ANALYTICAL STUDY ON CHARACTERISTICS OF CRITICAL HEAT FLUX IN SATURATED TWO-PHASE FLOW UNDER ZERO TO COMPARATIVELY LOW MASS FLUX IN VERTICAL HEATED CHANNELS

摘要

Quantitative analyses of critical heat flux (CHF) under stagnant flow conditions, that is, countercurrent flow limitation (CCFL) to comparatively low velocity, upward-saturated two-phase flow conditions in vertical heated channels were successfully carried out by applying a newly developed analytical model to each flow condition. Regarding CHF under CCFL, a criterion was applied to the vertical circular, rectangular and annular channels that CCFL should be determined by maximizing the water mass flux falling down towards the upward flow of steam generated in the heated channel with respect to the water film thickness. As regards CHF under comparatively low-velocity, upward-saturated two-phaseflow conditions, a completely separated two-phase flow model was applied to the model of vapour blanket over the macro-liquid-sublayer on the heated wall at the CHF point. It was clarified that the analytical results gave good predictions of existing experimental results, identifying the factors determining CHF under CCFL conditions as well as the differences in characteristics of CHF under low mass flux between circular and rectangular channels.