Experimental and theoretical investigations of collision efficiency in

Experimental and Theoretical Investigations of Collision Efficiency in A Wide Range of Reynolds Numbers a t Strongl y Retarded Bubble Surface 

A comparison was carried out by Nguen Van and Kmet (1992) between the theoretical results and the experimental data as a function of particle radius and two dimensionless parameters Reynolds number and Galileo number. Thus, four parameters were varied in the experiment bubble radius, flow velocity, particle radius and density. The experiment as a whole has confirmed the theoretical dependence for all of the four parameters as predicted by the authors. Because of the importance of these results we will discuss some points which need further clarification. 

The non-trivial part of the study consists in calculations of the hydrodynamic field and its effect on collision efficiency. To check this result, the collision efficiency should be studied at a minimum difference between particle and water densities. Unfortunately this was not done. 

Justification for a separate microflotation theory has created favourable conditions for the development of a new and independent section of surface and colloid science, which can be called Derjaguin-Dukhin microflotation theory. After more than thirty years, it can be evaluated to what extent this theory is correct and useful it can also be pointed out which further stages of development and unsolved problems exist. 

The most important distinction of an elementary flotation act of small particles from a similar act of large particles consists in the fact that transport of particles to a bubble surface controls the flotation kinetics rather than the sticking stage. Therefore the main reserve of intensification of water purification and selective flotation is connected with the increase of the number of collisions of particles with a collective of rising bubbles. 

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