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Convert Flat Oval Ducts to Round Sizes Formula and Calculator
Convert Flat Oval Ducts to Round Sizes, Formula and Calculator
To convert round ducts to flat oval sizes, use Equation (1) (Heyt and Diaz 1975), the circular equivalent of a flat oval duct for equal airflow and resistance.
To determine the round duct size, enter oval duct minor and major axis sizes to calculate round duct diameter De.
De = ( 1.55 AR0.325 ) / P0.250
where AR is the cross-sectional area of flat oval duct defined as
AR = ( π a2 / 4 ) + a ( A - a )
and the perimeter P is calculated by
P = π a + 2 ( A - a )
De = circular duct diameter for equal length, fluid
resistance, and airflow, in.
a = length one side of duct, in.
P = perimeter of flat oval duct, in.
A = major axis of flat oval duct, in.
a = minor axis of flat oval duct, in.
AR = cross-sectional area of flat oval duct, in2
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