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Mechanistic Modeling of Water Vapour Condensation in Presence of Noncondensable Gases
KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
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: urn:nbn:se:kth:diva-4483ISBN: 978-91-7178-747-7 (print)OAI: oai:DiVA.org:kth-4483DiVA: diva2:12488
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
List of papers
1. CFD modeling of laminar film and spontaneous condensation in presence of noncondesable gas
Open this publication in new window or tab >>CFD modeling of laminar film and spontaneous condensation in presence of noncondesable gas
2006 (English)In: Archives of Thermodynamics, ISSN 1231-0956, Vol. 27, no 2, 23-36 p.Article in journal (Refereed) Published
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-7453 (URN)
Note

QC 20100623

Available from: 2007-09-10 Created: 2007-09-10 Last updated: 2016-05-11Bibliographically approved
2. Multidimensional Multicomponent Model of Condensation in Presence of Non-Condensable Gases
Open this publication in new window or tab >>Multidimensional Multicomponent Model of Condensation in Presence of Non-Condensable Gases
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.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-7454 (URN)
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
3. Numerical analysis of solitary wave influence on the filmwise condensation in presence of non - Condensable gases
Open this publication in new window or tab >>Numerical analysis of solitary wave influence on the filmwise condensation in presence of non - Condensable gases
2006 (English)In: International Conference on Nuclear Engineering, Proceedings, ICONE, 2006Conference paper, Published paper (Refereed)
Abstract [en]

This paper is dealing with the analysis of condensation in presence of non-condensable gas on a laminar liquid film falling down on a vertical smooth surface. Particular interest is focused on the influence of solitary waves on the condensation process. Solutions to the pressure, velocity, temperature and additional scalar variable fields are obtained numerically by solving two - dimensional Navier - Stokes equations formulated in a general coordinate system and applying the artificial compressibility method. The whole system of equations together with adequate boundary conditions is implemented using the finite difference method and solved in the Matlab® 7 code. Both implicit Crank - Nicolson and Euler schemes for the time derivatives are initially used and the latter one is chosen as a more stable. All computations are carried out with prescribed geometry for a film and gas domains and a special attention is focused mainly on the modelling of the influence of the interfacial boundary conditions on the heat transfer process between gaseous mixture and liquid phases. Description of the physical, mathematical and numerical models and several examples of the solutions are presented. Conclusions on the wave hydrodynamics influence on the heat transfer during phase change process are drawn. Copyright

Series
International Conference on Nuclear Engineering, Proceedings, ICONE, 2006
Keyword
Artificial compressibility, Laminar liquid films, Non-condensable gases, Phase change, Time derivatives, Boundary conditions, Finite difference method, Heat transfer, Hydrodynamics, Mathematical models, Navier Stokes equations, Numerical analysis, Condensation
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-155854 (URN)10.1115/ICONE14-89677 (DOI)2-s2.0-33845776095 (Scopus ID)0791837831 (ISBN)9780791837832 (ISBN)
Conference
Fourteenth International Conference on Nuclear Engineering 2006, ICONE 14, 17 July 2006 through 20 July 2006, Miami, FL
Note

QC 20141118

Available from: 2014-11-19 Created: 2014-11-13 Last updated: 2015-01-30Bibliographically approved
4. Laminar filmwise condensation of vapor in presence of multi-component mixture of non-condensable gases
Open this publication in new window or tab >>Laminar filmwise condensation of vapor in presence of multi-component mixture of non-condensable gases
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.

Keyword
Condensation, Noncondensable gas, Ternary mixture
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-7456 (URN)2-s2.0-44349158431 (Scopus ID)978-089448058-4 (ISBN)
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
5. Multidimensional effects in laminar filmwise condensation of vapor in binary and ternary mixtures with non-condensable gases
Open this publication in new window or tab >>Multidimensional effects in laminar filmwise condensation of vapor in binary and ternary mixtures with non-condensable gases
2008 (English)In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 238, no 6, 1373-1381 p.Article in journal (Refereed) Published
Abstract [en]

This paper is dealing with the multidimensional modelling of gravity driven water vapour free convection condensation from binary and ternary mixtures of condensable and noncondensable gases. In the case of ternary mixtures, a special attention is paid to the influence of the light gas on the transport phenomena in the gaseous phase. Two solution methods have been applied: an analytical solution employing the boundary layer similarity approximation and a numerical solution of multi-fluid, multi-component formulation of the conservation equations. It has been demonstrated that the two methods are equivalent when applied to binary mixtures in simple geometries. However, to capture the spatial effects and the ternary mixture phenomena the latter method must be used.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-7457 (URN)10.1016/j.nucengdes.2007.11.003 (DOI)000256122700010 ()2-s2.0-42249111344 (Scopus ID)
Note

QC 20100623

Available from: 2007-09-10 Created: 2007-09-10 Last updated: 2016-06-09Bibliographically approved

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