Help with an ejector stack
Hi,
I am trying to reproduce the results of a physical test. The arrangement is shown in "3D model.png" attached. Ambient air (inlet 1) is blown into a stack. The reduced throat (a venturi) causes a drop in the static pressure, and this lower pressure draws in the hot gases from a furnace (inlet 2). The gases are then vented to the atmosphere.
In my analyses, I apply the known flow rate and temperature of the ambient air (Inlet 1). I apply an assumed flow rate and known temperature of the hot gases. The solution should be able to calculate the pressure of the hot gases entering the stack. I have tried every variation that I can think of, but my results are not consistent. The calculated pressure matches the measured pressures at some flow rates but not at other. So it may be (somewhat of) a coincidence that it matches the pressure at some of the flow rates.
Because the 3D model takes a couple of hours to run, I am trying to get the procedure to work with a 2D axisymmetric model, and ignoring the 3D effects of the inlet. I would not expect a perfect match because of this approximation, but I would expect some reasonable correlation. I have tried steady state and transient, fixed air properties and variable air properties, compressible, subsonic, and incompressible, advects 1, 2, and 5. Nothing seems to give the consistency that I would expect. Any suggestions would be welcomed.
I have attached the 2D model. (I needed to rename the .cfz extension to .zip to get it to attached.) These are the results that I am getting:
Flow Inlet 2 | calculated pressure inlet 2 | measured pressure inlet 2 from test
1222 ft^3/min | -1.88 inch H2O | -2.0 inch H2O
2263 ft^3/min | -1.85 inch H2O | -1.6 inch H2O
3043 ft^3/min | -1.46 inch H2O | -1.3 inch H2O
3823 ft^3/min | -1.85 inch H2O | -1.0 inch H2O
4604 ft^3/min | -1.75 inch H2O | -0.7 inch H2O
Thanks.
