Naked Science Forum

General Science => General Science => Topic started by: neilep on 27/05/2017 12:42:55

Title: Where Do The Bubbles Come From When A Propeller Propels ?
Post by: neilep on 27/05/2017 12:42:55
Dearest Bubbleologists,

As Sheepy I of course luff making bubbles. Bubbles are my all time favourite thin sphere of globular liquidy thing containing gas etc. I especially lufff making bubbles in the bath though for some reason whomever (whoever versus whomever......I dunno !!) I am sharing da bath with seem to make a hasty exit !!..hmmmmm !!


Take a look at this propeller !....Its making bubbles !!...its NOT doing 'bottom burps'

* bubbles.jpg (31.46 kB . 1280x720 - viewed 5320 times)
Bubbles Being Made JustMoments Ago !!

Where do the bubbles come from ?

You see, I dont know....do ewe ?

Hugs and shmishes


mwah mwah mwah !!

Sheepy
xxxxxxx

It's lewd, it's rude, it's awfully crude
Especially fun when you're in the mood
Brings a laugh when you're in the nude
Flapajack flapajack spray spray spray
Soft or silent blasted any way
Fart, guff, windypop
Never to be done in a crowded shop
 
Blow off, blow off, fart fart fart
Rubacheek, rubacheek it's an art art art
Underneath the bed sheets
Bubbles in the bath
Open up the window
Cuts oxygen by half
 
Rubbery cheeks and stained underwear
There's a fart around
Better beware !
 




Title: Re: Where Do The Bubbles Come From When A Propellor Propels ?
Post by: chiralSPO on 27/05/2017 15:01:56
I believe this is an example of cavitation. (a quick search confirms!) https://en.wikipedia.org/wiki/Cavitation
Title: Re: Where Do The Bubbles Come From When A Propellor Propels ?
Post by: Colin2B on 27/05/2017 15:05:09
The effect is called cavitation. It's a real problem for boat propellers because it causes wear.
As the prop rotates the sudden changes in pressure cause vapour bubbles to form, so no nasty smell.

I'm thinking of experimenting by attaching a sheep to a prop to see if the wool will absorb the bubbles.
Might work, certainly lanolin is widly used as a corrosion inhibitor so maybe we can find a use for other sheepy parts ;D

EDIT - looks like chiralSPO answered while I was typing
Title: Re: Where Do The Bubbles Come From When A Propellor Propels ?
Post by: neilep on 27/05/2017 15:17:41
The effect is called cavitation. It's a real problem for boat propellers because it causes wear.
As the prop rotates the sudden changes in pressure cause vapour bubbles to form, so no nasty smell.

I'm thinking of experimenting by attaching a sheep to a prop to see if the wool will absorb the bubbles.
Might work, certainly lanolin is widly used as a corrosion inhibitor so maybe we can find a use for other sheepy parts ;D

EDIT - looks like chiralSPO answered while I was typing

And where on earth are ewe going to find a sheep dumb enough to help with this empirical study ?

erhmmm...I volunteer !!...DOH !!

ok, so...what is the vapour inside the bubbles ?.....is it  oxygen ?
Title: Re: Where Do The Bubbles Come From When A Propellor Propels ?
Post by: Colin2B on 27/05/2017 15:40:28
ok, so...what is the vapour inside the bubbles ?.....is it  oxygen ?
It's actually water vapour. The pressure increases and then when suddenly released drops below the vapour pressure of the water.
Title: Re: Where Do The Bubbles Come From When A Propellor Propels ?
Post by: chiralSPO on 27/05/2017 16:40:22
Incidentally, there are actually there are actually marine critters that use this phenomenon to hunt! Pistol shrimp ( https://www.wired.com/2014/07/absurd-creature-of-the-week-pistol-shrimp/ ) use their claws to cavitate water near their prey, and the resulting shock wave deals the lethal blow!
Title: Re: Where Do The Bubbles Come From When A Propeller Propels ?
Post by: Colin2B on 27/05/2017 23:08:55
the resulting shock wave deals the lethal blow!
I have heard reports (not a pun) that their shockwave has broken aquarium glass.
Title: Re: Where Do The Bubbles Come From When A Propeller Propels ?
Post by: evan_au on 28/05/2017 12:53:17
Quote from: wikipedia
The bubble eventually collapses to a minute fraction of its original size, at which point the gas within dissipates into the surrounding liquid via a rather violent mechanism which releases a significant amount of energy in the form of an acoustic shock wave and as visible light. At the point of total collapse, the temperature of the vapor within the bubble may be several thousand kelvin, and the pressure several hundred atmospheres
Some people hoped that cavitation in heavy water (eg from an ultrasonic source) could produce nuclear fusion.

Unfortunately, like previous attempts at cold fusion, it was a damp squib.

See: https://en.wikipedia.org/wiki/Bubble_fusion
Title: Re: Where Do The Bubbles Come From When A Propeller Propels ?
Post by: jeffreyH on 28/05/2017 13:01:08
Bet they didn't try converging ultrasonic sources.
Title: Re: Where Do The Bubbles Come From When A Propeller Propels ?
Post by: Colin2B on 28/05/2017 23:15:34
Bet they didn't try converging ultrasonic sources.
Or shrimps
Title: Re: Where Do The Bubbles Come From When A Propeller Propels ?
Post by: jeffreyH on 29/05/2017 00:40:18
Bet they didn't try converging ultrasonic sources.
Or shrimps

Fission chips. Yum yum!
Title: Re: Where Do The Bubbles Come From When A Propeller Propels ?
Post by: PmbPhy on 30/05/2017 07:19:14
An interesting fact about those bubbles is that they're noisy. In fact a great deal of effort goes into the design of the propellers on nuclear subs so that they don't make those bubbles. Otherwise the subs would be easy to track. You may notice that when  nuclear sub is dry dock they cover the props so that their design cannot be copied.

For details please see: http://americanhistory.si.edu/subs/anglesdangles/taming2.html
Quote
It is so secret that when a sub comes in from patrol its propeller is shrouded with a large covering, and if a sub is drydocked for any length of time, it is commonly removed and stored away from the ship for servicing and prying eyes

However there are photos easily available online:
https://www.google.com/search?q=nuclear+sub+propeller+design&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjSndXh_ZbUAhVKwYMKHdhkCQ8QsAQINw&biw=1600&bih=768