Scale-up Design Of Mixing Section In Co-rotating Twin Screw Extruder For Solid Propellant

Solid propellant has been widely used in the field of the national defense and the aerospace,which provides necessary power for rockets and missiles.As a guarantee of national defense forces,its manufacturing equipment and technology have attracted the attention of researchers all over the world.As a mixing equipment for solid propellant,co-rotating twin-screw extruder is more attractive for their continuous production and high safety performance.In this paper,the mixing section of a small-scale twin screw extruder for solid propellant was scaled up by numerical simulation method.Firstly,the screw elements in the mixing section of the small-scale co-rotating twin screw extruder for solid propellant was scaled up by the Mckelvey scal-up method and use the POLYFLOW software to simulate the isothermal and non-isothermal numerical simulation on the small-scale and large-scale extruders.According to cumulative residence time,mean back-flow coefficient,shear stress,pressure and temperature to characterize the dispersive and distributive mixing ability and safety performance of the solid propellant in the screw element flow channel.The results showed that the distributive and dispersive mixing properties of solid propellants in large-scale extruder were higher than those in small-scale extruder and the safety performance decrease slightly.Structural parameters of screw element were designed by the orthogonal test.The meshing ratio,pitch and clearance between screw and barrel were selected as the test factors and the distributive mixing ability,dispersive mixing ability and safety performance were used as evaluation indexes.The results showed that the high meshing ratio and clearance were beneficial to improve the distributive mixing ability and safety performance of solid propellant.The results of isothermal and non-isothermal numerical simulation of kneading disc elements with different thickness and kneading block elements with different staggered angle show that as the thickness of the kneading disc increases,the distributive mixing ability decreases,the dispersive mixing ability increases and the safety performance decreases.With the increase of staggered angle,the distributive and dispersive mixing ability increases,but the temperature rise changes greatly and the safety performance decreases.The four screw configurations of the large-scale extruder mixing sections were designed by geometric similarity scale-up.The simulation results showed that the staggered arrangement of screw elements was more beneficial to improve the distributive mixing ability and safety performance than concentrated arrangement.