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A First DNS Investigation of Turbulent Collisions in Flotation
Benedikt Tiedemann, Jochen Fröhlich
Institute of Fluid Mechanics, TU Dresden, Germany
ABSTRACT: The collisions between particles and bubbles are crucial to the performance of the flotation
process. However, experimental, and numerical data on these collisions, particularly, in turbulent flow are
scarce. Therefore, bubble-resolved, and particle-modelled Direct Numerical Simulations were conducted to
investigate the collision frequency between particles and bubbles and the factors influencing it. This contribution
compares two simulation cases, one where externally forced turbulence and gravity are present, and another one
where particle and bubble motion is only governed by gravity. The simulations demonstrate that turbulence
significantly increases the particle-bubble collision rate by increasing the relative velocity between particles and
bubbles due to turbulence. Furthermore, the presence of isotropic turbulence leads to a more uniform collision
angle distribution on the bubble surface. As gravity causes a deterministic component of particle and bubble
motion under a preferential direction, particles preferably collide and accumulate at the upper half of the
bubble. Under the influence of turbulence, these effects on the particle-bubble collision process are significant.
Hence, particles approach the bubble from all sides, leading to an increase in potential collision partners. leading
to an increase in potential collision partners.
INTRODUCTION
Flotation as an important process in mineral separation
relies on the attachment of mineral particles to air bubbles.
The efficiency of this process is heavily influenced by the
collision dynamics between particles and bubbles. Due
to its significant and direct impact on flotation perfor-
mance, understanding the physics behind these collisions
is important for optimising flotation performance and,
consequently, the overall efficiency of mineral recovery.
Importantly, optimising flotation through a detailed under-
standing of collision behaviour helps to reduce energy con-
sumption and to improve the sustainability of the process.
However, analysing collision frequency and collision behav-
iour in the highly turbulent flow of a flotation cells with
high solids and gas loading proves to be extremely chal-
lenging. Experimental measurements, in particular, present
significant difficulties (Lee, et al., 1987 Thorn, et al., 1997)
(Lee, et al., 1987 Thorn, et al., 1997). In contrast, three-
phase Direct Numerical Simulations (DNS) enable detailed
investigations of the collision behaviour and its influenc-
ing factors on small scales. DNS also has the advantage of
allowing analysis of not only particle-bubble collisions but
also resolving all details of the turbulent flow and includ-
ing a large number of particles and resolved bubbles. This
contribution compares and analyses two simulation cases
under gravity, one with forced turbulence and one with-
out, focusing on their collision dynamics and influencing
factors.
THEORETICAL BACKGROUND
Particle-bubble collisions play a crucial role in flotation
as they directly affect the flotation rate constant (Nguyen
&Schulze, 2004)(Nguyen &Schulze, 2004). A collision
A First DNS Investigation of Turbulent Collisions in Flotation
Benedikt Tiedemann, Jochen Fröhlich
Institute of Fluid Mechanics, TU Dresden, Germany
ABSTRACT: The collisions between particles and bubbles are crucial to the performance of the flotation
process. However, experimental, and numerical data on these collisions, particularly, in turbulent flow are
scarce. Therefore, bubble-resolved, and particle-modelled Direct Numerical Simulations were conducted to
investigate the collision frequency between particles and bubbles and the factors influencing it. This contribution
compares two simulation cases, one where externally forced turbulence and gravity are present, and another one
where particle and bubble motion is only governed by gravity. The simulations demonstrate that turbulence
significantly increases the particle-bubble collision rate by increasing the relative velocity between particles and
bubbles due to turbulence. Furthermore, the presence of isotropic turbulence leads to a more uniform collision
angle distribution on the bubble surface. As gravity causes a deterministic component of particle and bubble
motion under a preferential direction, particles preferably collide and accumulate at the upper half of the
bubble. Under the influence of turbulence, these effects on the particle-bubble collision process are significant.
Hence, particles approach the bubble from all sides, leading to an increase in potential collision partners. leading
to an increase in potential collision partners.
INTRODUCTION
Flotation as an important process in mineral separation
relies on the attachment of mineral particles to air bubbles.
The efficiency of this process is heavily influenced by the
collision dynamics between particles and bubbles. Due
to its significant and direct impact on flotation perfor-
mance, understanding the physics behind these collisions
is important for optimising flotation performance and,
consequently, the overall efficiency of mineral recovery.
Importantly, optimising flotation through a detailed under-
standing of collision behaviour helps to reduce energy con-
sumption and to improve the sustainability of the process.
However, analysing collision frequency and collision behav-
iour in the highly turbulent flow of a flotation cells with
high solids and gas loading proves to be extremely chal-
lenging. Experimental measurements, in particular, present
significant difficulties (Lee, et al., 1987 Thorn, et al., 1997)
(Lee, et al., 1987 Thorn, et al., 1997). In contrast, three-
phase Direct Numerical Simulations (DNS) enable detailed
investigations of the collision behaviour and its influenc-
ing factors on small scales. DNS also has the advantage of
allowing analysis of not only particle-bubble collisions but
also resolving all details of the turbulent flow and includ-
ing a large number of particles and resolved bubbles. This
contribution compares and analyses two simulation cases
under gravity, one with forced turbulence and one with-
out, focusing on their collision dynamics and influencing
factors.
THEORETICAL BACKGROUND
Particle-bubble collisions play a crucial role in flotation
as they directly affect the flotation rate constant (Nguyen
&Schulze, 2004)(Nguyen &Schulze, 2004). A collision