• 한국전산유체공학회:학술대회논문집
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• 2005.04a
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• pp.223-227
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• 2005

최근 전산 유체의 발달로 이상 유동해석의 캐비테이션 모델 적용 방법이 발전되어 왔으나 다양한 수력학적 시스템에서 발생하는 캐비테이션 유동은 난류이며 물과 공기 사이에서의 복잡한 상호 작용을 가지고 있으므로 그 적용 예가 아직은 미흡한 상태이다. 본 연구에서는 수중에서의 캐비테이션 해석과 이상 유동 해석을 위한 코드 개발 및 검증을 목적으로 3차원 회전체 주위의 캐비테이션 유동을 여러 가지 조건들의 변화를 적용하여 해석하였다. 또한 캐비테이션 발생과 관련한 다른 난류 모델에 적용하여 비교 분석을 수행하였다. 해석을 위한 모델의 지배방정식은 이상유동 Wavier-Stokes 방정식, 질량$\cdot$모멘텀 방정식의 혼합된 형태로 구성되어 있으며 방정식의 해를 구하기 위한 방법으로 유한차분법을 이용하였다. 해석결과의 신뢰성을 고려하여 반구형 실린더 주위의 캐비테이션 유동의 실험치와 비교 분석하였다. 그 결과, 본 연구의 수치 해석 방법과 실험적 방법의 결과가 강한 양의 상관관계를 가짐을 알 수 있었으며, 이러한 수치적 뒷받침은 본 연구의 전산수치 해석 방법이 앞으로의 여러 유동 해석으로의 적용 가능성을 보여준다.

• Journal of the KSME
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• v.30 no.4
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• pp.310-321
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• 1990

기체, 액체 고체상(相)이 섞여서 함께 흐르는 유동을 다상유동(multiphase flow)이라고 하며, 그 중 2개의 상이 섞여서 흐르는 경우를 2상유동(two-phase flow)이라고 일컫는다. 다상유동의 현상은 일상적인 생활에서도 많이 접하며(예컨대, 눈, 비가 내리는 현상, 안개, 황사, 스모그 현상 등) 특히 열전달과 관련하여 비등 및 응축을 수반하기도 한다. 특히 기계공학적 시스템에의 응 용측면에서는 다상유동의 전문지식이 증발기, 응축기 등 각종 열교환기기의 설계에 적용되므로 본 해설에서는 기체-액체(gas-liquid) 2상유동으로 그 내용을 한정하기로 한다. 2상(two-phase) 유동은 동일한 화학적 성분을 가진 물질이 서로 다른 상을 유지하면서 공존하여 흐른다는 점에서 2개의 다른 화학성분으로 구성된 2성분(two-component) 유동(예컨대 공기-물의 혼합유동)과는 엄밀하게는 다르나, 두 유동은 제반 형상이 유사하고, 해석 및 실험방법면에서도 많은 유사성이 있어서 총괄적으로 두 유동을 모두 2상유동이라고 칭하고 있다(1). 본 해설에서는 이러한 기체 -액체 2상유동분야에서 다루는 연구내용을 개괄적으로 소개하고자 한다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.3
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• pp.203-209
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• 2003

Control algorithms of an air handling unit by using the mixing box plenum pressures were developed and verified by experiments. Control algorithms developed for this study were the setpoint algorithms for the outdoor damper position, the outdoor/fixed plenum pressure, and the return/exhaust plenum pressure. The outdoor/fixed plenum pressure setpoint was used to control the bypass damper position, and the return/exhaust plenum pressure setpoint was used to control the return fan speed. Experimental results showed the good control of the required outdoor air demand. Therefore, setpoint algorithms developed for this study may effectively be applied for the control of the VAV air handling unit.

• Journal of Animal Environmental Science
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• v.17 no.sup
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• pp.43-50
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• 2011

This study was conducted to verify the effect of chlorine dioxide ($ClO_2$) on odor reduction at a commercial swine facility consisting of a windowless piglet barn and a grower/fattening barn. The windowless piglet barn used a duct ventilation system. Air velocity at very below the upper duct was 4.53 m/s. Air velocity at the lower space around the living space of pigs in the grower/fattening barn was 0.26 m/s. $NH_3$ concentration was around 9ppm and less than 3 ppm before and after the $ClO_2$ spraying, respectively, which was over 70% reduction. There was no $H_2S$ detection. $NH_3$ concentrations measured in the windowless grower/fattening barn and at the exhausted air were 26 ppm and 11ppm, respectively. $NH_3$ concentration at a biocurtain outside was less than 1 ppm. Hence, $ClO_2$ spraying at windowless barns was effectively decreased malodor such as $NH_3$.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.3
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• pp.353-362
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• 2015

Platform screen door (PSD) installed at underground subway station has reduced the safety accident, but it may cause poor air ventilation condition due to the isolated exhaust duct in the subway tunnel area. In this study, the additional ventilation system was suggested, which can be installed at a void space (i.e., storage room under stairs) of platform in order to improve efficiency of air ventilation rate. Exhausted air from platform was directed to underneath of platform and joined with existing ventilation duct of train exhaust system (TES). One subway station in Seoul city was selected to predict the effectiveness of the suggested lower exhaust system by using the computational fluid dynamics (CFD) analysis. The predicted mean age of air was decreased by 16.5% which proves the improvement of air ventilation efficiency when the suggested lower exhaust system was applied.

• Proceedings of the KAIS Fall Conference
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• 2012.05a
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• pp.436-439
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• 2012

본 연구는 오존수 제조장치에 인젝터를 이용한 오존 주입방식을 도입하여 소형화, 저전력화를 실현하고자 하였다. 오존발생기, 물-오존 혼합기(인젝터), 오존용해조, 배오존 처리기로 구성된 시스템을 제작하여 인젝터 주입방식에 의한 오존수 제조장치의 오존 용해특성과 그 적용성을 검토하였다. 오존 용해 특성으로 물-공기량에 따른 인젝터 성능, 용해조에서의 오존 용해능 등을 검토하였다. 인젝터 방식은 기존의 가압용해방식에 비하여 저농도 용해능을 보였으나, 인젝터 내부의 물-오존 접촉효율이 높아 평형농도에 도달되는 시간이 단축됨을 확인하였다. 제조된 오존수의 적용 효용성은 용존오존의 잔류시간과 미생물 살균능 검사를 통하여 실시하였다. 횡형식 인젝터 시스템에 의해 용해된 용존오존의 잔류시간이 기존의 가압용해방식에 비하여 다소 짧았으나 미생물의 살균능에는 크게 차이가 나지 않았다.

• Korean Journal of Optics and Photonics
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• v.9 no.4
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• pp.264-269
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• 1998

The Measurement of concentration patterns for $C_2$, CH and OH radicals in the premixed propane-air flame could be managed through an image processing technique. This technique was applied to the three kinds of flames on a bunsen burner-mixtures of fuel to be lean, optimum and excessive respectively. The image processing system was complished by treating single wavelength flame images around the eac radical luminescence band, which was obtained by using a set of narrow band pass filters, an image intensifier, CCD and PC. It was possible to observe and predict the reaction zone and the concentration distribution of the radicals, Spatial distribution of each radicals in the raaction zone gave us enough informations to analyze the reaction mechanisms in $C_mH_n$ combustion process. According to this informations, the image of $C_2$ radical exists at front zone, following the images of CH and OH radicals at downstream.

• Journal of the Korean Institute of Gas
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• v.24 no.6
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• pp.1-10
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• 2020

Reactivity controlled compression ignition (RCCI) combustion is one of dual-fuel combustion systems which can be constructed by early diesel injection during the compression stroke to improve premixing between diesel and air. As a result, RCCI combustion promises low nitrogen oxides (NOx) and smoke emissions comparing to those of general dual-fuel combustion. For this combustion system, to meet the intensified emission regulations without emission after-treatment systems, exhaust gas recirculation (EGR) is necessary to reduce combustion temperature with lean premixed mixture condition. However, since EGR is supplied from the front of turbocharger system, intake pressure and the amount of fresh air supplementation are decreased as increasing EGR rate. For this reason, the effect of various EGR rates on the brake power and thermal efficiency of natural gas/diesel RCCI combustion under two different operating conditions in a 6 L compression ignition engine. Varying EGR rate would influence on the combustion characteristic and boosting condition simultaneously. For the 1,200/29 kW and 1,800 rpm/(lower than) 90 kW conditions, NOx and smoke emissions were controlled lower than the emission regulation of 'Tier-4 final' and the maximum in-cylinder pressure was 160 bar for the indurance of engine system. The results showed that under 1,200 rpm/29 kW condition, there were no changes in brake power and thermal efficiency. On the other hand, under 1,800 rpm condition, brake power and thermal efficieny were decreased from 90 to 65 kW and from 37 to 33 % respectively, because of deceasing intake pressure (from 2.3 to 1.8 bar). Therefore, it is better to supply EGR from the rear of compressor, i.e. low pressure EGR (LP-EGR) system, comparing to high pressure EGR (HP-EGR) for the improvement of RCCI power and thermal efficiency.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.4
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• pp.405-412
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• 2012

In the MCFC power generation system, the combustor supplies a high temperature mixture of gases to the cathode and heat to the reformer by using the off-gas from the anode; the off-gas includes high concentrations of $H_2O$ and $CO_2$. Since a combustor needs to be operated in a very lean condition and avoid local heating, a catalytic combustor is usually adopted. Catalytic combustion is also generally accepted as one of the environmentally preferred alternatives for generation of heat and power from fossil fuels because of its complete combustion and low emissions of pollutants such as CO, UHC, and $NO_x$. In this study, experiments were conducted on catalytic combustion behavior in the presence of Pd-based catalysts for the BOP (Balance Of Plant) of 5 kW MCFC (Molten Carbonate Fuel Cell) power generation systems. Extensive investigations were carried out on the catalyst performance with the gaseous $CH_4$ fuel by changing such various parameters as $H_2$ addition, inlet temperature, excess air ratio, space velocity, catalyst type, and start-up schedule of the pilot system adopted in the BOP.

• Clean Technology
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• v.27 no.4
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• pp.367-371
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• 2021

The oxy-combustion system is one of the carbon recovery and storage technologies (CCS: Carbon capture & storage) that performs coal combustion using pure oxygen and recirculated flue gas. This is a technology that facilitates storage of carbon dioxide by generating an exhaust gas consisting of only carbon dioxide without a process of separating carbon dioxide and nitrogen when coal is burned using pure oxygen and recirculated flue gas mixture instead of a conventional air combustion system that produces carbon dioxide and nitrogen mixed exhaust gas. In this study, the characteristics of generated NO and SO₂ as atmospheric pollutants during oxy-combustion were examined using O₂/CO₂ mixed simulation gas. The reaction temperature was varied from 900 ℃ to 1200 ℃ and oxygen partial pressure was varied from 30% to 50%. The results showed that NO and SO₂ concentrations in flue gas increased as the oxygen concentration and the reaction temperature in the furnace increased. The partial pressure of CO₂ in flue gas also increased as the oxygen concentration and the reaction temperature in the furnace increased. As a results of comparing NO production of 30% O₂/CO₂ oxy-combustion with air combustion, NO in flue gas increased with reaction temperature in both experiments and NO of oxy-combustion was 40 ~ 80 ppm lower than that of air combustion.