I got a pipe with an orifice plate attached which reads:
F(upstream)= 10^(-5)Cubic meter/second
F(downstream)= 3*10^(-5) cubic meter/second

I am looking for the dimensions D1, D2
D1 being the Upstream diameter of the pipe
D2 being the orifice diameter.

I started by assuming Cd = Fup*Sqrt(SG/DeltaP)
Cd = Fdown*Sqrt(SG/DeltaP)

Cd: Coefficient of Discharge,
SG: Special Gravity (water=1),
Fup, Fdown: flow rated respectively up or down the pipe.
By Equalizing the Cd Equations I ended up with Cd = 9.

Then logically Delta P should be the same in both cases. Which is not true if u solve for Dp upsteam u get 3.333*10^-3 and Dp down u get 1.111*10^-6. Which I understand that they are related with a specific ratio.

That's all i got for the moment any comment or advice it will really be appreciated. Kind of stuck for the moment.

thanks

 

I suppose you could consult ISO 5167.

If you can google, google "Free Orifice Plate Sizing calculation spreadsheets"
Some you pay for and some are free.

http://lmgtfy.com/?q=+free+orifice+plate+sizing+calculation+spreadsheet&l=1