竖直管道内间歇式两相流动沸腾特性分析

Study on Geysering Flow and Boiling Characteristics for Two-phase Flow in Vertical Channel

自然循环或重力注水过程的热功率、冷却剂流量等操作条件较小,易出现各种流动不稳定现象,影响核反应堆事故的发展进程,间歇式流动沸腾现象就属于其中的一种。以去离子水为工质,采用2×2加热棒束,对内径为32mm竖直通道内的间歇式流动沸腾现象进行了实验研究,分析了不同热流密度下间歇式流动沸腾不稳定现象的变化规律,讨论了热流密度对间歇式沸腾周期的影响。结果表明,在一定的热流密度条件下,当加热通道内流体达到饱和并过热时,会发生周期性地剧烈喷涌及冷液回流现象,期间伴随泡状流、弹状流、搅混流及环状流等多种流动形态;间歇喷涌周期取决于沸腾停滞时间,随热流密度的不断增大,沸腾停滞时间缩短,间歇喷涌周期也缩短。当热流密度增大到一定程度时,间歇式流动沸腾现象消失,从而转变为另一种两相流动不稳定现象。

The geysering-induced instability has significant potential impact on nuclear reactor accident transient during natural circulation or gravity driven reflooding process with low power density and mass flow rate etc. By employing electric heating of 2 X 2 rod bundles, the geysering flow and boiling characteristics were experimentally studied in a vertical tube with the inner diameter of 32 mm. The instability characteristics of the geysering flow and boiling were investigated and the effects of the heat flux density on the geysering boiling period were discussed. The results show that when the fluid in the channel under certain heat flux density reaches saturated and overheating states, the abrupt eruption of vapor and refilling of subcooled liquid will appear intermittently accompanied with various flow patterns, such as bubbly, slug, churn and annular flows. The eruption period of geysering boiling depends on the delay time of boiling which decreases with the increase of heat flux density. The geysering flow and boiling phenomenon will disappear and change into another type of two-phase flow instability when the heat flux density increases beyond a threshold.