NPSH Calculation
 

Hi,

I am calculating a flow of diesel trough a valve. Therefore the outlet is defined by a mass flow while the inlet is specified as static pressure with pressure 0. The pressure of the diesel in the pipe is about 250bar. So I put the ambient pressure in domain settings to that value. I calculated the flow in the valve and now I am trying to get the NSPH-value for this specific case. The definition of NSPH=(Totall Pressure inlet-Pvap)/(g*Density). I have to problems:
1. Does anybody know the vapor pressure of Diesel at abot 30-40°C and a global pressure of 250 bar?
2. If I use the total pressure at inlet to calculate the NSPH value I get unreasonable values. The flow at inlet is about 3 cm/s and so the dynamic pressure is about some tenth of Pa. Do I need to use the absolue pressure for that specific case. Otherwise If I had a velocity equal to zero it would mean that I get cavitation already at the inlet with zero velocity (makes no sense).

I appreciate any help on the questions! Thanks in advance.

You will have to look up the vapour pressure for Diesel. And by the way, the ambient pressure has nothing to do with the vapour pressure - make sure you understand the concept of vapour pressure before doing simulations on it.

Yes, you need to use the absolute pressure in the NPSH calculation - again, make sure you understand the concept of vapour pressure before doing simulations on it.

Thanks for your fast answer. Yes we will defitnily dig into cavitaition theory. Vapor pressure is dependent ond material and temperature.