In this work, the results of the experimental investigations of oil-water flow in the absence and presence of water-soluble drag-reducing polymer in two different horizontal pipe diameters (55.7 and 74.67-mm ID) and their comparisons with the results in horizontal 30.6-mm ID pipe were presented. During the study, mixture velocity of the oil-water flow was varied from 0.1 to 1.6 m/s while the input oil volume fraction was varied from 0.05 to 0.9. At each experimental run, the polymer master solution of 2000 ppm concentration was injected into the flow at a controlled flow rate such that 40 ppm concentration of the polymer was achieved in the water phase. The six flow patterns previously observed in the 30.6-mm ID pipe reduced to four in the larger pipes. Although the presence of the polymer only affected the water-continuous flow patterns just like in the 30.6-mm ID pipe, the increase in the pipe diameter increased the regions of separated flow patterns before and after the addition of the polymer. Similarly, the frictional pressure gradients were significantly decreased by the polymer addition in all the three pipes resulting to huge drag reductions, which virtually decreased with increase in the pipe diameters.
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