复杂瞬变外力场作用对过冷沸腾局部相界面特性的影响研究

The existing local phase interface characteristics and constitutive relationship of interphase mass, momentum and energy transfer for subcooled boiling are mostly obtained under the stationary condition, and it need to be further studied whether these rules and constitutive relationship obtained under stationary conditions could be directly extrapolated and applied under transient motion conditions. In this project, local interfacial characteristics as the breakthrough point,and phase distribution characteristics and interfacial heat and mass transfer for subcooled boiling will be studied by use of the experimental technology of phase distribution and visualization under the transient motion condition. The experimental data under the action of transient external force field such as void fraction, interfacial velocity, bubble diameter and so on will be obtained. Based on the experimental results, interfacial area concentration model, interfacial heat transfer model and force model acting on bubbles will be built. Three-dimensional numerical model and its numerical simulation method will be present, which can be used to describe the local interfacial characteristics of subcooled boiling under the transient external force field. Finally, phase distribution characteristics, two-phase flow field, temperature field and the evolvement of interfacial mass and heat transport under the transient external force field will be obtained, and influence mechanism of complex transient force field on local phase interfacial characteristics of subcooled boiling will be explained. The results obtained in this project improve the research on two-phase flow and heat transfer in present, and which can provide technical support for thermal-hydraulic calculation and safety analysis under transient motion conditions.

现有过冷沸腾下局部相界面特性以及相间质量、动量与能量作用的传输本构关系更多是基于静止条件下获得的，基于静止条件下获得的沸腾传热规律和模型能否直接外推并应用于瞬变运动条件下热工水力特性预测有待于进一步研究。本项目以局部相界面特性为切入点，采用瞬变运动条件下相分布和可视化实验技术，针对过冷沸腾通道内相分布特性和界面传热传质两个基础问题开展研究，获得瞬变运动条件下过冷沸腾通道内空泡份额、界面速度、汽泡直径和频率等实验数据，建立瞬变外力场作用下过冷沸腾界面浓度模型、相界面换热模型以及受力模型，形成一套描述瞬变外力场作用下过冷沸腾相界面特性三维数值模型及模拟方法，获得瞬变外力场作用对过冷沸腾相分布特性、相间质量和能量传输机理，以及两相流场和温度场演化规律，揭示瞬变外力场作用对过冷沸腾局部相界面特性的影响机制。丰富现有两相流动和传热研究，可为海洋条件运动下反应堆热工水力计算和安全分析提供技术支撑。

浮动式、船用反应堆受到海洋环境的影响，反应堆处于三维六自由度运动状态，产生了时空瞬变外力场作用，可能会改变堆芯内两相流动和传热特性。本项目针对过冷沸腾通道内相界面和相分布特性基础问题开展研究，提出了多周期同相位叠加法、整周期平均法和分区域积分法，掌握了运动条件下两相相分布时空分布实验及分析技术，获得了瞬变运动条件下过冷沸腾通道内空泡份额、界面速度、汽泡直径、汽泡频率等实验数据。建立瞬变外力场作用下孤立汽泡区域内汽泡受力模型，发现运动条件引起的外力较浮力、曳力等其他力小6-7个量级，对孤立汽泡区域汽泡生长和脱离影响较小，热工水力参数仍起主导作用，浮力沿流动方向周期性变化是汽泡脱离直径小幅度波动的原因。汽泡群作用区域，汽泡数量增多后，瞬变外力场引起汽泡数目及尺寸分布不均、运动速度发生改变；局部瞬时空泡份额呈现周期性波动，峰值在最大倾角时刻，近壁面附近波动最大；随着摇摆角度增大，空泡份额波动幅度增加，摇摆周期增大，空泡份额增大。基于上述实验数据和规律分析，构建了瞬变外力场下过冷沸腾空泡份额计算模型以及相场汽泡尺寸分布模型等，并经数据验证，形成瞬变外力场作用下过冷沸腾相分布特性三维数值计算方法，获得了过冷沸腾相分布场，速度场、温度场演化特性。基于流场和温度场等数据和受力分析，从汽液相间作用力角度揭示了瞬变外力场作用对过冷沸腾相分布特性的影响机理，发现汽泡群作用区摇摆条件下升力、湍流分散力、壁面润滑力及浮力发生周期性波动，决定了径向相分布在近壁面局部瞬时波动特性；轴向方向上，在外力场和浮力耦合作用下，汽泡群附近局部流体速度发生波动，导致剪切升力、曳力和水动力发生波动，改变了汽泡群运动特性。本项目研究成果已应用于973项目研究中，丰富了现有两相流动和传热研究，为我国自主软件的研制提供了基础数据，为舰船核动力、海洋核动力平台热工水力计算和安全分析提供技术支撑。