Design methodology for the swirl separator

A methodology is proposed for designing the swirl separators that are commonly used for removing waste solids in recirculating aquaculture systems. The size of the swirl separator is calculated based on the desired solids removal efficiency and the water flow rate to be treated. The approach was validated by performing experiments on swirl separators with diameters of 0.6 and 1.5 m and by carrying out CFD simulations. Results show that tank height and the position of the inlet have a minor influence on separation performance compared to outlet geometry, inlet diameter and tank diameter. It is also shown that solids separation is mainly due to gravity rather than centrifugal forces. Separation follows closely the theory of sedimentation in well-mixed systems and can be predicted using a simple analytical model. The swirl flow generates relatively strong horizontal mixing but relatively weak axial mixing. As a result, particles are uniformly distributed across the tank, and separation is mainly by sedimentation. The settling velocity of the particles was accurately predicted by a new correlation that takes particle shape into account.