Effect of Inflow on the Hydrodynamic Behavior of Ponds in Recirculating Aquaculture Systems

Constant and proper mixing of water in fish farms is essential for creating maximum uniformity, minimizing stagnant areas, properly distributing oxygen, and removing solid waste from the bottom of the ponds. The effect of the inflow installation mode and inflow momentum force in octagonal ponds was examined on the hydrodynamic flow mixing by laboratory modeling. For this purpose, the inflow was analyzed in three modes with angles of 90, 60, and 30° and the inflowing force at four levels with values of 0.004, 0.009, 0.013, and 0.018 N by the residence time distribution curve and hydraulic efficiency of octagonal ponds. The laboratory modeling results revealed that the inflow at the 90° mode for all four-momentum forces does not form an eddy current and short circuit in the pond's flow, as the result of which the hydraulic efficiency of the pond falls in the weak range. To improve the hydraulic efficiency of the pond, the inflow was installed at 60 and 30° modes; the results demonstrated 2.68 and 3.26 times higher efficiency than the 90° mode. Moreover, for all three inflow installation modes, the hydraulic efficiency had an inverse relationship with the inflow momentum force.