| 1. |
- Anghel, Ionut, et al.
(författare)
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Wall Temperature Prediction in Annular Geometry during Post-Dryout Heat Transfer
- 2014
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Ingår i: Journal of Power Technologies. - 2083-4187 .- 2083-4195. ; 94, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- In this paper a new approach to predict wall temperature during post-dryout heat transfer in annuli with flow obstacles is presented. The proposed approach takes into account the obstacle specifics and location in the channel to determine the onset of post-dryout patch. The wall temperature in the dry patch area is predicted from a correlation that is taking into account the developing post-dryout heat transfer regime. The method is applied to post-dryout conditions in annulus with pin-spacers and a significant improvement of prediction accuracy in comparison to other reference methods is demonstrated.
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| 2. |
- Anglart, Henryk
(författare)
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Dry Patch Formation in Diabatic Annular Two-Phase Flows
- 2014
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Ingår i: Journal of Power Technologies. - 2083-4187 .- 2083-4195. ; 94, s. 85-95
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Tidskriftsartikel (refereegranskat)abstract
- Conditions for the formation of a stable dry patch in vertical annular two-phase flows in heated channels are investigated. An analytical model of the force balance for the leading edge of the liquid film is developed. In addition to surface tension, evaporation thrust and capillary forces, the model includes the effect of turbulence, the pressure gradient and the interfacial shear stress. Numerical evaluations are performed to validate the model and to indicate the importance of various factors on the dry patch stability and on the resulting minimum wetting rate of the liquid film. The analyses indicate that good agreement with measurements is obtained in case of stagnant patch formed on liquid film flowing down a vertical surface. It is shown that for low and moderate mass flow rate of the gas phase in vertical co-current annular flow, the force balance is dominated by the stagnation and the shear stress forces. With growing mass flow rate of the gas phase, the pressure gradient and the interfacial shear stress are increasingly important. As a result, in accordance with measurements, the predicted minimum flow rate of the liquid film at which the patch is re-wetted decreases.
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| 3. |
- Anglart, Henryk
(författare)
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Modelling of Liquid Film Flow in Annuli
- 2014
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Ingår i: Journal of Power Technologies. - 2083-4187 .- 2083-4195. ; 94, s. 8-15
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Tidskriftsartikel (refereegranskat)abstract
- One of the challenges in thermal-hydraulic analyses of BWRs is correct prediction of dryout occurrence in fuel assemblies. In practical applications the critical powers in fuel assemblies are found from correlations that are based on experimental data. The drawback of this approach is that correlations are valid only for these fuel assemblies on which the experiments have been conducted. Other restrictive factors are the limited ranges of experimental working conditions including pressure, mass flux and axial power distributions. To overcome the above-mentioned limitations, several different approaches have been proposed to predict the dryout occurrence. One of them is to employ a phenomenological model of annular flow, in which the mass transfer between the liquid film and the gas core is based on entrainment and deposition correlations. Most of these correlations are derived from water-air flows in vertical tubes and their applicability to other geometries in general, and rod-bundles in particular, should be analysed. This paper presents an analysis of the entrainment rate in vertical annuli. Using the standard approach to calculate the entrainment rate, one can demonstrate that the results deviate from measurements. It has been shown that modifying the entrainment correlation based on data obtained in the annulus geometry leads to an essential improvement in the predictive capability of the phenomenological model of annular two-phase flow.
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| 4. |
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| 5. |
- Pegonen, Reijo, et al.
(författare)
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Investigation of Thermal Mixing in the Control Rod Top Tube Using Large Eddy Simulation
- 2014
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Ingår i: Journal of Power Technologies. - : Institute of Heat Engineering. - 2083-4187 .- 2083-4195. ; 94:1, s. 67-78
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Tidskriftsartikel (refereegranskat)abstract
- Thermal mixing and thermal fatigue has led to component failures in the nuclear industry. The thermal fatigue phenomenon is intimately linked with the mixing of streams of different temperatures in proximity to a solid wall. Due to conjugate heat transfer, temperature fluctuations are induced in the wall. One of the key issues is to predict the amplitude and the frequency of the fluctuations. This paper presents pre-calculations of the thermal mixing experiments that are under preparation at the KTH Royal Institute of Technology as part of the THEMFE project (Thermal Mixing and Fatigue Experiment).The proposed geometry is a simplification of a reactor control rod and consists of a top-tube and control rod stem, which are modeled as concentric cylinders. In addition there are only two hot inlet jets and two cold inlet jets, whereas in reality there are 8 upper inlets and 4 lower inlets for hot bypass water and the cold flow is annular.Thermal mixing was studied by using a transient Computational Fluid Dynamics (CFD) solver for the incompressible filtered Navier-Stokes equations and employing a Large Eddy Simulation model of turbulence implemented in OpenFOAM. The aim was to verify that the proposed simplified geometry and the flow conditions of the experiment will lead to low frequent temperature fluctuations of the order of 0.1-1 Hz, as seen in previous experiments with the real geometry. Such low frequencies are typical for the thermal fatigue phenomenon. The study was focused on the region near the control rod stem and therefore a refined grid was used in that region. The final mesh consisted of over one million cells.The results did indeed reveal low frequent temperature fluctuations in the lower part of the mixing region near the control rod stem. The results of this paper indicate that the length of the mixing region is 23 cm, which is large enough to be resolved in the experiment. It was also found that the most dangerous region, where the dominant high amplitude temperature fluctuations have a frequency of the order of 0.1 Hz, is 4 cm long. As expected, the instant flow field is asymmetric with large secondary flows. The present results verify that the proposed geometry and flow conditions can be applied in the experiment.
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| 6. |
- Kupecki, Jakub, et al.
(författare)
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Sensitivity Analysis of Reacting Two-Phase Flow in Nuclear Heat-Based Gasification Process
- 2011
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Ingår i: Journal of Power Technologies. - Warsaw : Warsaw University of Technology. - 2083-4187. ; 91:2, s. 54-62
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Tidskriftsartikel (refereegranskat)abstract
- Current work investigates influence of operating parameters on chemical reactions occuring within two-phase reacting flow. This particular flow analysed corresponds to processes in coal gasifier unit supplied in heat by a high temperature gas cooled nuclear reactor (HTGR).
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