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Multidimensional Multicomponent Model of Condensation in Presence 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
2005 (English)Conference paper, Published paper (Other academic)
Abstract [en]

Non-condensable gases, even in small quantities, are known to significantly influence the heat transfer and the condensation rate. Near the condensate interface, which typically forms liquid films on walls, the non-condensable gases will accumulate and create a mass transfer resistance. Thus, a proper prediction of the heat and mass transfer rates require an accurate estimation of the concentration of non-condensable gases in the boundary layer in the direct proximity of the condensate. This phenomenon plays an important role in many industrial applications, e.g. inside the steam-generation tubes during a small-break loss of coolant accident (SB-LOCA) in pressurized water reactors (PWRs). It can also take place during the course of a hypothetical sever accident in PWRs, when hydrogen can be produced and distributed in the containment due to convective and diffusive processes. High local hydrogen concentration can lead to detonations and the structural integrity of the containment may be in danger. In the present paper a new model for the condensation of vapor in presence of non-condensable gases is presented. The model has been implemented into a commercial CFD code CFX and has a full multidimensional capability. Both convective and diffusive terms responsible for the transport of the non-condensable gases are taken into account in the model. In that way the mass transfer rate at the condensate interface is modeled in a mechanistic way. The liquid films which are formed in the course of condensation on walls are modeled in detail. The film model predicts the local parameters which influence the local heat transfer intensity. This includes liquid film thickness and the temperature distribution in the liquid film. The current model has been validated against separate-effect experiments performed by Choi et al. (2002) and Malet et al. (2003) and promising results have been obtained. In the full paper a detailed description of the model will be given and a thorough validation will be presented.

Place, publisher, year, edition, pages
2005.
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-7454OAI: oai:DiVA.org:kth-7454DiVA: diva2:12484
Conference
The 11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11)
Note

QC 20100623

Available from: 2007-09-10 Created: 2007-09-10 Last updated: 2016-10-10Bibliographically 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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