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CFD simulations of particle laden flows: Particle transport and separation

:	David Schellander
:	CFD simulations of particle laden flows: Particle transport and separation
:	Anchor Academic Publishing
:	9783954896714
:	1
:	CHF 40.10
:

:	Technik
:	English

:	152
:	kein Kopierschutz/DRM
:	PC/MAC/eReader/Tablet
:	PDF

This study presents the basic models for discrete and continuous particle laden flow simulation. An overview of the two main approaches, the Lagrangian discrete particle model and the Eulerian granular phase model is given. Moreover these two approaches are combined to a hybrid model to use the benefits of the discrete and continuous description. This safes computational time and increase the efficiency of particle laden flow simulations. Furthermore the models are extended to poly-disperse particles including a simple agglomeration model based on a population balance equation. Finally the usability of the models is shown at a pneumatic particle transport system including particle strand building and the separation of particles using an industrial cyclone.

Dr. David Schellander was born on 17th of December 1983 in Hall in Tirol in Austria. After his study of mechatronics he wrote his PhD-thesis at the Johannes Kepler University in Linz in the field of particle laden flow simulations. During his study he wor

Text Sample: Chapter 2.7, Turbulence modeling: In the preheating tower, the gas flow has a Reynolds number of more than Re = 105. Furthermore, the gas flow is turbulent. One problem due to computational limitations, is that the grid size must be in a range where it is not possible to resolve all turbulent scales. Hence, the turbulence of the gas phase is commonly represented by turbulence models to account for the influence of unresolved eddies in the mean flow. Turbulence models that are commonly used in industrial cases are the Reynolds Averaged Navier-Stokes (RANS) models (for example ke, RSM) because they include the influence of small vortices. In literature there are two basic approaches to extend single phase RANS to multiphase flows. One approach is the mixture approach and the second one is the dispersed approach. In the mixture approach a dilute to medium density particulate flow is assumed and for the dispersed approach a dilute particulate flow is assumed. Furthermore, in dense particulate flow regimes, the gas flow through the particles is assumed to be laminar. The mixture model is a good choice if the density ratio between the phases is around one [ANSYS, 2009], which is not the case in our flow situation. Consequently, in this work we used the dispersed RANS model as turbulence model, because it is important to model the physics of turbulence in dispersed regions correctly. 2.8, Boundary Conditions: The main challenge at the wall is to calculate the shear stresses t kcs and the flux of fluctuation energy, q, from the wall into the domain. Particles hitting a wall can either slide, roll or are directly reflected back. Johnson and Jackson [1987] presented a model, which is nowadays commonly used for simulations. However, this model ignores the fact that a granular medium sliding at a wall can only exert a shear stress limited by Coulumbs law to the wall. This, in term, implies that these boundary conditions overestimate t kcs and q in rapid granular flows. This is recognized by the model of Jenkins and Louge [1997]. The paper of Schneiderbauer et al. [2012b] is a generalization of the boundary conditions derived in Jenkins and Louge [1997]. The new set of boundary conditions for the Eulerian phase described in Schneiderbauer et al. [2012b] has been applied during this survey. In the case of the preheating tower, simulating wall bounded particle conveying is crucial because of the high impact of walls on strand formated particle-laden flows. Obviously, this requires a thorough modelling of particle-wall interactions. Hence this new boundary condition should be used for the simulations.

	CFD simulations of particle laden flows	1
	Preface	5
	Abstract	6
	Contents	7
	Abbreviations	10
	Chapter 1: Introduction and motivation	11
	1.1 Numerical simulation of particle-laden flow	14
	1.2 Aim of this work	19
	1.3 Organization of this book	19
	Chapter 2: Eulerian granular phase modelling	21
	2.1 Continuity equation	22
	2.2 Moment balance	23
	2.3 Granular temperature	24
	2.4 Radial distribution function	26
	2.5 Drag coefficient and interphase momentum exchange	30
	2.6 Solids Stresses	31
	2.7 Turbulence modelling	35
	2.8 Boundary Conditions	35
	Chapter 3: Lagrangian discrete phase modelling	42
	3.1 Force balance and torque balance	43
	3.2 Forces on a particle	44
	3.3 Torque	49
	3.4 Turbulent fluctuations	49
	3.5 Particle wall collisions	51
	Chapter 4: The hybrid model EUgran+Poly	55
	4.1 Motivation and overview	55
	4.2 Coupling and exchange forces	57
	4.3 Coupling forces on the Eulerian granular phase	59
	4.4 Coupling forces on the Lagrangian tracer particles	62
	4.5 Simulation sequence and implementation	65
	Chapter: Agglomeration	67
	5.1 Simple models	69
	5.2 Particle population balance equation	70
	5.3 Bus stop model	82
	5.4 Volume population balance model	84
	Chapter 6: Validation by lab-scale experiments	88
	6.1 Dilute poly-dispersed flow in a duct	89
	6.2 Mono-dispersed flow in a medium laden duct	95
	6.3 Agglomeration of poly-dispersed particulate flow in a vertical pipe	100
	Chapter 7: Application to cyclone seperation	103
	7.2 Hybrid Model	104
	7.2 Agglomeration	111
	Chapter 8: Conclusion and Outlook	113
	A: Restitution coefficients are no constants	116
	B: Computation of Lagrangian particle-wall collision	118
	C: UDF Structure of hybrid model	122
	D: Cyclone dimensions based on Muschelknautz theory	127
	E: Nomenclature	133
	List of Figures	138
	List of Tables	142
	Bibliography	143