Posted: Wed Oct 18, 2006 10:49 pmOrifice flow in a pipe, thanks to Greenlight for this spreadsheet. It is a rather large file (almost 2 megs)
Note that there are two sheets included in the spreadsheet, one to calculate the density of moist air and the other to calculate the flow through the orifice.
To use the spreadsheet:
1) Go to the sheet, labeled "Moist Air Density", that calculates the density of air using the Temp, Baro. Press, and %RH. Input values in the bold outlined cells, click on the calculate button and read the air density.
2) Go to the sheet labeled "Orifice Flow". Enter values into the bold outlined cells for density, orifice dia., inlet dia., and Pressure Differential. Then click on the calcualate button.
3) Using the values in the yellow cells near the two graphs, determine the appropriate values for the compressibility factor and the discharge coefficient. Input these values into the appropriate bold outlined cells. Click on the calculate button and read the mass flow rate and volume flow rate through the orifice.
I'm sorry that it's not more user friendly, but my intention was for personal use only when I originally developed this spreadsheet ~12 years ago.
You will also notice that as the ratio of orifice diameter vs. pipe diameter increases beyond ~5:1 there is little or no difference in the flow rate through the orifice. This phenomenon is known as the "wall effect" and the rule of thumb is that the wall effect is trivial beyond the 5:1 ratio.
For a "plenum style" bench I use 10" or so for the pipe diameter and the results should give accurate results.