Document ZJjEMxgJeNzKqnd0EjddNLYEO

802 CHAPTER 31 1957 Guide 03 2 3 .? sb <o o Bs Ph o 1* <' GO 2N Under the best practice, 0.7 to 0.8 of the change in velocity pressure is actually recovered, but for practical design an average recovery of 0.5 is assumed. Hence, the actual regain Pr is: Design charts based on Equation 13 and rectangular ducts having aspect ratios of 3 to 1 or less are presented in Figs. 12 and 13. The duct length of any section should include the equivalent length of any elbows or transitions within the section. The charts apply to construc tions where regain takes place unaccompanied by radical change in direc tion; namely, to straight-through sections of divided-flow fittings. i f (Static Regain Method). A duct layout is shown in Fig. 14. The fi ufiwers cfm. Outlets 1, 2, 3 and 4 deliver 1500 cfm each, and outlets 5 and t C i ac*V The operating pressure loss at all outlets is 0.12 in. water. Initial nmk velocity is assumed as 1500 fpm; the area of the trunk duct will then be 5.33 ahi +an<* s-ze ^ x in. It is assumed that for this example it is desir- o t0 njaintain a 16-in. depth on all duct sections. Determine the sizes of duct nhf -0DSj ' T and G so that substantially the same static pressure will be t-ained at each of the outlets, and find the total pressure loss of the system. Solution: r A-. lze Section F by the equal friction method so that it has the same rate of anA l?n lss 48 Section A. Section A is equivalent to a 29.2 in. round duct (Table 1) rat* f Pressure loss from Fig. 3 is 0.13 in. per 100 ft. For 2000 cfm flowing at this of pressure loss, the indicated round duct diameter for Section F is approxi-