• Water for future
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• v.29 no.5
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• pp.215-222
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• 1996

An expression for the cross covariance of the logconductivity and the head in nonstationary porous formation is obtained. This cross covariance plays a key role in the inverse problem, i.e., in inferring the statistical characteristics of the conductivity field from head data. The nonstationary logconductivity is modeled as superposition of definite linear trend and stationary fluctuation and the hydraulic head in saturated aquifers is found through stochastic analysis of a steady, two-dimensional flow. The cross covariance with a Gaussian correlation function is investigated for two particular cases where the trend is either parallel or normal to the head gradient. The results show that cross covariances are stationary except along separation distances parallel to the mean flow direction for the case where the trend is parallel to head gradient. Also, unlike the stationary model, the cross covariance along distances normal to flow direction is non-zero. From these observations we conclude that when a trend in the conductivity field is suspected, this information must be incorporated in the analysis of groundwater flow and solute transjport.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.09a
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• pp.221-222
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• 2005

• The Korean Journal of Pesticide Science
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• v.18 no.4
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• pp.330-335
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• 2014

This study was conducted to investigate residue levels of chlorantraniliprole and ethaboxam in inner part and outer leaves of a head-type Korean cabbage. Further, reduction of residues was measured after water washing, blanching and heat-cooking of the outer leaves. For chlorantraniliprole, residues in inner part and outer leaves were <0.01 mg/kg and 0.0757 mg/kg, respectively, in case of three-time spraying 30 days before harvest and <0.01 mg/kg and 1.19 mg/kg, respectively, in case of four-time spraying 10 days before harvest; for ethaboxam, <0.05 mg/kg and 0.216 mg/kg, respectively and <0.05 mg/kg and 1.18 mg/kg, respectively. Chlorantraniliprole and ethaboxam were not detected in inner part of the head-type Korean cabbage. Residue levels in outer leaves were very high as 10-100 fold as those in inner part of the cabbage. Therefore, there is no concern for safety of pesticide residues on kimchi prepared with the inner part of a head-type Korean cabbage. In addition, it needs to be noted that outer leaves should be carefully removed at harvest of the cabbage. Outer leaves water washed and blanched are called as Woogeogi, which is consumed after heat-cooking. In Woogeogi, residue concentrations of two compounds reduced to less than 10%, and further less than 5% by heat-cooking. This indicates that considerable amount of the test pesticide residues in outer leaves of a head-type Korean cabbage removed through water washing, blanching and heat-cooking.

• Journal of Environmental Science International
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• v.24 no.12
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• pp.1551-1558
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• 2015

In Korea, many drinking water treatment plants (DWTPs) have introduced and are going to introduce biological activated carbon (BAC) process to treated dissolved organic matter (DOM) in water which are difficult to control by conventional water treatment processes. Even though more decade have passed since introduced BAC in Korea, most of BAC operating method was followed to the modified sand filter operating manuals. In case of BAC backwashing, many DWTPs set the periods of backwashing about 3~5 days. In this study, we have collected data to set the proper BAC backwashing periods from both pilot-plant and real DWTPs. We had measured heterotrophic plate count (HPC), turbidity, water temperature, dissolved organic carbon (DOC) and headloss from just after backwashing to the next backwashing time for two years. Considering water quality factors, the BAC run time from backwashing to the next backwashing could extend more 30 days without water quality deterioration if the head loss do not reach the limited level which depends on each BAC facilities' condition. It means the BAC treated water could be saved in the proportion of extended the backwashing period to the existing backwashing period.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.8
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• pp.1134-1139
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• 2014

Recently the need for renewable energy development is expanding due to the global climate change, the environmental issues and the limited fossil energy resources. Dependence of energy on overseas is high in Korea. To resolve the environmental problems and to improve the energy independence rate, the development of renewable energy is more required. The small hydro power, one of the renewable energy resources, has been developing and operating from a long time ago. If we are new developing a small hydro power with the use existing dams and reservoirs, we will design the length of inlet pipe and the diameter suitable for it. However, in case of using the existing water supply pipe which had been designed suitable for water service, the designer has to review and check that the pipe is suitable for operating a generator. In this paper, the design of small hydro power using the existing long pipe of water supply, we suggest the optimum way to reduce the water hammer in pipe which causes the unsteady flow during the load-shutdown of generator, the generator operation plan for the stable supply of water and the design factor of determining the generator capacity through the analysis between discharge and head-loss.

• Journal of Korea Water Resources Association
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• v.41 no.3
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• pp.305-314
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• 2008

Urban sewer systems are designed to operate in open-channel flow regime and energy loss at circular manholes are usually not significant. However, the energy loss at manholes, often exceeding the friction loss of pipes under surcharge flow, is considered as one of the major causes of inundation in urban area. Therefore, it is necessary to analyze the head loss associated with manholes, especially in surcharge flow. Hydraulic experimental apparatus which can be changed the invert type(CASE A, B, C) and step height(CASE I, II, III) was installed for this study. The range of the experimental discharges were from $1.0{\ell}/sec$ to $5.6\;{\ell}/sec$. As the manhole diameter ratio($D_m/D_{in}$) increases, head loss coefficient increases due to strong horizontal swirl motion. Head loss coefficient was maximum because of strong oscillation of water surface when the range of manhole depth ratios($h_m/D_{in}$) were from 1.0 to 1.5. The average head loss coefficients for CASE A, B, and C were 0.45, 0.37, and 0.30, respectively. Accordingly, U-invert is most effective for energy loss reduction at circular manhole. This head loss coefficients could be available to design the urban sewer system with surcharge flow.

• International Journal of Air-Conditioning and Refrigeration
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• v.10 no.2
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• pp.97-105
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• 2002

A centrifugal water chiller using alternative refrigerant R134a has been developed. The prototype was designed to have refrigerating capacity of 300RT. Its compressor employs a single high-speed impeller, airfoil diffuser and collector. Newly developed, enhanced tubes were installed in the evaporator and the condenser to reduce the required head for the compressor. Off-design characteristics at various conditions, performance test of the compressor and analysis of the refrigeration cycle were performed. So the probability of use in part load condition was checked and the direction for revision was suggested.

• 유체기계공업학회:학술대회논문집
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• 2005.12a
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• pp.813-818
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• 2005

Cooling seawater of thermal power plant which amounts about 5 cms per 100 MWe has hydro energy of about 3,000 kW at the thermal power plant complex, but this useful hydro energy has not been developed. Therefore, the feasibility study on hydro energy development of three power plants located in the southern and western coast of Korea was performed. Three target power plants are Samcheonpo, Boryeong and Hadong thermal power plant. The design head to discharge cooling water by gravity and the head caused by tidal level in the southwestern coastal area, could be used for the production of electric power. The various alternatives were studied and technical feasibility and economical efficiency were clearly proved.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.5
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• pp.333-340
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• 2001

A centrifugal water chiller using alternative refrigerant R134a have been developed. The prototype was designed to have refrigeration capacity of 300RT. Its compressor employs a single high-speed impeller, airfoil diffuser and collector. Newly developed enhanced tubes were installed in the evaporator and the condenser to reduce the required head for the compressor. Off-design characteristics at various conditions, performance test of the compressor and analysis of the refrigeration cycle were performed. So the probability of use in part load condition was checked and the direction for revision was suggested.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.393-393
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• 2022

상수도관망의 압력은 물공급 서비스의 질을 나타내는 중요한 인자이다. 압력이 낮으면 물 사용성이 크게 저하되며, 이러한 이유로 보통의 수도사업자는 압력을 중요한 모니터링 변수로 고려하고 있다. 압력을 기반으로 여러 가지 변수를 계산할 수 있지만, 그 중에서도 압력경사(Pressure Head Gradient)는 수요량, 관경, 관의 파괴 등 독립변수 또는 독립요인의 변화에 따른 종속변수로서의 압력 민감도를 나타낸다. 압력경사의 계산은 매우 간단하면서도 활용도가 높다. 따라서, 다양한 종류의 압력경사를 계산하고, 상수도관망 설계, 운영, 관리 목적에 어떻게 사용할 것인가를 연구할 필요가 있다. 본 연구에서는 먼저 관의 상태, 관경, 절점수요량을 독립변수로 하고 이를 변화시켜 그 결과로의 압력종속변수를 계산, 압력경사를 결정하였다. 이를 기반으로, 히트맵을 구축하여 결과를 비교하였다. 그 후 각각의 압력경사에 대한 모듈을 구축하였으며, 개별 압력경사 모듈의 특징을 고려하여 활용방법을 수립하였다.