Numerical investigation of liquid film instabilities and evaporation in confined oscillating slug-plug flows

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Abstract

An enhanced volume of fluid (VOF)-based numerical simulation framework that accounts for conjugate heat transfer between solid and two-phase flow regions and phase-change due to boiling/condensation, is utilised in order to investigate the effect of flow oscillation amplitude and frequency on the liquid film evaporation and instability formation in slug-plug flows within heated channels, in saturated flow boiling conditions. Various series of parametric numerical simulations are performed, for different values of flow oscillation amplitude and frequency for a variety of working fluids. For one of the working fluids two different channel diameters are also tested. The oscillations in each case are induced by applying an oscillating pressure boundary condition at the inlet of the channel, keeping the pressure constant at the outlet, after an initial period of constant pressure drop between the inlet and the outlet. Capillary ridges that are initiated at the liquid film, in the vicinity of the leading edge of the considered vapour slugs, are identified as a result of the imposed oscillations, which are translated in the form of capillary waves towards the rear end of the bubbles. It is shown that the formation frequency as well as the geometric characteristics of the generated ridges, are directly related to the corresponding frequency and amplitude of the induced flow oscillations. Furthermore, it is shown that in the initial stages of the bubble fate after the application of the oscillations liquid film evaporation is enhanced with the increase of the oscillation amplitude while it degrades as the frequency of the oscillation becomes higher. However, for large oscillation amplitudes and channel diameters, liquid jets penetrate into the elongated bubbles leading in a lot of cases to bubble break-up.

Original languageEnglish
Title of host publicationComputational and Experimental Methods in Multiphase and Complex Flow X
EditorsS. Hernández, P. Vorobieff
Pages127-138
Number of pages12
Volume123
DOIs
Publication statusPublished - 23 Jul 2019
Event10th Conference on Multiphase flow, ICMF 2019 - Rio de Janeiro, Brazil
Duration: 19 May 201924 May 2019

Publication series

NameWIT Transactions on Engineering Sciences
Volume123
ISSN (Print)1743-3533

Conference

Conference10th Conference on Multiphase flow, ICMF 2019
CountryBrazil
CityRio de Janeiro
Period19/05/1924/05/19

Keywords

  • Conjugate heat transfer
  • Micro-channel
  • Oscillating vapour slug
  • Volume of fluid

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    Cite this

    Andredaki, M., Georgoulas, A., Miche, N., & Marengo, M. (2019). Numerical investigation of liquid film instabilities and evaporation in confined oscillating slug-plug flows. In S. Hernández, & P. Vorobieff (Eds.), Computational and Experimental Methods in Multiphase and Complex Flow X (Vol. 123, pp. 127-138). (WIT Transactions on Engineering Sciences; Vol. 123). https://doi.org/10.2495/MPF190121