Hydrodynamics of waste collection in a recirculating aquaculture tank with different numbers of inlet pipes

To improve the utilization of energy input from inlet pipe jets and the efficiency of waste collection in a recirculating aquaculture system (RAS), the hydrodynamics and self-purification efficiency of square fillet aquaculture tanks were studied under different numbers of inlet pipes and particle physical properties. First, a numerical model was established by reference to the experimental model, and the validity of the numerical method was verified by comparing the experimental results. Then, the hydrodynamics of the aquaculture tanks were analyzed, including velocity distribution, vorticity strength, energy utilization efficiency, flow uniformity index and self-purification efficiency. Finally, the discharge rates of particles at overflow and underflow with different densities and diameters were also analyzed. The results reflect that the swirling velocity, flow uniformity index, energy utilization efficiency, turbulence and secondary flow intensity increase under steady injection, which is conducive to improving the self-purification efficiency in the RAS. In the case of a single inlet pipe and a particle density of 1300 kg/m3, the discharge rate is the highest, and the residence time is relatively short. The smaller the particle size is, the longer the residence time and the lower the discharge rate. The larger the particle size is, the faster the removal rate increases, and the effect is not obvious for particles larger than 2.0 mm in diameter. The inclusive analysis not only explores the hydrodynamics in aquaculture tanks with different water injection structures but also recommends RAS structural optimization design.