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Residence time distribution characterization of the flow structure in dissolved air flotation

Lundh, Måns LU and Jönsson, Lennart LU (2005) In Journal of Environmental Engineering 131(1). p.93-101
Abstract
A numerical and analytical investigation is performed on a dissolved air flotation (DAF) pilot tank by using the residence time distribution (RTD) of the conservative dye rhodamine measured with a fluorometer. The experiments are numerically analyzed with regard to the total volume of the DAF tank separation zone in order to detect differences between observed separation zone flow structures in previous studies. The mean hydraulic detention time, the variance, and the estimated number of completely mixed tanks (N-cstr) in a series model are calculated. The variance is found to relate to the flow structure and the N-cstr is used for characterizing the occurrence of a stratified flow structure, which is beneficial for particle separation by... (More)
A numerical and analytical investigation is performed on a dissolved air flotation (DAF) pilot tank by using the residence time distribution (RTD) of the conservative dye rhodamine measured with a fluorometer. The experiments are numerically analyzed with regard to the total volume of the DAF tank separation zone in order to detect differences between observed separation zone flow structures in previous studies. The mean hydraulic detention time, the variance, and the estimated number of completely mixed tanks (N-cstr) in a series model are calculated. The variance is found to relate to the flow structure and the N-cstr is used for characterizing the occurrence of a stratified flow structure, which is beneficial for particle separation by DAF. The result shows a significant difference in RTD depending on expected flow structure. Analytically, a conceptual model is defined by dividing the DAF tank into an upper and a lower layer. In the upper layer, the water flow is horizontal and in the lower the water flow is vertical. The hypothesis is that mixing of the tracer takes place in the upper layer and that there is no significant mixing in the lower layer. Two simple mixing models are evaluated for the upper layer; the completely mixed tanks in series model, characterized by the number of tanks, and the dispersed plug flow model, characterized by the Peclet number. The models show good agreement with the experiments when the stratified flow structure is expected, but less agreement when the flow deviates from the stratified flow structure. The dispersed plug flow model shows the best fit with the experiments. The completely mixed tanks in series model is less sensitive, generating greater changes to the modeled RTD curve, which makes it more difficult to fit the model to the experiments. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Journal of Environmental Engineering
volume
131
issue
1
pages
93 - 101
publisher
ACSE
external identifiers
  • wos:000225818800012
  • scopus:11844305902
ISSN
0733-9372
DOI
10.1061/(ASCE)0733-9372(2005)131:1(93)
language
English
LU publication?
yes
id
01dfffa1-278a-43e3-98ff-98e56f17ce14 (old id 258417)
date added to LUP
2007-08-23 17:01:13
date last changed
2017-04-02 03:24:29
@article{01dfffa1-278a-43e3-98ff-98e56f17ce14,
  abstract     = {A numerical and analytical investigation is performed on a dissolved air flotation (DAF) pilot tank by using the residence time distribution (RTD) of the conservative dye rhodamine measured with a fluorometer. The experiments are numerically analyzed with regard to the total volume of the DAF tank separation zone in order to detect differences between observed separation zone flow structures in previous studies. The mean hydraulic detention time, the variance, and the estimated number of completely mixed tanks (N-cstr) in a series model are calculated. The variance is found to relate to the flow structure and the N-cstr is used for characterizing the occurrence of a stratified flow structure, which is beneficial for particle separation by DAF. The result shows a significant difference in RTD depending on expected flow structure. Analytically, a conceptual model is defined by dividing the DAF tank into an upper and a lower layer. In the upper layer, the water flow is horizontal and in the lower the water flow is vertical. The hypothesis is that mixing of the tracer takes place in the upper layer and that there is no significant mixing in the lower layer. Two simple mixing models are evaluated for the upper layer; the completely mixed tanks in series model, characterized by the number of tanks, and the dispersed plug flow model, characterized by the Peclet number. The models show good agreement with the experiments when the stratified flow structure is expected, but less agreement when the flow deviates from the stratified flow structure. The dispersed plug flow model shows the best fit with the experiments. The completely mixed tanks in series model is less sensitive, generating greater changes to the modeled RTD curve, which makes it more difficult to fit the model to the experiments.},
  author       = {Lundh, Måns and Jönsson, Lennart},
  issn         = {0733-9372},
  language     = {eng},
  number       = {1},
  pages        = {93--101},
  publisher    = {ACSE},
  series       = {Journal of Environmental Engineering},
  title        = {Residence time distribution characterization of the flow structure in dissolved air flotation},
  url          = {http://dx.doi.org/10.1061/(ASCE)0733-9372(2005)131:1(93)},
  volume       = {131},
  year         = {2005},
}