| Energetic materials have been generally used in the fields of aerospace,national defense,military and civil.They are not only the power source of the launching,propulsion,transportation and damage,but also the essential materials in exploitation of oil and minerals,airbag,welding and demolition of building blasting.In various processes of producing energetic materials,the mixing process was one of the most important processes,and the mixing performance of the mixing equipment used in the mixing process directly affected the stability and reliability of the products,and determined the degree of energy releasing in the products.Due to the high sensitivity to friction and the characteristics of flammable and explosive of energetic materials,high dispersion mixing reduced the safety of processing,and high distribution mixing was more conducive to improve the performance of products.Therefore,it was very important to study the mixing performance of the mixing equipment.In this paper,the mixing section of counter rotating non-intermeshing twin-screw extruder(CRNI)for processing energetic materials was simulated to study the mixing performance by numerical simulation method.Firstly,the single-thread screw elements in the mixing section of CRNI were designed,and the screw elements in CRNI under four different leads were modeled(28mm、30mm、35mm、40mm),then eight different flow channels of CRNI were formed according to two different arrangements of screw elements,matched arrangement and staggered arrangement.The isothermal and non-isothermal numerical simulations for the mixing process of energetic materials in eight kinds of flow channels of CRNI were simulating by adopting POLYFLOW simulation software,and the dispersion mixing coefficient and distribution mixing coefficient were established by analyzing the simulation results of the CNRI flow channels of the pressure fields,temperature fields,weighted average shear stress,cumulative maximum shear stress,cumulative residence time distribution and mean back-flow coefficient for the evaluation of the mixing performance.The results showed that for the flow channel of the single-thread screw elements in CRNI,with the increase of the lead of screw elements,the conveying capacity increased,and the dispersion mixing performance decreased,while the distribution mixing performance increased.For the same lead of screw elements,the dispersion mixing performance of the matched screw elements was stronger than that of the staggered screw elements in CRNI,but the distribution mixing performance was weaker.Considering the requirements of mixing process of energetic materials,based on the dispersion mixing performance,distribution mixing performance and the safety of processing,select the flow channel of the single-thread screw elements with the lead of 30mm in CRNI,which had better dispersion mixing performance and distribution mixing performance.Based on the optimized selection of the lead and arrangement of screw element,the influence on the number of threads of elements on the mixing performance was studied.Therefore,the flow channel model of double-thread screw elements with the lead of 30mm at staggered arrangement in the mixing section of the CRNI was established,and the isothermal and non-isothermal numerical simulation for the mixing process were simulated.The simulation results were compared and analyzed with the optimized results of flow channel of the single-thread screw elements with the lead of 30mm in CRNI.The results showed that the conveying capacity of the double-thread screw elements was weaker,the dispersion mixing performance of the double-thread screw elements was higher and the distribution mixing performance of the double-thread screw elements was lower.The mixing performance of energetic materials was closely related to the different types of twin-screw extruders used.Thus,based on the optimized flow channel of single-thread screw elements in CRNI,the flow channel model of intermeshing co-rotating twin-screw extruder with the same lead of screw elements,same center distance and the same clearance between screw elements and barrel were established.And the isothermal and non-isothermal numerical simulations for the mixing process of energetic materials were simulated.The results showed that the pressure difference between exit and inlet,temperature,weighted average shear stress and cumulative maximum shear stress in the flow channel of intermeshing co-rotating twin-screw extruder were higher than that of flow channel of single-thread screw elements in CRNI,and the dispersion mixing performance in the flow channel of intermeshing co-rotating twin-screw extruder was stronger.While the cumulative residence time distribution and mean back-flow coefficient in the flow channel of intermeshing co-rotating twin-screw extruder was lower than that of flow channel of double-thread screw elements in CRNI,and the distribution mixing performance in the flow channel of intermeshing co-rotating twin-screw extruder was weaker,however,the flow channel with the helical“∞”shape increased the distribution mixing while delivery the energetic materials.As the results showed that optimized flow channel of the single-thread screw elements in CRNI was beneficial to the mixing and the safety of processing for energetic materials.Therefore,during the mixing process of energetic materials,the CRNI with the single-thread of screw elements at staggered arrangement also had a certain degree of great potential. |
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