• Journal of the Korean Society of Visualization
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• v.18 no.3
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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.

• Journal of Environmental Science International
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• v.7 no.6
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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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.8
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• pp.503-510
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• 2016

Incinerators generally emit pollutants such as NOx and CO during the combustion process. In this paper, pollutant emissions and temperature distributions were studied in a simulated incinerator with a reversed (relative to the flue gas flow) secondary air injection system. The experiments were performed by using a lab-scale furnace in order to evaluate the effects of the injection location, direction and flow rate of secondary air jets. The emission of NOx was lower in the case of reversed secondary air injection than in the case of cross injection, due to the recirculation and mixing of the exhaust gas. In the reversed air injection cases, thermal NOx emissions decreased as secondary air ratio increased from 30 to 60 and slightly increased at secondary air ratios higher than 60. In most cases, CO emissions were not detected except for a few reversed secondary air injection cases, in which cases CO concentrations below 2ppm were observed.

• Journal of Korean Society on Water Environment
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• v.25 no.6
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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.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.8
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• pp.8-13
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• 2018

Nitrogen oxides (NOx) have recently been very influential in the generation of ultrafine dust, which is of great social interest in terms of improving the atmospheric environment. Nitrogen oxides are generated mainly by the reaction of nitrogen and oxygen in air in a combustion gas atmosphere of high temperature in a combustion apparatus such as thermal power generation. Recently, research has been conducted on the combustion that recirculates the exhaust gas to the cylindrical burner by using a piping using a Coanda nozzle. In this study, three types of burners were carried out through computational fluid analysis. Case 1 burner with the outlet of the combustion gas to the right, Case 2 burner with both sides as gas exit, Case 3 burner with left side gas exit. The pressure, flow, temperature, combustion reaction rate and distribution characteristics of nitrogen oxides were compared and analyzed. The combustion reaction occurred in Case 1 and Case 2 burner in the right direction with combustion gas recirculation inlet and Case 3 burner in the vicinity of mixed gas inlet. The temperature at the outlet was about $100^{\circ}C$ lower than that of the other burners as the Case 2 burner was exhausted to both sides. The NOx concentration of Case 1 burner at the exit was about 20 times larger than that of the other burners. From the present study, it could be seen that it is effective for the NOx reduction to exhaust the exhaust gas to both side gas exits or to exhaust the exhaust gas to the opposite direction of inlet of recirculation gas.

• Proceedings of the KIEE Conference
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• 2009.07a
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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.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.11
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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.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.11
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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.

• Proceedings of the KSME Conference
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• 2004.11a
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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.

• Journal of the Korean Society of Combustion
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• v.16 no.3
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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.