• Journal of Wetlands Research
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• v.16 no.2
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• pp.261-268
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• 2014

A sewage was treated using serially combined vertical(VFCW)and horizontal flow sand-filled reed constructed wetland(HFCW) with intermittent feeding. The sand had 1~3 mm diameter. The sewage entering the sewage treatment plant of Gyeonsang National University was fed into the reed constructed wetland bed for 10 minutes every 6 hours at the hydraulic load of $314L/m^2{\cdot}day$ based on the surface ares of the VFCW. In the VFCW effluent pH values were lower than those of the influent, whereas they were higher than those of the influent in the HFCW. DO values were increased in VFCW, but they were decreased in the HFCW. The OTR was $58.72gO_2/m^2{\cdot}day$ in the VFCW and $7.72gO_2/m^2{\cdot}day$ in the HFCW. Average removal efficiencies were SS 94.80%, BOD 90.77%, $COD_{Cr}$ 85.87%, $COD_{Mn}$ 87.72%, T-N 64.74%, $NH_4{^+}$-N 86.44%, T-P 87.70%. Nearly, half of T-N in the effluent was $NO_3{^-}$-N but the concentration of $NO_2{^-}$-N in the effluent was less than 0.64 mg/L.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.2
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• pp.264-270
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• 2011

The Characteristics of the flowfield around three circular cylinders in tandem arrangement was investigated by PIV. Strouhal numbers, vorticity, velocity vectors and velocity profiles were observed at centre-to-centre space ratios of P/D=1.25~3.75, and Reynolds number of Re=$3.0{\times}10^3{\sim}5.0{\times}10^3$. As the results the Strouhal numbers measured in the rear region of 3rd the cylinder were distinguished three kind of regions with the space ratios and The flow pattern in the wake of each cylinder was different according to these regions. The time averaged flow at region of each cylinder was almost stagnated and the size of the stagnated region was small in order of 1st, 2nd and 3rd cylinder. The direction of vortex at the front and rear region of 2nd cylinder was opposed each other with the small difference(${\alpha}= {\pm}5^{\circ}$) of the attack angle ${\alpha}$.

• Journal of Wetlands Research
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• v.23 no.1
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• pp.94-105
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• 2021

Two vertical flow biofilters in series (BFS) employing synthetic fiber (FBF) followed by woodchip (WBF) was investigated in order to assess its potential as an alternative to the typical vertical-horizontal flow configuration in removing nonpoint source pollutants specifically nutrients and organics. These lab-scale column biofilters were operated for 176 days alongside three other columns that were added for control and sampling purposes. The biofilter columns were fed with either a semi-artificial piggery stormwater or artificial stormwater with specific ammonia and nitrate contents. Results reveal that the BFS was more effective than a single biofilter in removing pollutants especially nitrogen. FBF was found to remove up to 100% of ammonia from the stormwater with corresponding increase in nitrate in the outflow which shows evidence of active nitrification. Meanwhile, the succeeding vertical WBF was able to subsequently remove 77% of the nitrate. The effective reduction of nitrate in a vertical flow biofilter was believed to be due to the use of woodchip which can provide a carbon source that is required for denitrification. However, further investigation is needed to support this claim. Nonetheless, the study shows the potential of vertical flow BFS as a nitrogen removal mechanism especially in areas where enough land space for horizontal flow biofilters is limited.

• The Transactions of the Korean Institute of Power Electronics
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• v.16 no.5
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• pp.415-429
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• 2011

In this study, a single-phase quasi Z-source AC-AC converters with a series connection of the output terminals is proposed. The proposed system has configuration that the input terminals of two quasi Z-source AC-AC converters are connected in parallel and its output terminals are connected in series. The out of phase mode and in phase mode of the proposed system are presented. To verify the validity of the proposed converter, a DSP controlled hardware was made and PSIM simulation was executed. As a result, controlling the duty ratio of the converter, the desired buck-boost output voltages could be generated. For each modes, as compared with the single converter operation, the proposed converter could enhance the efficiency and input power factor according to different loads. Also, in case of the out of phase mode under the constant load, the efficiency and input power factor of the proposed system are increased 10[%], 35[%] respectively in compared with the single converter. And, the output voltage is constantly controlled in dynamic state in case while the load is suddenly changed.

• The Journal of the Acoustical Society of Korea
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• v.15 no.5
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• pp.44-52
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• 1996

Acoustical characteristics of internal pipe structures and a loudspeaker of the thermoacoustic refrigerator are analyzed by using the transfer matrix method. The resonator system is dismantled into verious basic acoustic elements, and then linearized transfer matrices are serially combined with the dynamical system of linearized loudspeaker model, that the total system of thermoacoustic refrigerator can be analyzed in terms of frequency characteristics and acoustic field shape. Additionally, by using equations for energy flow through the capillary stack, the temperature distribution over the stack is numerically estimated. After expressing the acoustic work flow, thermoacoustic flow, and energy loss per unit length in a single capillary duct by using the transverse functional variations, overall energy flow rate and energy balance are obtained for the whole capillary stack. The final expression for energy flow through the stack is numerically evaluated by varying physical parameters obtained from the sound field analysis. After confirming good agreements between predicted and experimental results for the interior sound field of a refrigerator model, the thermoacoustic characteristics of Hofler's apparatus is analyzed by the proposed method and it is observed that the results agree well with Hofler's experimental results.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.9
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• pp.753-760
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• 2006

The purpose of the present work is to investigate the influence of the refrigerant adulteration by LiBr solution on the cooling capacity and COP for three different types of abso게tion chillers: a single-effect type, a series-flow double-effect type and a parallel-flow with double-effect type. A simulation program has been prepared for the cyclic analysis of absorption chillers. With some assumptions, the calculations have been performed by solving the mass balance equation, energy balance equation and the state equation simultaneously. The range of the LiBr concentration of refrigerant was 0% to 20% in the present study. For the single-effect absorption chiller, the maximum decrease in the cooling capacity was 10% at the 20% of LiBr concentration. For the double-effect chiller, the capacity was decreased by 11.1% for the parallel-flow type and the series-flow type. Also, the COP was reduced by 3.0% in single-effect, 2.8% in series-flow type (SR=0.4) and 2.3% in parallel-flow type.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.743-748
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• 2005

김남원 등(2004a, b)에 의해 개발된 SWAT-MODFLOW 모형은 SWAT 모형과 MODFLOW 모형의 Recharge Package와 River Package를 직렬로 연결한 모형이다. 그러나 MODFLOW 모형에는 지하수 흐름방정식의 해석에 관련된 Package를 제외하더라도 Well, Drain, Evapotranspiration 등의 Package가 더 있어 대수층으로부터의 우물의 함양과 배출, 배수관을 통한 지하수의 배출, 지하수의 증발산으로 인한 손실 등을 수행할 수 있다. MODFLOW 모형의 Well Package는 SWAT 모형에서 대수층의 물이동, Drain Package는 SWAT 모형의 토관배수, Evapotranspiration Package는 SWAT 모형의 얕은 대수층에서의 증발산과 밀접한 관계가 있다. 본 연구에서는 이들 세 개의 Package를 SWAT 모형과 완전 연동시킴으로써 사용자가 좀 더 다양한 조건에 대하여 SWAT-MODFLOW 결합모형을 적용할 수 있도록 기능을 향상시켰다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.2
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• pp.288-298
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• 1996

The gas-fired absorption refrigeration system to utilize treated sewage is available for environmental protection and energy conservation. Simulation analysis on the double-effect absorption refrigeration cycles with parallel or series flow type has been performed. The working fluid is Lithium Bromide and water solution. The main purpose of this study is evaluating the possibilities of effective utilization of treated sewage as a cooling water for the absorber and condenser. The efficiency of a couple of cycles has been studied and simulation results show that higher coefficient of performance could be obtained for parallel flow type. The other purpose of the present study is to determine the optimum designs and operating conditions based on the operating constraints and the coefficent of performance in the paralledl flow type.

• Proceedings of the KIPE Conference
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• 2002.07a
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• pp.546-550
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• 2002

본 논문에서는 다이오드 정류기에 단상인버터와 변압기를 이용하여 영상고조파 전류를 주입함으로서 순수한 정현파 입력전류를 얻을 수 있는 새로운 방식의 고조파 저감기술을 제안한다. 본 방식은 주 전력의 흐름에 직렬로 스위칭소자가 연결되지 않아 전력손실이 적으며 보조회로로서 사용된 변압기의 턴비를 조정하면 인버터 스위치의 전류정격을 작게 구현할 수 있다. 본 방식의 타당성을 실험을 통하여 입증하였다.

• Proceedings of the KIPE Conference
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• 2016.11a
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• pp.67-68
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• 2016

본 논문에서는 높은 승 강압비를 갖는 비절연형 양방향 컨버터를 제안한다. 제안하는 양방향 컨버터는 입력-병렬/출력-직렬(Parallel-Input/Series-Output, PISO) 구조로 인터리빙효과와 높은 전압이득을 얻을 수 있고 소자들의 전압정격이 고전압측 전압의 1/4배 수준으로 소자 선정이 용이하다. 또한, PWM plus Phase-Shift(PPS) 제어기법을 적용하여 전력의 흐름을 제어하면서 소프트스위칭을 최적화할 수 있다. 2kW급 시작품을 통해 듀티(D) 0.51 ~ 0.64를 사용하여 7 ~ 10배의 승 강압비를 달성하였으며 최고효율 96.1% 96.1%, 정격부하에서 95.9%, 96.0%를 달성하였다.