中文摘要：

压力容器内滞留（IVR）策略可在反应堆发生严重事故后,有效地将堆内熔融物滞留在压力容器内,是防止放射性物质外泄的关键技术。纳米流体是将粒径小于100nm的固体颗粒加入到基液中以提高换热特性的稳定悬浮液,其热物性以及换热特性与传统固液悬浮液相比有较大区别,适宜的纳米流体种类及配比可强化换热。本文采用引入了无网格对流格式的移动粒子半隐法（MPS方法）研究了体积份额为1.0%的Al2O3/H2O纳米流体和纯水中加热面朝下时气泡在加热面上的成长、脱离以及附着形成气膜的过程,探索了气泡脱离的临界角度及其影响因素,为加速纳米流体的工业应用、增强IVR能力提供理论基础。

英文摘要：

The in-vessel retention（IVR）strategy is a key technology to retain the core melt in reactor vessel and prevent the leakage of radioactive material after severe accident happened to the nuclear reactor.The nanofluid is a fluid with steady suspension of solid nanoparticles,in which solid particles with diameters below 100 nm are added to base fluid to improve heat transfer characteristics of working fluids.Its thermal physical properties and heat transfer characteristics are much different from the conventional solid particle suspended working fluid.Thus,the nanofluid with appropriate nanoparticle type and volumetric concentration can enhance heat transfer.In this study,the MPS-MAFL（moving particle semi-implicit method-meshless advection using flow-directional local grid）method was used to simulate the growth,departure and attaching and gas film forming of the bubble on the downward-facing heating surface in pure water and nanofluid（volume fraction is 1.0%Al-2O-3/H-2O）flow process.The critical departure angle of bubble and its influence factors were studied.This research work lays the theoretical foundation of enhancing IVR capacity and accelerating the industrial application of nanofluid.