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Laminar filmwise condensation of vapor in presence of multi-component mixture of non-condensable gases
KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.ORCID iD: 0000-0001-5595-1952
2007 (English)In: Proceedings - 12th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH-12, 2007Conference paper, Published paper (Refereed)
Abstract [en]

Degradation of heat transfer during water vapour free convection condensation in the presence of two noncondesable gases with significant difference in molecular weights is investigated in this paper. Ternary diffusivity coefficients are derived from the Maxwell-Stefan equation and the boundary layer approximation, both for liquid and gas sides, is formulated and, with appropriate boundary and interface conditions, numerically solved. The similarity method has been used in order to simplify partial differential equations to the system of ordinary differential equations. The new model has been validated against experimental data for free convection condensation of water vapour in presence of air. Numerical results show good agreement with experimental data. The same model has been applied to study the condensation of water vapour in presence of two noncondensable gases with significantly different molecular weights. It has been observed that addition of even small amount of the light gas into the initial binary mixture of water vapour with a heavy species creates significant resistance to the heat transfer process. It has been concluded that both the diffusivity of the lighter gas as well as the buoyancy effects close to the film-mixture interface are the major contributors to the increase of the heat transfer resistance. Finally, the conditions that can lead to the accumulation of the lighter gas are discussed.

Place, publisher, year, edition, pages
2007.
Keyword [en]
Condensation, Noncondensable gas, Ternary mixture
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-7456Scopus ID: 2-s2.0-44349158431ISBN: 978-089448058-4 (print)OAI: oai:DiVA.org:kth-7456DiVA: diva2:12486
Conference
12th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH-12; Pittsburgh, PA; United States; 30 September 2007 through 4 October 2007
Note

QC 20100623

Available from: 2007-09-10 Created: 2007-09-10 Last updated: 2014-11-06Bibliographically approved
In thesis
1. Mechanistic Modeling of Water Vapour Condensation in Presence of Noncondensable Gases
Open this publication in new window or tab >>Mechanistic Modeling of Water Vapour Condensation in Presence of Noncondensable Gases
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis concerns the analytical and numerical analysis of the water vapour condensation from the multicomponent mixture of condensable and noncondensable gases in the area of the nuclear reactor thermal-hydraulic safety.

Following an extensive literature review in this field three aspects of the condensation phenomenon have been taken into consideration: a surface condensation, a liquid condensate interaction with gaseous mixtures and a spontaneous condensation in supersaturated mixtures. In all these cases condensation heat and mass transfer rates are significantly dependent on the local mixture intensive parameters like for example the noncondensable species concentration.

In order to analyze the multicomponent mixture distribution in the above-mentioned conditions, appropriate simplified physical and mathematical models have been formulated. Two mixture compositions have been taken into account: a binary mixture of water vapour with heavy noncondensable gas and a ternary mixture with two noncondensable gases with different molecular weights. For the binary mixture a special attention has been focused on the heavy gas accumulation in the near-interface region and the influence of liquid film instabilities on the interface heat and mass transfer phenomena. For the ternary mixture of gases a special attention has been paid to the influence of the light gas and induced buoyancy forces on the condensation heat and mass transfer processes.

Both analytical and numerical methods have been used in order to find solutions to these problems. The analytical part has been performed applying the boundary layer approximation and the similarity method to the system of film and mixture conservation equations. The numerical analysis has been performed with the in-house developed code and commercial CFD software. Performing analytical and CFD calculations it has been found that most important processes which govern the multicomponent gas distribution and condensation heat transfer degradation are directly related to the interaction between interface mass balances and buoyancy forces. It has been observed that if the influence of the liquid film instabilities is taken into consideration the heat transfer enhancement due to the presence of different types of waves is directly related to the internal film hydrodynamics and shows up in the mixture-side heat transfer coefficient. The model developed for the dispersed phase growth shows that degradation of the condensation heat transfer rate, which is a consequence of degradation of the convective mass flux, should be taken into account for highly supersaturated gaseous mixtures and can be captured by combination with the mechanistic CFD surface condensation model.

Keywords: condensation, noncondensable gases, CFD simulation, boundary-layer approximation, binary and ternary mixtures

Place, publisher, year, edition, pages
Stockholm: KTH, 2007
Series
TRITA-FYS, ISSN 0280-316X ; 2007:63
National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:kth:diva-4483 (URN)978-91-7178-747-7 (ISBN)
Public defence
2007-09-27, FD5, Albanova University Center, Roslagstullsbacken 21, Stockholm, 10:00
Opponent
Supervisors
Note

QC 20100623

Available from: 2007-09-10 Created: 2007-09-10 Last updated: 2015-01-30Bibliographically approved

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Anglart, Henryk

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