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Title: Evaporation dynamics of microbubbles
Authors: Zimmerman, William B.
Al-Mashhadani, Mahmood K.H.
Bandulasena, Hemaka C.H.
Keywords: Microbubbles
Fluidics
Evaporation
Heat transfer
Distillation
Direct contact evaporation
Issue Date: 2013
Publisher: © Elsevier
Citation: ZIMMERMAN, W.B., AL-MASHHADANI, M.K.H. and BANDULASENA, H.C.H., 2013. Evaporation dynamics of microbubbles. Chemical Engineering Science, 101 pp. 865 - 877
Abstract: Until recently, generating clouds of microbubbles was a relatively expensive proposition, with the smallest bubbles requiring high energy density from either the saturation–nucleation mechanism or Venturi effect. Due to the expense of processing with microbubbles, exploration of the acceleration effects of microbubbles for physico-chemical processes are largely unstudied, particularly those that are combined effects. In this paper, the trade-off between heat transfer and evaporation on the microbubble interface are explored, largely by computational modelling but supported by some experimental evidence. The hypothesis is that both processes are inherently transient, but that during short residence times, vaporization is favoured, while at longer residence times, sensible heat transfer dominates and results in re-condensation of the initially vaporized liquid. The computational model address how thin a layer thickness will result in the maximum absolute vaporization, after which sensible heat transfer condenses the vapour as the bubble cools. This maximum vaporization layer thickness is estimated to be a few hundred microns, on the order of a few microbubble diameters at most. If the maximum vaporization estimate and the contact time necessary to achieve it are accurately estimated, these are engineering design features needed to design a vaporizing system to achieve maximum removal of vapour with minimum heat transfer. The modelling work presented here should be considered in light of the humidification experiments also conducted which showed the exit air at 100% saturation, but increasing gas temperature with decreasing layer height, and decreasing water temperature with decreasing layer height, all of which are consistent with the predictions of the computational model.
Description: This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-No Derivative Works License, which permits non-commercial use, distribution, and reproduction in any medium, provided the original author and source are credited. Full details of this licence are available at: http://creativecommons.org
Sponsor: WZ would like to acknowledge support from the EPSRC [grant no. EP/I019790/1]. WZ would like to acknowledge the Royal Society for a Brian Mercer Innovation. MKAM would like to thank the Republic of Iraq for a doctoral scholarship.
Version: Published
DOI: 10.1016/j.ces.2013.05.026
URI: https://dspace.lboro.ac.uk/2134/14676
Publisher Link: http://dx.doi.org/10.1016/j.ces.2013.05.026
ISSN: 0009-2509
Appears in Collections:Published Articles (Chemical Engineering)

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