Experiments on Cryogenic Chilldown of a Tube Segment

Kurzfassung

This Master thesis is dedicated to the continuation of the test stand at the German Aerospace Center in Bremen, which investigates the cryogenic chilldown process. The aim is to carry out demonstrative experiments for cryogenic tests in orbit and to check the repeatability and comparability with the literature. The test setup is based on a borosilicate glass tube segment with an inner diameter of 6 mm, through which liquid nitrogen flows vertically in an upward direction. Temperature, pressure and video data describing the chilldown are recorded for analysis. For comparability, a test procedure and a test matrix are created that vary the pressure differences between the cryostat and the back pressure and therefore regulate the mass flow. The results are processed analysed to show that the different boiling regimes and characteristics like the rewetting at the Leidenfrost point and the critical heat flux are recognisable and reproducable in a realistic margin. The flow is analysed and predicted using the flow patterns and dimensionless numbers, which are compared with the video data, validating the predictions as accurate. The results are then used to calculate coefficients of common correlations and analyse their applicability, showing, that some correlations give promising results. In addition, the resulting boiling curves are compared and categorised with comparable experiments from the literature. The thesis shows that the test setup provides realistic and repeatable measurement data, which will enable future experiments to improve the understanding of chilldown.