• 한국수소및신에너지학회논문집
• /
• 제34권5호
• /
• pp.514-525
• /
• 2023

This study conducted numerical simulations with the purpose of analyzing the impact of variations in outlet pressure conditions under extreme temperature conditions on the fluid dynamics and performance of a check valve utilized in hydrogen refueling systems. Under the extreme temperature conditions, changes in outlet pressure conditions of the check valve were investigated to analyze velocity distributions, pressure distributions, and temperature distributions in the operational and connection regions. The analysis results indicated that changes in outlet pressure had a significant influence on the internal temperature variation of the check valve. Furthermore, due to density variations in the connection region caused by the cooling effect of excessively cooled hydrogen, a bias in the primary flow direction towards the lower part of the valve outlet was observed in the outlet area. Through a comparison of the results of the valve's inherent flow performance, represented by the flow coefficient, it was observed that when the pressure difference between the inlet and outlet was below 0.37 MPa, sufficient flow was not ensured.

• Journal of Biosystems Engineering
• /
• 제24권4호
• /
• pp.335-342
• /
• 1999

Air and flue gas temperature distributions in the space heater for greenhouse were measured to develop a thermal design technology for the space heater. Also, the characteristics of the fan supplying air to the space heater were investigated. The temperature of the flue gas inside the flue gas tube was linearly decreased as the lenght of than those of the flue gas with the oxygen concentration of 8.25% at the last exit of the second flue gas tube. Thus, the operating efficiency of the space heater could be increased with low air ratio decreased exhausting gas temperature and saved the energy consumption with decreased excess air flow. The temperature of the air supplied by fan was increased slowly around the first flue gas tube, meanwhile, increased sharply around the second flue gas tube due to large LMTD (Logarithmic Mean Temperature Difference) at the first flue gas tube than which of the second flue gas tube.

• 한국철도학회논문집
• /
• 제9권6호
• /
• pp.695-700
• /
• 2006

This study investigates the effects of the material properties and the fatigue behavior in the SM490A material specimens due to the low-temperature atmosphere. In the fatigue behavior, the low-temperature affects the fatigue life. As the temperature get low, the fatigue limit increase, also As the yield strength and the tensile strength increase, the impact absorbed energy decrease. The difference of fatigue lift represents to normal distribution and it is larger between the room temperature and the low temperature, but in the result of the cumulative density function, the effect of temperature is not too large on it.

• 생물환경조절학회지
• /
• 제29권3호
• /
• pp.259-264
• /
• 2020

본 연구에서는 겨울철 보온으로 인해 야간 및 새벽에 상대습도가 높아지는 온실에 대향류형 환기장치를 설치하고 그 효과를 분석하였다. 대향류형 환기장치는 크기 0.96×0.65×0.82(W×D×H, m)의 케이스에 크기 0.54×0.40×0.75(W×D×H, m)의 PE소재의 열교환 소자와 급기와 배기를 위한 송풍팬(풍량 6,800㎥/h, 소비전력1.7kW) 2대가 내부에 있다. 환기장치는 총 2대를 이용하였으며 토마토의 적정 생육 환경을 고려하여 설정 습도를 80%하고 18시부터 익일 8시까지 온실 내 온도 및 습도를 측정하고 분석하였다. 관행 온실에서 야간 평균 온도 및 습도는 14.9℃, 82.8%, 시험구 온실에서 야간 평균 온습도는 15.1℃, 79.9%로 측정되어 온도는 0.1℃, 습도는 약 3% 차이가 났다. 온실 평균 온도 및 습도를 월별로 비교하고 독립표본 t검정을 통해 분석해 본 결과, 유의수준 1%에서 각 월의 온도는 차이가 없는 것으로 나타났으며 습도는 차이가 있다고 판단된다. 따라서 대향류형 환기장치의 사용이 온실의 습도를 관리하고 작물 생육에 적합환 환경을 조성하여 작물 생산성 향상에 도움을 줄 수 있다고 판단된다. 이 외에도 환기장치 사용에 따른 난방비 증가와 같은 손실적 요소와 이익적 요소를 복합적으로 고려한 추가적인 연구도 필요할 것으로 사료된다.

• 한국전자통신학회논문지
• /
• 제10권5호
• /
• pp.623-628
• /
• 2015

현재의 시설하우스에서의 난방 방식은 한 곳에 고정되어져서 위치에 따른 온도 편차가 심해 질 수밖에 없는 실정이다. 채소나 과일 작물 등을 재배하는 시설하우스는 적정 온도의 유지가 필수적인데 하우스 내부의 상하 온도 차이로 인해 적정 난방 또는 냉방을 위한 에너지 소모가 많다. 본 논문에서는 하우스 내부의 공기 순환을 효율적으로 할 수 있는 새로운 형태의 난방 방식인 수직형 교반 히터 자동 제어 시스템을 제안한다. 시설하우스 상 하부의 온도를 이용하여 수직형 교반 히터의 공기 순환 팬과 히팅을 상황에 맞게 독립적으로 제어함으로써 최소한의 전기 소비로 난방의 효율을 극대화 시켜 계획 가능한 작물 생산과 난방비 절감이 가능하다.

• 태양에너지
• /
• 제18권1호
• /
• pp.57-67
• /
• 1998

쾌적한 실내환경을 유지하고, 공기조화 설비에 있어서 냉방동안 에너지를 절약하기 위한 실내로 유입되는 냉기의 열유동 특성에 관한 연구이다. 실물 크기의 모형room에 대하여 실내로 유입하는 냉기의 유속(1, 2, 3m/s)과 실내온도와 유입냉기와의 기준온도차(10, 20, $30^{\circ}C$)를 변화시키고, 또한 유입구 형상을 아네모스형과 베인형으로 하면서 실내의 온도분포를 파악하여 열유동 특성 및 혼합특성에 대하여 고찰하였다. 연구 결과, 아네모스형이 베인형보다 혼합이 빨리 진행되었고 유입속도에 의한 영향이 기준 온도차에 의한 영향보다 지배적이었다.

• Journal of Mechanical Science and Technology
• /
• 제18권12호
• /
• pp.2182-2189
• /
• 2004

In the recent years, environmentally conscious design and manufacturing technologies have attracted considerable attention. The coolants, lubricants, solvents, metallic chips and discarded tools from manufacturing operations will harm our environment and the earth's ecosystem. In the present work, the Tukey method of multiple comparisons is used to select the minimum level of coolant required in a turning process. The amount of coolant is varied in 270 designed experiments and the parameters cutting temperature, surface roughness, and specific cutting energy are carefully evaluated. The effects of coolant mix ratio as well as the amount of coolant on the turning process are studied in the present work. The cutting temperature and surface roughness for different quantity of coolant are investigated by analysis of variance (ANOVA) - test and a multiple comparison method. ANOVA-test results signify that the average tool temperature and surface roughness depend on the amount of coolant. Based on Tukey's Honestly Significant Difference (HSD) method, one of the multiple comparison methods, the minimum level of coolant is 1.0 L/min with 2% mix ratio in the aspect of controlling tool temperature. F-test concludes that the amount of coolant used does not have any significant effect on specific cutting energy. Finally, Tukey method ascertains that 0.5 L/min with 6% mix ratio is the minimum level of coolant required in turning process without any serious degradation of the surface finish. Considering all aspects of cutting, the minimum coolant required is 1.0 L/min with 6% mix ratio. It is merely half the coolant currently used i.e. 2.0 L/min with 10% mix ratio. Minimal use of coolant not only economically desirable for reducing manufacturing cost but also it imparts fewer hazards to human health. Also, sparing use of coolant will eventually transform the turning process into a more environment-conscious manufacturing process.

• 한국진공학회지
• /
• 제17권4호
• /
• pp.302-310
• /
• 2008

진공 챔버 내부에서 열접촉된 시료가열장치와 시료 사이의 열전달 현상을 고찰하였다. 열전달은 가스 유량과 기체 압력에 따른 대류현상, 시료와 접촉하는 기판가열장치의 표면 거칠기 및 접촉압력에 따른 전도현상, 기판가열장치의 표면 방사율에 따른 복사현상으로 나누어 푸리에 식과 슈테판-볼츠만 식을 이용하여 열흐름 값을 분석하였다. 실험은 시료가열장치의 온도를 $100\;-\;500^{\circ}C$ 사이에서 일정하게 유지하면서 300 mTorr - 1 Torr 사이의 압력에 따른 시료의 온도를 측정하고, 푸리에 식과 슈테판-볼츠만 식을 이용하여 열흐름 값을 계산하였다. 열흐름 값의 산출에 사용된 푸리에 계수의 정확성을 확인하기 위해, 역으로 열흐름 값으로부터 온도차를 구하는 방법을 사용하였으며 0.33 % 오차 내에서 재현됨을 확인하였다.

• 한국환경과학회지
• /
• 제30권12호
• /
• pp.1067-1079
• /
• 2021

The coastal water is a space where salmon (Oncorhynchus keta), critical energy-conveying mediator, stay to adapt to different environments while traveling between ocean and river ecosystems for spawning and growth. The mid-eastern coast of Korea (MECW) is the southern limit of salmon distributed in the North Pacific Ocean. Understanding the distribution and migration characteristics of salmon in the MECW is important for the prediction of changes in the amount and distribution of salmon related to changes in the future marine environment. We analyzed the relationship between the salmon migratory timing ascending the Wangpi river and change in vertical seawater temperature and tidal elevation. Overall results highlight that (1) Salmon began to ascend the river when the sea surface water temperature (SST) decreased below 20℃; (2) The number of salmon ascending the river increased when the temperature difference between the upper and lower layers decreased, but decreased when the temperature difference was higher than 5℃; (3) The number of salmon ascending the river peaked, when the SST was 18℃-19℃ and sea levels rose at high tide. This study provide important insight into predicting changes in the ecosystem energy circulation through climate change at its southern distribution limit.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1999년도 하계학술대회 논문집 D
• /
• pp.1768-1770
• /
• 1999

Porous silicon were prepared under various anodization condition on n-Si substrates. Chronoamperometric curves of porous silicon depended on potentials, composition and temperature of electrolytes. and intensity of UV irradiation. Anodic current density decreased continuously at low potential $(\leq0.5V)$ but increased at high potentials (>2V vs. Ag QRE). the difference in chronoamperometric curve is due to different activation energy in the processes involved in porous silicon formation.