Evaluation of Destratification Efficiency by Combined Effect of Adjacent Plumes through 2-Phase and 3D Hydrodynamic Analysis in a Stratified Fluid

수중폭기장치로 저수지 성층을 파괴시켜 저수지 수질을 개선시키기 위한 방법이 최근 널리 이용되고 있다. 본 연구는 주요 성층 파괴기작인 Bubble Plume(공기 부력류)의 수리동역학적 거동특성과 플륨 간격에 따라 변하는 모멘텀 중첩효과가 성층파괴 효율에 어떠한 영향을 미치는지에 대하여 수행하였다. 이를 위해 전산유체(CFD) 소프트웨어를 이용한 2상(공기-물) 3차원의 탈성층모델을 개발했으며, 이로부터 계절에 따라 변하는 다양한 성층강도와 주입공기량에 따라 변하는 비정상상태의 성층파괴 발달과정은 물론 최적 탈성층 효율을 갖는 플륨간격을 제안할 수 있었다. 모델검증을 위한 실험을 위해 대형 실험조를 개발했으며, 온도성층은 소금물을 이용했던 기존연구와는 달리 가열순환수를 이용한 자연성층을 재현시켜 수행하였다. 연구결과 탈성층 효율은 디퓨서 배치간격에 크게 영향을 받는 것으로 밝혀졌으며, 플륨간격이 수심의 약 1.5배 이내일 때 중첩영향이 강하게 일어났고, PN가 클수록 간격에 영향을 상대적으로 크게 받았다. 또한, 간격이 수심보다 작을 때는 효율이 PN에 비례해서 선형적으로 증가한 반면 그 이상에서는 효율이 상대적으로 감소하면서 비선형적으로 증가하는 현상을 밝혀냈다. 이상의 연구결과를 통해 주입공기량은 PN가 약 1000, 디퓨서 배치간격은 수심의 1.5배일 때가 최적의 성층파괴 조건인 것으로 나타났다

성층유체의 수리동역학적 2상 3차원 거동분석과 인접 플륨간 중첩영향을 고려한 최적 플륨간격 및 탈성층 효율평가

학위논문(박사) - 한국과학기술원 : 건설및환경공학과, 2004.2, [ vi, 79 p. ]The use of air diffuser system to ameliorate the reservoir by breaking stratification is now widespread. More than about 370 air-blowing systems are being operated in 30 man-made reservoirs for drinking water supply in Korea. But, still there is lack of more specific design and operational guidelines such as spacing between adjacent plumes and optimal airflow rate, especially, due to more reliance on hydrodynamic analysis of stratified fluid behaviors and effectiveness of air blowing. Therefore, this study focuses on the hydrodynamic behavior of bubble plumes, which are the major mechanism of destratification and their effect on adjacent plumes and destratification efficiency. For these, a 2-phase (3-D) Computational Fluid Dynamics (CFD) technique was used as a new analytical method. Lab experiments were also carried out to verify the model in thermally stratified fresh water. It was then verified that the CFD model performs well for the cases with a plume number $(P_N)$ range of 30 to 600. Thermal stratification was created in experiments using a heating pipe, in which hot water, heated in a separate heating tank circulated continuously. The heating pipe was movable upward or downward and capable of making a temperature range from 45℃ to ambient($\approx 18^＼circ C$), which is enough temperature range for real reservoirs. Linear stratification conditions were adopted in these lab experiments. Consequently, this model enables us to simulate more complicated stratification conditions with different density intensities and source strengths. From this, we can suggest the optimal diffuser spacing having optimal destratification efficiency by simply analyzing the complex destratification procedures varying with the seasonal stratification intensity and bubble flow rate. This study shows that the mixing efficiency strongly depends on the spacing of neighboring plumes. When diffuser spacing is less than 1.5 times the depth, the combined effect is stronger; as...한국과학기술원 : 건설및환경공학과

An Evaluation of Hydrodynamic Behaviors of Bubble Plumes with the Density Distribution and Turbulent Flow Field in a Stratified Fluid

공기방울을 이용한 저수지의 주요 성층파괴 기작인 버블플륨(Bubble Plume)의 거동특성과 비정상상태의 흐름에 대한 연구를 수행하였다. 이를 위해 전산유체(CFD) 소프트웨어를 이용한 2상(공기-물), 3차원의 탈성층 모델을 적용하였으며, 이로부터 여러 복잡한 성층강도 및 주입공기량에 따라 변하는 탈성층 과정을 정량적으로 밝힐 수 있었다. 동 모델을 검증하기 위해 실험실 규모의 실험을 수행했으며, 그결과 Plume Number(PN)가 30~600 범위에서 모델이 성층파괴 과정을 성공적으로 모의하고 있음을 확인 할 수 있었다. 또한 기존의 1차원 모델로는 설명하기 어려웠던 버블플륨의 수리동역학적 거동과 난류흐름을 3차원으로 설명할 수 있게 되었다. 연구결과, 기존의 연구와는 달리 탈성층 효율은 PN가 증가함에 따라 증가했으며, Asaeda 등(1989, 1993)이 정의한 성층강도와 주입공기량에 따른 3가지 형태의 흐름은 그들이 제안한 PN 범위에서 발생하지 않았다. 이는 공기방울의 크기를 고려하지 않았기 때문인 것으로 판단된다

Effect and effective distance of rust and scale suppression by zinc device in piping

The electrical connection between zinc metal and iron in contact with water prevents oxidation of iron until all zinc is dissolved, which is called a zinc sacrificial anode phenomenon. In the case of water pipes, zinc is often attached to the outside of the pipe, but examples of mounting zinc inside the pipe to prevent iron corrosion are not well known. Zinc devices sold for water pipes vary in the amount of zinc installed depending on the diameter of the pipe and the conditions of use, but the life of the product is generally expected to be 10-20 years until all zinc dissolves and disappears. Zinc ions dissolved from zinc to water in the pipe react with the calcium carbonate scale generated inside the pipe to consume zinc ions, and it was confirmed that the needle-shaped aragonite was converted into highly crystalline calcium after observing the scale crystal through an electron microscope. In addition, it is estimated that calcium ions of scale are replaced by zinc ions, gradually losing crystallinity, being deintercalated into the pipe, and oxygen in the water is consumed during the dissolution of zinc ions from zinc metals, turning red rust hematite (Fe2O3) into magnetite (Fe3O4). In addition, zinc ions were expected to move hundreds to thousands of meters depending on the diameter of the pipe in the new pipe, but it was confirmed that the travel distance was shortened in the case of pipes with many corrosion products

아연 이온화 장치에 의한 상수배관 내 스케일 및 녹 생성 억제효과 실증 연구

Scale and rust generation in water pipes is a common phenomenon when cast iron water pipes have been used for a long time. A physical water treatment device is known among various means for suppressing rust in a water pipe, and a zinc ionization device for putting zinc metal into a pipe and emitting the zinc cation into water is one of such devices. This research measured the amount of zinc ion generated, which is known to exhibit an effect of inhibiting rust and scale generation in a pipe, and examined the scale and rust inhibition effect of the ionization device installed for ground or building water supply. In the case of distilled water, the concentration of zinc ion increased by circulating water in the ionization device several times, and it was verified to be hundreds of μg/L, and in the case of discharging ground or tap water, it was verified to be tens of μg/L. In addition, a verification pipe was installed to confirm the change inside the pipe before and after installation of the zinc ionization device, and the internal condition of the pipe was observed 3 months to several years after installation. It was confirmed that the corrosion area of the surface of the pipe was no longer increased by installing a corrosion inhibitor, and if the pipe was already filled with corrosion products, the amount of corrosion products gradually decreased every year after installation. The phenomenon of fewer corrosion products could be interpreted as expanding the space in the pipe due to the corrosion product as Fe2O3 adhered to the inner surface of the pipe and turned into a smaller black Fe3O4. In addition, we found that scale such as CaCO3 together in the corrosion by-products gradually decreased with the attachment of the ionization device