Answer Posted / bn
when the local pressure in a liquid falls below the vapour
pressure, for that temperature, the liquid boils locally
and forms bubbles; this is flashing.
If the pressure subsequently increases, the bubbles colapse
violently; this is cavitation.
If the liquid contains dissolved gases, when the local
pressure is reduced gas bubbles will form before the liquid
starts to boil.
If the pressure is subsequently increased, the gas bubbles
will colapse but much slower than the colapse of a vapour
bubble. This is pseudo-cavitation.
It is the colapse of vapour bubbles which causes noise,
vibration and local damage. Pseudo-cavitation may not do
much damage to rotodynamic pumps. Pseudo-cavitation will
destroy some pd pumps just like cavitation. Pump operating
conditions, pumped liquid and pump design are critical
factors.
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