I have a case where I am trying to size a new control arrangement (control valve and orifice plates, etc) for the problem valve I talked about in:
This fluid is at 333 psig upstream of the valve and needs to drop to ~80 psig downstream. The vapour pressure is 0.57 psiA. So that tells me that if I drop roughly 348 psi from my inlet pressure, I will flash and the system will recover to 80 psig and I will cavitate. Okay...
So why is the max pressure drop (for choked flow) only about 93.5 psi using the ISA sizing equations? Doesn't choked mean the formation of vapour bubbles?
Ff=0.96-0.28(Pv/Pc)^0.5 = ~0.943 (Pc=152.2 psia)
Therefore, DPmax = ~93.5 psi drop.
This is substantially less than 348 psi. Is this strictly based on turbulence velocities that are higher than bulk flow velocities such that local low pressure areas can form?