Experimental Investigation of the Effects of Air Pocket Configuration on Fluid Transients in a Pipeline

Air pockets entrapped in pipeline systems are required to be non-intrusively diagnosed by fluid transients. In this study, experimental investigations are used to compare the transient transmission and reflection effects of stationary inline and offline air pocket volumes along a pipe under zero base flow conditions. Comparison with theoretical modeling indicated that the difference in the transient response between the two configurations is primarily due to the inertia in the connecting water column associated with offline air pockets. This means that the transient response depends on both the volume of the pocket and the dimensions of the cavity. Analysis in the frequency domain showed that the offline air pocket may be characterized by the resonant frequency, at which reflection is maximized, while the inline pocket is characterized by a cutoff frequency above which there is little reflection. The damping of the transient signal may also be used to diagnose air, as the presence of air increases the damping rate by a factor of 3-4.