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I would like to essentially flatten or smooth the surface of a viscous liquid after dropping an object into it, without actually touching the liquid. For example, if I drop a rock into a tub of oil, I need the oil to move into the void and return to having a smooth surface as fast as possible.

It seems that I need to create some sort of force that acts against the liquid surface from above, or a force from the sides that acts as a kind of 'wiper' to smooth it out.

I have looked into using ferrofluids and electromagnets on the sides or bottom of the liquid vat/container, however many demonstrations I have seen result in a 'spiky' surfaces when magnets are brought near the liquid due to non-uniform field lines.

I have also looked into trying to suspend diamagnetic nanomaterials in the liquid which could be repelled by a magnetic field from above the vat, however I'm not sure about whether diamagnetic materials exist which would could be used like ferrofluids in the sense of staying suspended in the liquid.

My job depends on being able to do this, so if anyone has any ideas I'd really appreciate hearing them.

706Astor
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user88720
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1 Answers1

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Some quick dimensional analysis for a Newtonian fluid suggests that the settling time scales as follows:

$$\tau = \sqrt{\frac{L}{g}} f\left(\frac{\nu}{\sqrt{g L^3}}\right)$$

where $\tau$ is the time it takes for the liquid surface to settle, $L$ is some characteristic length of the dropped object (say, the diameter of a ball), $\nu$ is the kinematic viscosity, and $g$ is the acceleration due to gravity. I expect the function $f$ to increase as the parameter inside it increases, which makes sense. The higher the viscosity, the slower the settling, and the stronger the gravity, the faster the settling.

So, influencing these parameters in some way could help. Unfortunately, you have no control over these parameters aside from the viscosity, which you might influence via heating.

An oscillation applied to the container could help smooth things out. The speed by which this occurs surely is strongly dependent on the viscosity for a Newtonian fluid. For a non-Newtonian fluid (say, peanut butter), I'm not sure this will necessarily work.

I also imagine an air jet applied parallel to the surface could help, depending on the viscosity, especially if its direction is varied. Targeted jets striking at an angle to the surface might help too, but this could require a complicated control system or manual human intervention to do the targeting.

Suction applied directly above the hole may help, again, depending on the viscosity.

(After writing this, I noticed Chuck said some similar things in the comments. He also recommended a centrifuge, which I didn't think of.)

Ben Trettel
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