The mass transfer in dual in-plane short radius bends arranged in an S-configuration was measured for different separation distances (L/D) between the two bends. Experiments were performed using a wall dissolution technique with gypsum test sections at a Schmidt number (Sc) of 1280 for L/D from 0 to 5 at a Reynolds number (Re) of 70,000. The maximum mass transfer was found to occur between the outlet of the first bend outer wall and the inlet of the second bend inner wall in all cases. The maximum mass transfer occurred for L/D = 0 and was 3.2 times larger than the average mass transfer in a fully developed pipe flow under the same flow condition. The maximum mass transfer decreased as the separation distance between the two bends was increased. The effect of Re on the mass transfer enhancement for a separation distance of L/D = 0 was examined for Re in the range 40,000-130,000. The peak mass transfer was found to scale as Re-0.93 and was similar to that of the peak mass transfer in a single bend. (C) 2014 Elsevier Ltd. All rights reserved.