• Journal of Advanced Marine Engineering and Technology
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• v.40 no.3
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• pp.174-179
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• 2016

To protect the ocean environment, the use of liquefied natural gas (LNG) carriers, bunkering ships, and fueled ships is increasing. Recently, Korean shipbuilders have developed and supplied a partial reliquefaction facility for boil-off-gas (BOG). Despite reasonable insulation, heat leakage in vessel storage tanks causes LNG to be continuously evaporated as BOG. This research analyzed the maximum liquid yield rate for various partial reliquefaction systems (PRS) and considered related factors affecting yields. The results showed a liquid yield of 48.7% from an indirect PRS system (heat exchanges between cold flash gas and compressed natural gas), and 41% from a direct PRS system (BOG is mixed with flash gas and discharged from a liquid-vapor separator). The primary factor affecting liquid yield was heat exchanger effectiveness; the exchanger's efficiency and insulation characteristics directly affect the performance of BOG reliquefaction systems.

• Journal of Energy Engineering
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• v.11 no.2
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• pp.130-135
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• 2002

Bypass air conditioning systems are divided into three types; outdoor air bypass, mixed air bypass and return air bypass system. Among bypass air conditioning systems, a return air bypass system is more effective than other two systems because it doesn't induce unconditioned outdoor air into conditioned room. The numerical study on the bypass air conditioning system shows this system can maintain indoor RH(Relative Humidity) less than a conventional CAV (Constant Air Volume) air conditioning system by adjusting face and bypass dampers at part load. A simulator was built to compare results of a numerical experiment and those of a simulator experiment. The results of the simulator experiment was nearly same as those of the numerical experiment; when a design sensible load (the ratio of sensible load to total sensible load) was 70 percent (at this time, RSHF=0.7), indoor relative humidity (in case of both numerical experiments and simulator experiments) was maintained below 60% specified by ASHRAE STANDARD 62-1999. The bypass air conditioning system is expected to be applied to many buildings where the Percentage of latent loads or air change tate is high.

• Journal of Biosystems Engineering
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• v.29 no.2
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• pp.141-150
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• 2004

우리가 소비하는 가공 식품은 위생상 안전하도록 살균처리가 이루어진다. 식품 내에 존재할 수 있는 유해 세균은 일정 살균온도에서 살균에 필요한 시간 동안 노출되면 사멸하며, 일반적으로 살균온도가 높을수록 살균에 필요한 시간은 단축된다. 연속살균장치는 혼합 및 저장탱크에 담겨진 식품을 점프로 이동시키면서 가열 열교환기에서 살균온도로 가열하고 단열관을 거치는 동안 살균온도를 유지시켜 살균을 완료한다. 또한 살균된 식품은 냉각용 열교환기에서 상온으로 냉각되며 이 과정에서 회수되는 열은 저장탱크에서 유입되는 식품의 예열에 사용되어 에너지 효율을 제고하는데 사용되기도 한다. 이와 같이 관을 이동하면서 가열되는 살균장치는 기존의 배치식 살균방법에 비하여 균일하게 가열이 이루어지므로 130C의 고온으로 살균할 수 있어서 살균에 필요한 시간을 수초에서 수십초 정도로 단축시킬 수가 있고 그에 따라 열손상을 크게 줄일 수 있다. 또한, 상온으로 냉각된 식품을 포장함으로써 저렴한 가격의 포장용기를 사용할 수 있고 상온에서 저장할 수 있으므로 저장비용이 저렴한 장점이 있다. 그러나, 가공식품에 고기나 야채와 같은 고체 상태의 식품이 함유된 경우에는 액상 식품이 열 교환기에서 순간 가열되며, 고상 식품은 액상식품과의 대류에 의한 열전달로 가열된다. 이 과정에서 고상식품은 이동관 내벽이나 다른 고상식품과 부딪치거나 회전하면서 이동관 내부에서 자유롭게 운동하게 된다. 이 과정에서 액상식품과의 상대이동 속도가 발생하여 이것이 대류열전달에 영향을 미치게 된다. 이 상대이동속도에 따른 대류 열전달계수는 고상식품의 내부온도 결정에 사용되는 연속살균장치의 중요한 설계인자이다. 대류열전달계수는 연속살균장치에서 자유로이 이동하는 고상식품의 중심부의 온도를 측정하여 결정할 수 있으나 이는 현실적으로 어렵다. 따라서 본 연구에서는 고정된 고상식품에 액상식품을 이동시켜 상대속도를 재현하고 액상식품의 온도와 고상식품의 중심온도를 측정하는 장치를 개발하였으며, 각 상대속도와 액상식품의 점도 별 대류열전달계수를 결정하는 프로그램을 유한차분법을 이용하여 개발하였다. 이 장치를 분당 15, 30, 40 리터의 유량에서 유체의 점도를 0에서 15 centipoise 사이의 세 수준에서 정육면체 소고기를 모델 고상식품으로 내부 온도분포를 측정하였으며, 유한차분법 프로그램으로 대류열전달계수를 결정하였다. 대류열전달계수는 792에서 2,107 W/m$^2$로 분석되었다. 대류열전달 계수는 액상식품과의 상대속도가 증가함에 따라서 증가하였고, 점도가 증가함에 따라서는 감소하였다.

• KIEAE Journal
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• v.14 no.3
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• pp.87-95
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• 2014

The purpose of this study is to evaluate the correlation coefficients between the airtightness and sound insulation performance of Han-style windows in New Han-ok. To achieve these goals, field measurements were accomplished in 18 bedrooms of 16 Han-oks in which actual residents were living, and then lab measurements were proceeded in the reverberation lab for evaluating the sound insulation performance. Followings are results. The results of the correlation analysis between the airtightness(Air change per hour at 50 Pa, ACH50) and sound insulation performance(Sound reduction index, Rw) in bedrooms of actual Han-oks, it was found that there were no significant correlation between two evaluating values. On the other hand, it was analyzed that the correlation coefficients of total 24 structures(double casement windows, single casement window, casement and sliding windows, single sliding window, 6 types per each structure) were located on 0.6757 exponentially and 0.4154 lineary in the lab evaluating conditions. But, The results of evaluating 4 structure classificatorily, it was found that there were high correlation coefficients(0.8665~0.9273 at ACH50, 0.8414~0.9346 at Rw). These results were signified that the correlation coefficients were changed according to the each structure and case by case analysis were necessary at the same time.

• Journal of Energy Engineering
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• v.22 no.3
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• pp.307-311
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• 2013

Heating and hot water has accounted for 68% of Korea's household energy usage. Boiler makes up the bulk of the heating and hot water production. Hence a highly efficient boiler is needed in order to reduce energy consumption. A condensing boiler that recovers latent heat is known to be highly efficient. However, it is expensive and takes more space to necessitate research for improvement. In the present study, we investigated condensation heat transfer of a surface roughened by etching treatment. The etched plate showed 9.2% increase in heat transfer compared to original plate.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.31 no.6
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• pp.35-39
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• 2002

최근, 산업의 발달로 인하여 생활수준이 향상되어 대량생산과 대량소비현상이 발생하고 도시의 밀집도가 높아 단위 면적당 거주하는 인구가 증가되면서 거주지역에서 발생되는 부산물이 현저히 증가되어 환경측면에서 복합적인 환경문제에 직면해 있다. 최근까지 대책마련에 고심하고 있는 도시에서 발생된 다량의 쓰레기 처리문제는 경제적인 측면에서 몇 년 전 까지는 대부분을 매립에 의존해 왔으나, 매립 방식에 의존하였으나 지가 및 공사설비의 상승, 일부 비위생적으로 조성된 매립장에서 배출되는 침출수 및 악취 등의 환경오염이 심각한 사회문제로 대두되면서 매립장의 확보나 증설은 해당 지역주민의 반발로 지방자치단체의 골치 아픈 과제로 등장하였다. 이러한 문제점을 보완하기 위해, 최근에는 매립지 확보의 어려움과 환경보존을 위하여 쓰레기를 정적이고 위생적으로 처리하기 위하여, 소각시설이 표 1과 같이 증가하고 있으나 소각 때 발생하는 다이옥신 등 인체에 치명적인 오염을 유발시키기 때문에 소각로 건설에 대한 환경운동단체와 주민들의 반발이 거세게 제기되고 있는 현실이다. 이러한 영향에 의해 앞으로는 소각보다는 쓰레기 자체를 감량.재사용.재활용하는 처리방식이 표 1과 같이 증가되는 현실이다. 쓰레기를 소각하는 것은 제 2오염을 유발시키고, 소각장 건설비용과 유지관리에 많은 예산이 소요된다. 쓰레기소각장을 건설할 때, 인근주민이나 환경단체로부터 반대의견에 직면하게 되는데, 그 사유는 쓰레기 처리과정의 전 단계인 반입.공급 과정에서 악취발생과, 후단계인 소각설비에서 발생되는 배출가스 오염원을 완전히 제거하라는 것이다. 최근에는 소각장의 설계.시공과정에서 최대한 악취발생과 확산을 억제하는 시설에 투자를 하고 있으며, 또한 주민 편익 시설과 부대 복리 후생시설은 소각시설 주변지역 주민틀의 소각시설에 대한 부정적 이미지를 불식시키며, 외부 방문객이나 운영 관리 요원들에게 쾌적한 환경조성과 업무효율 및 근무환경의 개선에 일익을 담당하고 있다. 본 고는 환경 친화적인 쓰레기 소각장을 설계하는 측면에서 1998년도에 턴키방식으로 발주되었고 2001년 12월에 준공하여 운전하고 있는 경기도 구리시 자원회수시설의 환기설비에 적용된 설계 및 시공개념을 소개하고자 한다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.8
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• pp.44-54
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• 2018

Stress and fatigue of the distributor, an equipment of the high-pressure evaporator for the HRSG, were evaluated according to ASME Boiler & Pressure Vessel Code Section VIII Division 2. First, from the results of the piping system analysis model, reaction forces of the tubes connected to the distributor were derived and used as the nozzle load applied to the detailed analysis model of the distributor afterward. Next, the detailed model to analyze the distributor was constructed, the distributor being statically analyzed for the design condition with the steam pressure and the nozzle load. As a result, the maximum stress occurred at the bore of the horizontal nozzle, and the primary membrane stress at the shell and nozzle was found to be less than the allowable. Next, for the transient operating conditions given for the distributor, thermal analysis was performed and the structural analysis was carried out with the steam pressure, nozzle load, and thermal load. Under the transient conditions, the maximum stress occurred at the vertical downcomer nozzle, and of which fatigue life was evaluated. As a result, the cumulative usage factor was less than the allowable and hence the distributor was found to be safe from fatigue failure.

• Journal of Korean Home Economics Education Association
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• v.19 no.3
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• pp.61-76
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• 2007

The purpose of the study is to identify and understand problems existing in the middle school home economics practice rooms in Jeju Special Self-Governing Province. The findings are based on the examination and the analysis of the indoor environment and the condition of the facilities and equipment. Study method employs on-site research and a survey. The on-site research was conducted about temperature, humidity, intensity of illumination, and status of teaching instrument in 10 out of 41 middle schools in Jeju Special Self-Governing Province from August 16 to September 30, 2006. Meanwhile, the survey was implemented by mail for 95 teachers in charge of manual training and home economics education in 41 middle schools in Jeju from November 1 to 23, 2005. 64 questionnaires out of total 95 were collected, including those collected during the period of on-site research. Finally, 61 questionnaires which were effective among the answered ones were used for analysis. Collected materials were analyzed with the SPSS Win.12.0 program for frequency, percentile analysis. In conclusion, the study determines that the condition of the home economics practice rooms of the middle school in JSSGP in terms of temperature, humidity, lighting and ventilation is very inadequate. The structure of the practice room represents an inefficient work flow pattern. Further, the facilities and equipment are in a very poor condition because the facilities are old and the retention rate of teaching tools is low. Therefore, to address these problems, the study suggests that improvements on the facilities and equipment should be made and teaching tools should be replenished in accordance with the industry standard.

• Journal of the Korean Institute of Gas
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• v.19 no.4
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• pp.35-40
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• 2015

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.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.9
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• pp.627-632
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• 2011

As an innovative effort to secure economically viable heat recovery system, various fin shapes for industrial fin-tube heat exchangers have been studied for better performance. In this study, the waste gas heat recovery from four different fin shapes was experimentally performed for heat transfer rate and pressure drop. According to the tested results, the twist and wavy shape fins of rectangular type show the superior performance in terms of Goodness factor and jH/f factor ratio, whereas the circular spiral fin shows the inferior values. Experimental results shows good comparison with the numerical results with a slight discrepancy of 5%, which is quite resonable.