Velocity of air through an open nozzle

  • Thread starter jfischer
  • Start date
I am trying to figure the velocity of air through an open nozzle. We are contemplating using air to dry parts on an conveyer. I am curious to know how much CFM will be expeled. I have searched many of my refrence books with no success. If the compressor which is also providing air for several other pieces of equipment maintanes a pressure between 70 and 100 PSI and the nozzle is apx 1/4" in diamter what will be the velocity of the air through the nozzle? More importantly how do you relate the pressure to the velocity?
That depends upon the actual pressure at the inlet of the nozzle and downstream pressure of the nozzle. At 100psig, it can be about 60scfm. This is a ballpark figure and you should get your hands on Crane Technical Paper 410, the best reference I have ever seen and widely referred world over. At 40USD, it is an invaluable tool.


Science Advisor
You'll need to know the pressure drop at the throat of the nozzle plus the discharge coefficient for that nozzle. If it is a nozzle that is purchased from a vendor, the vendor should have an acceptable calculation for you to use. If that is not the case then you can at least get a good approximation using the standard nozzle equation:

[tex]q = YCA \sqrt{\frac{2g(144) \Delta P}{\rho}}[/tex]

[tex]q[/tex] = Volumetric flow in [tex]\frac{ft^3}{sec}[/tex]

[tex]Y[/tex] = Expansion Factor

[tex]C[/tex] = Flow coefficient. C can be calculated from the discharge coefficient by:

[tex]C = \frac{C_d}{\sqrt{1-\beta^4}}[/tex]

[tex]\beta[/tex] = Ratio of small to large diameters in the nozzle and pipe

[tex]A[/tex] = Cross sectional area in ft^2

[tex]g[/tex] = Acceleration due to gravity 32.2[tex]\frac{ft}{sec^2}[/tex]

[tex]\Delta P[/tex] = Pressure differential across nozzle in [tex]\frac{Lb_f}{in^2}[/tex]

[tex]\rho[/tex] = Weight density in [tex]\frac{Lb_f}{ft^3}[/tex]

I'll reiterate Quark's suggestion to get Crane's TP. It's worth it's weight in gold.
thanks for the help. An aproximation will be enough and I will look into the refrence suggested.

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