Structural Design And Performance Optimization Of Helical Fish Lifting Device

With the sustainable development of China's aquatic industry,the design and use of fishing machinery began to be promoted,and became an important equipment in fishing production.Fish lifting machine is required for fry and juvenile fish to have certain lifting ability while ensuring the non-destructive of fish body.The screw pump is the earliest water pump in the world.It was originally used for pumping water.After continuous development,the screw pump has been transformed into conveyor,mixer,shearer,fish lifter and so on,which is used in many fields.Compared with other lifting machines,the screw pump-based lifting machine has a smaller damage rate,which meets the actual needs of live fry and juvenile fish lifting.Aiming at the needs of fish fry and juvenile fish with body length less than 150 mm,this paper starts with the design theory of screw pump,determines the design parameters to meet the transmission requirements based on the design theory of screw pump,establishes the three-dimensional model of screw fish lifting device through Workbench according to the parameters,and then imports the three-dimensional model into the meshing software ICEM.The grid file is then imported into CFX software to set up and calculate,and finally to the data output of CFX.Because of the complexity of gas-liquid two-phase flow,the first step is to calculate 100% liquid in the fluid field,modify the three-dimensional model and adjust the CFX parameter settings according to the calculation conditions,until the calculation converges and is consistent with the actual situation,then further start the simulation settings of the two-phase flow,restore the internal flow state and obtain the model of the helical fish lifting device which meets the transmission capacity requirements.After obtaining the model parameters,the prototype is designed and manufactured by using Solidworks three-dimensional modeling software.The actual performance of the spiral fish lifting device was investigated through experiments.In the experiment,the lifting capacity and the damage rate of the fish body of the helical fish lifting device were taken as performance indicators,and the performance of the helical fish lifting device was compared and analyzed under different rotational speeds,external diameter,lead and external diameter ratios.In the experiment,the damage rate of fish body was counted by image recognition technology,and the transmission speed was obtained by weighing the fish in the subsequent fish distributor.The experimental results show that the ratio of lead to outer diameter has greater effect on fish body damage rate than that of outer diameter at a fixed speed.When the ratio of lead to outer diameter is 1.25,the damage situation of fish body is obviously better than that of other two kinds of lead,and the larger the outer diameter,the higher the damage rate.The influence of outer diameter on lifting ability is much greater than that of lead to outer diameter ratio,and the ratio of lifting ability to outer diameter and lead to outer diameter is both.There was a positive correlation.Because the damage rate of fish body still exists,it needs to be optimized.After analysis,the low volume fraction of liquid is the main cause of mechanical damage,too large external diameter will lead to too large pressure gradient,and will also cause damage to fish.The liquid volume fraction and pressure gradient of each chamber during the operation of the helical fish lifting device are the factors affecting the damage rate.In the subsequent optimization,only the liquid volume during the operation of the device needs to be considered.According to the experimental results,the best performance of the prototype is selected as the initial model of optimization.The VKI multi-purpose optimization system developed by Von Karman Institute of Hydrodynamics in Belgium is used to optimize its performance,aiming at maintaining the transmission capacity and increasing the volume fraction of water in the helical chamber.The data obtained from the experiments show that when the ratio of the outer diameter of the guide is 1.3 and the inner diameter and the outer diameter are 172 and 430 mm respectively,the damage rate of the fish body decreases to less than 2%,and the lifting capacity increases by 3%,which improves the overall performance of the spiral lifting device.The device not only guarantees the ability of fish lifting,but also successfully reduces the damage rate of fish body and labor intensity.It has great advantages over other fish lifting machines and provides a reference for the future development of fish lifting machines.Generally speaking,the spiral fish lifting device designed in this paper meets the requirements of modern aquaculture in reducing fish body damage rate,improving fish lifting capacity,saving resources and reducing costs.It has good application and promotion prospects,and can further enhance the level of aquaculture engineering in China.