| The stirring action of the agitator is to make the materials in the tank can be fully mixed,and the materials can be exchanged and contacted in time,and the solid and liquid are uniformly mixed.How to enhance the mixing effect is the key to the optimization design of the mixing equipment.Different variables have different mixing effects.The stirring process in the stirred tank can be reflected by the flow field distribution,but the solid-liquid two-phase flow is complicated.It is difficult to analyze the microscopic characteristics of the stirring process by theoretical analysis and experimental methods.Therefore,the computational fluid dynamics method is used to study the internal flow field characteristics and solid-liquid suspension characteristics of the horizontal pig manure straw anaerobic fermentation tank under different variables,so as to determine which variable has a good mixing effect in the tank.The main research contents of the thesis are as follows:(1)Taking single-phase flow as the research object,the effects of different stirring speed and liquid viscosity on the flow field characteristics were analyzed.Establish 3D geometric models,divide meshes;establish mathematical models,physical models;set boundary conditions and other numerical simulations.The analysis shows that the greater the speed in a certain speed range,the larger the average velocity of the flow field,the better the flow effect,but the higher the speed,the better the flow characteristics at 3 rpm and 5 rpm.The greater the viscosity,the smaller the maximum velocity of the fluid,the greater the turbulence intensity and the better the flow effect.(2)Taking the pig manure straw-water solid-liquid two phases as the research object,the flow field characteristics in the tank at 3rpm were analyzed.It is concluded that the flow pattern in the tank is mainly caused by the circulation motion around the stirring shaft,and the axial movement is not obvious.The average density of the bottom of the tank is higher than that of the middle and the top,and the bottom area of the tank is prone to form a dead zone.And along the axial direction,the density of the right side wall is greater than the density of the left side wall.(3)Analyze the solid-liquid suspension characteristics of the tank under the three variables of different stirring speed,solid particle diameter and solid phase solid content.It is concluded that increasing the stirring speed is beneficial to the uniform stirring of the solid particles in the mixing tank,but the greater the rotation speed,the better.When the rotation speed is 5 rpm,the input energy has reached the energy required by the solid itself,and the increase of the stirring speed has little effect on the uniformity of the solid phase mixing,so the rotation speed of 5 rpm is the optimum rotation speed.The larger the particle size of the solid particles,the greater the average pressure that the agitator is subjected to,the more uneven the concentration distribution,and the more solid accumulation at the bottom of the mixing tank,which may increase the agitation force for large particles.The larger the initial volume fraction of the solid particles,the more uneven the radial distribution and the more uneven the dispersion of the particles.(4)By numerical simulation method,the stirring speed is 5 rpm,the solid particle diameter is 0.05mm-0.1mm,and the initial solid content of the particles is 10%-15%.The solid particles are more uniform in suspension and the stirring has a good effect. |
PDF Full Text Request