Abstract:

The differences in flow and mass transfer characteristics between a sub-millimeter bubble column and a conventional bubble column were explored systematically by using experimental and numerical simulation methods. A specific numerical simulation approach was proposed for the flow and mass transfer processes of sub-millimeter bubbles in gas-liquid bubbly flow. The results reveal that, under comparable operating conditions, the size distribution of bubbles in sub-millimeter bubble columns is narrower, with an average size reduced to approximately 3% of that observed in conventional columns. Moreover, the gas holdup increases by over two-fold, and the interfacial area enhances by two orders of magnitude. In addition, the radial distribution of gas and liquid in the submillimeter bubble gas-liquid two-phase flow is more uniform, and the degree of axial backmixing is smaller. Notably, the interfacial area within sub-millimeter bubble columns plays a pivotal role in intensifying mass transfer, even though their liquid-side mass transfer coefficient is lower compared to conventional columns. Leveraging the substantial interfacial area, the volumetric mass transfer coefficient within sub-millimeter bubble columns is approximately ten times that within conventional columns. Notably, simulation outcomes for large-scale bubble column reactors indicate that sub-millimeter bubbles have the potential to yield a more uniform gas holdup distribution, thereby exhibiting reduced sensitivity to initial gas-liquid distribution effects.

Key words: sub-millimeter bubble, bubble column, gas-liquid two-phase flow, mass transfer, numerical simulation, process intensification

摘要：

通过实验和数值模拟系统研究了亚毫米气泡鼓泡塔与常规鼓泡塔在流动和传质特性上的区别，并建立了适用于亚毫米气泡气液两相流流动和传质过程的数值模拟方法。研究结果表明，相比常规鼓泡塔，相同操作条件下亚毫米气泡鼓泡塔的气泡尺寸分布更窄，平均尺寸降至前者3%左右，气含率提高2倍以上，比表面积提高2个数量级。另外亚毫米气泡气液两相流中气液径向分布更均匀，轴向返混程度更小。亚毫米气泡鼓泡塔的相界面积是强化传质的关键控制因素，其液相传质系数虽低于常规鼓泡塔，但依靠巨大的相界面积，其体积传质系数是常规鼓泡塔的10倍左右。针对大规模鼓泡塔反应器的模拟结果也表明，亚毫米气泡可使反应器达到更均匀的气含率分布，受初始气液分布的影响小。

关键词: 亚毫米气泡, 鼓泡塔, 气液两相流, 传质, 数值模拟, 过程强化