On interaction of stationary particles and rising bubbles
Advancing the chemical engineering fundamentals
Multifase Flows - II (T2-5b)
Keywords: bubble - flotation, particle-bubble interaction, collision angle, bubble trajectory
On interactions of stationary particles and rising bubbles
M. Hubička, P. Basařová, D. Horn, M.Coufalová, V.Machoň
Department of Chemical Engineering, Institute of Chemical Technology- Prague, Technická 5, 166 28 Prague, Czech Rep., e-mail: pavlina.basarova@vscht.cz
The investigation of interaction between stationary spherical particle and single rising bubble was done. This process can be described by three steps:
- collision - approach of bubble and particle to the contact distance and subsequent collision
- attachment - adhesion of the bubble on bubble surface
- stability - detachment of the bubble from particle surface, when exists instability of bubble – particle aggregate
In this project we primarily focused on the collision process. To simplify the problem, we started to study interactions between stationary spherical particle and single rising spherical bubble. In contrast with the previous research we investigated the collision of particles greater or comparable in size with bubbles.
Theoretical models assume that particle-bubble collision occurs over the section of the particle surface between angles φ=0 and φ=φc,max where the angle φ is measured from vertical axis of the stationary particle and the connecting line between the particle centre and the bubble centre. The theoretical maximum initial angle is 90o corresponding with the situation when the distance of the bubble and the particle centres equals rp+ rb (sum of particle and bubble radius). In the real situation, due to the liquid flow the change of bubble trajectory is observed. In case of small bubbles (db < 1mm), only very small stream field was observed. The attachment angle φa characterizes the stabile bubble position on the solid surface. The effectiveness of the whole process is often represented by the efficiency of each step
E= Ec Ea Es
Here E, Ec, Ea, and Es, are the capture, collision, attachment, and stability efficiencies, respectively. The total efficiency, collision and attachment efficiencies are defined as the fraction of particles captured by a bubble, the fraction of particles colliding with a bubble, and the fraction of colliding particles which actually attach to the bubble surface, respectively.
The interactions between stationary spherical solid particle (silanized glass balls with various diameters) and single rising bubble (diameters in the range 0.3 – 1mm) were observed and captured by a high speed camera Redlake Motion Pro. The LUCIA software was employed for image analysis and data treatment. The information about bubble diameter, bubble velocity and bubble trajectory was obtained. The initial, collision and attachment angles were evaluated.
We found that the trajectory deviation caused by the presence of a stationary solid spherical particle is very small and it is observed only in the immediate vicinity of the surface. For bubbles much smaller than particle (db/dp<0.1) no influence of bubble size on the change of bubble trajectory was observed. Also, the bubble velocity decreases in the immediate vicinity of the solid surface.
This work has been supported by the grant no.104/05/2566 from the Grant Agency of Czech Republic and by the Grant Research Project MSM60446137306 of the Czech Ministry of Education.
See the full pdf manuscript of the abstract.
Presented Monday 17, 16:40 to 17:00, in session Multifase Flows - II (T2-5b).
