传热传质耦合影响的水中气泡上浮特性研究

Floating Characteristics of Bubbles in Water Considering the Coupling Effects of Heat and Mass Transfer

针对海水密度人工跃变技术中的气泡上浮过程,分别建立气泡传热、传质及其速度、半径等各微分方程,进而构建水中高温气泡运动的耦合模型,数值模拟得出不同大小气泡运动的两个结论:一是在气泡上浮初期,气泡温度急剧降低,半径减小而速度升高,且都分别呈先快速后平缓的规律;气泡初始半径越大,其平均热流密度变化幅度、温度下降速率与半径减小趋势都将越缓慢,而速度升高趋势则更显著。二是当气泡温度降至液温后,气泡近似作匀加速运动,半径稳定、缓慢增大,而初始半径越大的气泡,其加速度更大并更快到达水面。经验证该模型能够有效模拟水中高温气泡的上浮过程及其特征规律,为制备合适气泡群,应用于海水密度人工跃变技术研究提供理论指导.

In consider of the bubble floating process of the artificial pycnocline techniques, the differential equations of heat and mass transfer, velocity and radius are deduced, respectively. A coupling motion model is then developed for the superheated bubble. Two provable characteristics of the rising bubble with different sizes are concluded by numerical simulation. Firstly, bubbles are sharply cooled down during the initial rising period, which leads to the radius reduction and the increase of velocity with both first quick back slow trend. Moreover, for a larger initial radius, the rate of decrease of bubble average heat flux, temperature and radius are slower with the velocity more obviously. Secondly, after cooling down to the liquid temperature, bubbles will approximately conform a uniformly accelerated motion with the radius steadily and slowly increasing. Bubbles with larger initial sizes can reach the liquid surface faster for higher accelerometer. The model is successfully validated in the superheated bubble floatation process and characteristics, which is a theoretical basis of bubble formation and artificial pycnocline techniques.