Microgravity Fluid Physics

In general, the forces imposed on liquids govern flow conditions, in which certain properties of the liquid and interface may dominate the net force applied, such as cohesion and capillarity. Spacecraft system designs involving liquids should take into account these passive forces in microgravity, especially for liquid-solid-gas interfaces. The boundary conditions for multiphase operations may be critical design factors.

Space Lab® researches passive fluid flow in microgravity with the goal of developing systems with lower Equivalent System Mass (ESM), especially reducing resource utilization, and higher robustness for all system states.

Below is an example simulation of a water droplet inside an interior corner geometry (or wedge), which is used to investigate the contact angle, γ, with respect to corner angle, 2α. For capillary behavior in a wedge, Concus and Finn (1969) provided the relationship

α + γ < π / 2

Analysis with Surface Evolver Fluid Interface Tool (SE-FIT®)

Space Lab® currently investigates this interior corner geometry for 1) water and nutrient delivery for space crop production systems and 2) for passive collection in condensers. These interior corners not only allow passive liquid flow by the capillary force, but also act as a passive phase separator allowing the separation between liquid and any entrained gases from the process.

In addition to analytical verification, Space Lab® conducts prototype testing via drop towers and flight tests furthering the fidelity and viability of the design.

Microgravity Investigation of Thin Film Hydroponics (MITFH)

Space Lab® is very excited to test the μg-Lilypond™ water transport loop and harvester technology on an upcoming sub-orbital technology demonstration flight. This flight will test the effects of microgravity on water transport and plant harvesting in the µg-Lilypond™ growth chamber.

The Space Lab® team will observe water traveling through capillary-driven growth beds with different flow paths, a stable water film resting on the beds, water lentil transport from the beds into a harvester, and finally biomass-effluent separation during plant harvest. This flight will also allow the team to observe the mechanical interaction between water lentils and the nutrient solution when in microgravity.

Space Lab Flight Opp Team (2020)

A sub-orbital flight trajectory provides a few minutes of microgravity, which is enough time to observe the complete water loop operation. The team will use high definition video cameras to visually observe fluid and plant behavior and to measure flow rate through the growth bed capillary channels.

Follow us on Twitter and LinkedIn for more updates about Space Lab's flight opportunity.

Drop Tower Investigation

In December 2019, Space Lab® along with University of Colorado, Boulder (CU) team members conducted experiments at the Portland State University Dryden Drop Tower, to understand microgravity effects on a capillary-fed growth bed. Tests investigated the effects of bed material, manufacturing method, and capillary channel geometry on passive capillary flow into interior corner channels.

Drop Tower Testing at Portland State University Dryden (2019)