Mariog,

Thanks for your input.

I will try to put my question in more clear terms.

I am totally in agreement with the first part of the API expression i.e. the momentum part.

My question is about the second term i.e. Area at exit x Exit Pressure.

API does not provide any expression for exit pressure.

Considering choked flow and adiabatic conditions, we can write an expression for exit pressure as :

P exit= (W/Ae)x SQRT( 2RTo/(k(k+1)M)

Where is the mass flow rate (kg/sec)
Ae= exit area
R=universal gas constant
k=Cp/Cv
M=molecular weight
To= vessel stagnation temp

Using this expression and also the ratio of To/Te where Te is the exit temp ( which is =(k+1)/2),I am getting the following expression for Pexit x A exit

=WXSQRT(R'Te/k)...(1)

where R' is the characteristic gas constant=R/M

This expression is close to but not same as what is there in my original post, which I am rewritting for ready reference.This time I am writing the full expression with the units.

WX1.88 SQRT(k.g.R'.Te)/g....(2)This is in Newton

where g stands for gravitaional acceleration in m/sec^2. Unit of R' in (2) is in J/kg K , Te is in K

I am not sure how to prove that (1)=(2)

Kindly throw some light.

Regards