Experimental and Theoretical Investigation of Phase Separation through Screen Channel Liquid Acquisition Device in Earth’s gravity and Microgravity

Technological advancements in propellant depots and the ability to refuel spacecraft in orbit can unlock immense opportunities for deep-space exploration. Rather than being constrained by a launch vehicle’s lift-off capacity, mission durations can be significantly extended, enabling a more cost-effective operational approach. However, transferring liquid in microgravity is a complex process influenced by various factors. One critical challenge is achieving effective phase separation to ensure gas-free removal of liquid from the supply tank for transfer. In the absence of gravity-driven phase separation, microgravity conditions require specialized Liquid Acquisition Devices (LADs) designed for efficient and reliable liquid extraction during longduration storage.
Among various LADs, the Screen Channel Liquid Acquisition Device (SCLAD) is recognized as highly reliable for long-duration propellant storage and transfer, making it particularly well suited for depot applications. SCLADs effectively manage complex fluid dynamics, providing steady, gas-free liquid flow and accommodating higher flow rates without gas ingestion. Their robust performance and extensive flight heritage spanning over five decades with both storable and cryogenic liquids, make them a promising solution for propellant management in orbital depots. This thesis specifically investigates the performance of SCLAD, emphasizing key phenomena such as pressure drop through the screen and bubble breakthrough.
The research presented in this thesis is application-oriented, aiming to enhance the fundamental understanding necessary for developing future in-orbit refueling technologies. A comprehensive experimental and analytical study was conducted on the phase separation behavior of the SCLAD under normal gravity and microgravity conditions using the ZARM drop-tower facility. This work is part of the Zero Boil-Off Tank Filling and Transfer (ZBOT-FT) project, designed to investigate in-space refueling by transferring liquid from a supply tank through a transfer line into a receiver tank. The primary focus was on examining the performance of the SCLAD, specifically flow through screen pressure drop, bubble point breakthrough, and changes in the wetted-screen area under various operational conditions. All experiments utilized HFE-7500, a similitude storable test fluid, under controlled isothermal conditions.
In the ground experiments, three different DTW screens were tested to compare their phase separation capability at various volumetric flow rates. These tests highlighted the influence of pressure drop components, including hydrostatic pressure and screen resistance, on phase separation near critical conditions. Drop tower experiments extended this investigation to microgravity conditions, exploring interactions among liquid reorientation, capillary rise between parallel plates, pressure drop across the screen, and wetted screen area dynamics, particularly focusing on bubble point breakthrough at different flow rates. Analytical models complemented the experimental findings by quantifying critical parameters and providing theoretical predictions. This integrated approach provides a thorough assessment of SCLAD performance, essential for the design of future space-based propellant depots.