Formula for calculating flow by using Orifice:

C [*none*]: discharge coefficient

β [

*none*]: Diameter ratio (β=d/D, where D is Pipe diameter)

ε [

*none*]: Expansion factord [mm]: Bore diameter

Δp[kPa]: Differential pressure

ρ1[kg/m3]: Up stream fluid density

For example, the spec of Orifice is found as following:

Then we will find:

C = 0.60851

β = 0.74881

ε = 1 (for water and other liquids which are considered incompressible)

d = 368.5252 mm

Δp = 14 kPa

ρ1 = 992.3992 kg/m3

Apply those number to formula, we get:

Qm=13,067,104.00

but the unit for this Qm is (10^-4)Kg/(s.10^-0.5)

Change this into Kg/s, we get: Qm=413.218 (Kg/s)

Change this into m3/s, we get: Qm=0.4163829 (m3/s)

Finally, change this into m3/h, we get Qm=1498.9786 (m3/h)

Nearlly same as spec of Orifice! (1500m3/h)

But it take me a long time to make calculation. In my plant, this flow transmitter is over range sometimes, so i want to change the range of measuring from 1500m3/h into 2100m3/h. Then i convert the formula into:

Qm=alpha*sqrt(deltaP).

alpha is not changed.

We can get alpha from specification of Orifice: 1500m3/h=alpha*sqrt(14kPa),

then calculate deltaP for range of 2100m3/h, i get deltaP=27.44kPa.

Fortunately, the flow transmitter works well when i change from 14kPa into 27.44kP.

**Useful Link**Online caculation for differential pressure flow meter

Calculation document 1

Calculation document 2

Fundamental of Orifice 1

Fundamental of Orifice 2

## No comments:

## Post a Comment