Dynamic voids measurement during geysering phenomenon in a natural circulation loop

摘要

This paper presents the measurement of void fraction of steam-water system at the riser section of a short-tube natural circulation evaporator (STNCE) at low heat ux and low pressure. The motivation behind the work is to derive a correlation between void fraction and loop ow rate, and subsequently, validate the numerical simulation of geysering instability phenomenon in the evaporator during the startup phase. An impedance-based void probe (needle) was designed and developed for local measurement of void fraction. Statistical analysis based on ANOVA indicated a strong correlation between the void fraction obtained by the probe and void fraction by inverted manometer with the coefficient of 0.9742 and the confidence limit of above 95%. The calibration also indicated that at low void fraction, the probe measured the lower values compared to those by the manometer and at high void fraction, the probe gave higher values compared to those by the manometer.