Experimental study on sewage collection and related performance of square arc angle aquaculture tank 

Abstract In order to study the influence of the diameter to depth ratio of the square arc angle aquaculture tank on the flow field and sewage discharge characteristics in the aquaculture tank, a reduced physical model test system of the aquaculture tank with single-drain sewage discharge structure was established based on the actual size of the recirculating aquaculture tank. Under the conditions of different positions of the inlet pipe (single inlet pipe set at arc wall, double pipe set at opposite arc wall), the number of daily water cycle times (40 times, 60 times), the inflow angle (0°, 45°) and other parameters, the influence of the variation of diameter to depth ratios (2:1~7:1) (that is, the ratio of the length of the tank to the depth of water) on the flow field characteristics and sewage discharge effect was systematically analyzed. The results show that the appropriate diameter to depth ratio is the key to improve the sewage discharge efficiency in the tanks. The smaller the diameter to depth ratio is, the higher the sewage discharge efficiency is. When the diameter to depth ratios of the tanks with square arc angle are 2:1~3:1, the sewage discharge efficiency is good. When the diameter to depth ratio are 3.5:1~4.5:1, the sewage discharge effect is better. When the diameter to depth ratio are 5:1~7:1, the sewage discharge effect is weakened greatly. The self-purification capacity of aquaculture tanks and the discharge efficiency of sewage can be improved by choosing the proper diameter to depth ratio, increasing the daily water cycle times times and adjusting the placement of inlet pipes and inflow angle according to the actual needs. The the flow field characteristics in the aquaculture tank are closely related to the distribution and discharge efficiency of sewage. The high uniformity of the flow velocity is conducive to the accumulation of sewage. And the higher the flow velocity is, the higher the discharge efficiency is. The research results can provide theoretical basis and reference for the optimal design of diameter to depth ratio of square arc angle aquaculture tank.