Abstract:

Rayleigh convection phenomenon caused by interfacial concentration gradient can significantly improve the mass transfer rate of CO₂ absorption process, but the mechanism of mass transfer enhancement in this process is not clear at present. In order to explore the enhancement mechanism of Rayleigh convection mass transfer process, water absorbing CO₂ process was selected as the research object, and realized the visualization and quantitative measurement of interfacial convection based on particle image velocimetry (PIV) and laser induced fluorescence (LIF) technology under different CO₂ partial pressure conditions. It was found that the average interface concentration would drop instantaneously at the critical time of the convection and would rise after the formation of the ordered self-organization structure, the final average interface concentration would descend with the decrease of CO₂ partial pressure in gas phase. After convection, the mass transfer capacity enhancement of the system was divided into two stages, vorticity field played a leading role before the formation of the ordered self-organization structure, but after the formation of the ordered self-organization structure, the mass transfer capacity enhancement was the result of the joint action of vorticity field and interface concentration. After the formation of the ordered self-organization structure, the average instantaneous mass transfer coefficients of different systems had a strong correlation with the corresponding average vorticity, indicating that the vorticity field formed by the interaction of concentration field and velocity field played an important role in the process of convective mass transfer enhancement.

Key words: CO₂ capture, Rayleigh convection, mass transfer, laser induced fluorescence, particle image velocimetry

摘要：

界面浓度梯度导致的Rayleigh对流现象能够显著提高CO₂吸收过程的传质速率，然而目前该过程的传质强化机制尚未清晰。为探究Rayleigh对流传质过程的强化机制，本文以水吸收CO₂过程为研究对象，基于粒子图像测速技术（PIV）和激光诱导荧光技术（LIF）实现了不同气相CO₂分压条件下界面对流的可视化与定量测量。实验发现，界面平均浓度在对流发生的临界时刻会瞬间下降并在有序的自组织结构形成后上升，最终的界面平均浓度会随着气相CO₂分压减小而减小；对流发生后，系统传质能力的提高分为两个阶段，涡量场在有序的自组织结构形成前起主导作用，有序的自组织结构形成后，系统传质能力的提高则是由涡量场与界面浓度共同作用的结果；有序的自组织结构形成后，不同系统的平均瞬时传质系数与平均涡量具有很强的相关性，表明浓度场与速度场相互作用形成的涡量场在对流传质强化过程中发挥着重要作用。

关键词: 二氧化碳捕集, Rayleigh对流, 传质, 激光诱导荧光, 粒子图像测速