Despite recent advances, particle processing still lags significantly behind its counterpart of fluid processing. The unifying theme of this proposal is the adaption of concepts from fluid processing in order to develop novel techniques for particle applications. Specifically, we target the mixing of dissimilar materials in surface flows of cohesionless (free flowing) materials as well as novel particle separation techniques. The underlying hypothesis of the first focus area of this work is that by exploiting flow perturbations a technique with a long history in fluid processing we can develop, for the first time, a general method for limiting particle segregation in free flowing systems, perhaps the most common and well studied of granular flows. The key to this approach lies in recognizing that it takes a finite time for material to segregate and that there is always a preferred direction that particles tend to segregate. In order to exploit these two facts, one needs to perturb the flow at a high frequency and in such a way that the surface layer is inverted. Particle separations techniques are typically quite low tech and often are energy intensive (e.g., sieving) or environmentally unfriendly (e.g., froth floatation) or both. The underlying hypothesis of the second focus area of this work is that we can develop rate based separations techniques based on granular temperature driven segregation and non-equipartition of (granular) energy. Specifically, we aim to build an analog of a granular chromatograph using a shaking table that imparts a gradient in vibration energy and hence, a gradient in granular temperature. Additionally, we plan to explore granular ratchets in analogy to Brownian ratchets from microfluidic studies because non equipartition of energy will yield the equivalent of the species dependent diffusion coefficient necessary for ratcheting to function for separations. These fluids inspired particle separations devices should not only overcome several of the shortcomings of traditional particle separations techniques, but also will help to validate kinetic theory based models in a very practical context. The chief intellectual merit of this work will be evidenced through advancing knowledge and understanding across fields of engineering and physics via:
1. Expanding our preliminary mixing results past the proof of concept stage and into a general methodology for limiting both single (density or size) and mixed mode segregation in a variety of surface dominated flows, including developing a set of validating experimental and simulation results that demonstrate the utility of flow perturbations for limiting segregation.
2. Establishing design heuristics for segregation free operation of a variety of particle processing devices.
3. A series of experiments that can be used as a test bed for variations on kinetic theory expressions.
4. Two novel particle separation devices: a granular chromatograph and a granular ratchet apparatus The primary broader impacts will be related to the economic impact on the wide variety of industries that deal with particle processing for whom mixing/segregation and particle separation have dramatic product/revenue implications. Additional broader impacts of the work lie in integrating teaching and research. This teaching/research integration will take two forms: training of two graduate students and several undergraduate researchers (with emphasis on under represented groups), and the development of a novel handson K-12 teacher training/partnership program focused on building interest in science in disadvantaged youths. Coupling a particle technology researchers natural propensity for hands-on instruction with a desire to have a positive impact on the the disadvantaged youth in the local community, the PI is proposing to form a partnership with the Academy Charter School (www.theacademysystem.com). This 8-12 grade school is the only charter school in the US exclusively focused on educating court ejudicated youth. Hands-on or inquiry based science education has been shown to not only improve student attitudes toward science, but also to foster higher overall achievement as well as a more flat response as a function of demographic background. The proposed partnership will comprise workshop like sessions between the PI and instructors in the Academy Charter School aimed at developing and/or adapting inquiry based educational modules suitable for science/engineering education in this unique learning environment highly competitive nature of the proposals submitted to the Program and the panel recommendation, the Program Director recommends that this proposal be awarded.
The importance of studying granular processing and flow is well recognized in the physics and engineering communities and has been an important area of research since the work of Reynolds in 1881. This is due, in part, to the fact that it has been estimated that approximately $61 billion in the U.S. chemical industry is linked to particle technology. Despite recent advances, particle processing still lags significantly behind its counterpart of fluid processing. The unifying theme of this work is the adaption of concepts from fluid processing in order to develop novel techniques for particle applications. Specifically, we target the mixing of dissimilar materials in surface flows of cohesionless (free-flowing) materials as well as novel particle separation techniques. Prior to the onset of this project, there was no general method for controlling segregation in free flowing systems. The underlying hypothesis of the first focus area of this work was that by exploiting flow perturbations we could develop, for the first time, a general method for limiting particle segregation in free flowing systems, perhaps the most common and well-studied of granular flows. The key to this approach lies in recognizing that it takes a finite time for material to segregate and that there is always a preferred direction. In order to exploit these two facts, one needs to perturb the flow at a sufficiently high frequency, f, such that f>ts-1 (where ts is the characteristic segregation time) and in such a way that the surface layer is inverted. In this work, we demonstrate this elegantly simple idea in two model systems where periodic flow inversions are used to effectively eliminate segregation in free-surface flows. While mixing and segregation avoidance/control is critical to a wide range of industries, particle separation is equally vital, yet has received considerably less attention in the recent literature. Particle separations techniques are typically quite 'low tech" and often are energy-intensive (e.g., sieving) or environmentally unfriendly (e.g., froth floatation) or both. The underlying hypothesis of the second focus area of this work is that we can develop rate-based separations techniques based on analogous fluids separation techniques. Specifically, we have developed a both a simple analogue of a gas chromatograph for the separation of cohesive particles, as well as a completely passive (gravity-based) separation device for free-flowing materials. One key advantage of the passive device over traditional sieving (for size separation) is the fact that a sieve "clogs by design", requiring significant energy input to continually dislodge the larger particles from the openings in order to allow the smaller particles to fall, while our board can be used in-line for any gravity-driven transport (as the peg spacing is always dramatically larger than both/all particle diameters). The chief intellectual merit of this work is evidenced through advancing knowledge and understanding across fields of engineering and physics. Eliminating segregation, even if limited only to surface-dominated flows, is a tremendous boon to the discipline of the engineering of particle processing. The techniques used to affect this elimination are easily implemented and could be incorporated into particle handling applications in a simple way and has the potential to transform how researchers tackle segregation problems both academically and industrially. Our separation devices represent yet another example of how one can learn about granular systems by exploring similar systems. Moreover, all of our fluid-inspired separation technologies show promise as low energy devices, thus they are likely to be very efficient. The primary broader impact of this work is related to the economic impact on the wide variety of industries that deal with particle processing for whom mixing/segregation and particle separation have dramatic product/revenue implications. Additional broader impacts of the work lie in integrating teaching and research. Both computational and experimental skills have been either developed or improved for the graduate students involved in the project. The primary graduate student on the project during the first portion of the work, Tathagata Bhattacharya, has developed novel discrete element modeling (DEM) code capable of simulating both free-flowing and adhesive particles in vibratory conveying rigs. Tatha has completed his studies, defended his PhD, and is now employed by Arcelor Mittal. A second student, Diana, has been involved in the development of the chromatographic theory and has been instrumental in the design of our experimental rig. She has also performed a series of computational studies that will set the stage for our next generation of experiments. She is set to complete her PhD within the next calendar year.
