Calculation of Flow Rate - Intergraph Smart Instrumentation - Reference - Hexagon

Calculate internal pipe diameter at floe temperature:

Calculate correction factor for steam quality (For lliquid, water, and steam, Fs=1):

Calculate orifice diameter at flow temperature.

1. For Venturi tubes and Nozzles:

   

2. For orifice plates:

   

Calculate b - ratio:

Checking for Critical flow and some initial calculations.

Liquid /Water case

1. Calculate downstream pressure:

   

2. If the the flow is critical. If not then the floe is sub-critical.

   1. For critical flow:

   

   1. For sub-critical flow:

      Classic Venturi tube:

   

3. 1. Nozzles

      

   2. Orifice plates:

      

   3. Calculate first estimate for flow rate (W0 [kg/s]):

      

4. Gas/Steam case

   1. Calculate critical pressure ratio and define whether the flow is critical.

      

      If the the flow is critical. If not the flow is sub-critical.

5. Initial calculation for critical flow.

   1. Gas Expansion factor:

      

   2. First estimate for flow rate (W0 [1b/h], T[R], D[in], P1[psi-a])

      

6. Initial calculations for sub-critical flow.

   Differential pressure to be used in flow rat calculation:

   1. For classical Venturi tube:

      

   2. For Nozzles:

      

   3. For orifice plates:

      

7. Gas expansion factor:

   1. For Venturi tubes and nozzles:

      

      where

   2. For orifice plates:

      

   3. First estimate for flow rate (W0[kg/s]):

      

Calculate Reynolds number.

1. For gas/steam critical flow (Bore Reynolds number):

   

2. For liquid/water and gas/steam sub-critical flow (Pipe Reynolds number):

   

Calculate discharge coefficient. See Appendix.

For orifices in the case of gas/steam sub-critical flow, calculate DP and gas expansion factor:

Calculate new flow rate:

1. For gas/steam at critical flow:

   

2. For other cases (W[kg/s]):

   

Repeat steps 6 to 10 until the relative change in the flow rate is less than 0.0001.