The flow process of unplasticized polyvinyl chloride （U PVC） through the mixing zone of intermeshing counter rotating and co rotating twin screw extruders （TSEs） were numerically simula ted by the finite element m...The flow process of unplasticized polyvinyl chloride （U PVC） through the mixing zone of intermeshing counter rotating and co rotating twin screw extruders （TSEs） were numerically simula ted by the finite element method. Three dimensional isothermal flow field of U-PVC in two kinds of TSE was calculated. The mixing performance of the screw elements of the extruders was statistically analyzed by particle tracking method. The dispersive mixing performance was characterized by the mixing index, the logarithm of stretching, and the segregation scale. The distributive mixing per forulance was characterized by the resident time distribution. The results indicate that the counter rotating TSE can build higher pressure and generate higher axial velocity and shear rate, whereas the co rotating TSE has better performance in dispersive and distributive mixing.展开更多
The residence time distribution (RTD) evolution along a co-rotating twin-screw extruder with a split barrel was experimentally investigated by using the pre-mixed particles of polystyrene (PS) with anthracene as the t...The residence time distribution (RTD) evolution along a co-rotating twin-screw extruder with a split barrel was experimentally investigated by using the pre-mixed particles of polystyrene (PS) with anthracene as the tracer.The samples on the screw were taken out from the specially designed extruder, which could be dead-stopped at a given time and its barrel opened within several seconds.A three-parameter function was used to fit the experimentally measured RTD.The calculated results fit the experimental data very well.The reverse screw elements and kneading block had much longer residence time and resulted in effective mixing.Based on the average residence time of different screw zones and volume flow rate of molten PS, the fill degree in different screw zones was estimated.The fill degree results proved that the similar structure of screw elements might have different degrees of fill due to the effect of neighboring elements, and too close alignment of kneading zones might lead to ‘besiegement’ of materials in the zone between them.展开更多
基金Supported by the Industrial Foundation(20091041038)
文摘The flow process of unplasticized polyvinyl chloride （U PVC） through the mixing zone of intermeshing counter rotating and co rotating twin screw extruders （TSEs） were numerically simula ted by the finite element method. Three dimensional isothermal flow field of U-PVC in two kinds of TSE was calculated. The mixing performance of the screw elements of the extruders was statistically analyzed by particle tracking method. The dispersive mixing performance was characterized by the mixing index, the logarithm of stretching, and the segregation scale. The distributive mixing per forulance was characterized by the resident time distribution. The results indicate that the counter rotating TSE can build higher pressure and generate higher axial velocity and shear rate, whereas the co rotating TSE has better performance in dispersive and distributive mixing.
文摘The residence time distribution (RTD) evolution along a co-rotating twin-screw extruder with a split barrel was experimentally investigated by using the pre-mixed particles of polystyrene (PS) with anthracene as the tracer.The samples on the screw were taken out from the specially designed extruder, which could be dead-stopped at a given time and its barrel opened within several seconds.A three-parameter function was used to fit the experimentally measured RTD.The calculated results fit the experimental data very well.The reverse screw elements and kneading block had much longer residence time and resulted in effective mixing.Based on the average residence time of different screw zones and volume flow rate of molten PS, the fill degree in different screw zones was estimated.The fill degree results proved that the similar structure of screw elements might have different degrees of fill due to the effect of neighboring elements, and too close alignment of kneading zones might lead to ‘besiegement’ of materials in the zone between them.
