SUMMARY

The behavior of an evaporating thin liquid film on a non-uniformly heated cylindrical rod with both parallel and cross vapor flow will be numerically investigated. The aim is to develop a mechanistic model for local dryout in boiling water reactors (BWRs). Interest in this problem has been motivated by the fact that the liquid film on a full-length BWR fuel rod may experience significant axial and azimuthal heat flux gradients and cross flow due to variations in the thermal-hydraulic conditions in surrounding subchannels caused by proximity to inserted control blade tip and/or the top of part-length fuel rods. Such heat flux gradients coupled with localized cross flow may cause the liquid film on the fuel rod surface to rupture by hydrodynamic instability, thereby forming a dry hot spot. These localized dryout phenomena can not be accurately predicted by traditional subchannel analysis methods in conjunction with empirical dryout correlations. To this end, a numerical model based on the Level Contour Reconstruction Method will be developed. The model includes a ghost-cell extrapolation technique to handle the complex interface geometry. Additionally, a sharp interface temperature technique will be implemented. The model will be applied to BWR fuel rods to determine whether localized cross flow coupled with heat flux gradients can lead to liquid film rupture and dry spot formation. Different coordinate systems will be examined to enhance the resolution of the Level Contour Reconstruction Model. Additionally the interface model will be enhanced by incorporating such effects as disjoining pressure, non-equilibrium distribution of phase interface temperature, and contact line dynamics to capture the correct film behavior after its rupture. Comparison will be made between the model predictions and experimental data.