Question

when a liquid enters a vacuum filled space, it vaporises i think. For the liquid to cavitate, doesn't the pressure have to first increase above the vapor pressure, and if this increase was slow, i.e. liquid flow rate was small, shouldn't cavitation be minimal? Since, from what i've understood, cavitation requires a sudden increase in pressure to above vapor pressure. If what i'm saying is right, how fast does the increase in pressure have to be to cause cavitation? Thanks

Answer 1

Cavitation forms at places inside the liquid where the pressure is relatively low. During cavitation, the vapor pressure of liquid reduces to such a point that the liquid will boil (will convert to steam) at room temperature (As pressure decreases the boiling point of liquid also decreases). Cavitation doesn't require sudden changes in pressure, a low-pressure region can trigger cavitation. Cavitation is any phenomenon where the liquid starts to boil due to increase in pressure only (no change in temperature). So as the liquid enters vacuum region, you can't stop the liquid from boiling.

The bubbles formed during the cavitation is due to that liquid converted to steam, around the normal liquid which hasn't been converted. (This happens during boiling a liquid also, small bubbles from bottom of the pot comes up and pops)