Mass transfer measurements in a decaying swirl flow in a pipe were carried out, using the electrochemical limiting diffusion current technique. The measurements were taken from local electrodes of 1 mm diameter without a developing concentration boundary layer around. Swirl was generated using short helical guide-vanes with vane angles between 15 and 60 degrees at the outer edge of the vanes to the duct axis. The pressure drop measurements were also taken to perform an energy analysis. For a Reynolds number range of 1700-10000, the overall energy correlation for a representative length of 36.5 diameter were evaluated to be Sh(s)(Sc)(-0.33) = 0.3705(1 + tan theta(0))(-0.120) X-0.236, where theta(0) is the vane angle at the outer edge of the helical swirler and X is the energy dissipation parameter.