The Characteristics of Air Flow through a Rectangular Orifice, and in Circular Duct with a Branch

Abstract

This paper deals with results of tests made on the following matters.
(1) The flow through the rectangular orifice fitted on a rectangular air duct.
(2) The divided flow at the tee branch for a circular air duct.
As the results of expeiments, the following empirical formulae have been obtained
(1) Coefficient of resistance at the rectangular orifice.
ζ= (A_d/αA₀-1) ²
α=0.625+0.375 (A₀/A_d) ³
(2) Loss in the divided flow at the tee branch for a circular air duct.
Main duct P=0.05 Hm 0.6 S²Hm
Branch duct P=0.99 Hm+0.341 Hb
Where
ζ=coefficient of resistance
A₀=sectional area of orifice
A_d=sectional area of duct
P=pressure loss, mmAq
H_m=velocity head in the main duct, mmAq
H_b=velocity head in the branch duct, mmAq
S=flow quantity ratio