• 한국가시화정보학회지
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• 제18권3호
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• pp.96-102
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• 2020

Oral cancer surgery changes the morphologic characteristics of the human upper airway. These changes can affect the flow patterns. In this study, computational fluid dynamics (CFD) simulations with transient solver were performed to numerically investigate the air flows in the human upper airways depending oral cancer surgery. 3D reconstructed models were obtained from 2D CT images of one patient. For the boundary condition, the realistic breathing cycle of human was applied. The hydraulic diameters of cross-sections for post-surgical model are changed greatly along streamwise direction, so these variations can cause higher wall shear stress and flow disturbance compared to pre-surgical model. The recirculation flows observed in the protruding region result in the relatively large pressure drop. These results can be helpful to understand the flow variations after resection surgery of oral cancer.

• 한국환경과학회지
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• 제7권6호
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• pp.745-751
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• 1998

The well-mixed room model has been traditionally used to predict the concentrations of contaminants in indoor environments. However, this is inappropriate because the flow fields in many indoor environments distribute contaminants non-uniformly, due to imperfect air mixing. Thus, some means used to describe an imperfectly mixed room are needed. The simplest model that accounts for imperfect air mixing is a two-zone model. Therefore, this study on development of computer program far the two-zone model is carried out to propose techniques of estimating the concentration of contaminants in the room. To do this, an important consideration is to divide a room into two-zone, i.e. the lower and upper zone assuming that the air and contaminants are well mixed within each zone. And between the zones the air recirculation is characterized through the air exchange parameter. By this basic assumption, the equations for the conservation of mass are derived for each zone. These equations are solved by using the computational technique. The language used to develope the program is a VISUAL BASIC. The value of air exchange coefficient($f_12$) is the most difficult to forecast when the concentrations of contaminants in an imperfectly mixed room are estimated by the two-zone model. But, as the value of $f_12$ increases, the air exchange between each zone increases. When the value of $f_12$ is approximately 15, the concentrations in both zone approach each other, and the entire room may be approximately treated as a single well-mixed room. Therefore, this study is available for designing of the ventilation to improve the air quality of indoor environments. Also, the two-zone model produces the theoretical base which may be extended to the theory for the multi-zone model, that will be contributed to estimate the air pollution in large enclosures, such as shopping malls, atria buildings, atria terminals, and covered sports stadia.

• 대한기계학회논문집B
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• 제40권8호
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• pp.503-510
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• 2016

일반적으로 연소로는 연료의 연소과정에서 NOx, CO등의 공해물질을 배출한다. 본 연구는 소각연소로를 대상으로 2차 공기를 연소가스 흐름의 역방향으로 주입시키는 방법의 NOx 및 CO 배출특성에 대한 연구를 수행하였다. 연구의 주요변수는 1, 2차 공기의 유량비와 2차 공기의 투입 방향으로 설정하였다. 변수에 따른 NOx 및 CO 배출특성을 묘사하기 위해서 축소모형실험 연구를 수행하였다. 실험결과 1차 공기유량이 감소하고 2차 공기유량이 증가할수록 NOx가 감소되다가 일정 유량비 이상에서 다시 NOx가 다소 증가하는 형태가 나타났다. 역방향으로 빠른 유속의 2차 공기가 투입될 때 연소로 내부에 유동 재순환이 발생하여 혼합이 증가하고 이로 인해서 온도 영역이 고르게 분포되는 것으로 나타났으며 그 결과로서 thermal NOx의 저감 효과를 확인할 수 있었다. CO는 2차 공기가 역방향에서 높은 비율로 투입되는 조건이외에서는 측정되지 않았다. 측정된 경우도 CO의 농도는 2 ppm 이내로 안정적인 연소 조건으로 나타났다.

• 한국물환경학회지
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• 제25권6호
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• pp.896-901
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• 2009

In this study, in order to apply the air and pure oxygen in the Jet Loop Reactor (JLB) in which the oxygen transfer rate is high, differentiate the operation mode according to each air flowrate and liquid flowrate and investigate the oxygen transfer characteristic, an experiment was carried out. The oxygen concentration with the air flowrate ($Q_g$) and liquid flowrate ($Q_L$) was identical but the oxygen transfer coefficient ($K_L{\cdot}a$) is linear depending on degree of two factors. The width of an increase is small in $0.1min^{-1}$ when the air flowrate is 0.2 L/min with increasing the liquid flowrate. Whereas, the increment was exposed to be very high for $1.5min^{-1}$ when the air flowrate was 5 L/min. In the experiments using the pure oxygen, it was 30 mg/L of oxygen concentration finally and it was 3.5 times than using the air. But the time reached the saturated concentration was similar to using the air, and $K_L{\cdot}a$ was similar to using the air too. Analysis between two independent variable and oxygen transfer of the correlation is the same model like $K_L{\cdot}a={0.0161Q_L}^{1.5371}{Q_g}^{0.5433}$ using with coefficient non linear regression analysis. It was resulted that the liquid flowrate were approximately three times than air flowrate on effect to oxygen transfer rate.

• 한국산학기술학회논문지
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• 제19권8호
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• pp.8-13
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• 2018

질소산화물은 최근에 초미세먼지 발생에 많은 영향을 주고 있어서 대기환경 개선 측면에서 사회적으로도 크게 관심이 되고 있다. 질소산화물은 주로 화력발전 등의 연소기기에서 고온의 연소가스 분위기에서 공기 중의 질소와 산소가 반응하여 발생한다. 이에 대한 저감 방법으로 원통형 버너에 코안다 노즐을 이용한 배관으로 배기가스를 재순환하는 연소에 대한 연구가 최근에 이루어지고 있다. 본 연구에서는 코안다 노즐을 사용하여 배기가스를 재순환하는 원통형 버너의 연소가스 출구의 위치를 오른쪽으로 하는 버너(Case 1 버너), 양쪽을 출구로 하는 버너(Case 2 버너), 왼쪽을 출구로 하는 버너(Case 3 버너) 형상에 대하여 전산유체해석을 통해 연구를 수행하였으며 연소 유동의 압력, 유선, 온도, 연소 반응 속도와 질소산화물의 분포 특성을 비교 분석하였다. 연소반응은 Case 1과 Case 2버너는 연소가스 재순환 유입구가 있는 오른쪽 방향으로 일어나고 Case 3 버너는 혼합가스 유입구 부근에서 일어나고 있었다. 출구에서의 온도는 Case 2버너가 양쪽으로 배출되면서 다른 버너 보다 약 $100^{\circ}C$ 정도 온도가 낮게 나타났으며 출구에서의 NOx 농도는 Case 1버너가 다른 형상 버너 보다 약 20배 크게 나타났다. 이로부터 NOx 저감을 위해서는 배기가스 재순환 버너의 출구는 양쪽으로 배출되게 하거나 연소가스 재순환 유입구 반대 방향으로 배출 되도록 하는 것이 효과적임을 알 수 있었다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.1070_1071
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• 2009

Recently, small hydropower attracts attention because of its clean, renewable and abundant energy resources to develop. Therefore, a cross-flow hydraulic turbine is proposed for small hydropower development in this study. The turbine‘s simple structure and high possibility of applying to the sites of relatively low effective head and large flow rate can be advantages for the introduction of the small hydropower development. The purpose of this study is not only to investigate the effects of air layer in the turbine chamber on the performance and internal flow of the cross-flow turbine, but also to suggest a newly developed air supply method. CFD analysis for the performance and internal flow of the turbine is conducted by an unsteady state calculation using a two-phase flow model in order to embody the air layer effect on the turbine performance effectively. The result shows that air layer effect on the performance of the turbine is considerable. The air layer located in the turbine runner passage plays the role of preventing a shock loss in the runner axis and suppressing a recirculation flow in the runner. The location of air suction hole on the chamber wall is very important factor for the performance improvement. Moreover, the ratio between air from suction pipe and water from turbine inlet is also significant factor of the turbine performance.

• 설비공학논문집
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• 제17권11호
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• pp.1072-1078
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• 2005

The present study has been conducted to tune a PID controller for large thermal systems such as a thermal environment chamber. In spite of large thermal mass of the thermal chamber under test, its response delay time was found to be negligible mainly due to high air recirculation rate. In general, heating and cooling capacities tend to be small compared the size of a thermal environment chamber, which leads to long transient periods of one hour or so. In the study, a PI tuning method is suggested which makes system responses faster while reducing overshoots and hunting by utilizing efficiently proportional band of actuators.

• 설비공학논문집
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• 제27권11호
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• pp.559-566
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• 2015

The main objective of this work is to experimentally investigate the effect of angle variation on the distribution of two-phase flow at header-channel junctions. The cross-sections of the header and the channels were fixed at $16mm{\times}16mm$ and $12mm{\times}1.8mm$, respectively. Air and water were used as the test fluids. Four different header-channel positions were tested : Vertical header with Horizontal channels (case VM-HC), Horizontal header with Horizontal channels (case HM-HC), Horizontal header with Vertical Downward channels (case HM-VDC), and Horizontal header with Vertical Upward channels (case HM-VUC). In all cases, liquid flow distribution tended to decrease gradually in the upstream header region. However, in the downstream region, different trends could be seen. The reason for these different tendencies were identified by flow visualization in each case. The standard deviations for the liquid and gas flow distribution in each case were calculated, and the case of VM-HC had the lowest values compared to other cases because of the symmetrically distributed liquid film and strong flow recirculation near the end plate.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1686-1691
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• 2004

The effect of recirculated exhaust gas on performance and exhaust emissions with FGR rate are investigated by using a natural circulation, pressurized draft and water tube boiler with FGR system operating at several boiler loads and over fire air(OFA) damper openings. The purpose of this study is to apply the FGR system to a power plant boiler for reducing $NO_{x}$ emissions. To activate the combustion, the suction damper of two stage combustion system installed in the upper side of wind box is opened by handling the lever between $0^{\circ}$ and $90^{\circ}$ , and the OFA with 0 to 20% into the flame is supplied, as the combustion air supplied to burner is reduced. It is found that the fuel consumption rate divided by evaporation rate does not show an obvious tendency to increase or decrease with rising the FOR rate, and $NO_{x}$ emissions are decreased, at the same OF A damper opening, as FOR rates are elevated and boiler loads are dropped.

• 한국연소학회지
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• 제16권3호
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• pp.12-20
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• 2011

Oxy-coal combustion for $CO_2$ capture in coal power plants entails a mode switching from air-firing to oxyfiring. In this study, procedure of the mode switching was investigated and discussed through experiments in pilot scale facilities: (1) a 0.3 $MW_{th}$ furnace with a vertical single burner and a FGR(Flue Gas Recirculation) system (2) a 1 $MW_{th}$ furnace with horizontal 4 burners and a FGR system. Principle of the mode switching was established and performed with control of FD fan, FGR fan, ID fan and oxygen flow rates. We have found that equivalence ratio in the oxy-firing mode should be increased more than that in the air-firing to achieve stable mode switching. Control of FD, ID and FGR fans should be performed carefully in the mode switching, in the sense of complete combustion and flame attachment. Moisture contents in the ash and the flue gas recycled to the primary oxidizer stream should be removed to prevent condensation, corrosion and duct clogging.