Effect of Paddle-Wheel Pulsating Velocity on the Hydrodynamic Performance of High-Rate Algal Ponds

High-rate algae ponds (HRAPs) are widely used in increasing biofuel production because of their effective design in terms of cost and power consumption. Using modeling and simulation techniques is an economical approach for improving the design of raceways. Previous modeling studies reported the use of a flat velocity profile, thus failing to depict the real phenomena involved. However, in practice, the rotating paddle wheel in HRAPs produces a pulsating velocity that is necessary for culture growth. In this study, the hydrodynamic characteristics of algal ponds were investigated using a coupling algorithm to map the effects of a two-dimensional paddle wheel on a three-dimensional raceway model. HRAPs with and without paddle wheels were compared in terms of hydrodynamic mixing, dead zones, and power consumption. The results revealed that compared with a flat velocity at the inlet, the pulsating velocity of a paddle wheel produced a large dead zone volume with reduced power consumption, shear stress, and turbulence. A few pond design modifications were tested with this realistic situation and an additional recirculation zone was found near the paddle wheel. This zone needs to be addressed in future pond designs.