CFD Simulation Of Spinning Dope Fluid Flow Behavior In Twin-screw Extruder

The defoaming is a key factor for the production of regenerated cellulose fibers through dry-jet wet by dissolving cellulose in ionic liquid.Traditional stirred tank is widely used as the core equipment of spinning dope preparation defoaming process,but it has disadvantages such as long material processing time,discontinuous operation and low economic efficiency.The processing method of spinning dope with twin-screw extruder as the carrier overcomes the above shortcomings and is a new type of process with application potential.In this article,the ionic liquid 1-ethyl-3methlimidazole diethyl phosphate([Emim]DEP)is used as the solvent to dissolve cellulose,and the computational fluid dynamics method is used to explore the conveying process of the twin-screw extruder.The influence of processing conditions on the internal gas-liquid flow field.By changing the processing conditions,including the screw speed,screw rotation mode,screw model and medium,the flow field parameters under different conditions can be obtained,which provides theoretical guidance for selecting suitable processing conditions.The main research contents are as follows:(1)The ionic liquid[Emim]DEP was synthesize by the one-step synthesis method,and the synthesized product was verified by infrared analysis and nuclear magnetic analysis.The viscosity,contact angle and interfacial tension were measured,and the rheological curve of the ionic liquid[Emim]DEP-cellulose solution was fitted by the power law equation of non-Newtonian fluid.(2)According to the data of the real factory,design two-dimensional physical models of two twin-screw extruders to perform grid division and independence inspection work.For the simulation of gas-liquid two-phase inside the flow field and the grid change of the computational domain caused by the rotation of the twin screw,the volumetric method of multiphase flow model(VOF)and dynamic grid technology are respectively introduced to solve the problem.(3)Comparative analysis of the difference in screw rotation mode on the gas-liquid flow field inside the two physical models,including changes inflow field velocity,pressure,viscosity,shear rate,and bubble motion dynamics.Provides theoretical guidance for plant equipment selection.The main conclusions of this article include:as the rotating speed increases,the velocity,pressure difference and shear rate of the flow field will increase,and the viscosity will decrease accordingly.When the screw rotation mode is co-rotating,compared with Model 1,when the rotation speed is 60 rpm and the flow field medium is ionic liquid[Emim]DEP-cellulose,the flow velocity of Model 2 is 70 cm/s,and the weighted average pressure is 655 KPa.The viscosity is 16.40 Pa·s,the shear rate is 25000s^-1,bubble breakage and coalescence are observed during the simulation.When the screw rotation mode is counter-rotating,the Model 2 still outperforms the Model 1 in all aspects.When the rotation speed is 60 rpm and the flow field medium is ionic liquid[Emim]DEP-cellulose,the maximum flow rate in Model 2 is about 25 cm/s,the pressure difference can reach 10⁵ Pa,the maximum viscosity is 17.14 Pa·s,and the maximum shear rate is about 18500 s^-1.Therefore,the co-rotating twin-screw extruder of Model 2 should be selected in practical applications.