3362 (RP-403) -- Duct Velocity Profiles and the Placement of Air Control Sensors PDF

Pitot tubes were used to determine air velocities downstream of 69 sheet metal duct fittings, including elbows, conical contractions, conical diffusers, round-to-round junctions, and rectangular-to-round junctions. For target mass-average velocities of 1000 and 2500 fpm, centreline velocities were measured at distances of 1, 2, 4, 6, and 10 diameters downstream of the fittings. Vertical and horizontal velocity profiles were obtained at the same stations for a target mass-average velocity of 1750 fpm. For junctions, measurements were made over a range of main-to-branch flow rate ratios. For one elbow and two tees, profiles were also obtained at downstream distances larger than 10 diameters. Results are expressed as the ratio of measured velocity to average velocity. Flow is not fully developed for any case. Flow rate calculations using profile data for 20 cases yield large errors at 1 diameter downstream of any fitting. However, the error is significantly lower at the 10-diameter station. Typical vertical and horizontal profiles at each measuring station are shown graphically. Measured centreline velocities are tabulated.

KEYWORDS: variable volume air conditioning, controls, speed, ducts, air flow rate, sensors, measuring, location, fittings, calculating, accuracy, air conditioning.