A new generation of swirl-inducing pipes with continuously varying cross-sectional geometry have been designed with surprisingly beneficial results. The advantages of swirl induction in pipes, particularly for improved transportation of particle-bearing liquids, are established. Coarse particles in water do not generally form stable suspensions and are of especial concern for a number of industrial processes. Swirling flow results in better particle distribution, requires low flow velocities to keep particles in suspension, and helps prevent pipeline blockage. Improved wear performance can be inferred from greater numbers of particles supported by the flow, and reduced impact angles and impact velocities. Historically, research into swirl-inducing pipes has indicated a lobed helical geometry of fixed cross section and constant helix as the near optimum design in swirl induction, at a low pressure cost. In addition to its hydraulic advantages, the lobed design dredges particles into the flow in a smooth mechanical action. Transition ducts to such swirl pipes were designed for the primary purpose of reducing entry and exit pressure losses. However, increased exit swirl intensities and reduced rate of swirl decay indicate swirl pipes with continuously varying cross-sectional geometry are the way forward. (c) 2007 American Institute of Chemical Engineers.