• International Journal of Air-Conditioning and Refrigeration
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• 제15권3호
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• pp.122-128
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• 2007

Heat transfer distributions and friction factors in square channels (3.0 ${\times}$ 3.0 cm) with twisted tape inserts and with twisted tape inserts plus interrupted ribs are respectively investigated. The rib height-to-channel hydraulic diameter ratio, $e/D_h$, is kept at 0.067 and test section length-to-hydraulic diameter ratio, $L/D_h$ is 30. The square ribs are arranged to follow the trace of the twisted tape and along the flow direction defined as axial interrupted ribs. The twisted tape is 0.1 mm thick carbon steel sheet with diameter of 2.8 cm, length of 90 cm, and 2.5 turns. Two heating conditions are investigated for test channels with twisted tape inserts and rib turbulators: (1) electric heat uniformly applied to four side walls of the square duct, and (2) electric heat uniformly applied to two opposite ribbed walls of the square channel. Results show that the twisted tape with interrupted ribs provides a higher overall heat transfer performance over the twisted tape with no ribs.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2402-2407
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• 2007

Heat transfer distributions and friction factors in square channels (3.5 ${\times}$ 3.5 cm) with twisted tape inserts and with twisted tape inserts plus interrupted ribs are respectively investigated. Tests are performed for Reynolds numbers ranging from 8,900 to 29,000. The rib height-to-channel hydraulic diameter, e/Dh, is kept at 0.057 and test section length-to-hydraulic diameter, L/Dh is 30. The twisted tape is 0.1 mm thick carbon steel sheet with diameter of 3.3cm, length of 90cm, and 2.5 turns. The square ribs are arranged to follow the trace of the twisted tape and along the flow direction defined as axial interrupted ribs. Each wall of the square channel is composed of isolated aluminum sections. The following conclusions from the experimental study were drawn as: 1) In the 4 heating wall channel with twisted tape inserts, Nusselt number based on bottom wall temperature is enhanced by 1.2 - 1.6 times if adding the axial interrupted ribs on the bottom wall only. 2) The twisted tape with interrupted ribs under the two-sided heating condition produces the highest heat transfer performance. 3) Friction factor data obtained for the square channel with twisted tape inserts plus axial interrupted ribs are less than those in the past publications for circular tubes with axial interrupted ribs and twisted tape inserts.

• Nuclear Engineering and Technology
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• 제54권10호
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• pp.3962-3973
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• 2022

Several critical heat flux (CHF) correlations including the look-up table in the MARS code have been assessed for the prediction of CHF in a downward-flow narrow rectangular channel. For the assessment, we built an experiment database that covers pressures between 1.01 and 39.0 bar, gap sizes between 1.09 and 6.53 mm, mass fluxes up to 25,772 kg/m²s, and under one-sided and two-sided heating conditions. The results of the assessment showed that the Kaminaga correlation has the best overall prediction compared to others. However, because the correlation uses global variables, such as inlet and outlet subcooling and total heat transfer area, it is difficult to use in a system code. A new CHF correlation is then proposed by replacing the global variables in the Kaminaga correlation with local ones and adding correction factors to consider the effect of gap size, mass flux, and the number of heating walls. Additional correction factor is added to consider the effect of inlet subcooling. It is shown that the new one is better than the Kaminaga correlation and it is easy to implement to any system code.

• 동아시아식생활학회지
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• 제14권3호
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• pp.294-301
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• 2004

This study was conducted to investigate the quality assessment of performance of the university foodservice. Self administered questionnaires were collected from 305 students living in Incheon. Statistical data analysis was completed using a SPSS v. 10.0 program. The results were summarized as follows: 61.4% of male students and 48.1% of female students responded to have lunch regularly. Only 23.4% of male students and 14.1% of female students used the university foodservice daily. Reasons for the irregularity of lunch were responded as “lecture”, “eating when I want” and “appointment with friends”, etc. The quantity, temperature, nutritional value, appearance, hygiene, taste and freshness of foods and price of menus were evaluated as appropriate but using seasonal foods, number of side-dishes, etc. as unsatisfactory. Service speed, cloth hygiene, neatness and kindness of employee were evaluated as appropriate. For the facilities of foodservice, counter location, menu board and lighting facilities were evaluated as appropriate but heating facilities, disposition of tables and chairs of dining hall were as unsatisfactory. Sanitation of floors and walls of dining hall, restroom and utensils, etc. was evaluated as low.

• 대한기계학회논문집B
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• 제21권1호
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• pp.15-23
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• 1997

An experimental investigation of two-dimensional steady natural convection cooling in a vertical open top cavity with conducting side walls of finite thickness is presented. The various heat-generating discrete heaters are located on one vertical wall of the cavity. When each heater dissipates different amount of power, the purpose of the work is to obtain the optimal array condition of the heaters. The four cases of non-uniform heating conditions are considered. The temperature fields in the cavity were visualized by the interferometer and local temperatures of the vertical wall were measured by thermocouples. The heaters were arranged in two configurations: flush-mounted on a vertical wall or protruding from the wall about 4.5 mm. The vertical wall was constructed out of copper or epoxy-resin sheet. Experiments have been conducted for air with constant Prandtl number(Pr=0.7), the aspect ratio of 4.6, 7.5, 9.5, power input in the range of 0.9 W ~ 4.2 W. For the enhancement of the cooling effectiveness, the upper and lower of vertical wall would give the better position for the heaters of higher heat flux.

• 한국터널지하공간학회 논문집
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• 제19권1호
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• pp.29-39
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• 2017

본 연구에서는 3면이 지중과 접하는 형태의 전력구에서 온도상승을 방지하기 위한 환기시스템 설계에 필요한 벽면에서 열전달계수 등 열설계 자료를 수치해석적인 방법으로 검토하였다. 수치해석 모델은 터널 벽체에서의 열전달을 고려하기 위해서 전력구의 터널의 라이닝을 포함하는 것으로 모델링하였으며, 전력구에 설치되는 전력케이블의 발열량(117~468 kW/km), 전력구내 풍속(0.5~4.0 m/s)에 따른 터널내 공기온도 및 벽체온도, 벽체를 통한 발열량을 CFD시뮬레이션에 의해서 구하였다. 또한 해석결과로부터 벽체열전달계수를 계산하고 환기구간의 터널내 공기온도를 유지하기 위한 한계거리를 검토하였다. 벽체표면에서 대류열전달계수는 입구영역에서는 불안정한 변화를 보이나 약 100 m정도의 이후에는 일정한 값에 수렴한다. 터널벽체열전달계수는 풍속에 따라 $3.1{\sim}9.16W/m^2^{\circ}C$정도이며, 이를 무차원식으로 표현하면 $Nu=1.081Re^{0.4927}({\mu}/{\mu}_w)^{0.14}$이 된다. 열저항 해석기법에 의해서 터널내 온도 예측방법을 제시하였으며, 약 3%이내의 편차로 예측이 가능한 것으로 평가되었다.

• 한국환경생태학회지
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• 제29권6호
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• pp.936-946
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• 2015

본 연구는 도심의 열환경 개선 및 건물에너지저감 효과가 입증된 벽면녹화 중 기존 건물에 적용 가능한 패널형 벽면녹화 식재기반 유형에 따른 건물에너지 저감 성능을 분석하고자 하였다. 식재기반 유형은 총 4가지 유형으로 하였으며, Case A는 벽면녹화가 미적용된 유형으로 콘크리트 + 단열재로 구성하였다. Case B는 식재층 + 무기다공성블록 + 콘크리트 + 단열재로 구성하였으며, Case C는 식재층 + 코코피트블록 + 콘크리트 + 단열재로 구성하였다. Case D는 식재층 + 마사토블록 + 콘크리트 + 단열재로 구성하였다. 분석항목으로는 열전도율, 열관류율, 건물에너지시뮬레이션을 실시하였다. 식재기반 유형별 열전도율은 Case C(0.053W/mK) > Case B(0.1W/mK) > Case D(0.17W/mK)의 순이었다. 에너지시뮬레이션 결과 중 단위면적당 냉방피크부하저감은 미적용인 Case A 대비 Case C(1.19%) > Case B(1.14%) > Case D(1.01%)이며, 난방피크부하저감은 Case A 대비 Case C(2.38%) > Case B(1.82%) > case D(1.50%)로 산정되었다. 연간 냉 난방부하저감은 미적용 Case A대비 벽면녹화 유형에서 0.92~1.28% 저감률을 나타내었다. 연간 냉난방에너지사용량은 3.04~3.22%의 저감률을 보였으며, 1차에너지사용량은 Case A대비 나머지 유형에서 평균 5,844 kWh/yr의 저감량을 보였다. 연간 이산화탄소발생량은 벽면녹화 미적용 Case A대비 평균 996kg 저감량을 보였다. 식재위치별 에너지성능평가 결과 동향 > 서향 > 남향 > 북향 순이었다. 벽면녹화비율에 따른 에너지성능평가 결과 녹화 비율이 높아짐에 따라 양호한 결과를 나타내었으며, 20~80%의 비율보다 100% 녹화시 약 2배의 저감률을 보였다.