自然循环流动沸腾逆流实验研究

An experimental investigation of flow reversal under natural circulation flow boiling

为了研究加热通道中逆流的特征和机理,本文进行了低压高入口过冷度下的自然循环实验。通过采用逐渐增加实验热流密度的方法,在自然循环流动沸腾实验中识别了3种自然循环模式:稳态自然循环、流动不稳定性(无逆流)和逆流。对比实验热流密度和经验关系式计算的临界热流密度预测值,解释了逆流的机理:流动不稳定性诱发了间歇干涸型沸腾临界,间歇干涸导致了逆流的产生。分析了自然循环工况和回路结构对逆流的影响,并结合实验段出口水温波动、壁温分布和间歇干涸的发生建立了流动不稳定性工况下实验段内的流型,单相流体和两相混合物的交替通过加热段出口。本文给出不同热流密度下的自然循环模式,可为自然循环系统的设计和安全分析提供参考。

Natural circulation experiments were performed under low pressure and high inlet sub-cooling conditions to investigate the characteristics and mechanism of flow reversal in a heated channel.Three natural flow modes were found by gradually increasing the heat flux under a natural circulation flow boiling experiment:steady-state natural circulation,and flow instabilities with and without flow reversal.The mechanism of flow reversal was given by correlating experimental heat flux with critical heat flux predicted by empirical correlation,i.e.,flow instability induced periodic dryout boiling criticality,and flow reversal was caused by periodic dryout.The influences of natural circulation conditions and loop geometry on flow reversal were also taken into account.The flow regime inside the heated test section was depicted based on the exit water temperature oscillation,heating surface temperature profile,and the occurrence of periodic dryout.Single-phase liquid and two-phase mixture appeared alternatively at the exit of the heated channel.This study identifies natural circulation flow modes under different heat fluxes and provides a reference for the design and safety analysis of natural circulation systems.