The mass transfer in S-shape dual in-plane short radius bends is investigated under annular air-water flow conditions. Experiments were performed for a Schmidt number (Sc) of 1280 for different lengths of straight pipe (LID) between the bends. Standard 90 bends with radius of curvature (r/D) of 1.5 were tested for LID from 0 to 40 for water (J(L)) and air (J(v)) superficial velocities of 0.28 and 29 m/s, respectively. The maximum mass transfer was found to occur on the outer wall of the first bend in all cases. The region of high mass transfer in the second bend is located near the outlet of the bend outer wall and was approximately 60% of that in the first bend for the L/D = 0 case. This value increased and the location moved upstream as the separation distance was increased, with a magnitude of approximately 85% of that in the first bend at LID of 40. The effect of J(v) and h. on the mass transfer for LID = 0 was determined for J(v) and J(L) in the range 0.17-0.4 m/s and 22-30 m/s, respectively. The local mass transfer distribution was similar in all cases, with J(v) having a more significant effect on the mass transfer enhancement. The phase redistribution within the dual bend for LID = 0 was visualized using laser induced fluorescence. The high mass transfer locations were found to correlate well with the locations of liquid impingement. (c) 2014 Elsevier Ltd. All rights reserved.