• Journal of Korea Water Resources Association
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• v.55 no.11
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• pp.865-875
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• 2022

Field measurements and numerical simulations using EFDC model were performed to quantify the changes of water circulation near Gusipo coast located in the Yellow Sea of Korea to estimate the impact of the construction of the coastal structures (jetty, groin, Gusipo port and bridge). The model predicted tide and tidal currents agreed reasonably well with the measurements. The maximum currents during spring tide near the Gusipo Beach (GB) have the range of 20~40 cm/sec whereas those off the GB range from 60 to 80 cm/sec. The typical patterns of tidal current show parallel with the local isobath. Tidal currents flow northeastward during the flood tide whereas the currents during the ebb tide flow southwestward. The current speeds at shielded waters after the construction of coastal structures strongly decreased as compared with those before the construction. The tidal volume due to the construction of coastal structures was estimated using the depth averaged velocity for 24 hours of spring tide. Tidal volume after construction of coastal structures was compared with initial state (before construction). Tidal volume at present state (after construction of jetty, groin, Gusipo port and bridge) decreased by 28.4% as compared with that of the initial state. The volume after construction of jetty and groin decreased by 21.3%, and the volume after construction of Gusipo port and bridge decreased by 9.8%.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.4
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• pp.639-650
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• 2000

The main object of this study was to investigate experimentally the characteristics of cyclone-bag filter with bottom inlet to decrease the high pressure drop which was one of main problems of fabric bag filter. The experiment was executed for the analysis of collection efficiency and pressure drop(specially, pressure drop of fabric filter) characteristics of the cyclone-bag filter in comparison with those of general fabric bag filter with various experimental parameters such as the inlet velocity, dust loading and variation of vortex region, etc. In the results, the tangential inlet type showed higher collection efficiency for submicron particles below $1{\mu}m$ in diameter than of center inlet, and over 99% for overall collection efficiency. For the inlet particle concentration $100mg/m^3$, pressure drop reduction ratios were shown as 15~38% with the inlet velocity in case of large bag, while 30~48% for small bag due to the increase of vortex region.

• KSBB Journal
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• v.4 no.2
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• pp.177-184
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• 1989

In separating mycelia from antibiotic fermentation broths, high permeate flux was obtained by cross-flow filtration using modified regenerated cellulose membrane. The flux was increased most effectively by increasing the flow rate. There existed a critical mycelium density (about 20% PMV) at which the highest flux was observed. In a batchwise concentration of the fermentation broth, the system suffered from a severe fouling problem, which was relieved drastically by applying diafiltration technique, although it increased the permeate volume. A combined concentration/diafiltration process was ideal in keeping relatively high flux together with a high product recovery yield. The best result was obtained by starting diafiltration after concentrating the broth to 20% PMV. By doing so, a 98% product recovery yield was achieved in the shortest time while keeping the permeate volume at a minimum level.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.3
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• pp.309-314
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• 2012

Flame flickering occurs mainly because of the buoyancy force for pool fires under ambient air. The cup-burner flame was used for experimental investigation of the effect of the oxidizer velocity on the gravitational instability. The results showed that the flickering frequency decreased with increasing oxidizer velocity. The frequency-buoyancy relation with nondimensional variables coincided with that of the buoyant flume and pool fires when the characteristic velocity was defined as the difference between the fuel and oxidizer velocities, which implies that the origin of the gravitational instability is the Kelvin-Helmholtz instability in the shear layer. The effect of the oxidizer composition on the instability was also examined through nitrogen dilution in the oxidizer stream. As the concentration of inert gas increased, the length of the blue flame increased and lift-off behavior was observed. The oscillation frequency was independent of the dilution ratio, but was related to the local flame structure.

• Clean Technology
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• v.8 no.3
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• pp.119-128
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• 2002

In the present study the membrane filtration characteristics of a commercially available synthetic water-based cutting oil through two kinds of ultrafiltration membranes (HF1-45-CM50 and HF1-43-CM100) with molecular weight cut-offs of 50,000 and 100,000, respectively, have been investigated in detail. Among these membranes, the hydrophilic one (HF1-45-CM50) was found to show a satisfactory result for both the permeate flux and the permeability of oil components, whereas the permeate flux obtained with the hydrophobic membrane (HF1-43-CM100) appears to be significantly low, indicating that synthetic cutting oil was easily wetted on the hydrophobic membrane surface and induced more membrane fouling. The effect of material characteristics of the membrane on the filtration characteristics was found to be much more significant compared with the mean pore size of the membrane. Backflushing by nitrogen gas was applied to reduce the formation of a gel layer and membrane fouling. With the hydrophilic membrane, the backflushing was found to increase the permeate flux, whereas the backflushing resulted in a decrease in flux for the hydrophobic membrane. The flux recovery was observed to be highest when the membranes fouled with waste synthetic cutting oil were immersed into a cleaning solution for more than 72 hours and then backflushed by nitrogen gas.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.5
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• pp.314-319
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• 2019

The numerical simulation method was used to analyze the flow velocity change and mechanical coefficient characteristics of the blade in the shroud system that changes with the initial flow velocity and the blade rpm. In the analysis condition, the initial flow velocity was varied from 0.35 m/s to 1.0 m/s, and the blade rpm varied from 50 rpm to 300 rpm. Through this, the mechanical coefficient was estimated. The flow velocity changes tended to increase more than 1.8 times at the middle point compared to the inlet. When the flow velocity ratio was 0.75 m/s compared to the initial flow velocity of 0.5 m/s, the flow velocity ratio decreased. The mechanical coefficient using the torque of the blade also showed the highest coefficient at 0.5 m/s, and the trends were similar. On the other hand, the maximum coefficient was estimated to be about 20.88% in TSR 4.77 when the initial flow velocity was 0.5 m/s. The mechanical coefficient analysis of blades in this study is expected to provide the basic data for hydraulic model experimental.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.253-253
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• 2022

수문조사 방법 및 기준은 각 국가별 기후, 유역 및 하천특성에 따라 다르게 제시되고 있으며, 세계기상기구(WMO)나 국제표준화기구(ISO)에서는 국제적으로 통용될 수 있는 기준을 제시하고 있다. 대부분의 국가에서는 국제기구 또는 수문조사 선진국(미국, 일본, 영국 등)에서 제시한 기준 및 방법을 도입하여 적용하고 있으며, 국내의 경우도 국제기준과 더불어 미국의 기준과 우리나라와 기후, 지형 및 하천특성이 비슷한 일본의 기준을 많은 부분에서 도입하였다. 유속계에 의한 유량측정 시 측선수를 늘리면 정확도를 높일 수 있지만 대하천 또는 수위(유속)가 급변하는 경우에는 측선수를 많이 해서 측정시간이 길어지면 오히려 정확도를 떨어뜨릴 수 있다. 특히, 국내에서 홍수시 신속한 측정에 사용되는 부자와 전자파표면유속계는 기존의 회전식유속계 측선수 기준을 적용하는 것은 적합하지 않다. 이에 따라, 우리나라 수문조사 전담기관인 한국수자원조사기술원에서는 전자파표면유속계 측선수 기준을 실무적으로 제시하고 있으나 이에 대한 기술적인 검토가 부족한 실정이다. 본 연구에서는 2016년~2020년까지 한국수자원조사기술원에서 측정된 58개 지점의 총 739개의 전자파표면유속계 측정성과에 대하여 수면폭 및 측선수 현황을 살펴보았다. 한국수자원조사기술원 일반기준 이상 측선수 비율은 646개(87.4%), 긴급기준 이상 측선수 비율은 739개(100.0%) 그리고 전체 평균값 이상 측선수 비율은 404개(54.7%)로 나타났다. 일반기준 이상 측선수가 많은 원인을 파악해보기 위하여 측선수를 최대구간유량비 20% 이상일 때까지 측선수를 10%씩 감소하여 산정된 유량의 변화를 검토하였다. 유량 변화 검토 결과 현장에서 유량측정 시 측선수의 등유량 배치, 최대구간유량비(20%) 및 불확도(±10%) 기준을 준수하기 위해서 기준 이상의 측선수를 확보하는 경향으로 판단되었다. 이러한 문제를 해소하기 위하여 측선수 감소에 따른 유량 편차율 ±10%와 불확도 ±10% 조건을 만족하는 수면폭 구간별 최소 기준을 제시하였으며, 이 기준을 적용할 경우 전자파표면유속계로 현장에서 보다 신속하고 정확한 유량측정을 수행할 수 있을 것으로 기대된다.

• Water for future
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• v.27 no.3
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• pp.123-134
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• 1994

The reattachment of buoyant effluent to shore in a crossflow is investigated experimentally. The effluent is produced by discharging warm water through projecting side channel into a confined cross-flow of the same depth. In the projecting effluent, the size of recirculating region, which is formed by defleted thermal plume on the lee of the effluent, tends to increase, but the maximum temperature decreases in the direction of the crossflow and it has more even transverse spreading compared to non-projecting type. The heat flux across the crossflow is found to be independant of the projected length of the side channel under relatively low buoyancy flux on the contrary to high buoyancy flux. The reattachment of the effluent can be specified by both velocity ratio and densimetric Froude number, whereas only the velocity ratio is governing factor to the reattachment of the effluent in the case of non-projecting type.

• KSBB Journal
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• v.14 no.4
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• pp.452-459
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• 1999

A two-stage continuous stirred tank reactor (CSTR)/trickling biofilter reactor (TBR) system was developed for the degradation of gas-phase trichloroethlene (TCE) using Methylosinus trichoporium OB3b. Mrthylosinus trichosporium OB3b was immobilized on activated carbons in TBR and the microbial growth reactor of a CSTR was coupled for the reactivation of the deactivated cells during TCE degradation. The effect of operation variables on TCE conversion and degradation rate were studied. At inlet TCE concentrations ranging from 10 to 80 $\mu$mol/L, TCE degradation rate was increased up to 525 mg TCE/Lㆍday with 75% conversion. The TCE degradation rates were also increased with increse in broth recycle flow rate, gas flow rate and dilution rate. When the temperature of TBR was changed from 3$0^{\circ}C$ to 15$^{\circ}C$, TCE degradation rate and TCE conversion were increased due to the enhanced TCE transfer from gas-phase. The two-stage reactor system was found to be stable and has been operated for more than 270 days.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.6
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• pp.581-589
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• 2005

Recently, membrane processes have been replacing the conventional processes for waste water treatment to produce better quality of effluent and to meet more stringent regulations because of water shortage. However, using membrane processes for water treatment has confronted with fouling and difficulty in treating dissolved organic pollutants. In this study, membrane process equipped with crossflow microfiltration is combined with coagulation process using alum and PAC to improve permeability and treatment efficiency. The effects of coagulant dosage and optimum membrane operating conditions were investigated from measurement of permeate flow, cumulative volume, total resistance, particle size, dissolved organic pollutant, dissolved aluminium and quality of effluent. Characteristic of PAC coagulation was compared with that of alum coagulation. PAC coagulation reduced membrane fouling because of forming larger particle size and increased permeate velocity and cumulative volume. Less dissolved organic pollutants and dissolved aluminum made decreasing-rate of permeate velocity being lowered. At using $0.2\;{\mu}m$ membrane, cake filtration observed. At using $0.45\;{\mu}m$ membrane, there was floc breakage due to shear stress occurred born circulating operation. It made floc size smaller than membrane pore size, which subsequently to decrease permeate velocity and to increase total resistance. The optimum coagulation dosage was $300{\pm}50\;mg/L$ for both alum and PAC. PAC coagulation was more efficiently used with $0.2\;{\mu}m$ membrane, and the highest permeate flux was in using $0.45\;{\mu}m$membrane. The greatest efficiency of treatment was as follows; turbidity 99.8%, SS 99.9%, $BOD_5$ 94.4%, $COD_{Cr}$ 95.4%, T-N 54.3%, T-P 99.8%.