Design and optimisation of swirl pipes and transition geometries for slurry transport
This thesis is primarily concerned with the design and optimisation of transition ducts for lobed swirl-inducing pipes. Single-phase swirl-inducing pipe flows were modelled and optimised using Computational Fluid Dynamics (CFD). Optimised pipes were manufactured using rapid prototyping and an experimental investigation examines their effect on settling slurries of different densities. The CFD model was successfully validated by experimental measurements of pressure loss and tangential velocity. An optimum transition geometry was determined for use as an entry and an exit duct with optimised swirl inducing pipe. Transition pipes either before or after the swirl inducing pipe reduced entry and exit pressure losses by providing a gradual transition from circular to lobed cross-section. They also increased induced swirl and reduced swirl decay. CFD simulations with carboxymethyl cellulose (CMC) instead of water as the flow medium indicated that as the viscosity increased, a smaller pitch, thereby a tighter twist, is required in the swirl-inducing pipe to achieve effective swirl induction. Settling slurry experiments showed that swirl induction resulted in better particle distribution and prevented solids dragging along the bottom of the pipe. This suggests reduction in localised erosion and provides an opportunity to operate at lower flow velocities without blockage. Lower velocities mean lower energy costs and further erosion reduction. When transitions were incorporated pressure losses across the swirl inducing pipe were reduced and the length of particle suspension increased. It was proven, by CFD and experimentation, that entry and exit transition should be an integral part of the swirl inducing pipe. This results in an efficient swirl induction which reduces energy costs from high pressure losses that otherwise occur due to sudden changes in flow geometry.