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Model predictions of turbulent gas-particle shear flows


Respondent	Huvudhandledare	Bihandledare	Datum
Tobias Strömgren	Gustav Amberg	Arne Johansson	2010-03-29

Opponent
Martin Sommerfeld, Martin-Luther-Universität Halle-Wittenberg, Germany

Betygsnämd
Lars Davidsson, CTH Pavel Kudinov, Division of Nuclear Power Safety Johan Revstedt, LTH

Abstract

A turbulent two-phase flow model using kinetic theory of granular flows for the particle phase is developed and implmented in a finite element code. The model can be used for engineering applications. However, in this thesis it is used to investigate turbulent gas-particle flows through numerical simulations. The feedback from the particles on the turbulence and the mean flow of the gas in a vertical channel flow is studied. In particular, the influence of the particle response time, particle volume fraction and particle diameter on the preferential concentration of the particles near the walls, caused by the turbophoretic effect is explored. The study shows that when particle feedback is included the accumulation of particles near the walls decreases. It is also found that even at low volume fractions particles can have a significant impact on the turbulence and the mean flow of the gas. The effect of particles on a developing turbulent vertical upward pipe flow is also studied. The development length is found to substantially increase compared to an unladen flow. To understand what governs the development length a simple estimation was derived, showing that it increases with decreasing particle diameters in accordance with the model simulations. A model for the fluctuating particle velocity in turbulent gas-particle flow is derived using a set of stochastic differential equations taking into account particle-particle collisions. The model shows that the particle fluctuating velocity increases when particle-particle collisions become more important and that increasing particle response times reduces the fluctuating velocity. The model can also be used for an expansion of the deterministic model for the particle kinetic energy.
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