Field study on the dynamic characteristics of sewage collection in a circular aquaculture tank

Abstract To solve the problem of low performance in sewage collection of the circular aquaculture tank, this paper systematically studies the influence of flow rate Q of the jet pipe, the deployment distance ratio d/r (d is the distance between the midpoint of the axis and the nearest tank wall, and r is the radius of the circular aquaculture tank), the deployment angle θ, and the structure of the jet pipe on the dynamic characteristics of sewage collection. In the field study, a high-definition camera was used to record the distribution of sewage, the distribution of the flow field in the aquaculture tank was measured by the Acoustic Doppler Velocimetry. Thus, the distance between the sewage and the center of the tank was quantified. Meanwhile, the sewage collection performance of the aquaculture tank was evaluated by comparing the maximum distance between the sewage and the center of the tank under different working conditions. The results indicated that the formation of an effective horizontal circulation in the circular aquaculture tank is the primary condition for sewage accumulation to the center of the tank, and different flow rate Q of the jet pipe, the deployment distance ratio d/r, the deployment angle θ, and the structure of the jet pipe all can affect the sewage collection effect in the tank. In the horizontal single-pipe single-hole jet pipe structure mode, the best sewage collection result was obtained at the deployment angle θ of 0°, the deployment distance ratio of 1/4, and the deployment flow rate Q of 7 L/s; when the deployment flow rate Q was less than 7 L/s, the sewage accumulated near the tank wall, and the sewage particle dispersion was relatively high. In the vertical single-pipe porous jet pipe structure mode, better sewage collection performance was obtained when the deployment flow Q was adjusted to 7 ~ 9 L/s, the deployment angle θ was set to 45°, and the deployment distance ratio d/r was set to 1/4. The sewage collection performance of the aquaculture tank under the vertical single-pipe porous jet pipe deployment mode was obviously better than that of the horizontal single-pipe single-hole jet pipe mode. The results can directly and effectively guide the inlet design of such kind aquaculture tanks to reduce the flow rate and energy consumption and improve sewage collection performance.