微重力池沸腾中生长气泡周围细观流动与传热机理研究

Focusing on nucleate pool boiling phenomenon, a single-bubble-boiling model with accurately temporal and spatial location will be adopted in the present project. Experiments with different orientation of the heating surface both in normal gravity on Earth and in short-term microgravity utilizing the Beijing Drop Tower will be performed. Observation data of bubble shape and its growth, departure, and movement obtained in the experiments will be used to reveal the meso-structures of local flow and heat transfer around the growing bubble and their influences on the performance of heat transfer. Elaborate measurements of local temperature distribution on the heating surface underneath the growing bubble will be used to re-construct 3D transient fields of temperature and heat flux inside the solid wall, and to reveal the influence of transient heat conduction with periodical absorption and release of heat on boiling heat transfer. The data will be helpful for understanding the coupling action between bubble thermal dynamical behavior and local heat transfer, the evolvement of micro-liquid-film underneath the growing bubble in boiling process. Integrating theoretical analysis and numerical simulation into the study, the results will be used to reveal the mechanism of boiling heat transfer from the meso-scale, to deepen the understanding of boiling heat transfer and related flow phenomena, to promote the development of boiling heat transfer theory.

针对核态池沸腾现象，采用时-空精确定位的单气泡沸腾模型体系，通过地面常重力和落塔短时微重力实验，获得常重力条件下不同的加热面安装方位和微重力条件下池沸腾现象中气泡形态及其生长、脱落、运动等热动力学行为的测试数据，揭示环绕气泡周围的细观流动与传热结构特征及其对传热性能的影响机制；获得单气泡底部加热面局部温度分布的精细观测数据，通过数值反演重构加热器内部三维温度场及热流场，揭示固壁瞬态导热与周期性蓄热对传热性能的影响机制，认识气泡热动力学与局部热量传输过程耦合作用以及气泡底部微液膜演化特征，揭示微液膜蒸发机制及固壁热容对沸腾传热性能的影响机制。结合理论分析与数值模拟研究，从细观层次上揭示沸腾传热机理，加深对沸腾传热与相关流动现象的理解，推动沸腾传热理论的发展。

本项目采用单气泡沸腾模型，通过数值模拟和不同重力条件下的实验观测，研究了低热流条件下的核态池沸腾传热现象特征及其规律。在实验方面，成功研制了单气泡池沸腾实验用集成微加热器，通过脉冲电加热局部过热方法可实现单气泡激发及其生长的时-空精确定位，便于实验观测；提出并细致研究和验证了集成微加热器局部温度传感器与主加热器温度测量的“同步”标定技术，利用同一次实验过程中调整液池温度器件的实验数据标定集成微加热器局部温度传感器与主加热器温度输出信号，可以避免加热历史冲击的影响，获得精确的温度实测结果；将集成微加热器成功应用于地面常重力、落塔短时微重力和空间长期微重力单气泡沸腾和常规池沸腾实验，观测到不同重力条件下的气泡热动力学特性及相应传热性能，获得了微重力条件下单气泡生长过程中生长气泡底部加热面上局部温度分布的精细观测数据，通过数值反演重构加热器内部三维温度场及热流场，为揭示环绕气泡周围的细观流动与传热结构特征及其对传热性能的影响机制提供了可靠的实验依据。同时，构建了包括加热固壁内部的瞬态热传导及其周期性的蓄-放热效应对气泡热动力学行位的影响在内的数值模型，编制了相应的数值仿真计算软件，对不同重力条件下的FC-72单气泡池沸腾现象进行了数值模拟，分析了生长气泡周围局部对流与传热结构特征，揭示固壁瞬态导热与周期性蓄热对传热性能的影响机制，探讨了沸腾传热现象中的重力标度规律。本项目研究从细观层次上探讨了沸腾传热机理，加深了对沸腾传热与相关流动现象的理解。