Experimental investigations of turbulent fragmenting stresses in a rotorstator mixer. Part 2. Probability distributions of instantaneous stresses
(2017) In Chemical Engineering Science Abstract
Drop fragmentation in high intensity turbulent emulsification processing equipmentsuch as rotorstator mixers (RSMs)has traditionally been described in terms of a stress balance; between the stabilizing stress of the drop and the timeaveraged 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 timeaveraged 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... (More)
Drop fragmentation in high intensity turbulent emulsification processing equipmentsuch as rotorstator mixers (RSMs)has traditionally been described in terms of a stress balance; between the stabilizing stress of the drop and the timeaveraged 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 timeaveraged 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.
(Less)
 author
 Håkansson, Andreas ^{LU} ; Andersson, Ronnie; Mortensen, Hans Henrik and Innings, Fredrik ^{LU}
 organization
 publishing date
 20170623
 type
 Contribution to journal
 publication status
 epub
 subject
 keywords
 Emulsification, Fragmentation, Highshear mixer, Intermittency, Mixing, Rotorstator mixer, Turbulence
 in
 Chemical Engineering Science
 publisher
 Elsevier
 external identifiers

 scopus:85021756180
 wos:000409285000052
 ISSN
 00092509
 DOI
 10.1016/j.ces.2017.06.038
 language
 English
 LU publication?
 yes
 id
 9170e8222cdb4fdbbb5c469fef6556f0
 date added to LUP
 20170720 07:08:30
 date last changed
 20180116 13:21:28
@article{9170e8222cdb4fdbbb5c469fef6556f0, abstract = {<p>Drop fragmentation in high intensity turbulent emulsification processing equipmentsuch as rotorstator mixers (RSMs)has traditionally been described in terms of a stress balance; between the stabilizing stress of the drop and the timeaveraged 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 timeaveraged 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.</p>}, author = {Håkansson, Andreas and Andersson, Ronnie and Mortensen, Hans Henrik and Innings, Fredrik}, issn = {00092509}, keyword = {Emulsification,Fragmentation,Highshear mixer,Intermittency,Mixing,Rotorstator mixer,Turbulence}, language = {eng}, month = {06}, publisher = {Elsevier}, series = {Chemical Engineering Science}, title = {Experimental investigations of turbulent fragmenting stresses in a rotorstator mixer. Part 2. Probability distributions of instantaneous stresses}, url = {http://dx.doi.org/10.1016/j.ces.2017.06.038}, year = {2017}, }