On numerical simulation of flashing flows

Flashing of water into steam due to decompression or pressure loss is a familiar scenario during the LOCA accident of Light Water Reactors. Because of its relevance to the safety analysis there have been many research activities since the mid of last century. Nevertheless, the understanding of nucleation characteristics, bubble dynamics, as well as interphase exchanges remains insufficient, which makes it quite difficult to define the problem precisely in numerical simulations. As a result, a broad consensus on numerical methods for flashing flows is not available, and various models have been used even for the same case. For example, the critical flashing flow in a converging-diverging nozzle has been studied either with cavitation models or thermal phase change models, and there is little discussion on the contribution of mechanical and thermal effects under given temperature and pressure conditions. A guideline for selecting an appropriate model is desirable, which is clearly not an easy task due to complex physics and missing insights. Under the guidance of a baseline model concept presented in our previous work the present work will focus on the evaluation of existing numerical methods for flashing flows, and aim to discover the underlying laws with help of computational fluid dynamics and experimental data. The temporal and spatial distribution of evaporated steam will be reproduced numerically, and the effect of closure models for interphase exchanging rates as well as bubble dynamics will be discussed.