Tracer Study of Pipe Flow Behavior to within Two Microns of the Wall

Abstract

A high precision, high spatial resolution tracer technique was used to study low noise, steady air flow in a 1½ by ½ in. rectangular pipe with particular attention to the flow several microns from the pipe floor. The flows investigated had velocities which correspond to pipe Reynolds numbers of 16–4300. Experimental velocity profiles for the flows extrapolate to the no-slip condition at the floor. However, close attention to the measurements of the flow 2–10μ from the floor reveals a preponderance of data points lying on the high velocity side of the profile. The data are believed to mirror a real deviation of the flow velocity from the theoretical profile in the region of the floor and greater than 2 μ from it. The cigarette smoke tracers could be located within a micron from the floor, and the measuring error in determining the velocity varied from 0.02 mm/sec in flow of 5 mm/sec and less, to 0.15 mm/sec in a flow of 50 mm/sec.