HWAHAK KONGHAK, Vol.23, No.1, 19-31, February, 1985
비활성 고체입자의 첨가로 인한 물질전달속도 증진의 이론적 및 실험적 연구
Theoretical and Experimental Study on the Enhancement of Mass Transfer Rate by the Use of Suspended Inert Particles
초록
전해질용액내에 첨가된 비활성 고체입자가 물질전달속도에 미치는 영향을 조사하기 위하여 8가지 크기의 고체입자를 5∼25 vol% 첨가하고, 원판의 회전속도를 600∼3000 rpm으로 변화시키면서 반경이 0.564 cm의 음극회전원판에서 ferric cyanide가 환원될 때의 한계전류밀도를 측정하였다. 실험결과에 의하면 고체입자의 첨가로 인하여 한계전류밀도는 증가하였으며, 원판의 회전범위에서 2배까지 증가될 수 있었고, 입자의 크기로는 28.2 μm 정도의 것이 최대치를 나타내었다. 이와 같은 현상을 이론적으로 규명하기 위하여, 입자막은 전극표면과 접촉하고 전극표면에 평행하게 움직이면서 확산과정을 통하여 벌크용액으로부터 반응물을 흡수하여 전극표면에 방출하므로서 물질전달속도로 증진시킨다는 가정을 세워 다음과 같은 이론식을 제시하므로서 이를 잘 설명할 수 있다.
iL = nFNPWV△ Co*（0）[1-exp-K(D/a2)]
+iL,o（1-Φ）3/4 1+(ρr-1)Φ / (1+2.5Φ+10.5Φ2+0.00273exp(16.6Φ)1/6)
여기서, i L，o = 0.62048nFC∞Do（Ω/ν）1/2(ν/Do)1/3
iL = nFNPWV△ Co*（0）[1-exp-K(D/a2)]
+iL,o（1-Φ）3/4 1+(ρr-1)Φ / (1+2.5Φ+10.5Φ2+0.00273exp(16.6Φ)1/6)
여기서, i L，o = 0.62048nFC∞Do（Ω/ν）1/2(ν/Do)1/3
In order to investigate the influence of suspended inert solids on the rate of mass transfer, limiting current densities for the reduction of ferric cyanide at a rotating disk were measured in the presence of 5 - 25 % by volume of particles. Experiments were conducted with eight different particle diameters, and with rotation speeds in the range of 600-3000 rpm, using a 0.564 cm radius disk electrode.
It was found that at a given rotation speed upon addition of particles the limiting current density increased to about two times its value without particles, and this increase was greater at high rotation speeds; the 28.2μm particles yielded the highest value.
A mass transfer model was proposed to explain this behavior, assuming that the particle with its clinging film of fluid was in contact with the disk electrode and was rotating parallel to disk surface. The film promoted mass transfer rate by alternately absorbing and desorbing the diffusing species. The proposed model well explained the observed behavior of the limiting current density.
The proposed model could be expressed by the following correlation:
iL = nFNPWV△ Co*（0）[1-exp-K(D/a2)(W/V)]
+iL,o（1-Φ）3/4 1+(ρr-1)Φ / (1+2.5Φ+10.5Φ2+0.00273exp(16.6Φ))1/6
where
i L，o = 0.62048nFC∞Do（Ω/ν）1/2(ν/Do)1/3
It was found that at a given rotation speed upon addition of particles the limiting current density increased to about two times its value without particles, and this increase was greater at high rotation speeds; the 28.2μm particles yielded the highest value.
A mass transfer model was proposed to explain this behavior, assuming that the particle with its clinging film of fluid was in contact with the disk electrode and was rotating parallel to disk surface. The film promoted mass transfer rate by alternately absorbing and desorbing the diffusing species. The proposed model well explained the observed behavior of the limiting current density.
The proposed model could be expressed by the following correlation:
iL = nFNPWV△ Co*（0）[1-exp-K(D/a2)(W/V)]
+iL,o（1-Φ）3/4 1+(ρr-1)Φ / (1+2.5Φ+10.5Φ2+0.00273exp(16.6Φ))1/6
where
i L，o = 0.62048nFC∞Do（Ω/ν）1/2(ν/Do)1/3