Thermo-Hydraulics and Relaxation of Thermal Non-Equilibrium Two-Phase Flow

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The purposes of this work are to offer a fundamental data base for next generation light water reactors and to sophisticate numerical codes for transient two-phase flow. The effect of channel gaps on thermo-hydraulics and the relaxation process of superheated water have been investigated experimentally and analytically. From the results, the following insights are clarified :(1) For a channel gap narrower than 2mm, thermo-hydraulics of boiling two-phase flow is influenced by channels gaps, and new correlations of boiling heat transfer, two-phase friction multiplier.(2) The drift flux model is applicable to analyze boiling two-phase flow in channels narrower than 2mm.(3) During reflooding phase in channels narrower than 2mm, quench velocity becomes much lower than a reflooding rate, and pressure drop becomes so higher than that in channels wider than 2mm.(4) Underpressure at the relaxation inception point of superheated water and time required for the relaxation inception can be evaluated by modified Jones'model.(5) Macroscopic relaxation inception is governed by interfacial area density and integration of the superheating by the time passing through the superheated region.(6) A new correlation of interfacial heat transfer is proposed and the two-fluid model including this correlation explains well the relaxation process and thermo-hydraulics of superheated water.