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Study Design: Technical report. Objectives: Dural tear is one of the most common complications of endoscopic spine surgery. Although endoscopic dural repair of the durotomy area may be difficult, we successfully repaired the dural tear area using nonpenetrating clips during biportal endoscopic surgery. We introduce the surgical technique of dural repair using nonpenetrating titanium clips in biportal endoscopic spine surgery and report its clinical outcome. Methods: We retrospectively reviewed and analyzed 5 patients who were treated via primary dural repair using nonpenetrating titanium clips during biportal endoscopic lumbar surgery. The 2 methods of dural clipping and repair include 2 or 3 portals. We analyzed radiological parameters such as cerebrospinal fluid collection as well as clinical parameters, including postoperative clinical outcomes. Results: Five patients underwent biportal endoscopic dural repair using nonpenetrating clips. Incidental durotomy was successfully repaired using nonpenetrating titanium clips in all 5 patients. No cerebrospinal fluid collection was detected in the postoperative magnetic resonance images. Clinically, preoperative symptoms improved significantly after surgery ( P < .05). Conclusions: We repaired the dural tear area completely using nonpenetrating titanium vascular anastomosis clips in biportal endoscopic lumbar surgery. Dural repair via clipping method may be an effective alternative for incidental durotomy.

We investigated whether ADT use was associated with the risk of ischemic cardiovascular diseases (CVD) and cerebrovascular diseases (CrVD) in a nationwide population-based cohort. Claims data of the Health Insurance and Review Assessment system in South Korea were used. In total, 195,308 men with newly diagnosed prostate cancer between January 1, 2008 and December 31, 2017 were identified. After applying the exclusion criteria, 131,189 men were enrolled. The study cohort was divided into ADT and non-ADT groups. Study outcomes were newly developed CVD, cardiovascular intervention (CVI), and CrVD. To control for potential confounders, various cardiovascular risk factors were balanced between groups. Cox proportional hazard regression models were used to estimate adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) of events. Univariable analysis revealed that ADT was significantly associated with an increased risk of CVD and CrVD. Multivariable analysis did not reveal this association. In the propensity score matched cohort (n = 61,722), multivariable analysis demonstrated that ADT independently reduced the risk of CVD (HR 0.890; 95% CI 0.846–0.936; p

This study has comprehensively analyzed the ventilation system of an indoor coal storage shed using computational fluid dynamics (CFD). In addition, the effects of the plan to improve the ventilation system were investigated by synthesizing the results. First, the velocity of inlet wind entering through the natural ventilation system was measured. Then, the concentration of carbon monoxide inside the coal storage shed was measured at the spontaneous combustion of coal. The boundary conditions were set using the measurement results. The characteristics of carbon monoxide concentration, ventilation volume, and behavior of scattering dust were analyzed. According to the CFD analysis results, the upper recirculation strength increased as the flow rate of external air increased. The flow-stagnation area occurred on the center wall. In particular, the concentration of carbon monoxide was high in the flow-stagnation area. When the inflow velocity was 2.0 m/s, a risk of 30 ppm or more occurred in the area near the second-floor workspace and central retaining wall. When ventilation dropped sharply, coal dust emissions decreased to 14.5%. Thus, ventilation must be secured by installing a natural ventilation system, in case spontaneous ignition occurs in many cells or the ventilation sharply decreases. Finally, in order to improve the ventilation system, the effect on the additional installation of natural ventilation and the use of mobile blowers was analyzed. Finally, in order to improve the ventilation system, the effect on the additional installation of natural ventilation and the use of mobile blowers was analyzed. As a result of the analysis, we concluded that using a mobile blower is more effective than a method of additionally installing a natural ventilation device. Carbon monoxide may be locally diluted, and ventilation volume additionally secured.

In spite of various merit of algae as biofuel, the production cost of algae is a considerable obstacle for commercialization. The concurrent development of essential technologies is needed for the cultivating, harvesting, extracting and energy transformation. The production cost of algae biofuel has still higher than that of the other commercial biofuel. The major research activity has been focused on the cultivating and the research of other processes has been done with relatively lower activity. It is difficult to separate the algae from water because of the similar magnitude of density each other. The agglomeration and extracting of algae with the hybrid technology using ultrasonic wave is rare effect of environmental hazard and also it is appropriate technology for the next generation energy resources.The present research is investigated for the effective separation of algae from water with the ultrasonics wave. The aim of the present research is focused on the establishment of optimal design of algae agg-lomeration system. For this purpose, the computational fluid dynamic analysis has been conducted in the flow field with ultrasonic wave and algae flow to clarify the mechanism of algae separation by ultrasonic wave.

A heat exchanger tube array in a heat recovery steam generator is exposed to hot exhaust gas flow that can cause flow induced vibrations, which could damage the heat exchanger tube array. The characteristics of flow induced vibration in the tube array need to be established for the structural safe operation of a heat exchanger. Several studies of the flow induced vibrations of typical heat exchangers have been conducted and the nondimensional PSD (Power Spectral Density) function with the Strouhal number, fD/U, had been derived using an experimental method. The present study examined the results of the previous experimental research on the nondimensional PSD characteristics by CFD analysis and the basis for the application of flow induced vibration to the heat recovery steam generator tube array was determined from the present CFD analysis. The present CFD analysis introduced circular cylinder tube array and calculated using unsteady laminar flow for the tube array. The characteristics of lift and drag fluctuations over the cylinder tube array was investigated. The derived nondimensional lift and drag PSD was compared with the results of the previous experimental research and the characteristics of lift and drag PSD for a circular cylinder tube array was established from the present CFD study.

Heat exchanger tube array in a heat recovery steam generator is exposed to the hot exhaust gas flow and it could cause the flow induced vibration, which could damage the heat exchanger tube array. It is needed for the structural safe operation of the heat exchanger to establish the characteristics of flow induced vibration in the tube array. The researches for the flow induced vibration of typical heat exchangers have been conducted by using single cicular tube or circular tube array and the nondimensional PSD(Power Spectral Density) function with the Strouhal number, fD/U, had been derived by experimental method. From the present study, the basis for the application of flow induced vibration to the heat recovery steam generator tube array would be prepared. For the previous mentioned purpose, the present CFD analysis introduced a single fin tube and calculated with the unsteady laminar flow over the single fin tube. The characteristics of vortex shedding and lift fluctuation over the fin tube was investigated. The derived nondimensional PSD was compared with the results of the previous experimental researches and the characteristics of lift PSD over a single fin tube was established from the present CFD study.

Heat exchanger tube array in a heat recovery steam generator is exposed to the hot exhaust gas flow and it could cause the flow induced vibration, which could damage the heat exchanger tube array. It is needed for the structural safe operation of the heat exchanger to establish the characteristics of flow induced vibration in the tube array. The researches for the flow induced vibration of typical heat exchangers have been conducted and the nondimensional PSD(Power Spectral Density) function with the Strouhal number, fD/U, had been derived by experimental method. The present study examined the results of the previous experimental researches for the nondimensional PSD characteristics by CFD analysis and the basis for the application of flow induced vibration to the heat recovery steam generator tube array would be prepared from the present CFD analysis. For the previous mentioned purpose, the present CFD analysis introduced a single circular cylinder and calculated with the unsteady laminar flow over the cylinder. The characteristics of vortex shedding and lift fluctuation over the cylinder was investigated. The derived nondimensional PSD was compared with the results of the previous experimental researches and the characteristics of lift PSD over a single circular cylinder was established from the present CFD study.

Heat exchanger tube array in a heat recovery steam generator is exposed to the hot exhaust gas flow and it could cause the flow induced vibration, which could damage the heat exchanger tube array. It is needed for the structural safe operation of the heat exchanger to establish the characteristics of flow induced vibration in the tube array. The researches for the flow induced vibration of typical heat exchangers have been conducted and the nondimensional PSD(Power Spectral Density) function with the Strouhal number, fD/U, had been derived by experimental method. The present study examined the results of the previous experimental researches for the nondimensional PSD characteristics by CFD analysis and the basis for the application of flow induced vibration to the heat recovery steam generator tube array would be prepared from the present CFD analysis. For the previous mentioned purpose, the present CFD analysis introduced a single circular cylinder and calculated with the unsteady laminar flow over the cylinder. The characteristics of vortex shedding and lift and drag fluctuation over the cylinder was investigated. The derived nondimensional PSD was compared with the results of the previous experimental researches and the characteristics of lift and drag PSD over a single circular cylinder was established from the present CFD study.

A heat recovery steam generator consists of inlet expansion duct and heat transfer tube bank modules. For the enhancement of heat transfer in the tube bank modules, the flow should be uniform before the 1st heat transfer tube bank module. The present study has been carried out to analyze the flow characteristics in the inlet expansion duct of a heat recovery steam generator by using numerical flow analysis. The aim of the present study is to establish the proper heat transfer mechanism in the heat transfer tube bank modules by the comparison of the heat transfer models, the case with the constant heat loss per unit volume and the case with heat loss by using inner and outer convective heat transfer coefficient of heat transfer tube. From the present research, it could be seen that the heat transfer mechanism with using inner and outer convective heat transfer coefficient derives more proper temperature distribution results and the acceptance criteria of the temperature distribution within before SCR is satisfied with using this heat transfer mechanism.

본 논문은 냉장고의 열손실의 약 30%를 차지하고 있는 가스켓 주위의 열전달 해석시 복사열전달을 고려하지 않은 경우와 고려한 경우가 많은 차이가 있어서 가스켓 주위의 열전달 해석시 복사열전달 고려 여부에 따른 열손실 효과를 살펴보는 연구이다. 이를 위해 가스켓 주위를 단순화한 형상으로 모델링하여 열전달 전산해석을 수행하였다. 본 연구를 통해서 가스켓 내부의 공기층을 단순히 전도열전달만 고려한 경우 열손실이 $25.6W/m^2$ 이고 복사열전달을 함께 고려한 경우 $55.0W/m^2$ 로 약 2.2배 크게 나타남을 알 수 있었다. 가스켓 내부에 복사열전달 차단판을 0에서 7개로 변화하면서 복사열전달 저감 효과를 살펴본 결과 차단판 개수가 증가하여 7개 인 경우는 설치하지 않은 경우에 비하여 열손실이 $55.0W/m^2$ 에서 $36.7W/m^2$ 로 33% 감소함을 알 수 있었다. 또한 같은 개수의 복사 차단판일 경우는 냉장고 내부와 외부에 치우치는 쪽으로 설치하는 것이 가스켓의 가운데에 설치하는 것 보다 효과적임을 알 수 있었다. 【The present study has been accomplished to elucidate the effect of radiation heat transfer in the heat transfer analysis of refrigerator gasket, which has near 30% of refrigerator heat loss. The numerical heat transfer analysis has been conducted with the simplified modeling of refrigerator gasket. From the present CFD analysis, heat loss at the gasket is $25.6W/m^2$ for the case without radiation effect and that for the case with radiation effect is $55.0W/m^2$ , which is 2.2 times greater heat loss. The radiation protection layers were installed in the gasket from 0 to 7 and the case with 7 layers has 33% reduction effect of heat loss compared with the case without any radiation protection layer. Additionally, it is better effect of radiation heat loss reduction that the radiation protection layers would be placed to the outer or inner side of gasket rather than placing to the center of gasket.】

Chemical interaction on flame extinction in downstream interaction of syngas-air and CO-air premixed flames was investigated. Flame stability diagrams mapping the extinction limits for various fuel concentrations as functions of the strain rate were developed for the downstream interactions between syngas-air and CO-air premixed flames. Of particular concern was the impact of the chemical interaction on the flame extinction characteristics. The results showed that the lean extinction boundary was precipitously slanted for extremely small amount of syngas, finally causing the extinction boundary to open up in further increase of strain rate. There existed a critical syngas concentration below which the flame could not be sustained and above which the extinction boundary was double-valued. On the upper branch, hydrogen was produced via the reaction steps CO + H + M → HCO + M and HCO + H → H2 + CO near the highly rich CO-air premixed flame to participate in CO-oxidation. For highly stretched interacting flames, only a flammable island existed. The pure syngas-air diffusion flame was extinguished at a critical strain rate. Further increase of strain rate forced the flammable island to be shrunk and finally to be a point. For highly stretched interacting flames, a minimum CO concentration existed below which the flame could not be survived. In such flames, the diffusion flame can act as a parasite to the lean CO-air premixed flame through sharing hydrogen penetrated from the rich syngas-air premixed flame. Such chemical interactions were examined in detail to describe the flame extinction characteristics.

A MILD(Moderate and Intense Low oxygen Dilution) combustion, which is effective in the reduction of NOx, is considerably affected by the recirculation flow position of hot exhaust gas to the combustion furnace. A numerical analysis was accomplished to elucidate the flow characteristics in the MILD combustion incinerator for several cases with or without exhaust gas recirculation. It could be seen from the result of the present numerical study that the flow recirculation could be observed in the upper region over the vertical dividing wall for the case without exhaust gas recirculation. The optimal position of exhaust gas recirculation position was derived by the comparison of %RMS of x directional velocity for the cases with exhaust gas recirculation. The case with the exhaust gas recirculation position at the upper right of free board was the most effective with the smallest value of 57.4% RMS.

The present study used the MILD combustor, which has coaxial cylindrical tube. The outside tube of the MILD combustor corresponds to the exhaust gas passage and the inner side tube is the furnace passage. A numerical analysis was accomplished to elucidate the characteristics of exhaust gas entrainment toward the inner furnace with the changes of venturi nozzle geometrical parameters, nozzle position, nozzle gap between high pressure air nozzle and venturi nozzle, and with the change of high pressure nozzle inlet velocity. The entrainment flow rate for the case with the high pressure air nozzle attached at the exhaust gas wall has relatively small change with the change of nozzle gap. That for the case with the high pressure air nozzle exposed to the exhaust gas has monotonically increase with the change of nozzle gap. The flow rate ratio of entrainment flow rate has considerably increase tendency with relatively lower air inlet velocity, on the other hand, that with relatively higher air inlet velocity could be seen relatively small increase.

A MILD (Moderate and Intense Low oxygen Dilution) combustion, which is effective in the reduction of NOx, is considerably affected by the recirculation flow rate of hot exhaust gas to the combustion furnace. The present study used the MILD combustor, which has coaxial cylindrical tube. The outside tube of the MILD combustor corresponds to the exhaust gas passage and the inner side tube is the furnace passage. A numerical analysis was accomplished to elucidate the characteristics of exhaust gas entrainment toward the inner furnace with the changes of coanda nozzle geometrical parameters, nozzle passage gap length, nozzle passage length, nozzle angle and expansion length. The optimal configuration of coanda nozzle for the best entrainment flow rate was gap length, 0.5 mm, expansion angle, 4o and expansion length, 146 mm. The nozzle passage length was irrelevant to the exhaust gas entrainement.

The present study has been carried out to elucidate the optimal method for the performance test of a refrigeratorvacuum insulation panel (VIP), by using numerical heat transfer analysis. Three locations of heat flux meter have been tested,for deriving the best test method to clarify the normal or the abnormal condition of the vacuum insulation panel in a refrigerator.The first location of the heat flux sensor is at the same place as the heater, the second one is at the nearby side locationof the heater and the third one is at the opposite side location of heater in the refrigerator. The heat flux and 1/q” 2 orq” 4 were calculated for the cases with the normal VIP, and with the abnormal VIP, and their differences analyzed. From the present study, the first and the second method had a mere difference characteristics of heat flux and 1/q” 2 or q” 4 , betweenthe cases with the normal or the abnormal VIP. The magnitude of the heat flux after 300sec had a great difference between the cases with the normal or abnormal VIP for the third method, and it could be considered the most optimal method totest the performance of a refrigerator vacuum insulation panel.

The present study has been carried out to reduce the heat loss from a built in refrigerator by using reverse heat loss method to discern the region with larger heat loss. To perform this purpose, an infrared thermographic camera has been used to measure the surface temperature of the refrigerator and tried to improve the heat loss near the ice dispenser. The numerical heat transfer analysis also has been accomplished to clarify the heat transfer mechanism near the ice dispenser. The possible applicable method to reduce heat loss was increasing the curvature radius at the ice dispenser corner. The curvature radius has been changed from 0mm to 40mm to see the effect of the curvature at the corner. From the present research, the optimal curvature radius for the reduction of heat loss at the ice dispenser could be 30mm.

The present study has been carried out to analyze the effect of steam hammering on the steam piping system including the final superheater, the high pressure turbine, check valve and the first reheater by sudden stoping of main stop valve in a power plant. For the present steam hammering analysis, the well known Flowmaster software has been used to model the steam piping system and the time dependent characteristics of pressure and steam mass flow r ate has been conducted. Using the result of the unsteady pressure and steam mass flow rate, the forces acting on the elbows in the piping system has been derived. From the present analy-sis, it has been elucidated that the elbow just before the main stop valve and the elbow near the connection pipe between bypass pipe and check valve had the largest force among the elbows in the steam piping system. The structural safety diagnostics study on the elbow and the supporting structures of the steam piping system of a power plant will be conducted in the future by the present results of the forces acting on the elbow.Key words : steam hammering, steam piping system, power plant, final superheater, first reheater, main stop valve, check valve, elbow, pressure, steam mass flow rate, forceKIGAS Vol. 17, No. 2, pp 70~77, 2013 http://dx.doi.org/10.7842/kigas.2013.17.2.70(Journal of the Korean Institute of Gas)

The present paper has been accomplished to elucidate the characteristics of temperature change in a car washer heater system for removal of frost formed at the surface of a car. The previous studies had used a simplified mathematical modeling to analyse the temperature change characteristics for a car washer heater system. In the present study, an unsteady computational fluid flow and heat transfer analysis for a washer heater system has been done by using computational fluid dynamic analysis method. From the present CFD analysis, the time dependent temperature change in a car washer heater system has been analysed and derived the heating time and ejection temperature of the washer liquid to establish the optimal design basis for a washer heater system. Key Words : Washer heater system, Frost, Temperature distribution, Ejection temperature, Heating time, Thermistor * Corresponding Author : Ji-Soo Ha(Keimyung Univ.)Tel: +82-53-580-5919 email: jisooha@kmu.ac.krReceived December 14, 2012 Revised February 5, 2013 Accepted March 7, 2013

MILD (Moderate and Intense Low Oxygen Dilution) combustion is a technology that uses the recirculation of combustion gas to increase thermal efficiency not only by keeping down the concentrationof Nitric Oxides and temperature but also by uniformizing the internal temperature of the combustion furnace. This study is a trial to obtain MILD combustion characteristics by adjusting the equivalence ratiowith the air flow rate in the conical combustor while keeping the fuel flow rate and measuring the exhaustgas of the combustion furnace. Key words: MILD combustion, Exhaust gas recirculation, NOx(Nitric Oxides), CO(Carbon Monoxide), Equivalence ratio †교신저자(계명대학교 기계자동차공학과, E-mail: tkkim@kmu.ac.kr, Tel: 053-580-5551)1 계명대학교 환경과학과, E-mail: jisooha@kmu.ac.kr, Tel: 053-580-5919)2 계명대학교 기계공학과, E-mail: joarongs@naver.com, Tel: 053-580-6483) 1. 서 론 화석연료를 사용하는 연소기에서 발생하는 오염물질 중 질소산화물(NOx)은 도심지역의 오존문제와 산성강하물질 증가의 원인 등의 문제점들을 야기하므로 연소 효율증가와 더불어 반드시 저감 대책이 마련되어야 한다. 일반적인 연소기술들은 연소 효율 향상과 환경오염물질 발생 저감을 동시에 만족하는데 어려움이 있다. 연소 효율 증대를 위한 축열식 연소방법은 배기가스의 열교환을 통한 연소공기의 온도를 1500℃ 이상 가열하여 공급하였다. 그러나 온도에 의존하는 질소산화물 생성 특성과 맞물려서 다량의 질소산화물이 발생하는 문제점을 가지고 있다. 화염의 온도를 낮추어 질소산화물의 발생을 줄인 화염냉각 연소방법은 불완전연소를 유발하여 일산화탄소가 증가하고, 희박예혼합연소 또한 화염불안정 및 화염이 역류하는 문제점을 가지고 있다. 최근에 가장 많이 사용되는 배기가스 재순환을 이용한 연소방법은 산소가 결핍되어 있는 배기가스의 일부분을 연소실로 재순환시킴으로써 연소온도를 낮추어 질소산화물 생성을 억제하는 방법이다. 그러나 이 방법 역시 연소 효율측면과 연료자체의 질소 함유량에 따라 발생하는 질소산화물의 제어에 어려움이 있다. 이러한 수많은 국내외의 연구결과 중 MILD(moderate and

The present study has been carried out to elucidate the unsteady temperature characteristics of a refrigerator near gasket region by measuring time dependent temperature measurements. From the measured values of the time dependent temperature inside and outside region of a refrigerator, one could see that the temperature varies periodically with time from the effect of refrigerator operation. The measured mean temperatures at the wall had great different value from the previous other research results conducted by numeric ofheat transfer using improperfheat transfer boundary condition. The present study could give the experiment ofdata for the properfnumeric ofheat transfer an oysis and suggest more accuratefheat transfer boundary conditions for the inside and outside of a refrigerator.

The present study has been carried out to diagnose the temperature safety of a boiler desuperheater which decreases abnormally higher temperature of superheated steam in a reheater of a power plant. The liquid water in the desuperheater stays in a closed space. It becomes heated by the high temperature superheated steam and boiling could occur. Boiling might increase internal pressure and it could destroy the desuperheater if the internal pressure exceeds the allowable pressure of the desuperheater. The present study modeled reasonably the desuperheater and four cases of heat transfer analysis are executed with the consideration of insulator and natural convective fluid flow of the inside cooling water. For the case excluded the natural convective fluid flow, the temperature exceeds the allowable temperature and pressure. On the other hand, for the real case included natural convective fluid flow and insulator, the active heat transfer from higher temperature region to lower temperature region occurs and it makes the temperature in the cooling water below the allowable temperature and pressure. From this fact, it could be thought that the desuperheater in the reheater is safe from destroy or back flow.

The present study has been carried out to analyze the flow characteristics in the inlet expasion duct of a heat recovery steam generator by using numerical flow analysis. The inlet of HRSG corresponds the outlet of gas turbine exit and the flow after gas turbine has strong swirl flow and turbulence. The inlet flow condition of HRSG should be included the exit flow characteristics of gas turbine. The present numerical analysis adopted the flow analysis result of gas turbine exit flow as a inlet flow condition of HRSG analysis. Because the flow characteristics in the inlet duct of the tube bank is strongly related to the performance of a HRSG, it is most important for the optimal design of HGSG to understanding the flow phenomena in the inlet duct of HRSG. From the present study, the position of breakpoint in the inlet expansion duct should be lower than the reference breakpoint position for the optimal flow uniformity before the tube bank.

The present study has been carried out to predict the heat transfer characteristics of reverse heat loss method for a residential refrigerator by using numerical analysis and corresponding experiment. From the measured values of temperature and heat input, one can conclude that, the temperature inside the refrigerator has a nearly linear relationship with heat input. The effect of gasket heat loss was examined with the change of thermal conductivity of gasket region. The appropriate thermal conductivity of gasket region was acquired from the comparison of heat losses with the experimental result and numerical analysis. The result of calculated heat losses had accuracy within 1.8% error with the experimental result. With the selected thermal conductivity of gasket region, the effectiveness of reverse heat loss method was examined with the change of thermal conductivity of vacuum insulation panel.

The present study has been carried out to predict the heat transfer characteristics near the door gasket of a residential refrigerator. Temperature measurement and numerical heat transfer analysis were conducted and compared to each other to achieve a more proper numerical analysis method. Three cases of numerical analysis were tried while changing the boundary conditions. The calculated result of temperature using a uniform free stream temperature showed a great difference from the measured temperature. The numerical result including two dimensional fluid flow was also shown to be far from the measured result. The measured temperature had periodic characteristics which were divided into two parts, an increasing part and a decreasing part during an 18 minute period because of the operation of compressor in a refrigerator. The heat transfer might contain three dimensional forced and natural convective heat transfer phenomena near the door gasket. Instead of adopting the complicated three dimensional numerical analysis the two dimensional heat transfer analysis with the measured free stream temperature derived more accurate temperature prediction than the other numerical analyses.

The present study has been carried out to analyze the flow characteristics of a heat recovery steam generator with the change of inlet flow conditions by using numerical flow analysis. The inlet of HRSG corresponds the outlet of gas turbine exit and the flow after gas turbine has strong swirl flow and turbulence. The inlet flow condition of HRSG should be included the exit flow characteristics of gas turbine. The present numerical analysis adopted the flow analysis result of gas turbine exit flow as a inlet flow condition of HRSG analysis. The computational flow analysis result of gas turbine exit shows that the maximum axial velocity appears near circular duct wall and the maximum turbulent kinetic energy and dissipation rate exist relatively higher gradient region of axial velocity. The comparison of flow analysis will be executed with change of inlet turbulent flow condition. The first case is using the inlet turbulent properties from the result of computational analysis of gas turbine exit flow, and the second case is using the assumed turbulent intensity with the magnitude proportional to the velocity magnitude and length scale. The computational results of flow characteristics for two cases show great difference especially in the velocity field and turbulent properties. The main conclusion of the present study is that the flow inlet condition of HRSG should be included the turbulent properties for the accurate computational result of flow analysis.

A numerical analysis of reactive flow in a MILD(Moderate and Intense Low oxygen Dilution) combustor is accomplished to elucidate the characteristics of combustion phenomena in the furnace with the change of fuel and air nozzle position and air mass flow rate. For the case with the fuel nozzle located near center position of combustor, the reaction zone started at the fuel nozzle and had inclined shape toward combustor wall when the air mass flow rate was relatively smaller. On the other hand, the end of reaction zone moved toward center of combustor from combustor wall when the air flow rate was relatively larger. For the case with the air nozzle located near center position of combustor, the reaction zone started at the fuel nozzle and had inclined shape toward combustor wall when the air mass flow rate was relatively small, which was similar as the previous case with smaller air mass flow rate. On the other hand, the end of reaction zone moved toward combustor wall when the air flow rate was relatively larger. The maximum temperature increased as the air mass flow rate increasing for both cases, and the concentration of thermal NOx increased also from the previous reason of temperature characteristics. The concentration of NOx for the case with the air nozzle located near center position of combustor was considerably smaller than that for the case with the fuel nozzle located near center position of combustor. From the present study, the case with the air nozzle located near center position of combustor and theoretical air flow rate was the most effective condition for the NOx reduction and perfect combustion.

The present study has been carried out to predict the heat transfer characteristics of a residential refrigerator through insulation wall by using reverse heat loss method. The temperature time history characteristics were measured to achieve the steady state condition. In this experiment the steady state condition was reached at about 20 h of heating. The temperature and heat inputs were then averaged with one hour data and considered as the steady state temperature and heat input. From the measured values of temperature and heat input, one can conclude that, the temperature differences between the inside and outside of a refrigerator has a nearly linear relationship with heat input. The overall heat transfer coefficients have been derived by introducing the optimal heat loss function to analyze the heat loss characteristics. The accuracy of heat loss prediction has been checked with various experimental data and the normalized errors of the obtained result are found to be within 2.5%.

Flame propagation velocity is the one ofmainmechanismof the stabilization of triple flame. To quantify the triple flame propagation velocity, Bilger presents the triple flame propagation velocity depending on the mixture fraction gradient, based on the laminar jet flow theory. However, in spite of these many analyses, there was not presented any relation of these variables, triple flame propagation velocity, radius of flame curvature and scalar dissipation rate indirectly. In the present research, we have checked the results of numerical simulation with experiment and numerical analysis and verified the flame propagation velocity with a scalar dissipation rate proposed by Bilger through the numerical simulation. Also we have clarified that flame propagation velocity was depended on the radius of flame curvature and scalar dissipation rate.

Flame stability is the one of the main mechanism of laminar lifted flame and flame propagation velocity becomes a yardstick to measure the flame stability. Bilge has presented the flame propagation velocity of the triple flame and the flame stability mechanism related the flame configuration and mixture fraction. However, there was not able to observe all process of flame ignition and extinction for small nozzle diameter. In this paper, we have subdivided the flame configuration and stability mechanism and classified the flame behavior with a nozzle diameter. Also we have subdivided the `triple flame propagation opened` and the `triple flame propagation closed` from the triple flame propagation of triple flame criterion.

Numerical and experimental studies are conducted to grasp downstream interactions between premixed flames stratified with two different kinds of fuel mixture. The selected fuel mixtures are methane and a nitrogen-diluted hydrogen with composition of 30% H2 + 70% N2. Extinction limits are determined for methane/air and (30% H2 + 70% N2)/air over the entire range of mixture concentrations. These extinction limits are shown to be significantly modified due to the interaction such that a mixture much beyond the flammability limit can burn with the help of a stronger flame. The lean extinction limit shows both the slanted segments of lower and upper branches due to the strong interaction with Lewis numbers of deficient reactant less than unity, while the rich extinction limit has a square shape due to the weak interaction with Lewis numbers of deficient reactant larger than unity. The regimes of negative flame speed show an asymmetric aspect with a single wing shape. The negative flame always appears only when methane is weak. The extent of interaction depends on the separation distance between the flames, which are the functions of the mixtures’ concentrations, the strain rate, the Lewis numbers, and the preferential diffusions of the penetrated hydrogen from the nitrogen-diluted hydrogen flame. The important role of preferential diffusion effects of hydrogen in the flame interaction is also discussed.

This study has purpose of minimizing damage from fire incident as analyzing the fire characteristic about fire incident of multi-use hostel s, which is increasing recently. For this, CFAST, a verified analysis program for the fire incident was employed to prove the logicality of the study by comparing with a established result of the research work and working the fire simulation for an apartm ent house. On the basis of this, the study will help to improve safety of fire by analyzing the fire characteristic of Karaoke and Gosiwon which are typical model of multi-use hostels and by establishing how to deal with the fire incident. Key words: CFAST, Zone model, Fire Characteristics, Multi-use hostels †교신저자(계명대학교 기계자동차공학부, E-mail:tkkim@kmu.ac.kr, Tel: 053-580-5551)1 계명대학교 에너지환경과학과2 계명대학교 기계공학과3 인제대학교 보건안전공학과 1. 서 론 화재위험이 높은 것으로 지적되고 있는 고시원과 찜질방, 산후조리원, pc방 등의 다중이용업소의 수가 짧은 기간 동안에 급격하게 증가하고 있다. 소방방재청 집계에 의하면 노래방, 찜질방 등 다중이용업소로 신고등록 또는 허가된 업소는 2009년 기준으로 약 177,000여개 소이다.[1] 이들 업종의 특성상 지하층 영업과 실내 구조물의 다양화와 복잡함으로 인해 화재 시 많은 인명피해가 우려되고, 화재의 발생 및 확산형태도 예측하기 어려워졌다. 특히 최근에 발생한 부산 실내사격장(2009년)과 부산 영도구 노래주점(2009년) 및 용인 고시원(2008년) 등의 화재사고는 다중이용업소의 화재위험성 및 피해크기를 보여주는 대표적인 예이다. 이러한 실제 사례를 바탕으로 발생 가능한 화재를 예측하여 피해의 크기와 종류를 예측할 수 있다면 그에 대한 적절한 대처방법을 제시할 수 있게 될 것이다. 그러나 실제 화재실험은 그 위험성 때문에 현실적으로 어려운 사항이다. 이에 대한 대안으로 컴퓨

A numerical analysis of reactive flow in a liftoff flame is acc omplished to elucidate the characteristics of flame propagation velocity and volume integral of reaction rate with the variation of nozzle diameter and fuel in jection flow rate in a liftoff flame consisted with fuel rich region, fuel lean region and diffusion flame region. The increase of fuel injection velocity enhances flame propagat ion velocity for the selected three nozzle diameter(d=0.25, 0.30, 0.35mm), but its e ffect on the flame propagation velocity is not much greater than 4.3%. The increas e of fuel flow rate is directly and linearly related with the volume reaction rate and so the volume reaction rate, not the flame propagation velocity, might be considered t o accommodate the variation of fuel flow rate in a liftoff flame. Key words: Liftoff flame, Flame propagation velocity, Nozzle diameter, Volume integral of reaction rate, Flame surface area †교신저자(계명대학교 에너지환경과학과, E-mail:jisooha@kmu.ac.kr Tel: 053)580-5919)1 계명대학교 기계자동차공학부