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Bremen, Germany

Reichel Y.,Am Fallturm | Dreyer M.E.,Am Fallturm
Microgravity Science and Technology | Year: 2014

In upper stages of spacecrafts, Propellant Management Devices (PMD's) can be used to position liquid propellant over the outlet in the absence of gravity. Centrifugal forces due to spin of the upper stage can drive the liquid away from the desired location resulting in malfunction of the stage. In this study, a simplified model consisting of two parallel, segmented and unsegmented disks and a central tube assembled at the center of the upper disk is analyzed experimentally during rotation in microgravity. For each drop tower experiment, the angular speed caused by a centrifugal stage in the drop capsule is kept constant. Steady-states for the menisci between the disks are observed for moderate rotation. For larger angular speeds, a stable shape of the free surfaces fail to sustain and the liquid is driven away. Additionally, tests were performed without rotation to quantify two effects: the removal of a metallic cylinder around the model to establish the liquid column and the determination of the the settling time from terrestrial to microgravity conditions. © 2014 Springer Science+Business Media Dordrecht. Source


Schmitt S.,Am Fallturm | Dreyer M.E.,Am Fallturm
Cryogenics | Year: 2015

Experiments were performed to investigate the reorientation behavior and axial sloshing of liquid parahydrogen in a partly filled right circular cylinder due to a step reduction of gravity. Different temperature gradients along the cylinder wall in vertical direction were imposed to examine the influence of a wall superheat on the free surface. Experiments were conducted in the drop tower at the University of Bremen which provides a microgravity time of 4.7 s and a compensated gravity environment of 10-6 g0 (acceleration due to gravity). The thermal preparation of the experiments allowed to create defined wall temperature gradients and a stratified or homogenous liquid temperature distribution. Several sensors along the cylinder wall and in the vapor region monitored the temperature. The pressure inside the experiment was recorded and visual access was enabled by an endoscope. The experiments showed that the wall superheat has an influence on the free surface as well as on the temperature and pressure evolutions. © 2015 Elsevier Ltd. All rights reserved. Source

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