Document 0qQazNEb6govXnbvQmX5mKDvV

Air Duct Design .705 the air, and are therefore conveniently expressed as a fraction of the velocity head: and for standard air hr = c 2g (4) where hr = dynamic pressure loss, feet of fluid flowing. Hr = dynamic pressure loss, inches of water. v = velocity of fluid, feet per second. . V:: Fig. 4. Relation Between Velocity and Velocity Head fob Standabd Aib 2g = the velocity pressure corresponding to the mean velocity of flow, feet of fluid flowing. V = mean velocity of standard air, feet per minute. C = an experimentally determined constant (dynamic loss, coefficient). . It can be seen from Equation 4 that the dynamic loss coefficient is. inde pendent of both density and the units used, and that it represents the number of velocity heads lost at the conduit transition or bend. Values i Ihe dynamic loss coefficient for various duct elements are sometimes tabulated,*7-8 though it should be kept in mind that absolutely reliable dynamic loss coefficients have not yet been fully established for all duct elements. Fig. 4, which shows the relation of velocity pressure to velocity for stand- ardair (V = 4005\/Hr), can be conveniently used to find the total-dynamic Pressure loss for any duct element-with known dynamic loss coefficient C. ms coefficient is nearly independent of the air velocity and the roughness i the duct walls; therefore dynamic losses cannot theoretically be computed 88 friction losses. For duct components where intense eddying flow is not