Interesting Fact
May 2024
Interesting Fact: Behavior of Liquids in Space
Here on Earth, we all live in a state of gravity. Not only us, but everything around us, including water, is being pulled towards the center of the planet by gravity. True, it is nice that our dogs don’t float off into space, but when a child drops their ice cream (which is full of water, by the way) they don’t have to know about gravity to be upset. But, if you go far enough out in space, for instance to the International Space Station, gravity becomes negligible, and the laws of physics act differently than here on Earth. Just how might water act in a place of zero gravity? The photograph below of the water drop and air bubble gives you a good idea of how differently water behaves when the effects of gravity are counteracted
This unique picture shows not only a water drop but also an air bubble inside of the water drop. Notice they both behave the same….according to the laws of physics in space. They both form spheres. This makes sense, as without gravity to tug downward, the forces governing the objects are all the same. So, the water drop (and air bubble) form themselves so they occupy a shape having the least amount of surface area, which is a sphere. On Earth, gravity distorts the shape, but not in space.
Consider what would happen on Earth: The air bubble, lighter than water, would race upward to burst through the surface of the droplet. In space, the air bubble doesn’t rise because it is no lighter than the water around it—there’s no buoyancy. The droplet doesn’t fall from the leaf because there’s no force to pull it off. It’s stuck there by molecular adhesion.
Sticky water. No buoyancy. These are some of the factors spacefarers must take into account when they plan their space gardens. If water is sprayed onto the base of the plant will it trickle down to the roots? More likely it will stick to the stem or adhere to the material in which the plant grows. As humans spend more time and go farther out in space in the future, the physics of “space water” will need to be well understood.
Boiling is the conversion of a liquid into vapor. Boiling is used every day to cook food; generate steam to heat buildings or turn turbines; cool electrical generators; purify water; and help convert crude oil into gasoline.
A pot of boiling water is something most of us can picture in our heads. Think about the role gravity plays in this everyday phenomenon. As the water heats, gravity causes the hotter regions of liquid to rise–a process known as “convection”–which distributes heat throughout the water. Once the water heats to the boiling point, the gravity-induced buoyant force sends the bubbles upwards, producing a “rolling boil.”
But this familiar picture changes drastically in a microgravity environment. Gravity-driven convection and buoyancy are non-existent, and without their dominating influence, scientists grow closer to understanding the fundamentals of boiling.
The Boiling eXperiment Facility — Microheater Array Boiling Experiment, or BXF MABE — contains 96 individually controlled microheaters provided both location and time-dependent information to gain better insight into the boiling process. The experiment, which launched on STS-133 in 2011, was a collaboration between the University of Maryland in College Park and NASA’s Glenn Research Center in Cleveland, Ohio. It was one of two experiments in the station’s new boiling facility.
“Boiling is heavily influenced by gravity,” said Jungho Kim, principal investigator for the experiment at the University of Maryland. “The vapor bubble is less dense than its liquid; consequently, it wants to rise through the liquid. By reducing the effect of gravity, it becomes possible to examine other variables, such as how hot the heater is, how warm or cold the average liquid temperature is, and the effect of pressure and surface tension.”
Given our dependence on boiling liquids in food and drink preparation, it is easy to imagine why scientists are interested in studying boiling phenomena. But, beyond the kitchen, boiling is used in many engineering systems as an effective means of transferring heat. Excess heat can be dispelled through the vapor bubbles moving through a boiling liquid. Although boiling figures prominently in the mechanics of heating/cooling systems, power plants, and engines, a better understanding of this phenomenon could lead to more efficient and effective applications.
Pool boiling experiments conducted onboard an orbiting space shuttle provided scientists the first glimpse of boiling in space. In gravity, vapor bubbles form on the heater surface of the liquid and, due to buoyancy, quickly rise to the top. In microgravity, without buoyancy, the bubbles remain attached to the heater surface and continue to grow. As these bubbles grow, the liquid is no longer in contact with the heater surface to cool it down and therefore, the liquid is useless as a heat transfer device. This situation can lead to “dryout” which is the suspected cause of the infamous Chernobyl disaster.
James Bond might be the first to tell you that a well-shaken martini is a vast improvement over one that has settled and separated. A good mixture depends on understanding exactly how much to agitate a drink, as well as how quickly the ingredients will settle and if there are other mediating factors, such as temperature. If Bond really wanted to understand the science of his spirits, he could follow the examples of researchers who sent fluid mixture experiments to the International Space Station.
The Selectable Optical Diagnostics Instrument-Influence of Vibrations on Diffusion of Liquids, or SODI-IVIDIL, investigation addressed the question of fluid physics fundamentals while looking at how heat and particles move through liquids in microgravity. The scientists who conducted the space station investigation from October 2009 to January 2010 were not interested in cocktails, however, but instead wanted to verify current math models to predict liquid mixture behavior.
Researchers knew that studying reduced convection buoyancy – the transfer of heat by movement – aboard the space station could reveal fluid mixture behaviors hidden by gravity in experiments on the ground. Still, they needed to check if there were any side effects from the minor on-orbit tremors, known as g-jitter, such as crew movements or mechanical vibrations that could distort data.
To perform this series of experiments, researchers used the SODI optical instrument, which also helps with other station studies, such as SODI-Colloid. The European Space Agency, or ESA, built the SODI instrument for use aboard the station for fluids research in the space environment. The crew put the IVIDIL sample cells into SODI for processing and observation. The liquid binary solution samples, which are essentially fluids made up of a two-part mixture – similar to if Bond had vodka and water instead of his trademark martini – were then tested for their response to various vibrations.
After 55 repetitions of the experiment, researchers found that only major space station vibrations caused impacts, such as orbital debris avoidance maneuvers or dockings and undockings of spacecraft. The more common minor movements that are part of daily life aboard station did not influence the samples.
So what does this study mean for those of us on Earth, since we are not likely worried about Bond’s quest for the perfect martini in an orbital lounge? These results actually have direct applications to petroleum research.
Data from these space studies may help the oil industry generate formulas to predict correct measurements for the liquid to gas ratio in potential wells. This information aids geophysics and mineralogy experts as they evaluate the capacity of reservoirs – collections of natural resources that lay hidden in the ground. Using these formulas could prevent costly mistakes during exploration, leading to more accurate and affordable speculation.
Many things about liquids that we take for granted on earth can be very different in space. This creates problems for space mission planners. For instance, since It is nearly impossible to lift enough fuel for prolonged missions in one launch, scientists and engineers intend to store fuel and life support liquids, such as oxygen, water and ammonia, in depots in low-Earth, moon, or Mars orbits to provide ‘local’ supplies for longer crewed space flights.
However, for long-term storage in space it is difficult to predict the location of the liquid in the tank when it is time to withdraw it. Orbiting spacecraft travel in a low-gravity environment, due to the forces from the orbital motion balanced with the gravitational attraction of the moon, planet or sun. The resulting nearly weightless state prevents liquids from pooling at the bottom of a storage tank, and makes gas bubble locations nearly impossible to predict.
Engineers previously assumed the worst case, which was that the bubbles would disperse randomly throughout the tank. Such bubbles in the transmission lines would interrupt and interfere with the liquid flow and could lead to equipment failure. To solve this problem, scientists have begun using predictive computer modeling to determine the behavior of the liquid in the container. In one experiment the spacecraft was slowly rotated about its axis every 90 minutes. The slow rotation was enough to move the propellant to the top end of the tank, away from the bottom where the fluid would normally be located in a 1-gravity environment.
“This information is critical when trying to understand where the liquid is going to be located in the tanks,” said Greg Zimmerli with NASA’s Glenn Research Center, Cleveland. “SE-FIT can help determine where the liquid is located, which is critical to propellant management subsystems such as storage, liquid acquisition, and fuel gauging.”
Another problem is the state of liquid water in the vacuum of space. If you throw water out in space, about where we are in the solar system, any water that evaporates off it isn’t going to come back again – it’s a hard vacuum. It’s going to boil away and, as it does, it will get colder. At some point it might freeze,
but eventually it will sublime and turn into a gas. If you did the same thing where it’s very, very cold, out near Neptune or something, then it would just freeze. If you did get a bit of evaporation, it will cool down and freeze and essentially stay there as a lump of ice. If you use different liquids, different things will happen. Things like ionic liquids, they boil away so slowly that you could just have a blob of them which sat around as a liquid permanently.
So, if it’s not going to evaporate then the major force affecting it is surface tension, the only force which is left. So essentially, you get a huge droplet of water which is kind of held together by surface tension that would bobble around and just sit there, a perfect sphere, floating in space until someone drinks it or it hits something.
Thanks and attribution:
https://www.nasa.gov/mission_pages/station/research/news/Predict_Liquid2.html
https://www.thenakedscientists.com/articles/questions/how-do-liquids-behave-space
https://www.physicscentral.com/explore/action/fluids.cfm
https://peterengels.eu/portfolio/james-bond-actor-sean-connery-with-martini/
https://www.nasa.gov/mission_pages/station/research/bxf.html
