Experimental investigation on minimum film boiling temperature during reflooding in multi-rectangular narrow channels

Abstract

Determination of minimum film boiling temperature (Tmin) is significant in the nuclear reactor safety analysis. Tmin represents the start of quenching which is vital to mitigate the severity of the accident. In this paper, a bottom reflooding experiment is carried out to investigate Tmin and quench velocity in multi-rectangular narrow channels. Effects of working conditions, including inlet subcooling, reflooding velocity, initial wall temperature, and system pressure on Tmin and quench velocity, are analyzed in detail. It is found that Tmin and quench velocity distinctly increases with the increase of subcooling, system pressure, and reflooding velocity. However, the effect of reflooding velocity on Tmin and quench velocity is mild when the reflooding velocity is relatively high. Tmin increases with the increase of initial wall temperature, while quench velocity drops. Tmin at the upper position of the heating wall is lower than that at the lower position because the water subcooling changes when flowing along the heating channel. A prediction model of Tmin during reflooding in rectangular narrow channel is proposed, and very good agreement is achieved comparing with experimental data with ±10% uncertainty.