I actually just built a model from scratch, very easy to do. Although, I did have a starting place from a pump curve as the flow was between a vacuum pump, condenser, and dryer. Darcy-Weinbach, simplified Bernoulli, or other will give you a very good estimate for both flow rate and subsequent pressure drop and vice versa. The model works pretty well with what is observed in the process as well.
Density of Air
Viscosity of Air
Density of Steam
Viscosity of Steam
Percent Air
Percent Steam
Density of Mixture
Viscosity of Mixture
Length
Diameter
Roughness
Flow Rate
Velocity
Re
Friction Factor
Pressure Losses
Major Losses
Minor Losses
Total Losses
P2
Used these variables. Derived from equations, process data, ANSI, Crane's flow manual, and Perry's. Once you have these values or the equations to solve for these values it should be plug and chug.