# Velocity of air through an open nozzle

#### jfischer

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?

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#### quark

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.

#### FredGarvin

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:

$$q = YCA \sqrt{\frac{2g(144) \Delta P}{\rho}}$$

Where:
$$q$$ = Volumetric flow in $$\frac{ft^3}{sec}$$

$$Y$$ = Expansion Factor

$$C$$ = Flow coefficient. C can be calculated from the discharge coefficient by:

$$C = \frac{C_d}{\sqrt{1-\beta^4}}$$

$$\beta$$ = Ratio of small to large diameters in the nozzle and pipe

$$A$$ = Cross sectional area in ft^2

$$g$$ = Acceleration due to gravity 32.2$$\frac{ft}{sec^2}$$

$$\Delta P$$ = Pressure differential across nozzle in $$\frac{Lb_f}{in^2}$$

$$\rho$$ = Weight density in $$\frac{Lb_f}{ft^3}$$

I'll reiterate Quark's suggestion to get Crane's TP. It's worth it's weight in gold.

#### jfischer

thanks for the help. An aproximation will be enough and I will look into the refrence suggested.

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