Most of recent subchannel analysis codes are based on a multi-fluid model, and accurate evaluation of the constitutive equations in the model is essential. In order to get an accurate one of the interfacial friction force in two-phase bubble flows, experimental data on drag coefficient and interfacial area concentration have been obtained for air-water flows in 2×1 rods channel simplifying a BWR fuel rod bundle. In order to know the effects of liquid properties on the data, temperature of the test water was changed from 18 to 50 °C. The data are compared with the existing correlations reported in literatures. As a result, Hibiki and Ishii (2001) semi-theoretical correlation is found to give the best prediction against the present interfacial area concentration data. Delhaye and Bricard (1994) correlation also gives reasonably good prediction if their correlation were modified by incorporating liquid property effects. As for the drag coefficient, no correlation exist which can predict well the present data. Therefore, we developed a new correlation including three dimensionless numbers, i.e., bubble Capillary number, Morton number and Eo¨tvo¨s number. The correlation could predict well Liu et al.’s data (2008) as well as the present data.

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