Fluid-solid Thermal Coupling Analysis And Optimization Design Of Co-rotating Twin Screw Extruder

Meshing co-rotating twin screw extruder has been widely used in puffed food processing and feed processing.Due to the differences in extrusion parameters of different food materials,the twin-screw extruder sometimes has the problems of stuck,screw locking and even damage in the working process.According to the analysis,the above problems are caused by the excessive radial deformation of the barrel and screw.At present,the research on the extrusion process of twin screw extruder at home and abroad mostly focuses on the screw configuration design and the analysis of the corresponding flow field.Some studies use a single physical field to load the barrel and screw,which cannot truly reflect the stress and deformation of the barrel and screw.The optimum extrusion process parameters of general materials are often explored through experimental data,which takes a lot of time and material resources.Therefore,it is of great significance to study the stress and deformation of the twin-screw extruder during operation and guide the setting of specific parameters in production practice through experiments and simulation.In this paper,aiming at the problems of co-rotating twin screw extruder in food material extrusion process,using the method of combining numerical simulation and experiment,the 65 type(screw diameter is 65 mm)twin screw extruder(4 section heating)commonly used in the food industry is studied.The three-dimensional model of screw and barrel was constructed,the thermal-solid coupling deformation under different temperature and pressure conditions was studied,and the range of design clearance was obtained.The fluid-solid-thermal coupling analysis of the metering section screw(load section 3)was carried out,and the main factors affecting the mechanical properties of the screw were obtained.By optimizing and analyzing the size of the barrel model,the heat transfer efficiency is improved and the overall quality is reduced under the premise of meeting the mechanical properties.On the basis of single factor experiment,the flow characteristics of soybean protein isolate under optimum extrusion parameters and relative extrusion parameters were analyzed by orthogonal experiment and fluid simulation.Through experimental verification and simulation analysis,the main conclusions of this paper are as follows :(1)Through the thermo-solid coupling analysis of cylinder and screw,it is concluded that temperature is the main factor causing excessive deformation of cylinder and screw,and the axial thermal deformation of cylinder and screw is equivalent to the total deformation,which is greater than that of the other two directions;under the same temperature condition,the total deformation of barrel and screw decreases with the increase of external pressure.Therefore,the temperature range should be reasonably controlled in the application process of the extruder to avoid causing excessive deformation of the barrel and screw to damage the equipment.While meeting certain universality of twin-screw extruder,the design gap of twin-screw extruder should be greater than 0.4 mm.(2)Through the fluid-solid-thermal coupling analysis of the metering section screw,it is proved that the fluid pressure acting on the screw surface is asymmetric distribution.Therefore,the force of fluid on screw cannot be ignored in the analysis of screw force.In addition,the fluid-solid coupling and thermal-solid coupling of the metering section screw are further analyzed,which proves that temperature is the most important factor affecting the mechanical properties of the screw.(3)Based on the thermo-mechanical coupling analysis,the multi-objective optimization study on the size of the barrel was carried out,and the optimized barrel was analyzed with the same boundary conditions,which proved that the deformation of the optimized barrel along the X axis was reduced by 0.01175 mm compared with that before optimization.The deformation along the Y direction is reduced by 0.00709 mm,and the mass is reduced by7.5 % compared with that before optimization.The quality of the barrel is reduced and the heat transfer efficiency is improved.(4)Through orthogonal experiment and fluid simulation method,it is concluded that the factors affecting the extrusion quality of the product from large to small are material moisture content,screw speed and extrusion temperature.At the same time,the simulation results show that using soybean protein isolate as raw material,water content is 15 %,screw speed is 120 r / min,extrusion temperature is 160 °C,the extrusion machine can effectively establish pressure on the material,and the material flows to the exit to form an orderly pressure gradient,the flow is uniform and stable,and the extrusion product quality is good.