THE COLLISION RATE OF PARTICLES IN TURBULENT-FLOW

A review of previous derivations of particle collision rates in turbul ent fluid flow shows that these are applicable only to limited cases. A more general derivation is given, taking into account the effects of the inertia of the particles and the difference in densities of the f luid and the particles. A universal solution for the relative velocity of two particles due to turbulent accelerations in a gaseous or liqui d system is presented. In gaseous systems the acceleration mechanism b ecomes predominant at particle sizes far below the Kolmogorov microsca le of turbulence. In liquid systems, the particle inertial and added m ass effects become important above the Kolmogorov microscale. Here the particle collision rate cannot be estimated from the fluid turbulent velocity fluctuations only.