Pressure Drop
When using a sharp edged orifice the pressure drop across any hole size can be determined using the following formula.
FLOW1/SQ RT DELTA PSI1 = FLOW2/SQ RT DELTA PSI2.
This assumes that FLOW1 and DELTA PSI1 are known and the hole size remains the same.
That applies not only a sharp edge orifice, it applies to any orifice as a general equation where k=Q/sqrt deltaP. You are assuming/estimating that constant k is the same all throughout downstream. If two flow controls are in series, I guess k will vary at every orifice point.
Not sure what you are talking about. This equation is true for a knife edged orifice. The flow across the orifice must be "turbulent" not "laminar".
Your statement "You are assuming/estimating that constant k is the same all throughout downstream." makes no sense to me.