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Chapter 31 _________
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1945 Guide
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Air Duct Design __________'-
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required, it will be twice that of a 40 x 12-in. duct, or 2 X 23.3 = 46.6 in.
Elbow Friction Losses It is customary to express the dynamic and friction losses in elbows as
equal to a number of diameters of round pipe, or a number of widths of
rectangular pipe, or equivalent length of duct3. The curves in Fig. 5 are arranged to read the number of diameters or widths for determining the lineal feet of pipe having a frictional resistance equivalent to the pressure
*A.S.H.V.E. Research Report No. 1211--Pressure Loss Caused by Elbows in 8-1neb Round Venti lating Duct, by M. C. Stuart, C. F. Warner and W. C. Roberts (A.S.H.V.E. Transactions, Vol. 48,1942, p. 335).