flow measure by pressure loss through an aperture

Hi everyone,

I need a formula to compute the flow of a fluid by the pressure-difference before and after an aperture. Can you help me? I need a formula for gas as well as for liquid fluids. It needs to consider the transition from liquid to gas while expanding through the aperture. For Example: certain flow of propane C3H8 through a pipe with an aperture; before the aperture p=10 bar ->liquid, after the aperture p=3 bar ->gas. how many kg/sec pass through? My job is to define a flow measure by setting the pressure in front of the aperture. Thanks so far

unbertl, TU Munich

Hi everyone,

I need a formula to compute the flow of a fluid by the pressure-difference before and after an aperture. Can you help me? I need a formula for gas as well as for liquid fluids. It needs to consider the transition from liquid to gas while expanding through the aperture. For Example: certain flow of propane C3H8 through a pipe with an aperture; before the aperture p=10 bar ->liquid, after the aperture p=3 bar ->gas. how many kg/sec pass through? My job is to define a flow measure by setting the pressure in front of the aperture. Thanks so far

unbertl, TU Munich

Dear unbertl:

For no phase change:

David A. Smith

If I start by ignoring the phase change of the fluid, supposing simply that it is a 100% change of state at any flow of interest, I see how useful the following approximate formula for an orifice meter works out:

Mass flow = discharge coefficient of orifice times cross section area of orifice times sq root of ( 2g/gamma times delta p)

where g = gravitational acceleration, gamma = fluid density delta p is pressure drop past the orifice - all in compatible units naturally.

Discharge coefficient for the usual annulus can be 0.63 It might be different for a phase changing orifice naturally.

If your need for precision is not excessive, this might do the job for you?

Brian Whatcott Altus OK

You might try Googling for the words "cavitating" and "venturi". The method used for calculating the flow through one of those might give you some pointers to use for your cavitating orifice plate.

I Googled for "cavitation" and "orifice" and found this:

thank you very much guys, I'll see if it will help