| As aquaculture continues to develop,the variety of farmed aquatic products is increasing and production is rising,providing consumers with more choice and a richer source of protein and nutrients.At the same time,the quality and safety of farmed aquatic products have become one of the main concerns of consumers.The factors affecting the quality and safety of farmed aquatic products are complex and varied.The quality of aquaculture water is an important factor affecting the quality and safety of farmed aquatic products.In pond aquaculture,the main factor affecting the quality of the aquaculture water is the solid particle pollutants such as residual bait and feces produced during the aquaculture production process.Therefore,in order to maintain a good water quality environment,the treatment of solid particle pollutants such as residual bait and feces has been one of the important issues to be solved during the aquaculture production process.This thesis addresses the treatment of solid particle pollutants such as residual bait and feces generated during the production of recirculating water aquaculture in seawater ponds and designs a sewage collection device based on a seawater pond recirculating aquaculture system according to the actual situation of aquaculture production.The internal flow field distribution and the removal effect of solid particles are investigated by the computational fluid dynamics(CFD)method,which can provide some reference for the development of the sewage collection device.The main research elements of this thesis are as follows:(1)Numerical simulation method of the sewage collection device.The main components of the seawater pond recirculating aquaculture system and the main structure of the sewage collection device are introduced in detail.Based on the computational fluid dynamics method,the numerical simulation model of the sewage collection device is established.The Reynolds stress model(RSM)is used to numerically simulate the internal flow field of the sewage collection device.Solid particles such as bait and feces are assumed to be homogeneous spherical particles in density.The solid-liquid two-phase flow in the collector is described using a discrete phase model(DPM)based on Euler-Lagrange theory.(2)Verification of numerical simulation calculation model of the sewage collection device.A model is constructed for the fluid calculation domain of the sewage collection device.The structural parameters to be optimized for the sewage collection device are determined(inclination of the bottom of the collector cone,structural parameters of the diversion trough,and the height of the upper outlet).The fluid domain of the sewage collection device is meshed and the boundary conditions and appropriate physical parameters are set.Based on this,the flow field of the sewage collection device was simulated numerically on Fluent 19.2.Experimental measurements of the velocity of the flow field in the sewage collection device were carried out and compared with the numerical simulation results.The results show that the experimental measurement results are in good agreement with the numerical simulation results,which verifies the validity of the established numerical simulation calculation model.(3)Performance analysis of sewage collection device.The particle removal effect of the sewage collection device was investigated when solid particles were released at different locations and particle sizes at the inlet.The results show that when solid particles are released at different locations at the inlet,the particle removal rate at the bottom outlet of the collector gradually increases as the depth of the release location increases,and the average residence time of particles at the bottom outlet shows a trend of first decreasing and then increasing;when the particle size of solid particles is different,the particle removal rate at the bottom outlet of the collector gradually increases as the particle size increases,and the average residence time of particles at the bottom outlet first decreases and then increases.The average residence time at the bottom outlet decreases and then increases.The analysis shows that the closer the release position is to the bottom of the diversion trough,the better the solid particles flow out of the bottom outlet of the collector;the larger the particle size,the better the solid particles settle in the sewage collection device.(4)Structure optimization of the sewage collection device.The effect of different cone bottom inclinations,diversion trough structure,and the height of the upper outlet on the flow field distribution and particle removal in the sewage collection device was investigated when 150 μm particles were released from a depth of 0.8 m at the inlet.The results show that when the bottom inclination of the collector cone is 23.12°,the diversion trough offset distance is 1.25 m,the length of the straight trough section is 3 m and the height of the upper outlet is 0.2 m,the bottom outlet of the collection device has a higher particle removal rate,a shorter average particle retention time and better discharge performance. |
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