Hydrodynamics of waste collection in a recirculating aquaculture tank with different flow-guide discs

To improve the efficiency of waste collection in recirculating aquaculture tanks (RATs), this study proposed a dual-channel RAT with flow-guide discs on the overflow pipe close to the bottom. First, an experimental verification system was designed, and the validity of the two-phase flow model was verified by comparing the experimental results. Then, the liquidsolid flow characteristics were analysed by comparing the velocity distribution, particle trajectory, retention time and removal rate. Finally, the influences of the parameters of the flow-guide discs on the particle agglomeration effect were obtained by comparing the discharge rate of particles under different hydraulic retention times (HRTs). The results indicate that the flow-guide disc weakens local reflux, reduces the overcurrent area and the low-speed vortex area at the bottom of the tank, and thus shortens the residence time for particulate matters. As the diameter of the flow-guide disc increases within a certain range, the flow velocity gradient and eddy intensity near the disc will increase, resulting in a shorter residence time for particles. Furthermore, as the height of the flow-guide disc to the bottom of the tank decreases, the flow velocity below it accelerates, which is beneficial for improving the discharge rate of particulate matter. However, when the height of the flow-guide disc increases to a certain extent, the influences on the hydrodynamics of waste collection become weaker.