Velocity use for cal. the duct transition pressure drop

[THAPHE]

Can someone help to advise me.

I try to calculate the pressure drop on duct transition lenght around 0.7m (Round(diameter 22") to rectangular (1.93mx1.93m) which the velocity air inlet at round side is 18.6 m/s. I got the formula dp(Pressure drop) = Co x (1/2) x density x velocity^2 . So I'm not sure what the correct velocity use on this formula. As i know the air velocity in the duct to be change as diffent duct cross section (as continuity equation)

Thanks.

 

[willard3]

Read General Principles Of Ventilation in "Industrial Ventilation" published by the ACGIH or read SMACNA volumes covering the same thing.