磁重力补偿下冶金熔体/溶液中气泡动态行为基础研究

How about the gas bubbles dynamic behavior and how to control them in liquid melts or liquid solutions under reduced or micro gravity? These are important and common problems on optimizing many processing in space science and technology such as metallic foaming, welding, flow boiling heat transfer and water electrolysis. Due to limited availability experiments under reduced or micro gravity condition, the studies in this area is still quiet fragmentary and a general picture of the gas bubbles dynamic behavior is far to be completed. For this reason, magnetic gravity compensation, as a replacement way to achieve reduced or even micro gravity condition by imposing a magnetic volume force directly anti-parallel to the gravity force, make it possible to perform ground-based experiments under simulated reduced or micro gravity in a long term with reasonable cost. .This proposal will focus on the fundamental research on gas bubbles dynamic behavior in metallurgical melt or solution under magnetic gravity compensation caused by the superconductive gradient magnetic field. Following profound research are expected to be completed: (1) Similarity principle and design rules will be developed in order to simulate ground-based reduced and micro gravity condition by magnetic gravity compensation specially for studying gas-liquid two-phase flow and the gas bubbles behavior in liquid. (2) Visualization experimental device in the superconductive magnet will set up applying several gas-liquid systems with different magnetic susceptibility for in-situ observe the gas bubbles dynamic behavior.Thermo-capillary and interfacial tension at the gas-liquid-solid interface will be taken into consideration during the experiments of gas bubbles formation, growth and detach process. (3) A totally coupled multi-physics mathematic model including magnetic fields, flow field and the time dependant gas-liquid interface tracking will be established. The surface tension and interface tension, expressed as a contact angle, will be specially treated in a weak form frame. The time dependant gas bubble shape will be solved by level set method. The mathematic model will be validated by comparing with the experimental results..The research of this proposal will shed light on the gas bubbles dynamic behavior under reduced and micro gravity condition. From scientific point of view, a general picture about the gas bubble nucleation and growth on the solid surface, detach from the surface and float up from the liquid coupled with breakup or coalescence will formed. On the other hand, from the technological point of view, a new way for studying gas-liquid two phase flow under simulated reduced or micro gravity condition will be explored both theoretically and experimentally and some potential technologies by applying magnetic force will developed in order to control the gas bubbles dynamic behavior in space science and technology processing.

低微重力环境下气泡在液相中的运动规律及其控制，是优化和完善空间科学诸多关键技术所面临的共性问题。但由于低微重力实验条件获得不易，难以开展充分的研究。利用超导梯度强磁场产生的磁体积力来补偿或部分补偿重力，使在气液两相体系中开展长时间、低成本的低微重力实验成为可能，具有重要意义。为此，本项目提出，基于超导梯度强磁场的磁重力补偿效应，发展和完善针对气液两相体系模拟低微重力环境的相似理论和设计思想，采用磁化率不同的多种气-液体系进行气泡动态行为的可视化模拟实验，建立包括磁场、流场以及两相动态界面捕捉的多物理场耦合数学模型，重点对低微重力环境下气泡在液固界面以及液相中的形核-生长-脱附-上浮的动态行为进行研究。在科学层面，获得不同重力水平下气泡在熔体/溶液中运动行为的机制与一般规律；在技术层面，为在地面条件下模拟空间环境两相流进行理论和实验上的探索，为解决空间冶金及材料制备中的一些关键问题提供参考。

低微重力环境下气泡在液相中的运动规律及其控制，是优化和完善空间科学诸多关键技术所面临的共性问题。但由于低微重力实验条件获得不易，难以开展充分的研究，利用梯度磁场产生的磁体积力来补偿或部分补偿重力，使在气液两相体系中开展长时间、低成本的低微重力实验成为可能。本项目基于磁重力补偿下气-液两相系统动态界面演化这一科学问题，着重进行如下几个方面的研究：（1）发展了三种数学方法，即水平集法、相场法和动网格方法，来处理气液两相流中两相界面的动态演化问题；（2）设计并制作了针对磁流体的磁重力补偿装置。数学模拟和实测表明，在φ60×60mm的空间内，可以实现磁流体90%以上的均匀磁重力补偿；（3）进行了磁重力补偿下的泡沫动力学，包括二维泡沫粗化动力学，磁场作用下二维单分散类蜂窝泡沫结构可逆转变以及磁场作用下金属泡沫材料结构调控等方面的研究；（4）磁重力补偿下磁流体系统自然对流和沸腾换热过程的实验研究和数值模拟；（5）作为一种尝试和扩展，本项目还进行了磁场作用下二维晶体熔化和凝固的宏观模拟实验探索和磁场作用下附着液滴和悬浮液滴动力学等方面的研究。本项目的研究，为在地面条件下模拟空间环境两相流进行了理论和实验上的探索，为解决空间冶金及材料制备中的一些关键问题提供参考，同时也提出了一些新的值得研究的科学问题。