The Odd Physical Properties of Mixtures of Air and Water
Richard Hammond today, in his program called Engineering Connections about the Space Shuttle, showed how NASA use a wall of water droplets to protect the shuttle and the launch platform from the immense sound waves created by the rocket engines on lift off. I have seen a shuttle launch and even some miles away the noise was awesome and in some ways the most unexpected part of the event.
If I ask an averagely serious engineer or physicist to tell me the speed of sound in air and also that in water, they will give answers of 343.2 and 1497 metres per second respectvely with various conditions like dry air and pure water. So sound travels a lot faster in water than air.
So if you have a mixture of bubbles of air in water or vice-versa, a logical person would think it lies somewhere between the two.
But they would be wrong! According to this paper from 1969, by D. McWilliam and R. K. Duggins, it can be as low as 18.2 metres per second. This creates all sorts of problems and benefits. NASA’s engineers used it in one way and I invested in a company that used it to make an aerosol valve.
But it is a property that hasn’t been used to the full.
They say that oil and water do not mix.
But I have seen an experiment where bubbles of air was introduced into a mixture of water and oil and the resulting mixture was passed through a choke or restriction. A creamy liquid emerged, because the air bubbles in the restriction in trying to get into some form of steady state, mixed evetrything up.
I know that explanation isn’t very good, but who cares as the technique works.
In places like Saudi Arabia, there are large lakes of tar, that are just dumped in the desert. Perhaps by using natural gas as the gas, could this pollution be burned, whilst it is still hot?
I don’t know! But I do know that this abnormal property of mixtures of gases and liquids is not used for all the applications it can be.
The Anonymous Widower 