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

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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.