Two-phase vertical flows are of utmost importance for petroleum production, since underground petroleum reservoirs produce oil and gas simultaneously, which must flow together upward to the sea floor through wells, and from these to the production floating units through suspended pipes (risers). Along the pipelines, the mixture of oil and gas may develop several flow patterns — such as bubble, slug, churn and annular flow. These physical configurations present specific characteristics that demand distinct modeling of the head loss as a function of the flow rate. The correct characterization of the flow patterns, under given operational conditions, is fundamental to the modeling of the dynamics of the flow and to the relation between head loss and flow rate. In the literature, most studies on the establishment of the flow patterns have been carried with water and air, and have been restricted to the case of static pipes, while production risers are in constant movement due to the action of waves, sea currents and the displacement of the floating production unit. In the present work, an experimental study of vertical two-phase flow of water and air is conducted with the oscillatory movement of a long and slender flexible vertical pipe of 8,0 m of length and 25,4 mm of diameter. The head loss is measured for different frequencies of oscillation. Comparisons are made between the static and oscillating pipe, with regard to the flow patterns and head losses. The effect of the frequency of oscillation is detected.

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