曲率不同的朝下加热曲面上蒸汽泡的生长滑移和脱离机理研究

Because a vapor bubble plays a very important role in pool boiling heat transfer, understanding the mechanism of the interreaction between bubble behavior and heat mass transfer has important scientific significance and practical value. With the image intensifier,high speed camera and computer image processing technologies,an experimental investigation will be carried out to study the mechanism of a vapor bubble growth on and sliding along as well as departure from a downward facing heated curved surface with different curvatures. Based on experimental results, physical and mathematical models will be set up respectively to describe a vaper bubble growth on and sliding along as well as depature from the downward facing heated curved surfaces with different curvatures. Meanwhile, numerical methods to solve these mathematical models will be proposed and corresponding code will be written in order to accurately track the position of interfaces,deformation and motion of the bubble, whenever there is phase change or not. These numerical methods will be implemented into the our inhouse code so as to simulate these behaviors of the bubble mentioned above to reveal mechanism of interreaction between the bubble behavior and heat and mass transfer. Comparison of numerical and expimental results will be carried out for validating mathematical models. Eventually, the physical and mathematical models will be proposed to describe a vapor bubble growth on and sliding along as well as departure from a downward facing heated curved surface with different curvatures. Meanwhile, effects of curvatures, characteristics of the wall and flow and temperature fields aroud the bubble on these bahvior mentioned above will also be achieved. All results will be helpful to understand corresponding engineering processes. Final aim of the investigation is to realize the numerical simulation for practical processes.

汽泡在沸腾传热过程中扮演了极为重要的角色，因此对汽泡动力学行为与热质传递相互作用机理的研究有着极为重要的科学意义和应用价值。本项研究利用高速摄像和增强摄像相结合的技术及计算机图像处理技术，实验观测不同曲率朝下加热曲面上蒸汽泡的生长、滑移以及脱离现象。在此基础上，分别建立描述不同曲率朝下加热曲面上蒸汽泡的生长、滑移和脱离等行为的物理数学模型。研究求解描述这些过程数学模型的数值方法，能够准确跟踪有和无相变时汽泡界面位置、形状变化和滑移运动，并能捕捉脱离位置和脱离直径等物理量。模拟这些过程，获得蒸汽泡与热质传递间的相互作用和相互影响规律。将数值模拟结果与实验结果进行比较，修正模型，最终获得能够描述不同曲率朝下加热曲面上蒸汽泡的生长、滑移和脱离的过程与壁面曲率，壁面性质以及周围流场和温度场影响的关系的物理数学模型，为实现相应的工业过程的数值模拟奠定理论基础。

气泡的运动、变形长大是气液两相流及传热传质领域中十分重要的现象，对气泡动力学特性的研究也是气液两相流及传热传质领域的重要课题。蒸汽泡在被加热曲壁面上生成、长大、滑移、脱离及上升等一系列过程也是池内沸腾的基本物理过程，在此过程中，汽泡的动力学行为与周围介质之间的热质传递是紧密相关的，因此对汽泡动力学行为与热质传递相互作用机理的研究有着极为重要的科学意义和应用价值。首先，本项目针对过冷沸腾液体中不同曲率朝下壁面上汽泡的生长、滑移和脱离等过程进行了可视化研究，并与同等工况下汽泡在水平壁面的相应过程进行比较。在此基础上，建立了贴体坐标系下可以描述蒸汽泡沿曲面的生长、滑移和脱离等行为的格子Boltzmann模型。对模型进行验证之后，利用该模型研究了蒸汽泡沿倾斜表面运动，朝下圆形表面及椭圆形表面的运动规律和传热传质特性，获得了不同条件下蒸汽泡的体积、速度变化情况以及温度场的变化规律、曲率变化对气泡沿曲面生长、滑移及脱离过程的影响规律。开发了针对气泡沿曲面滑移过程进行详细地数值模拟的可视化软件，通过输入不同的网格参数、模型参数及计算条件，可以获得并输出气泡在运动过程中形态变化、上升速度等变化规律，为实现相应的工业过程的数值模拟提供了有效的手段。在本项目资助下，共发表期刊论文16篇，其中SCI检索10篇，EI检索13篇，会议论文10篇，其中EI检索1篇。申请软件著作权1项。2名博士研究生、7名硕士研究生顺利完成答辩并获得学位。