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An experimental investigation of the probability distribution of turbulent fragmenting stresses in a high-pressure homogenizer

Håkansson, Andreas LU (2018) In Chemical Engineering Science 177. p.139-150
Abstract

The high-pressure homogenizer (HPH) is, together with the rotor–stator mixer (RSM), the standard equipment for emulsification in many fields of chemical processing. Both give rise to intense turbulence which, in turn, gives rise to drop breakup. Previous investigations focus on average turbulent disruptive stress. However, turbulence is a stochastic phenomenon and drop breakup will be characterized by instantaneous stresses, or more specifically by the probability distribution of instantaneous turbulent stresses. This study uses high-resolution particle image velocimetry (PIV) data to measure the probability distribution of turbulent stresses in the HPH. It is concluded that stress distributions approximately follow a lognormal model... (More)

The high-pressure homogenizer (HPH) is, together with the rotor–stator mixer (RSM), the standard equipment for emulsification in many fields of chemical processing. Both give rise to intense turbulence which, in turn, gives rise to drop breakup. Previous investigations focus on average turbulent disruptive stress. However, turbulence is a stochastic phenomenon and drop breakup will be characterized by instantaneous stresses, or more specifically by the probability distribution of instantaneous turbulent stresses. This study uses high-resolution particle image velocimetry (PIV) data to measure the probability distribution of turbulent stresses in the HPH. It is concluded that stress distributions approximately follow a lognormal model and that the skewness of the distributions decreases with increasing distance from the gap exit until a constant distribution shape is obtained at the position where the turbulence is fully developed. This converged stress distribution is similar to that obtained for RSMs in previous studies, suggesting that stress distribution shape is a general property. Moreover, large differences are observed when comparing these experimental stress distributions to the most widely used expression for describing this stochastic effect in fragmentation rate models. This indicates that the traditionally used fragmentation rate models can be fundamentally flawed, at least in relation to RSM and HPH emulsification.

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author
publishing date
type
Contribution to journal
publication status
published
keywords
Emulsification, Fragmentation, High-pressure homogenizer, Rotor-stator mixer, Turbulence
in
Chemical Engineering Science
volume
177
pages
12 pages
publisher
Elsevier
external identifiers
  • scopus:85036452955
ISSN
0009-2509
DOI
10.1016/j.ces.2017.11.045
language
English
LU publication?
no
id
71267687-b1cf-467d-ba47-a8da8ae36984
date added to LUP
2019-03-11 13:03:10
date last changed
2020-08-26 04:41:04
@article{71267687-b1cf-467d-ba47-a8da8ae36984,
  abstract     = {<p>The high-pressure homogenizer (HPH) is, together with the rotor–stator mixer (RSM), the standard equipment for emulsification in many fields of chemical processing. Both give rise to intense turbulence which, in turn, gives rise to drop breakup. Previous investigations focus on average turbulent disruptive stress. However, turbulence is a stochastic phenomenon and drop breakup will be characterized by instantaneous stresses, or more specifically by the probability distribution of instantaneous turbulent stresses. This study uses high-resolution particle image velocimetry (PIV) data to measure the probability distribution of turbulent stresses in the HPH. It is concluded that stress distributions approximately follow a lognormal model and that the skewness of the distributions decreases with increasing distance from the gap exit until a constant distribution shape is obtained at the position where the turbulence is fully developed. This converged stress distribution is similar to that obtained for RSMs in previous studies, suggesting that stress distribution shape is a general property. Moreover, large differences are observed when comparing these experimental stress distributions to the most widely used expression for describing this stochastic effect in fragmentation rate models. This indicates that the traditionally used fragmentation rate models can be fundamentally flawed, at least in relation to RSM and HPH emulsification.</p>},
  author       = {Håkansson, Andreas},
  issn         = {0009-2509},
  language     = {eng},
  month        = {02},
  pages        = {139--150},
  publisher    = {Elsevier},
  series       = {Chemical Engineering Science},
  title        = {An experimental investigation of the probability distribution of turbulent fragmenting stresses in a high-pressure homogenizer},
  url          = {http://dx.doi.org/10.1016/j.ces.2017.11.045},
  doi          = {10.1016/j.ces.2017.11.045},
  volume       = {177},
  year         = {2018},
}