浸没射流条件下气溶胶水洗机理研究

Experimental Research on Aerosol Scrubbing Mechanism under Submerged Jet Condition

反应堆严重事故发生后,气溶胶池式水洗现象常发生于抑压水池排放过程中,掌握此条件下的气溶胶水洗特性对于严重事故后的放射性评估具有重要意义。本文针对浸没射流条件下的气溶胶水洗效率开展了实验研究,探究了气溶胶直径、液池温度、淹没深度、喷放压力等参数对气溶胶水洗效率的影响。气体穿过破口或喷管以射流的形式向液相内喷放时,由于高速气流剪切作用而产生的夹带液滴会通过惯性效应将气溶胶大量滞留在液相中,喷放压力的增加会增强此效应,而淹没深度的增加也会提高滞留时间及气溶胶接触气液界面的概率。液池温度降低后由于温度梯度及蒸汽冷凝速率的增加,会使水洗效率得到进一步地提高,但热泳、扩散泳等热驱动效应与惯性、液位效应间的作用占比存在一定的制约,通过对现有相关实验进行总结,并基于主导的水洗机制拟合了预测浸没射流条件下水洗效率的经验关系式,可为相关实验及模型提供数据及理论支撑。

In severe reactor accidents,the phenomenon of aerosols being captured and retained in the liquid as they follow the gas through the liquid phase often occurs during the discharge process of the suppression pool.It is one of the important thermal-hydraulic phenomena that affect the migration and release of radioactive source terms.Understanding the scrubbing characteristics of aerosols under this condition is of great significance for the radioactive assessment after severe accidents.The paper conducted experimental research on the scrubbing efficiency of aerosol under submerged jet conditions,exploring the influence of parameters such as aerosol diameter,liquid pool temperature,submergence,and injection pressure on the scrubbing efficiency of aerosol.When gas is injected into the liquid phase through a rupture or nozzle in the form of a jet,the entrained droplets generated by high-speed airflow shear will retain a large amount of aerosols in the liquid phase through the inertia effect.The experimental results indicate that an increase in injection pressure enhances the inertial effect,thereby improving the scrubbing efficiency.The increase in submergence also increases the residence time and probability of aerosols in contact with gas-liquid interfaces,ultimately leading to an improvement in scrubbing efficiency.Under steam jet conditions,the generation of thermophoresis and diffusiophoresis effects can improve the scrubbing efficiency of small-diameter aerosols.Under different submergence depths,there is a decreasing and then increasing relationship between scrubbing efficiency and aerosol diameter,with a turning point of around 0.3μm.The change in liquid and gas temperature can alter the steam condensation rate and temperature gradient,thereby altering the scrubbing efficiency by affecting the thermophoresis and diffusiophoresis effects.After the temperature of the liquid pool decreases,the increase in temperature gradient and steam condensation rate will further improve the scrubbing efficiency.There is an approximate logarithmic relationship between the scrubbing efficiency and the gas-liquid phase temperature difference under the same injection pressure and submergence conditions.However,there are certain constraints on the proportion of thermal effects such as thermophoresis and diffusiophoresis,as well as the effects of inertia and submergence.By summarizing existing relevant experiments and fitting empirical formulas for predicting scrubbing efficiency under submerged jet conditions based on the dominant scrubbing mechanism,the predicted relative deviation range is-15%-25%,which can provide data and theoretical support for relevant experiments and models.