CFD를 이용한 패들교반속도에 따른 속도경사 및 총물질전달시간 산정 = Evaluation of Local Velocity Gradient and Total Mass transfer Time at Various Rotating Velocity by Using Computational Fluid Dynamics

다국어 초록 (Multilingual Abstract)

Velocity gradient, G, a measure of the average velocity gradient in the fluid has been applied for complete mixing of chemicals in mechanical mixing devices. G values were calculated by the power input transferred to fluid in turbulent and transient range. Chemical reactions occur so fast that total mass transfer time required for even distribution of the chemicals determine the overall reaction time. The total mass transfer time is composed of the time for complete mixing through the reactor and for diffusion of the chemicals into the eddy. Complete mixing time was calculated by CFD (computer fluid dynamics) and evaluated by tracer tests in 2 liter jars at different rotating speeds. Turbulent range, Reynolds number above 10,000 in regular 2 liter jars occurred at revolution speed above 100 rpm (revolution per minute), while laminar range occurred at revolution speed below 10 rpm. A typical range of rotating speed used in jar tests for water and wastewater treatment was between 10 and 300 rpm, which covered both transient and turbulent range. G values supplied from a commercial jar test apparatus showed big difference from those calculated with power number specially in turbulent range. Diffusion time through eddy decreased 1.5 power-law of rotating speed. Complete mixing time determined by pumping number decreased increases in rotating speed. Total mass transfer time, finally, decreases as rotating speed increases, and it becomes 1 sec at rotating speed of 1,000 rpm. Complete mixing times evaluated from tracer tests showed higher than those calculated by power number at higher rotating speed. Complete mixing times, however, calculated by CFD showed similar to those of experimentally evaluated ones.

참고문헌 (Reference)

1 김승현, "가수분해 산물 분포를 이용한 급속혼화강도가 화학적 인 제거 효율에 미치는 영향의 규명" 대한상하수도학회 25 (25): 367-373, 2011

2 Han, M., "The(Relative)Insignificance of G in Flocculation" 84 (84): 79-91, 1992

3 Vrale, L., "Rapid mixing in water treatment" 63 : 52-58, 1971

4 Amirtharajah, A., "Mixing in Coagulation and Flocculation"

5 Kawamura, S., "Main Features of Large Water Treatment Plants in Japan" 74 (74): 148-159, 1991

6 Cleasby, J. Y., "Is Velocity Gradient a Valid Turbulent Flocculation Parameter?" ASCE 100 (100): 875-897, 1984

7 Camp, T. R., "Floc volume concentration" 60 : 656-673, 1968

8 Jung, K. S., "Effects of Coagulant dose and Rapid Mixing Time on Particle Growth and Turbidity Removal" 104-110, 2006

9 Hudson, H. E. Jr., "Design of Mixing and Flocculation Basins" 59 (59): 1257-1268, 1967

10 Clark, M. M., "Critique of Camp and Stein’s RMS Velocity Gradient" ASCE 111 (111): 741-754, 1985

11 Kawarnura, S., "Consideration in improving flocculation" 68 : 328-336, 1976

12 Jung, C. W., "A study of rapid mixing condition for improvement of water treatment process" 53-56, 2003