Mixing and Particle Tracking in a Single Screw Extruder (2)
Project Specifics
Several graduate and undergraduate students in Dr. Greg Campbell's laboratory decided to attempt using time period flow instead of spatially period flow to achieve chaotic mixing within the extruder. To do this, a third degree of freedom needed to be achieved, they made it possible to move the core of the screw separately from the helix. Using certain patterns of movement between the various extruder elements produces better mixing capabilities than with normal screw rotation and a more uniformly mixed output. The various combinations of movement give different mixing patterns.
Using normal screw extrusion gives a point stretched along the channel with no mixing (figure 1.a). Helical-motion only mixing provides stretching in the cross-channel section but not down the channel (figure 1.b) so the mixing is very poor again. The chaotic mixing (figure 1.c) forces the dye to mix in the cross-channel section and down the channel giving a better mix than a normal extruder.
To more easily analyze the flow of fluid down the channel, the channel can be 'unwrapped' from the core giving rise to a rectangular channel in which the top and bottom can be moved at specific velocities. This technique provides a good approximation of what really occurs and eliminates the need for the complicated math involved in working with helical coordinates. The points a, b, c, d in figure 2.a become a straight line down the channel (as transposed into figure 2.b) while the points e, f, g, and h define a square on the lid. Moving the barrel of the extruder equates to moving the lid of the channel, while moving the core is like moving the bottom.
As well as collecting data, a set FORTRAN computer programs were written modeling the data and theory. My task this summer has been to learn the programming language of FORTRAN, learn the theory behind the experiments and code, and begin to figure out what the existing code does. Not having had any of the classes that cover the basics of the theory has made understanding the theory difficult. Most of the theory appears to deal with fluid mechanics and transport phenomena in regards to highly viscous polymers. In turn, not grasping the theory well has made understanding the existing code more complicated. The code is largely based off the equations that dictate the fluid flow, so not grasping what the different variables mean and what they represent makes matching up the code with the theory rather difficult. I, however, am beginning to grasp the basics of the theory and the experiment as well as understand the existing code even though much still eludes me at this point in time. Continued work on this project would allow me to expand my understanding of the project, the theory of fluid mechanics and chaotic mixing, especially within an extruder.
Several graduate and undergraduate students in Dr. Greg Campbell's laboratory decided to attempt using time period flow instead of spatially period flow to achieve chaotic mixing within the extruder. To do this, a third degree of freedom needed to be achieved, they made it possible to move the core of the screw separately from the helix. Using certain patterns of movement between the various extruder elements produces better mixing capabilities than with normal screw rotation and a more uniformly mixed output. The various combinations of movement give different mixing patterns.
Using normal screw extrusion gives a point stretched along the channel with no mixing (figure 1.a). Helical-motion only mixing provides stretching in the cross-channel section but not down the channel (figure 1.b) so the mixing is very poor again. The chaotic mixing (figure 1.c) forces the dye to mix in the cross-channel section and down the channel giving a better mix than a normal extruder.
To more easily analyze the flow of fluid down the channel, the channel can be 'unwrapped' from the core giving rise to a rectangular channel in which the top and bottom can be moved at specific velocities. This technique provides a good approximation of what really occurs and eliminates the need for the complicated math involved in working with helical coordinates. The points a, b, c, d in figure 2.a become a straight line down the channel (as transposed into figure 2.b) while the points e, f, g, and h define a square on the lid. Moving the barrel of the extruder equates to moving the lid of the channel, while moving the core is like moving the bottom.
As well as collecting data, a set FORTRAN computer programs were written modeling the data and theory. My task this summer has been to learn the programming language of FORTRAN, learn the theory behind the experiments and code, and begin to figure out what the existing code does. Not having had any of the classes that cover the basics of the theory has made understanding the theory difficult. Most of the theory appears to deal with fluid mechanics and transport phenomena in regards to highly viscous polymers. In turn, not grasping the theory well has made understanding the existing code more complicated. The code is largely based off the equations that dictate the fluid flow, so not grasping what the different variables mean and what they represent makes matching up the code with the theory rather difficult. I, however, am beginning to grasp the basics of the theory and the experiment as well as understand the existing code even though much still eludes me at this point in time. Continued work on this project would allow me to expand my understanding of the project, the theory of fluid mechanics and chaotic mixing, especially within an extruder.
