Measurement of the entrance length and friction factor of ducts using tracer gas techniques.

We describe the use of constant injection and pulse injection techniques for measurement of airflow in a duct. Tracer-gas measurements were compared with measurements made using a pitot tube and a hot-wire anemometer. Tracer-gas concentration, air velocity and pressure distribution were measured at various distances from the duct wall and inlet. An empirical equation was obtained for the entrance length required to achieve fully-developed turbulent flow and this was compared with measurements made using a pitot tube and hot-wire anemometer. We present a relationship for the friction-factor and Reynolds number derived from tracer-gas measurements.