Calculate the dimensionless cavitation number for pipes and general flow.
Cavitation occurs when the static pressure in the fluid is less than or equal to the fluid vapour pressure. Bubbles of vapour form in the low pressure fluid, which then collapse when the fluid pressure increases causing noise and damage to equipment. The cavitation number is used to determine the likelihood of cavitation occurring.
`Ca = (Ps - Pv) / (Pd) `
`Pd = 0.5 ρ V^2 `
where :
Ca = Cavitation number
Ps = static pressure
Pv = vapour pressure
Pd = dynamic pressure
ρ = fluid density
V = fluid velocity
For flow with moving parts (eg an impellor), the maximum velocity of the moving part can be used rather than the fluid flowing velocity. The cavitation number is of similar form to the Euler number and the pressure loss factor or minor loss factor K (refer to Euler number and K factor).
For pumps the suction specific speed Nss and nett positive suction head NPSH are commonly used to determine the onset of cavitation.
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