Experimental investigations of turbulent fragmenting stresses in a rotor-stator mixer. Part 2. Probability distributions of instantaneous stresses
Artikel i vetenskaplig tidskrift, 2017

Drop fragmentation in high intensity turbulent emulsification processing equipment-such as rotor-stator mixers (RSMs)-has traditionally been described in terms of a stress balance; between the stabilizing stress of the drop and the time-averaged turbulent stress at the most intense position of the flow. As shown in part 1 of this series, this approach is often a fruitful first approximation. However, the instantaneous local stress experienced by drops differs,from the time-averaged local stress due to hydrodynamics in general and the stochastic nature of a turbulent flow in particular. This study estimates the probability distribution of instantaneous turbulent stresses in an RSM from velocity fields obtained using particle image velocimetry. Results show that regions with low average stress still have a substantial probability of having instantaneously high stresses. This explains why low probability breakup is observed at these positions in visualization experiments. Results also show that the probability distribution of instantaneous stresses is approximately lognormal. The results are compared to two commonly used models for how to take the stochastic variations into account: the exponential decay model, and the multifractal emulsification model. It is concluded that both models predict reasonable distributions shapes but underestimate the width of the stress distribution.

High-shear mixer

Fragmentation

Emulsification

Intermittency

Rotor-stator mixer

Turbulence

Författare

A. Hakansson

Högskolan i Kristianstad

Ronnie Andersson

Chalmers, Kemi och kemiteknik, Kemiteknik, Kemisk reaktionsteknik

H. H. Mortensen

Tetra Pak

F. Innings

Tetra Pak

Lunds universitet

Chemical Engineering Sciences

0009-2509 (ISSN)

Vol. 171 638-649

Styrkeområden

Produktion

Ämneskategorier

Kemiteknik

DOI

10.1016/j.ces.2017.06.038

Mer information

Senast uppdaterat

2018-10-10