The mass transfer distribution and flow separation behavior in a 90 degrees short elbow (radius to diameter ratio 1.0) were investigated experimentally in the Reynolds number range Re = (3-15) x 10(4). The mass transfer distribution in the 90 degrees short elbow showed two high peaks on both sides of the elbow centerline of the inner elbow wall at lower Reynolds numbers (Re = (3-5) x 10(4)). In order to characterize this phenomenon, velocity measurements were carried out using particle image velocimetry (PIV) to explain the flow separation in the short elbow, followed by the flow reattachment in the downstream. A comparative study of the mass transfer distribution and the flow fields on and near the inner wall indicated that the high mass transfer is highly responsible for the flow separation, where the turbulence intensity increased and contributed to the high mass transfer on the inner elbow wall. By increasing the Reynolds number, the flow separation region decreased in size and it came closer to the elbow centerline, which resulted in a lower mass transfer coefficient on the inner elbow wall at higher Reynolds numbers. (C) 2019 Elsevier Ltd. All rights reserved.