Experimental investigation of head resistance reduction by air bubbles in turbulent Couette-Taylor flow

The effect of samll bubles injecting on the head resistance of the flow closed between co-axial cylinders (Couette-Taylor system) was experimentally investigated In this research,. The Pressure difference of flow between two certain point along axis cylinders was measured to determaine haed resistance. According to variations of rotary and axial Reynolds numbers, the made Couette-Taylor flow was fully turbulent and Taylor vortices appeared in the annulus gap. Water as working fluid and the air with room condition were used to produce small bubbles which were injented into anuulus gap at the bottom of system. Flow visualization technique is used to determine diameters and distribution of bubbles in flow. The preliminary results showed that the air bubbles can reduce the head resistance up to up to 60% in the best case. Head resistance is increased as the rotary Reynolds number is increased, a phenomenon which can be explained in terms of the accumulation of bubbles into Taylor vortex cores and enhancement of momentum transfer. However, in the small rotary Reynolds numbers, the reduced fluid density by air bubbles plays a major role in head resistance reduction. In this regime, it observed that incresing axial Reynolds number promotes head resistance reduction, which is due to damping vortices by axial flow.