An experimental study has been carried out in a 36-m long, 10-cm diameter in horizontal multiphase system. Oil with a viscosity of 2.5 cP was used as the liquid phase and carbon dioxide was the gas phase. The effect of drag reducing agents (DRA) on average pressure drop, maximum pressure drop and slug characteristics for superficial liquid and gas velocities of 0.5 to 1.5 m/s and 2 to 12 m/s, respectively, was studied at DRA concentrations of 0, 20 and 50 ppm. Temperature was kept at 25 °C and pressure was maintained at 0.13 MPa.

The DRA was effective in reducing the average pressure drop significantly for all superficial liquid and gas velocities in both slug and annular flow. The average pressure drop reduction of up to 82% for slug flow and 47% for annular flow was achieved. For slug flow, the effectiveness generally decreased with increase in superficial liquid velocity. The maximum pressure drop across the slug also reduced with addition of DRA. The effectiveness for maximum pressure drop was over 28% at a superficial liquid velocity of 1.5 m/s for all gas velocities.

At superficial liquid and gas velocities of 0.5 and 2 m/s, the flow pattern changed from slug flow to stratified flow by decreasing the slug frequency to 0 slug/min. when 50 ppm DRA was added. At higher liquid and gas velocities, the slug frequency also decreased significantly. The effective height of the liquid film decreased with addition of DRA.

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