A novel mesoscale helical baffled design of oscillatory baffled reactor (OBR) has been constructed and characterised in the net flow laminar regime net flow Reynolds numbers (Re-n) (net flow Reynolds numbers Re-n <= 10). A high degree of plug flow can be achieved in this design of OBR. In conventional OBR designs, plug flow is generated by the formation of well-mixed volumes in series due to toroidal vortex formation generated by the interaction of the baffle geometry with an oscillatory motion superimposed upon the net flow. The helical baffled design represents a significant development in oscillatory baffled reactors, as this system can provide plug flow behaviour over a wider range of oscillatory Reynolds number (Re-o), (50-800). This is due to the combined effect of the swirling flow and vortex production. The oscillation amplitude was demonstrated to have a strong effect on the flow behaviour. The results revealed that the helical baffled design exhibited plug flow at high oscillation amplitudes (x(o) >= 2 mm or Strouhal number (Str), Str <= 0.2). The highest number of equivalent tanks-in-series was obtained at Re-o = 400-700. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.