Document 85YOVKyzbD1LRGEzNg0RDQee5

752 CHAPTER 41 1948 Guide ' Air Duct Design ableT 2. Circular Equivalents of Rectangular D ucts for Equal Friction--(Continued) Fig. 6. Loss of Pressure in Elbows Rectangular equivalents of round ducts are also given in the curves of Fig. 5 which are plotted from data based on Equation 7. To use the chart, locate the diagonal curve giving the diameter of the round duct. The width and height of an' equivalent rectangular or square duct may then be read as the abscissa and the ordinate of any point on the curve. Multiplying or dividing the length of each side of a pipe by a constant is the same as multiplying or dividing the equivalent round size by. the same constant. Thus, if the circular equivalent of an 80 x 24-in. duct is required, it will be twice that of a 40 x 12-in. duct, or 2 X 23.3 = 46.6 in. A comprehensive study of equivalent duct sizes is to be made by the A.S.H.V.E. Research Laboratory for the purpose of determining whether Table 2 and Fig. 5 should be revised. 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 duct6. The curves in Fig. 6 give the number of diameters or widths of pipe which have a frictional Table 2. Circular Equivalents of Rectangular Ducts for Equal Friction3 Sum Rectangular 8 8.5 9 9.5 10 10.5 11 11.5 12 12.5 13 13.5 14 14.5 15 15.5 Duct 16 3 5.2 5.4 5.5 5.7 5.8 5.9 6.0 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 7.0 7.1 3.5 5.7 5.9 6.0 6.2 6.3 6.5 6.6 6.7 6.9 7.0 7.1 7.3 7.4 7.5 7.6 7.7 7.8 4 6.1 6.3 6.5 6.7 6.8 7.0 7.1 7.2 7.4 7.5 7.7 7.8 7.9 8.1 8.2 8.3 8.4 4.5 6.5 6.7 6.9 7.1 7.2 7.4 7.6 7.7 7.9 8.0 8.2 8.4 8.5 8.6 8.7 8.9 9.0 5 6.9 7.1 7.3 7.5 7.7 7.8 8.0 8.2 8.3 8.5 8.7 8.8 8.9 9.1 9.2 9.4 9.5 5.5 7.3 7.5 7.7 7.8 8.1 8.3 8.5 8.6 8.8 9.0 9.2 9.4 9.5 9.6 9.8 9.9 10.1 Additional sizes; 4 X 5 = 4.9; 4X8'= 5.4; 4X7 = 5.8; 5X5 = 5.5; 5X8 = 13;5X 7 = 6.5. 753