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2 Journal of Power Technologies

2 2014

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Wall temperature prediction in annular geometry during post-dryout heat transfer

Anghel I. G., Anglart H.

Journal of Power Technologies

2014

Vol. 94, nr 5

1--7

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 takes into account the developing post-dryout heat transfer regime. The method is applied to post-dryout conditions in an annulus with pin spacers and achieves a significant improvement in prediction accuracy compared to other reference methods.

Modeling of liquid film flow in annuli

Anglart H.

Journal of Power Technologies

2014

Vol. 94, nr 5

8--15

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.