Hi,

I am task to do an small experiment by using a air pump set up to determine the Cd of orifice plate. A 14.5mm (D) PVC pipe with orifice diameter 8.5mm is installed and connected to an air pump. I put one pressure tab at upstream and one at downstream with distance D and D/2 from the orifice. An differential pressure is then measured by meter say 125 Pa. The pump that I am using without specification given, thus I do not know the pump speed and flow rate. I used manometer to measure the volume flow rate at the end of the pipe which given me 0.113 m³/s. I plug the measured measurement and known elements into the given equation, I couldn’t get the Cd around 0.65,

1) what is gone wrong on the calculate Cd?

2) What is appropriate the upstream pipe and downstream pipe length be for the set up?

3) Is the equation applicable to small pipe flow?

Equation:-

Q = Cd x Ao x Sq root ( 2x Diff Pressure /(air Density x (1- Bata^4))

Where:

Q = Volume flow rate through the pipe

Cd = Orifice Coefficient

Ao = Area of Orifice

P= Density of air Bata = Diameter of orifice /Diameter of pipe

I assumed the air flow is laminar as the flow speed is at about 7.8 m/s.

## Air flow with Sharpe Edge orifice experi

### Re: Air flow with Sharpe Edge orifice experi

Have you tried with orifice plate calculator?

There is also button that will launch theory page which gives you equation for flow coefficient.

There is also button that will launch theory page which gives you equation for flow coefficient.

Pipe flow calculations - since 2000