Experimental study on unstable free surface vortices and gas entrainment onset conditions
Experimental study on unstable free surface vortices and gas entrainment onset conditions
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DOI：
10.1016/j.expthermflusci.2013.09.015
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发表时间：
2014
影响因子：
3.2
通讯作者：
L. Cristofano;M. Nobili;G. Caruso
中科院分区：
文献类型：
--
作者：
L. Cristofano;M. Nobili;G. Caruso
多年来，自由表面涡流的形成一直是水力进水口的许多工程应用中的一个相关问题，因为强涡流池在进水口处引入旋流，导致漂浮物和气体（空气或其他气体）的夹带。气体卷吸（GE）现象也是近年来核工业中的一个重要课题，这是由于在表面形成自由涡旋的可能性，特别是在钠冷快堆（SFR）中。这种现象可能导致不太可能的正反应性插入事故，影响反应堆本身的安全性能。为了研究自由表面涡的发生，在原子能研究院热工水力学实验室建立了GETS实验装置（气体卷吸试验段）。该设备的主要目的是了解不同参数对自由表面涡的形成和演化的影响。本文给出了以冷水为工质，在不同的水箱水位、循环流量和出口管径下进行的实验测试和初步观察结果。所观察到的涡流已定性地分类在不同的“形成阶段”，并已确定通过无量纲分析的物理现象的影响的最重要的参数。经验相关性的基础上的无量纲参数的过渡边界之间的阶段，包括发病的气体夹带，已开发和讨论，和非常初步的考虑钠-水相似，弗劳德和韦伯数的基础上，介绍。
Free surface vortices formation has been, for many years, a relevant issue in many engineering applications with hydraulic intakes, since strong whirlpools introduce swirl flow at the intake causing entrainment of floating matters and gases (air or other gases). The Gas Entrainment (GE) phenomenon has also been an important topic in nuclear industry in the last years, due to the possibility of free vortex formation at the surface, especially in sodium-cooled fast reactors (SFRs). This phenomenon may result in unlikely positive reactivity insertion accident, affecting the safety performances of the reactor itself. The GETS experimental facility (Gas Entrainment Test Section) has been built in the thermal–hydraulics laboratory of the DIAEE in order to study free surface vortices occurrence. The main purpose of this facility is to understand the influence of different parameters on free surface vortices formation and evolution. Experimental tests and preliminary observations, carried out, with cold water as working fluid, different water level in the tank, circulating flow rate and outlet tube diameter, are presented as occurrence maps in this paper. The observed vortices have been qualitatively classified in different “formation stages” and the most important parameters that influence the physical phenomenon have been identified through a dimensionless analysis. Empirical correlations based on dimensionless parameters of the transition boundaries between stages, including the onset of gas entrainment, have been developed and discussed, and very preliminary considerations on the sodium–water similitude, based on the Froude and Weber numbers, are introduced.