3 ms·

It's all down to the Reynolds number, which relates viscosity ('sluggishness' of the fluid) n, length scale L and speed v. Re = v*L/n; if this number is low, st

It's all down to the Reynolds number, which relates viscosity ('sluggishness' of the fluid) n, length scale L and speed v. Re = v*L/n; if this number is low, stuff "happens slowly", if large, stuff "happens quickly". So if you scale things up, making L larger, you can get fluids that we usually think of as "slow" to act like they're "quick". Like magma: very sticky, but a big enough lava flow can outrun a car. <insert standard disclaimer about handwaving in above comment>

daveguy 10y ago
I wonder how large the pitch drop experiment would have to be before it produced continuous visible flow at room temperature. https://en.m.wikipedia.org/wiki/Pitch_drop_experiment https://en.m.wikipedia.org/wiki/Pitch_drop_experiment
- semi-extrinsic 10y ago
  Interesting question. It depends of course on the combination of how restrictive the nozzle is (as compared to the width of the column above), and the height of the pitch above the nozzle. If you take the geometry of the pitch drop experiment as fixed, varying only the radius (of both nozzle and column), keeping the pitch height constant, I believe that problem can be solved. Will think about it.
- semi-extrinsic 10y ago
  To clarify the question: do you mean that the flow is such that you can clearly see motion, or that the stream of pitch flowing down does not break up into droplets? (The latter depends also on surface tension, the former does not.)
  - daveguy 10y ago
    I was thinking such that there is sufficient flow to see motion (say 1 mL/min). I think the boundary between droplets vs continuous flow is a more difficult problem.
semi-extrinsic 10y ago
Also, as someone in fluid dynamics, I find it interesting that this student project is featured in the NY Times. I mean, it's not trivial, but it's certainly less work and less interesting/innovative than e.g. what the average PhD student produces. Would it have been in the NY Times if someone at a less prestigious university, led by a less well-connected advisor, had given this project? Somehow I doubt it.
- csours 10y ago
  Its also a popular culture reference. Some grad student somewhere is making a discovery about paint that will eventually make Behr a lot of money, but we won't hear about it until the commercials, and maybe not even then.
- davidf18 10y ago
  It paints a bizarre picture of people running from and being killed by waves of gooey, molten sugar, hence a story of interest to the general public, yet one based in science and engineering.
  - bcaulfield 10y ago
    There's an old saying in journalism "if it bleeds it leads." Holds true even in science coverage, and even at the New York Times.
- aaron695 10y ago
  > but it's certainly less work and less interesting/innovative than e.g. what the average PhD student produces. It kinda sounds like you think work alone should be rewarded rather than outcome? If PHD students create useless reports after a lot of work then that's their issue. Creating busywork to justify a PHD seems a flawed process. If PHD students create scientifically great reports then that has no place in the NYT, it's place is in scientific magazines. If no one has modeled this before (very surprising if true) then this is very interesting news, and pretty good science to boot.

daveguy 10y ago

I wonder how large the pitch drop experiment would have to be before it produced continuous visible flow at room temperature. https://en.m.wikipedia.org/wiki/Pitch_drop_experiment https://en.m.wikipedia.org/wiki/Pitch_drop_experiment

semi-extrinsic 10y ago
Interesting question. It depends of course on the combination of how restrictive the nozzle is (as compared to the width of the column above), and the height of the pitch above the nozzle. If you take the geometry of the pitch drop experiment as fixed, varying only the radius (of both nozzle and column), keeping the pitch height constant, I believe that problem can be solved. Will think about it.
semi-extrinsic 10y ago
To clarify the question: do you mean that the flow is such that you can clearly see motion, or that the stream of pitch flowing down does not break up into droplets? (The latter depends also on surface tension, the former does not.)
- daveguy 10y ago
  I was thinking such that there is sufficient flow to see motion (say 1 mL/min). I think the boundary between droplets vs continuous flow is a more difficult problem.

semi-extrinsic 10y ago

Also, as someone in fluid dynamics, I find it interesting that this student project is featured in the NY Times. I mean, it's not trivial, but it's certainly less work and less interesting/innovative than e.g. what the average PhD student produces. Would it have been in the NY Times if someone at a less prestigious university, led by a less well-connected advisor, had given this project? Somehow I doubt it.

csours 10y ago
Its also a popular culture reference. Some grad student somewhere is making a discovery about paint that will eventually make Behr a lot of money, but we won't hear about it until the commercials, and maybe not even then.
davidf18 10y ago
It paints a bizarre picture of people running from and being killed by waves of gooey, molten sugar, hence a story of interest to the general public, yet one based in science and engineering.
- bcaulfield 10y ago
  There's an old saying in journalism "if it bleeds it leads." Holds true even in science coverage, and even at the New York Times.
aaron695 10y ago
> but it's certainly less work and less interesting/innovative than e.g. what the average PhD student produces. It kinda sounds like you think work alone should be rewarded rather than outcome? If PHD students create useless reports after a lot of work then that's their issue. Creating busywork to justify a PHD seems a flawed process. If PHD students create scientifically great reports then that has no place in the NYT, it's place is in scientific magazines. If no one has modeled this before (very surprising if true) then this is very interesting news, and pretty good science to boot.