NASA: Capillary Cup
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Leonardo da Vinci observed Capillary Action making him remark that the paint brush was a gift from the gods. He rightfully observed paint brush has an unnatural, given our understanding at the time, attraction for paint. If you place the brush in a cup of paint, and come back some time later, the brush will have _pulled_ the paint into itself noticeably above the surface of the paint in the cup.
It wasn't until the early 1800s that we had the early versions of the Young-Laplace equation which attempted to quantitatively explain the phenomenon.
Fast forward to 1900, Albert Einstein's first paper was still exploring Leonardo's paint brush: https://web.archive.org/web/20171025203011/http://gallica.bn...
The wikipedia entry reminds me that this world is full of magic and wonder, everywhere you look. Something as simple as a paintbrush can reveal something peculiar that takes generations of study by the brightest of human minds to try and explain.
Go outside and turn over a rock, any rock, and there is a lifetime of wonder and mystery under it.
And, just because we can explain it now, doesn't mean Leonardo's paint brush isn't magic. It just means that the magic is real.
Apparently the thinning spout shape sucks up the glob of liquid into it by way of capillary action, with the dual benefit of making the glob stay inside the cup despite it being open, while also making it available for slurping at the edge.
Very cool.
I think it works because the narrowing channel has increasing surface area to volume ratio, as you proceed toward the spout, so the capillary forces pull along a gradient toward the spout, gently tugging the liquid toward it.
The bowl of the cup is lightly pinched around the brim to provide a kind of barrier to prevent the globule of zero-g liquid from just floatin' away! Hahaha :)
But, for exactly the same reasons, this thing is probably a pain to clean. Sharp corners and cleaning don't mix. That narrow seam will likely become caked in the dried residue of a hundred previous drinks. Even in an earth dishwasher, soap scum would be difficult to rinse out. I suspect these are not used many times.
On the other hand, without gravity there is convection, which means those corners probably don't dry out as quickly. If I'm right about that then rinsing left-over residue out with plain water is easier if you don't wait too long.
I dunno, given the size I imagine a regular toothbrush could dislodge anything dried, and small sponge-on-a-stick could get it acceptably dry.
It's also worth asking what it might replace: On the ISS do they clean any drink-pouches, or are they all treated as disposable? I imagine that they become trash, since the next drink (or dehydrated drink-to-be) was probably already shipped in its own flattened pouch.
The first analysis of the effect I know of is a paper by Concus and Finn (1969) [2], who realized that fluid can be carried arbitrarily high in a triangular groove, even against gravity, and proposed that trees may use this mechanism to carry water to their highest reaches. (The catch is that the fluid front becomes thinner and thinner as it gets higher. And it starts breaking down when it gets so thin that the continuum limit no longer applies).
If you like math, I'd highly recommend checking out Mark Weislogel's research [3] which deals with the dynamics of viscous flow in triangular grooves.
Shameless plug: chapter 4 of my Ph.D. thesis [4] gives an introduction to the subject.
[1] http://www.pmdtechnology.com/PMD%20Physics.html
[2] https://doi.org/10.1073/pnas.63.2.292
[3] https://scholar.google.com/citations?user=rNOJ49QAAAAJ
[4] https://theses.hal.science/view/index/identifiant/tel-040155...
Donald Pettit is tugut mang fo wa Earther. Oye, Beltalowda!
(note: im referring to the physics of said 2 objects and how they keep liquids in. this isnt some bad sexual joke in jest.)
IIUC spilling liquid in zero-gravity is extremely dangerous.
When you spill on earth, it falls to the floor.
When you spill in space, it floats around and globs up. Then that glob is attracted to, and sticks to, anything that’s hydrophilic. Which happens to include you. More alarmingly, your face.
If I remember correctly there was a recent incident where an astronaut’s dehumidifier in their suit gave out, and they almost drowned in the water being released from their own body (breath, sweat, etc)
Speaking of, how do they manage smells up there? Is "ISS smell management" someone's job at NASA?
https://www.space.com/international-space-station-smells-eur...
> Do you make it in the mug, or do you pour it into the mug after you make it?
The difference is that I make it. On the space station, their beverages are pre-made and pre-packaged. You can see the bags in the linked article.
> Why not pour it into a thermos?
Huh? I generally drink out of a mug, not a thermos, but I've used thermoses as well. Again, this situation is different because I generally make my coffee. It's not pre-made and prepackaged.
> And why don't you exclusively drink prepackaged coffee?
Again, huh? Because the coffee I buy comes as beans. I have to add water, heat it up, etc. I sometimes I drink pre-made coldbrew and I do often drink that out of the package it comes in (the bottle/can).
1. Packets filled with essentially instant coffee that they add hot water to: https://www.youtube.com/watch?v=PvIT3l9QYnQ
2. An espresso machine similar to a pod-based system. Fairly like an espresso machine on Earth since it relies on pressure. https://www.npr.org/sections/thesalt/2014/07/08/328130351/wh...
Principals like this are used in fuel/liquid handling in space already to make sure your tanks aren't pure chaos and your pumps don't run dry. A lot of rockets just do ullage burns with different motors to settle their fuel into the bottom of tanks but that's not possible for all fluids if you need to have them moving continuously or can't do burns just to settle them.
1/ is hard to build in space (big pieces that need to be assembled)
2/ needs to be big enough not to make everyone sick (the diameter must be quite large for the gradient of gravity not to be too noticeable)
3/ Not very useful when one of the main points of having a space station is to do ~zero g experiments
One Revolution per Minute [video]
(254 points, 155 comments)
Although you can by the NASA flight-certified version for the low low price of $650
So, if one wanted to make a capillary cup for custard, it'd be different dimensions? Would love to see a parametric version of this (OpenSCAD?) somehow that can be generated for different liquids ...