| 1. |
- Anglart, Henryk, et al.
(författare)
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Multidimensional Effects in Condensation of Water Vapour in Binary and Ternary Mixtures
- 2008
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Detailed studies have been performed to elucidate the mechanisms that govern the gravity-driven free convection condensation of water vapour from binary and ternary mixtures with noncondensable gases. Two major goals of the studies have been to investigate the multidimensional effects and to evaluate the influence of the lighter noncondensable gas in ternary mixtures on the over-all transport phenomena. Two modeling approaches have been used: a solution employing the boundary layer similarity approximation and a numerical solution of multi-fluid, multi-component formulation of the conservation equations. It has been shown that the two approaches are equivalent when applied to binary mixtures in simple geometries. The latter method must be used, howeve, to capture the spatial effects and the ternary mixture phenomena.
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| 2. |
- Coppo, Rosanna, et al.
(författare)
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Risk factors for progression in children and young adults with IgA nephropathy : an analysis of 261 cases from the VALIGA European cohort
- 2017
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Ingår i: Pediatric nephrology (Berlin, West). - : Springer Science and Business Media LLC. - 0931-041X .- 1432-198X. ; 32:1, s. 139-150
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Tidskriftsartikel (refereegranskat)abstract
- There is a need for early identification of children with immunoglobulin A nephropathy (IgAN) at risk of progression of kidney disease. Data on 261 young patients [age < 23 years; mean follow-up of 4.9 (range 2.5-8.1) years] enrolled in VALIGA, a study designed to validate the Oxford Classification of IgAN, were assessed. Renal biopsies were scored for the presence of mesangial hypercellularity (M1), endocapillary hypercellularity (E1), segmental glomerulosclerosis (S1), tubular atrophy/interstitial fibrosis (T1-2) (MEST score) and crescents (C1). Progression was assessed as end stage renal disease and/or a 50 % loss of estimated glomerular filtration rate (eGFR) (combined endpoint) as well as the rate of renal function decline (slope of eGFR). Cox regression and tree classification binary models were used and compared. In this cohort of 261 subjects aged < 23 years, Cox analysis validated the MEST M, S and T scores for predicting survival to the combined endpoint but failed to prove that these scores had predictive value in the sub-group of 174 children aged < 18 years. The regression tree classification indicated that patients with M1 were at risk of developing higher time-averaged proteinuria (p < 0.0001) and the combined endpoint (p < 0.001). An initial proteinuria of ae0.4 g/day/1.73 m(2) and an eGFR of < 90 ml/min/1.73 m(2) were determined to be risk factors in subjects with M0. Children aged < 16 years with M0 and well-preserved eGFR (> 90 ml/min/1.73 m(2)) at presentation had a significantly high probability of proteinuria remission during follow-up and a higher remission rate following treatment with corticosteroid and/or immunosuppressive therapy. This new statistical approach has identified clinical and histological risk factors associated with outcome in children and young adults with IgAN.
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| 3. |
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| 4. |
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| 5. |
- Karkoszka, Krzysztof, et al.
(författare)
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CFD modelling of laminar film and spontaneous condensation in presence of noncondensable gas
- 2006
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Ingår i: Archives of Thermodynamics. - 1231-0956 .- 2083-6023. ; 27:2, s. 23-36
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Tidskriftsartikel (refereegranskat)abstract
- A new mechanistic model for prediction of wall condensation in presence of noncondensable gas is presented. The model is based on the resolution of flow and temperature fields in the boundary layer to allow for prediction of diffusion and accumulation of noncondensable gas in the vicinity of a liquid film. Additionally, when the temperature in the vapour-gas mixture drops locally below the critical value defined by the Wilson's line, the fog formation is modelled. Both accumulation of noncondensable gas and fog formation can significantly influence the heat transfer process and thus they must be carefully modelled in many industrial applications. In particular, the degradation of heat transfer rates has an essential influence on the performance of safety systems in nuclear power plants. The present model has been implemented into a commercial computational fluid dynamics code CFX-4.
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| 6. |
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| 7. |
- Karkoszka, Krzysztof, et al.
(författare)
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Laminar filmwise condensation of vapor in presence of multi-component mixture of non-condensable gases
- 2007
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Ingår i: Proceedings - 12th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH-12. - 9780894480584
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 8. |
- Karkoszka, Krzysztof, 1976-
(författare)
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Mechanistic Modeling of Water Vapour Condensation in Presence of Noncondensable Gases
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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
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| 9. |
- Karkoszka, Krzysztof, et al.
(författare)
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Multidimensional effects in laminar filmwise condensation of vapor in binary and ternary mixtures with non-condensable gases
- 2008
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Ingår i: Nuclear Engineering and Design. - : Elsevier BV. - 0029-5493 .- 1872-759X. ; 238:6, s. 1373-1381
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Karkoszka, Krzysztof, et al.
(författare)
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Multidimensional Multicomponent Model of Condensation in Presence of Non-Condensable Gases
- 2005
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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