Granular flow modelling of rotating drum flows using positron emission particle tracking

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dc.contributor.advisorGovender, Indresanen_ZA
dc.contributor.authorPathmathas, Thirunavukkarasuen_ZA
dc.date.accessioned2015-12-08T11:50:04Z
dc.date.available2015-12-08T11:50:04Z
dc.date.issued2015en_ZA
dc.description.abstractTumbling mills are characterized by a flowing granular mixture comprising slurry, ore and grinding media. Akin to fluid flow, a rheological description underpinning granular flow has long been expected and pursued by many researchers. Unfortunately, no single theory has hitherto been able to successfully describe all the peculiar features and flow phases of granular systems. Tumbling mills exhibit a rich coexistence of all known flow phases and is arguably the most complicated of the granular flow geometries. Not surprisingly, current comminution models are almost entirely empirical with limited predictive capability beyond their window of design. Using Positron Emission Particle Tracking (PEPT) data we recover the key ingredients (velocity, shear rate, volume concentration, bed depth) for developing, testing and calibrating granular flow models. In this regard, 5 mm and 8 mm glass beads are rotated within a 476 mm diameter mill, fitted with angled lifter bars along the inner azimuthal walls and operated in batch mode across a range of drum rotation speeds that span cascading and cataracting Froude regimes. After averaging the PEPT outputs into representative volume elements, subsequent continuum analysis of the flowing layer revealed a rich coexistence of flow regimes - (i) quasi-static, (ii) dense (liquid-like), and (iii) inertial - that are consistent with the measured volume concentrations spanning these regimes in rotating drums. Appropriately matched constitutive choices for the shear stresses then facilitated the derivation of a new granular rheology that is able to (smoothly) capture all phases of the tumbling mill flow at transition points that match leading experimental findings reported in the literature. Limiting our models to athermal boundary conditions, we then derive the power density for better understanding of flow dissipation that ultimately drives the comminution purpose of tumbling mills. The rheology and power density models were then applied to the 5 mm and 8 mm glass bead data to reveal that shear power density is an order of magnitude larger than the normal component. Notwithstanding, the effective friction coefficient - which is akin to viscosity in typical fluids - remains relatively constant across most of the flowing layer with notable exponential growth across the interface from dense-to-inertial that continued into the inertial regime.en_ZA
dc.identifier.apacitationPathmathas, T. (2015). <i>Granular flow modelling of rotating drum flows using positron emission particle tracking</i>. (Thesis). University of Cape Town ,Faculty of Science ,Department of Physics. Retrieved from http://hdl.handle.net/11427/15707en_ZA
dc.identifier.chicagocitationPathmathas, Thirunavukkarasu. <i>"Granular flow modelling of rotating drum flows using positron emission particle tracking."</i> Thesis., University of Cape Town ,Faculty of Science ,Department of Physics, 2015. http://hdl.handle.net/11427/15707en_ZA
dc.identifier.citationPathmathas, T. 2015. Granular flow modelling of rotating drum flows using positron emission particle tracking. University of Cape Town.en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Pathmathas, Thirunavukkarasu AB - Tumbling mills are characterized by a flowing granular mixture comprising slurry, ore and grinding media. Akin to fluid flow, a rheological description underpinning granular flow has long been expected and pursued by many researchers. Unfortunately, no single theory has hitherto been able to successfully describe all the peculiar features and flow phases of granular systems. Tumbling mills exhibit a rich coexistence of all known flow phases and is arguably the most complicated of the granular flow geometries. Not surprisingly, current comminution models are almost entirely empirical with limited predictive capability beyond their window of design. Using Positron Emission Particle Tracking (PEPT) data we recover the key ingredients (velocity, shear rate, volume concentration, bed depth) for developing, testing and calibrating granular flow models. In this regard, 5 mm and 8 mm glass beads are rotated within a 476 mm diameter mill, fitted with angled lifter bars along the inner azimuthal walls and operated in batch mode across a range of drum rotation speeds that span cascading and cataracting Froude regimes. After averaging the PEPT outputs into representative volume elements, subsequent continuum analysis of the flowing layer revealed a rich coexistence of flow regimes - (i) quasi-static, (ii) dense (liquid-like), and (iii) inertial - that are consistent with the measured volume concentrations spanning these regimes in rotating drums. Appropriately matched constitutive choices for the shear stresses then facilitated the derivation of a new granular rheology that is able to (smoothly) capture all phases of the tumbling mill flow at transition points that match leading experimental findings reported in the literature. Limiting our models to athermal boundary conditions, we then derive the power density for better understanding of flow dissipation that ultimately drives the comminution purpose of tumbling mills. The rheology and power density models were then applied to the 5 mm and 8 mm glass bead data to reveal that shear power density is an order of magnitude larger than the normal component. Notwithstanding, the effective friction coefficient - which is akin to viscosity in typical fluids - remains relatively constant across most of the flowing layer with notable exponential growth across the interface from dense-to-inertial that continued into the inertial regime. DA - 2015 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2015 T1 - Granular flow modelling of rotating drum flows using positron emission particle tracking TI - Granular flow modelling of rotating drum flows using positron emission particle tracking UR - http://hdl.handle.net/11427/15707 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/15707
dc.identifier.vancouvercitationPathmathas T. Granular flow modelling of rotating drum flows using positron emission particle tracking. [Thesis]. University of Cape Town ,Faculty of Science ,Department of Physics, 2015 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/15707en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentDepartment of Physicsen_ZA
dc.publisher.facultyFaculty of Scienceen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherPhysicsen_ZA
dc.titleGranular flow modelling of rotating drum flows using positron emission particle trackingen_ZA
dc.typeDoctoral Thesis
dc.type.qualificationlevelDoctoral
dc.type.qualificationnamePhDen_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceThesisen_ZA
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