Study on Effective Absorption of Carbon Dioxide by Controlling the Surface Wave

本文从减少CO_2排放的角度出发，研究了水膜吸收CO_2的强化作用。实验中，纯CO_2气体中的水膜沿着垂直管道外侧向下流动，并施加一个横向振动，以激发出特定频率的表面波。结果表明，振动产生的周期性波动对传质速率有促进作用，特别是在50-90 Hz的频率范围内。通过对传质速率和频谱的比较，发现传质的增强程度与表面波振幅和频率的乘积成正比，并对表面波的形成和传质过程进行了数值模拟。实验结果表明，CO_2吸收过程中出现了与实验结果相似的大的离散波，波中循环流动的表面更新导致了传质的增强。结果表明，CO_2在碳酸盐溶液中的饱和吸收值比在纯水中的饱和吸收值提高了30倍，这是由于CO_2在盐溶液中的电离所致。在小流量下，CO_2浓度接近饱和值时，降膜吸收速率的提高是显著的。对薄膜中的化学反应和扩散过程进行了数值分析，结果表明化学反应受扩散过程的控制，薄膜中混合的增强也是重要的。

Enhancement of CO_2 absorption into water film has been investigated from the view point of the reduction of CO_2 discharge. In the experiment, water film flows down in a pure CO_2 gas along the outside of a vertical pipe, and an extenal vibration is applied to induce surface waves with a specified frequency. It was found that the mass transfer rate is enhanced by the periodic waves appear by the vibration, especially in the frequency range of 50-90 Hz. From the comparison of mass transfer rate and frequency spectrum, it was found that the enhancement of mass transfer is proportional to the product of wave amplitude and frequency.A numerical simulation was also made for the formation of surface wave and the associated mass transfer. It was shown that large discrete waves similar to the experimental observation appears, and the surface renewal by the circulating flow in the wave brings the mass transfer enhancement.Further, enhancement of CO_2 absorption by using aqueous salt solution as the working fluid has been investigated. It was shown that the saturated value of CO_2 absorption in aqueous carbonate solution is increased by up to the factor of 30 from that in pure water, which is caused by the ionization of CO_2 in the salt solution. The enhancement of absorption rate into the falling film is significant in the case of small flow rate, in which the concentration of CO_2 in the film approaches the saturated value. The chemical reaction and diffusion process in the film were numerically analyzed, and it was concluded that the chemical reaction is rate-controlled by the diffusion process, and the enhancement of mixing in the film is also important.