Experimental Investigation of Cryogenic Chilldown in a Tube Segment

Abstract

This thesis performed precursor cryogenic chilldown experiments with liquid nitrogen for the DLR lead FROST mission (Future-Oriented Research Platform For Orbital Cryogenic Storage Technologies). A test bench was designed and built utilizing upwards vertical flow through a transparent 6 mm tube segment. The outer wall temperature of the tube, the fluid pressure and temperature and flow rate were captured, as well as high speed video of the developing flow regime. From the data captured, the boiling curve for the chilldown process was constructed and discussed. The Biot number is calculated in order to judge the mathematical approach used. Furthermore, the Suratman number is constructed using a void fraction extracted from the video of the flow. Using the Suratman number, flow pattern maps are applied in order to classify the flow regime from the physical parameters and is subsequently validated by a manual visual investigation. The results are discussed in the frame of the literature and compared to previously published experiments. Lessons learned are drawn from the performed experiments and subsequently solutions and remedies for the occurring challenges are proposed. This enables future repetition of the experiments resulting in higher fidelity data. In addition, other aspects of the chilldown process to be analyzed are proposed.