The CFD simulation of single-phase heat transfer and flow boiling of liquid sodium has been performed in a narrow tubular channel that has a resemblance with the flow subchannel of SFR fuel subassembly. The Eulerian-Eulerian multiphase model (two-fluid model) has been developed with a suitable wall heat flux partitioning method for wall heat balance. The sodium boiling inception, the nucleate boiling regime, and further to high void fraction transition regimes (slug/churn dominant) are predicted using the model by considering suitable constitutive correlations required for sodium. The advanced model based on the interfacial area density has been used to detect the flow morphology and to use the corresponding set of closure relations.

The numerical model is validated with the benchmark experiments of liquid sodium flow boiling under quasi-steady conditions in a tubular channel for a range of inlet mass flow rates while keeping constant wall heat flux, outlet pressure, and inlet temperature. The basic characteristics of void growth and resultant two-phase pressure drop are studied numerically in the narrow tubular channel under different flow conditions. The numerical predictions for pressure drop are compared with the available empirical correlations for sodium two-phase flow. The predictions of void growth behavior along the axial and in the radial direction depict the dominance of the annular flow boiling pattern as observed in liquid sodium flow boiling experiments. The mechanistic model-based boiling heat transfer coefficient predictions are obtained from the modified wall heat balance model and a comparison is made with the available empirical correlations.