Evaluating the effects of elbows and duct size on the accuracy of hand-held Pitot traverse flow measurements

Abstract

This study determined the deviations between Pitot traverses performed by traditional hand-held methods and a traverse device designed to hold the Pitot tube perfectly in position, effectively eliminating errors due to yaw, pitch, and insertion point deviations. The hand-held measurements were performed twice by nine different test subjects, while each position was measured with the traverse device five times. Two ten-point traverse measurements were taken at various distances downstream and upstream from a 90º elbow. Two different-sized ducts were used in the study, a 3.875-inch and a 6.875-inch. Airflows determined from these measurements were compared to the presumed "gold-standard" values for each duct, which is the airflow at the most downstream location measured using the traverse device (Q Ref). The velocity in each duct was set to approximately 4500 FPM.