Water surface behavior under pressure change

In summary, the conversation discusses the behavior of the water surface in a compressed air vessel when the pressure drops from 10 bar to atmospheric pressure. It is noted that the water volume will not change due to the change in pressure and the surface may be temporarily disturbed by ripples caused by the escape of air. However, if the temperature is high enough, the water may start to boil. If the water has been in the vessel for a long time, gas may dissolve in it and escape when the pressure is released, leading to small bubbles. Otherwise, there is not much movement in the water.
  • #1
Bjott
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Hi togehter,

this may be an easy one for most, but I'm really struggling with imagining the process.
Suppose we have a compressed air vessel that is half filled with water. The pressure in the vessel drops from 10 bar to atmospheric pressure within a few seconds. How does the water surface behave? Is there any movement due to the pressure difference? Or does the water only move due to the flow of the escaping air. Or is there no movement at all?

Thank you very much!
 
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  • #2
Welcome to PF.

I assume the reduction in pressure is due to loss of air only, not water.
Water is not really compressible, so the water volume will not change due to the change in pressure. The position of the surface should not change. The surface may be disturbed with ripples temporarily, caused by the dynamic escape of the air from an asymmetric orifice.
 
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  • #3
It also may change due to changing strain in the pressure vessel itself. The pressure vessel will get smaller so the water will rise.

(Note, at this level you probably cannot consider the water to be completely incompressible either)
 
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  • #4
If the temperature happens to be above 100C (and below 160C), the water will start to boil.
 
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  • #5
If the water has stayed in this vessel with the high pressure air for a long period of time, then gas will dissolve in the water (at least, more than in atmospheric conditions). When the pressure is released the gas will escape again leading to small bubbles (also, already existing bubbles underwater will grow). Otherwise, not much movement as already pointed out.
 

FAQ: Water surface behavior under pressure change

What happens to the surface tension of water when pressure is increased?

Surface tension of water is primarily influenced by temperature rather than pressure. However, under extremely high pressures, the molecular interactions can be slightly altered, leading to minor changes in surface tension. These changes are usually negligible under normal conditions.

How does pressure affect the evaporation rate of water from the surface?

Increasing pressure generally decreases the evaporation rate of water. Higher pressure means that water molecules need more energy to escape into the vapor phase, thus reducing the rate of evaporation from the surface.

Does water behave differently at the surface under high pressure compared to low pressure?

Yes, water can behave differently at the surface under varying pressures. At high pressures, the density of water increases, which can affect the hydrogen bonding network and alter the surface properties. Conversely, at low pressures, water molecules have more freedom to escape into the vapor phase, affecting surface behavior.

How does pressure influence the formation of water droplets on a surface?

Pressure can influence the formation and stability of water droplets on a surface. Higher pressure can compress the water droplets, making them more spherical due to increased surface tension. Conversely, lower pressure can lead to larger, more spread-out droplets due to decreased surface tension.

What is the impact of pressure changes on the capillary action of water?

Capillary action is primarily driven by surface tension and adhesion forces between water and the surface. While pressure changes can slightly influence these forces, the effect is generally minimal under typical conditions. Extreme pressures might alter the liquid's density and surface tension, thereby affecting capillary action.

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