Supersonic CO2 flow during champagne cork popping | Hacker News Reader

Supersonic CO2 flow during champagne cork popping

aip.scitation.org

49 pointsgoatsneez25 comments

The conditions to reach sonic flow are surprisingly modest!

It's fully characterized through the pressure ratio between high-pressure reservoir (here: inside of bottle) and low-pressure surroundings, and a parameter characterizing the molecular structure, the isentropic exponent.

For diatomic molecules (our air), the isentropic exponent is 1.4, and the critical pressure ratio at which Mach 1 will be reached is ~0.5, i.e. as long as the high pressure is twice as high as the surrounding pressure, the flow will reach the speed of sound. For more complex molecules the isentropic exponent approaches 1.1, and for steam 1.14, with a critical pressure ratio of ~0.58.

I.e. when you release air from a >2 bar (30psi) car/bike tire, you have sonic flow right there!

Fascinating... I would like to subscribe to your newsletter!

Haha, thanks! Let me think about this! ;-)

Unfortunately this seems to be well beyond what the human lungs can do. I found this paper https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1501025/ suggesting that the most human lungs can do is about 1 meter of H20, or about a 0.1 bar. So it seems supersonic whistling isn't possible. Oh well.

I swear my ears beg to differ at the tones some people can reach, ow.

supersonic, as in whip crack or jet plane sonic boom, no.

ultrasonic, frequencies beyond the range of most human hearing, most certainly yes.

You can create audible shockwaves, like the crack of a whip or a sonic boom, easily with your hands. It's called 'clapping'.

Related: "Ophthalmologists warn: Flying champagne corks cause serious, blinding eye injuries each year" [0]

[0] https://www.sciencedaily.com/releases/2012/12/121217091015.h...

To prove your point, it can happen to the best. This was May 17th: https://www.eurosport.com/cycling/giro-d-italia/2022/biniam-...

switches vpn to the uk...

The PDF (free, linked in the page) has nice photos of the popping in page 8 and graphics of the simulation in page 11 and 12.

Here is a similar visualisation from Phantom using Schlieren:

https://youtu.be/kEw2msVaVy0

Ooh - Figure 4 of the linked PDF shows temperatures as low as -120 Celcius! And thats from a champagne pressure of just 4 bar.

Does that imply that a carefully shaped and designed nozzle, combined with slightly higher pressures, attached to a regular air compressor could be used to make liquid nitrogen?

It's amazing how often effects go to supersonic speeds in everyday life. It really makes sense why our hearing is logarithmic, otherwise we'd all be deaf just from a cork popping.

These are some very smart academics who have figured out how to get their institutions to fund their parties, and probably became very popular in their social circles

Plausible candidate for an Ig Noble Prize!

https://www.researchsquare.com/article/rs-1273542/v1

The end of a whip is supersonic when it “cracks”. It is thought that when towels are “popped” they too can be supersonic at the tip end.

Sounds like Oasis lyrics

I can't be the only one wondering this...

How many bottles of champagne were purchased for this research, and what was done with their contents afterwards?

> Computational Fluid Dynamics (CFD) simulations revealed the formation, evolution and dissipation of shock wave patterns during the first millisecond following champagne cork popping.

Probably not many, maybe even none.

Considering they have actual pictures of the cork popping, it's safe to say that they purchased at least one bottle of champagne.

They seem to have done measurements at different temperatures, so we can nudge the lower bound higher.

They also said they used transparent champagne bottles... Did they use Cristal for this? Now I really want to know what happened to the champagne! Although Cristal at 30 C may not be ideal to drink...

And what was their budget?

This is cool, but thank some higher power I decided against getting a masters / PHD. Imagine years of your life dedicated to understanding how a champagne cork explodes. Nightmare material.

Clearly you've made the right decision for yourself, but this is unironically the dream for some other people (a very specific type of person, I'll admit, but this type happens to include me and half the HN userbase).

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