Cross-sections:

Equations:     For both geometries: Q=VA, Q=Flowrate, V=Velocity, A=Flow Area
Rectangular:  A=Area=WH.  P=Perimeter=2(W+H).  D=Hydraulic Diameter=4A/P
Annular:  A=Area=PI(D₂²-D₁²)/4.  D=Hydraulic Diameter=D₂-D₁      References

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Enter all values in consistent units:  If you enter diameter in inches, then width and height will be output in inches.  If you enter width in cm, then you must also enter height in cm; and diameter will be output in cm.  If velocity is entered in cm/min, then flowrate will be cm³/min.

Using this page:
If you have a non-circular duct, the cross-sectional geometry can be converted to an hydraulic (equivalent) diameter using this page.  Then, velocity (not flowrate) can be computed using a) Design of Circular Liquid or Gas Pipes or b) Design of Circular Water Pipes based on the hydraulic diameter.  However, (a) and (b) will not compute the correct flowrate since they compute area based on a circular cross-section.  Therefore, you must multiply the velocity by the actual area of the duct.  The actual area is computed on this page.

If you wish to determine the cross-sectional geometry of a non-circular duct, you can use a) Design of Circular Liquid or Gas Pipes or b) Design of Circular Water Pipes if you know the velocity, not the flowrate (flowrate can only be converted to velocity if the actual duct area is used, not the area based on hydraulic diameter).  From the hydraulic diameter output from either (a) or (b), this page can be used to determine the geometry of the duct.

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LMNO Engineering, Research, and Software, Ltd.
7860 Angel Ridge Rd.   Athens, Ohio 45701  USA   Phone and fax: (740) 592-1890
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