Compensation Calculation For Variable Area Flow meters

Compensation Calculation For Variable Area Flow meters

IN CASE OF LIQUID MEASUREMENT

The liquid density change from the design condition produces indication error.

Actual Flow rate = Indicated flow rate Correction coefficient

Density correction coefficient

Design density (g/cm3)to be referred to Approval drawing

Density of the measuring liquid (g/cm3)the density of actual liquid

Density of float (g/cm3)differs by material, Refer to the following table.

Float material

Density of float *

Stainless steel

7.7 g/cm3PVC

2.7 g/cm3* Figures may have deviations due to final design.

Compensation Calculation ExampleOriginal design condition of flowmeter

Fluid : WaterDesign density : 1.0 g/cm3Actual process condition

Fluid : AlcoholActual density : 0.8 g/cm3Indication of flowmeter : 10m3/h

Actual flow rate of Alcohol = 10 1.134 = 11.34 m3/h

IN CASE OF GAS FLOW MEASUREMENT

In Gas Flow Measurement,

Density of the gas to be measured (under Normal condition, 0C,1atm)Operating pressureOperating temperature

as the factors of compensation.

Actual Flow rate = Indicated flow rate Correction coefficient

Density compensation

Density correction coefficient

Design density [kg/m3(nor)]to be referred to Approval drawing

Density of the gas to be measured [kg/m3(nor)]

Pressure compensation

Pressure correction coefficient

Design pressure (MPa)in Gauge pressure,to be referred to Approval drawing

Actual operating pressure (MPa)in Gauge pressure

Temperature correction

Temperature correction coefficient

Design temperature(C)to be referred to Approval drawing

Actual operating temperature(C)

Compensation Calculation ExampleOriginal design condition of flowmeter

Fluid : AirDesign density : 1.293 kg/m3(nor)

Design pressure : 0.2 MPaDesign temperature : 20C

Actual process condition

Fluid : CO2 GasDesign density : 1.977 kg/m3(nor)Actual operating pressure : 0.4 MPaActual operating temperature : 50C

Indication of flowmeter : 5m3/h(nor)

Actual flow rate of CO2 gas = 5 0.994 = 4.97 m3/h(nor)

IN CASE OF (SATURATED) STEAM FLOW MEASUREMENT

Correction calculation is done by the density of the steam to be measured

Actual Flow rate = Indicated flow rate Correction coefficient

Density correction coefficient

Density of actual steam (kg/m3)

Design density (kg/m3)

Compensation Calculation ExampleOriginal design condition of flowmeter

Fluid : SteamDesign density : 5.163 kg/m3Design pressure : 0.902 MPaDesign temperature : 180C

Actual process condition

Fluid : Steam Design density : 2.549 kg/m3Actual operating pressure : 0.3479 MPaActual operating temperature : 150C

Indication of flowmeter : 10 t/h

The steam density in operating condition is to be referred to Steam Table.

Actual Flow rate at 150C = 10 t/h 0.703 = 7.03 t/h