Orifice calculations

What is the best program or excel sheet for orfice calculations to download it

ASME 19.5 describes the calculation procedure. Also http://www.engineeringtoolbox.com/orifice-nozzle-venturi-d_590.html

or
http://www.efunda.com/formulae/fluids/calc_orifice_flowmeter.cfm

Tom
In the same kind of questions, do you know about a formula to calculate the area needed for air blowing thru.
In others words, if you want to validate how much opening you need in a cabinet for x amount of air flow CFM to keep a low static pressure requirement for some ordinary cooling fan...

Q = A x C x k x √P

Q = cu ft / min
A = sq ft
C = orifice coefficient, 0.6 for square edged orifices
k = 21,094 for these dimensions
P = psi

Note that this is based on standard ambient conditions, density = 0.075 lb/cu ft. Density affects the flow, but for most purposes I ignore it. The formula for density effects is more complex, but I can provide it if you want. For most ventilation purposes all the other errors and assumptions overwhelm density effects.

Also note that the flow changes as the square root of P Twice the flow = 4 times the pressure.

awesome!
Do C is for the shape of the orifice or for the finishing of it ? For exemple do i have to put anoter coeeficient when using rectangular orifice or circular one ?

I spend a lot of time looking for this on internet and most of the links return me to home exchanger calculs to balance pressure inside the house...

C is a function of the orifice cross section, not it's shape. A square or rectangular hole will have slightly different characteristics than a round hole of the same area, but the differences are negligible compared to all the other uncertainties. If you get pressure drop calculations within 10% of reality you are doing pretty good.

The attached is the basis for my post.