We describe the use of the constant injection tracer gas technique to study turbulent flow in a rectangular duct. A comparison between tracer gas measurements and measurements made using a hot-wire anemometer and a pitot tube is presented. Tracer gas concentration, air velocity and pressure distribution were measured at various distances from the duct wall and inlet. The Reynolds number based on the hydraulic diameter and the bulk velocity was varied between 7.5 x 103 and 18.6 x 103. An empirical equation for the entrance length required for fully developed turbulent flow was obtained and this was compared with experimental results.
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