Flow Element Sizing

The flow orifice/nozzle/venturi sizing software is based on the ISO standard:

ISO 5167 - Parts 1, 2, 3 and 4 - 2003

More precisely the equations and limits in part 2 are used for orifice plates, the equations and limits in part 3 are used for nozzles and venturi nozzles, and the equations and limits in part 4 are used for Venturis.

The formulas are all based on Mass Flow Rate. This is one of the safest way of sizing flow elements. The problem with people is they do not speak precisely enough when they speak in "volumetric" terms and end up confusing themselves and everyone else. Speaking in mass terms avoids confusion. (e.g. when told the flow is 1000 m3/h, one is left wondering if the speaker means flow rate at the operating pressure and temperature, or is it flow rate normalized to some base conditions and which base conditions are those, the Standard base (14.7 PSI and 60 °F) or the Normal one (101.325 kPa and 0 °C)? The error is usually small but not negligible if liquids are involved; it can be enormous in the case of gases).

The general equation from ISO5167 is:

Refer ISO5167 part 1 section 5.1

However, since and D is always known (Pipe ID) my own preference is to re-write the ISO 5167 equation as:

And in particular, when sizing a flow element, I find the expression of b as a function of the other variables particularly useful:

Equation 1

This is the formula I use in preference to that suggested by ISO5167 for the iteration procedure when calculating b. After each iteration, C is corrected (and for compressible fluids e) and recalculate.