CV based flows along with supplementary metrics

This calculation method uses the Cv curve of a valve to estimate the flow rate through it. Valve Flow Coefficient (Cv) is the flow capability of a control valve at open conditions relative to the pressure drop across the valve.

Flow Control Valves have a table of open % vs Cv value. XV’s or SV’s have a single CV value for when they are fully open. In addition to the Cv value, numerous physical properties for the respective gas flowing through the valve are used to compute the flow rate.

It’s method of estimating the flow based on interpolation of the flow chart. In following gdoc gdoc you can find set of examples and CV tables for each CV based metric.

Second part flow recovery rate interpolated based on FL table.

formula

Each set of metrics based on following formula inputs: psig_in, psig_out, valve, temp, gas

valve is between 0 and 100 and it’s %

Intermediate variables are computed:

psia_in         = psig_in + 14.696        #absolute pressure
psia_out        = psig_out + 14.696       #absolute pressure
pressure_change = psia_out / psia_in
rankine_temp    = temp + 460
cv              = cv_interpolation(valve)
fl_recovery     = fl_interpolation(valve)

Following constant are in use:

• gas_density_vs_air it’s physical constant dependant on gas type
• 1360 is a unit version factor for variables and output in imperial units
• 834 is a unit version factor for variables and output in imperial units
• gas_std_density it’s physical constant dependant on gas type
• 1.25 is a ratio applied to argon gas streams to estimate the N2 flow rate to condense the stream

Main formula returns lb/h:

• 0 if valve < 0 or 100 < valve or pressure_change >= 1
• (gas_std_density * cv) / (sqrt(gas_density_vs_air * rankine_temp) / (fl_recovery * 834 * psia_in)) if pressure_change < 0.53
• (gas_std_density * cv) / (sqrt(gas_density_vs_air * rankine_temp) / (sqrt((psia_in - psia_out) * psia_out) * 1360)) if pressure_change >= 0.53

At the end scfm = to_scfm(gas_type, lbh)

fcv_605_scfm, fcv_605_lbh, fcv_605_n2_use_lbh, fcv_605_n2_use_scfm

Inputs: psig_in=PT_605, psig_out=PT_250, valve=FCV605, temp=40°F, gas=Ar

Extra formula values:

• fcv_605_n2_use_scfm = fcv_605_scfm * 1.25
• fcv_605_n2_use_lbh = lbh(fcv_605_n2_use_scfm)

gdoc