• 상하수도학회지
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• 제21권2호
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• pp.177-185
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• 2007

Hydraulic efficiency($T_{10}/T$) in clearwell is often estimated by L/W ratio. However, this estimation is not accurate because other factors which give an effect on hydraulic efficiency such as shape of basin, diffuser wall and intra-basin is ignored. Therefore, in this research, hydraulic efficiency is predicted by the quantitative analysis of dead zone using CFD simulation in a pilot scale clearwell. The results show that the reason why higher L/W ratio increase the hydraulic efficiency is to decrease the dead zone of linear region which is located between baffles. Diffuser wall or intra-basin also affects on hydraulic efficiency with this process. Also, we conclude that hydraulic efficiency can not be reached to 0.8 or higher.

• 상하수도학회지
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• 제25권5호
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• pp.635-642
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• 2011

Hydraulic efficiency was a vital component in evaluating the disinfection capability of clearwell. Current practice evaluates these system based on the tracer test only. In this paper, CFD(Computational Fluid Dynamics) was applied on the clearwell for alternating or supplementing the tracer test. The baffle factor derived from the CFD modeling closely matched the values obtained from full scale tracer testing. And, for suggesting proper numerical model in clearwell; the turbulence model, discretization scheme, convergence criteria were investigated through separate simulation runs. The model validation was conducted by comparing the simulated data with experimental data. In the turbulence model, the realizable ${\kappa}-{\varepsilon}$ model and the standard ${\kappa}-{\varepsilon}$ model were found to be more appropriate than RNG ${\kappa}-{\varepsilon}$ model. The residuals of convergence criteria should be used as not $10^{-3}$ but $10^{-4}$ or $10^{-5}$. In discretization scheme, the difference of simulated values in 1st, 2nd, 3rd upwind scheme was found to be insignificant. Moreover, the result of this study suggest that CFD modeling can be a reliable alternative to tracer testing for evaluating the hydraulic efficiency.

• 상하수도학회지
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• 제24권4호
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• pp.425-432
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• 2010

From the results of tracer test for the existing clearwell in Y water treatment plant, $T_{10}$ and T10/T were calculated as 150 min and 0.24, respectively. Therefore it required the modification schemes for improving hydraulic efficiency, surrogated by $T_{10}$ and $T_{10}$/T, and disinfection performance. In this study, using transient CFD(Computational Fluid Dynamics) simulation technique, tracer tests on dynamic condition for the suggested schemes were simulated. From the results of simulation, it was revealed that 8~6 baffles are necessary to guarantee the disinfection ability in the existing clearwell. Also, installing orifice baffle in the vicinity of inlet could increase plug flow fraction within clearwell.

• 상하수도학회지
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• 제19권6호
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• pp.819-826
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• 2005

To guarantee the disinfection ability in clearwell, a value of CT is considered where C[mg/l] is disinfectant residual at the exit of clearwell and T[min] means $T_{10}$, the contact time when 10% of tracer is out of clearwell after introducing the tracer at the inlet. To meet a CT value required, increasing the C value is not recommended because high C value can increase potential of producing disinfection by product like THMs. Increasing the hydraulic efficiency surrogated by $T_{10}$ is thus an option widely recommended. Right now, it is widely adopted estimating $T_{10}$ considering LW ratio only due to the suggestions of previous researches. The authors think however there are other factors to consider including shape, flow rate, configuration of inlet and outlet, and the existence of intra basin. This study is initiated to closely look at the effects of two factor on hydraulic efficiency. The factors are shape and inlet flow velocity, i.e., inflow. For that, computational fluid dynamics (CFD) model is developed and pilot test is also carried out. The results show that at a L/W ratio, disinfection ability is overestimated with larger length in shape and higher inlet flow velocity. This suggests that in determining $T_{10}$, the shapes of clearwell and inlet flow velocity should also be considered as well as L/W ratio.

• 상하수도학회지
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• 제22권1호
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• pp.105-112
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• 2008

Disinfection is a basic and effective microorganism inactivation method and historically contributed a decrease in waterborne diseases. To guarantee the disinfection ability, improving T in CT value is important. Many indexes are used to estimate the hydraulic efficiency, however, these are black-box analysis. Therefore it is need to develope new estimation method. In this study, internal short-circuiting estimation method (ISEM) is developed using CFD and we inquire into the factor which causes increase of $T_{10}/T$ value as LW ratio increases. And the effect of shape on the relation of LW ratio and $T_{10}/T$ is analyzed. As LW ratio increases, internal short-circuiting index (ISI) of influent and effluent zone is rapidly reduced and recirculation and dead zone are reduced in channel zone. Therefore, as the $T_{10}/T$ value converges maximum value, ISI curve is changed from "V" shape to "U" shape and hydraulic efficiency is improved especially in downstream portion of clearwell. The less the shape ratio(width/length of clearwell) is the less the $T_{10}/T$ value is at a same LW ratio because the portion of turning zone increases as shape ration decreases, therefore more boundary separation is generated.

• 상하수도학회지
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• 제22권1호
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• pp.113-120
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• 2008

A large majority of clearwell must be modified with maintaining the present baffles since they were underground built with the material like concrete. Therefore it is unreasonable to apply the previous research in clearwell modification which is studied with the assumption that distance between baffles is constant. In this study, internal short-circuiting estimation method (ISEM), which has the advantage of being applied at any condition, is applied to evaluate modification of A clearwell and modify B and C clerwell which have unusual characteristics. After analyzing the hydraulic efficiency at current state, modifications, where baffles, intra basins and diffuser walls are additionally installed, are considered and evaluate using ISEM. And the effect of intra basin and diffuser wall on $T_{10}/T$ is estimated and application feasibility of ISEM is evaluated. The improvement of intra basins is almost same with that of baffles. Also, short-circuiting in effluent zone can be reduced with the same level of channel zone if intra basin is added in effluent zone. However, effect range is restricted to the next channel zone. Diffuser wall can obtain the lower ISI than minimum ISI of cases where baffles and intra basins are installed. Therefore, additional improvement of $T_{10}/T$ value can be expected after $T_{10}/T$ value converges maximum only using baffles

• 상하수도학회지
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• 제25권4호
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• pp.497-502
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• 2011

In order to examine the effects of combination of plug flow reactors in series on hydraulic characteristics, comparative tracer tests were conducted for the cases of the existing clear well and clear wells combined in series. From the results of tests, $T_{10}$/T within existing clear well was 0.62~0.68 depending on inlet flowrate, and that in the case of combination in series was 0.69~0.78. While it would be minor improvement in contact efficiency, it would be appropriate to combine two clearwell with pipe in series for expansion.

• 대한환경공학회지
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• 제33권6호
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• pp.432-438
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• 2011

현재 국내 정수지 도류벽은 형태와 장폭비에 대한 명확한 기준이 없고 장폭비가 너무 작아 소독능을 만족하지 못하거나 지나치게 큰 장폭비로 비경제적인 설계를 하는 등 많은 혼란을 겪고 있어 수리적으로 유리한 도류벽의 형태와 경제적인 장폭비를 결정하는 것이 시급한 실정이다. 본 연구는 다양한 도류벽의 형태와 장폭비에 대해 전산유체역학 기법을 활용하여 수리적으로 가장 유리한 도류벽의 형태를 제시하고 가장 경제적인 장폭비를 도출하였다. 연구결과, 정수지내 도류벽의 형태는 동일한 형태와 구조라 하더라도 수류의 방향전환 횟수가 적은 구조가 수리적으로 유리하다. 둘째, 최적 도류벽 형태는 좌우 우류식(model 2)이며 최악의 형태는 두 방향으로 분산되고 다시 모아지는 분산형(model 4) 형태이다. 좌우 우류식은 분산형보다 도류벽의 개수를 67% 정도 줄일 수 있다. 셋째, 좌우 우류식 도류벽인 경우 경제적인 장폭비는 30~50이며 50을 초과할 경우 공사비 대비 $T_{10}/T$ 값의 증가량이 미미하여 경제적이지 못하다.