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The efficacy of in-vessel through external reactor vessel cooling (IVR-ERVC) is strongly correlated with the critical heat flux (CHF) on the lower head of reactor pressure vessel (RPV). The high limit of CHF prevents the RPV from failure by extracting much heat out of the vessel through the circulation of working fluid in external flow channel. In present study, the deionized water is allowed to flow through curved flow channel having radius of curvature of 368mm and hydraulic diameter of 40mm with square cross-section. The heat flux of 1500kWm−2 is applied perpendicular to the convex wall of the channel. The CHF on the wall of flow channel has been predicted by incorporating CFD based two-phase (liquid-vapor) boiling model. The investigations on spatial variation of pressure, temperature, and velocity and heat flux acquired as a result of numerical simulations have been discussed in detail. The CHF and average HTC is predicted as 1.798e+04kWm−2 and 38.981kWm−2K−1 respectively.

The numerical calculations are performed to predict critical heat flux (CHF) during subcooled boiling of deionized water through 90° curved flow channel with square cross-section. Two types of flow regimes have been observed at low and high flow velocities. In case of low flow velocities, the continuous accumulation of vapors formed a vapor blanket on heating surface which consequently reduced heat dissipation out of the surface and triggered CHF due to drying out of liquid between vapor blanket and heating wall. On the other hand, coolant circulation at higher velocities hindered the formation of vapor blanket and allowed subcooled liquid for rewetting. The consistent rewetting led the formation of small and separate vapor blankets. The enhancement in CHF has been observed with increased degree of subcooling and by increasing flow velocity in present study.