• Tribology and Lubricants
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• 제38권6호
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• pp.241-246
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• 2022

This paper presents the effects of cryogenic temperature on the wear behavior of 22MnB5 blank under cold stamping. After immersing the blank in liquid nitrogen (LN2) for 10 min, a strip drawing test was performed within 10 s. The hardness was measured using the Rockwell hardness test, which increased from 165 HV at 20℃ to 192 HV at cryogenic temperature. The strip drawing test with 22MnB5 blank and SKD61 tool steel shows that for the different wear mechanisms on the tool surface with respect to temperature; adhesive wear is dominant at 20℃, but abrasive wear is the main mechanism at cryogenic temperature. As the friction test is repeated, sticking gradually increases on the tool surface at 20℃, whereas the scratch increases at cryogenic temperature. For the friction behavior, the friction coefficient rapidly increases when adhesive wear occurs, and it occurs more frequently at 20℃. The results for nanoindentation near the worn blank surface indicate a difference of 1.3 GPa at 20℃ and 0.8 GPa at cryogenic temperature compared to the existing hardness, indicating increased deformation by friction at 20℃. This occurs because thermally activated energy available to move the dislocation decreases with decreasing temperature.

• 한국농업기계학회:학술대회논문집
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• 한국농업기계학회 2000년도 THE THIRD INTERNATIONAL CONFERENCE ON AGRICULTURAL MACHINERY ENGINEERING. V.II
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• pp.246-253
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• 2000

The optimal equations to predict the soil tempratures of twelve cities in the region of the southern part of the Korea such as Changhung, Cheju, Chinju, Kwangju, Masan, Miryang, Mokpo, Muan, Pusan, Sogwipo, Ulsan, Yoosu, were suggested as function of time and soil depth and the time dependent variation and soil depth dependent distribution of temperature were analyzed for the back data of the geothermal energy utilization system design and agricultural usages. The equation form is $T(x,\;t)\;=\;T_{m}\;-\;T_{so}{\cdot}Exp(-\xi){\cdot}cos{\omega}(t\;-\;t_{o}\;-\;x\;/\sqrt{2{\alpha}{\omega}}$) and it can predict the soil temperatures well with the correlation factor of 0.98 or upwards for most data. The range of mean soil temperature was $14.99~18.53^{\circ}C$ and soil surface temperature swing, 11.65~14.54 days, soil thermal diffusivity, $0.025~0.069\;m^2/day$ except Mokpo of $0.100\;m^2/day$, and phase shift, 19.66~27.81 days. During about thirty years from 1960s to 1990s, the mean soil temperature was increased by $0.04~1.25^{\circ}C$. The temperature difference depending on soil depth was not significant.

• 토지주택연구
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• 제9권4호
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• pp.25-32
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• 2018

Application of geothermal energy in buildings has been gaining popularity as it provides the benefits of both heating and cooling a building. Among the various types of geothermal energy systems, ground-coupled heat pump system is the most commonly applied one in South Korea. A ground heat exchanger plays an important role as a heat source in winter and a heat sink in summer. For the stable operation of a ground-coupled heat pump system, a ground heat exchanger should be sized so that it provides sufficient heating and cooling energy. Heating and cooling energies generated in ground heat exchangers mainly depend on the temperature difference between the heating medium in ground heat exchangers and the surrounding ground. In addition, the performance of ground heat exchangers influences the change in ground temperature. Therefore, it is necessary to consider this interrelation between the change in the ground temperature and the performance of ground heat exchanger for an accurate estimation of its performance. However, previous thermal analysis models for ground heat exchangers are not competent enough to allow a complete understanding of this interrelation. Therefore, this study proposes a three-dimensional equivalent, transient ground heat exchanger analysis model. First, a previous thermal analysis model for ground heat exchangers, including an analytical model, a g-function, and a numerical model are analyzed. Next, to overcome the limitations of the previous models, a three-dimensional equivalent, transient ground heat exchanger model is proposed. Finally, this study validated the proposed model with the measurement data of the thermal response test, sandbox test, and TRNSYS DST model. All validation results showed a good agreement. These findings helped us to investigate the thermal performance of ground heat exchangers more accurately than the analytical models, and faster than the numerical models. Furthermore, the proposed model contributes to the design of ground heat exchangers by considering the different operation conditions of buildings.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 춘계학술대회 논문집
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• pp.418-421
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• 2009

Effects of aqueous ammonia soaking to three annual plants (hemp woody core, tobacco stalk and corn stover) awere investigated to focus on the enzymatic saccharification characteristics change by this treatment. At two different levels of treatment ($90^{\circ}C$-16 h and $45^{\circ}C$-6 days), higher temperature treatment led to more enzymatic saccharification of cellulose to glucose by commercial cellulase mixtures (Celluclast 1.5L and Novozym 342 from Novozyme Korea). Difference among annual plants were significant. corn stover was the best response to enzymatic saccharification of cellulose and xylan by comercial enzymes all treatment conditions but tobacco stalk was the worst response to all of them. chemical composition or physical structure difference may brought this difference.

• Structural Engineering and Mechanics
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• 제49권1호
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• pp.41-64
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• 2014

The main objective of this article is the exploitation of a stochastic hybrid mesh-free method based on stochastic generalized finite difference (SGFD), Newmark finite difference (NFD) methods and Monte Carlo simulation for thermoelastic wave propagation and coupled thermoelasticity analysis based on GN theory (without energy dissipation). A thick hollow cylinder with Gaussian uncertainty in mechanical properties is considered as an analyzed domain for the problem. The effects of uncertainty in mechanical properties with various coefficients of variations on thermo-elastic wave propagation are studied in details. Also, the time histories and distribution on thickness of cylinder of maximum, mean and variance values of temperature and radial displacement are studied for various coefficients of variations (COVs).

• 에너지공학
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• 제26권4호
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• pp.100-106
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• 2017

재가열로에서 분위기 온도에 따른 소재온도 변화를 예측하기 위해 SUS304, SS400 소재가 적용되었으며, 소재내부에 깊이 방향으로 열전대를 5개씩 설치한 후 분위기 온도를 1200도까지 상승시켰다. 그 결과 소재온도는 평균적으로 1150도 이상 도달했으며, 국부적으로 소재 표면과 내부는 10도 이상의 온도차를 나타내었다. 실험결과의 타당성 검증을 위해 열모델을 적용하여 수치해석 되었으며, 실험결과 대비 해석결과는 출구 평균온도 기준 15도 이내의 범위에서 오차를 나타내었다. 또한 오차는 SUS304 소재에 비해 비열 변화가 큰 SS400 소재에서 상대적으로 높게 나타났다. 결론적으로 재가열로에서 소재 온도는 분위기 온도 제어를 통해 달성할 수 있으며, 분위기 온도에 따른 소재 온도 변화는 출구에서 3% 오차범위 내에서 열모델을 사용하여 유추할 수 있음이 실험적으로 증명되었다.

• 에너지공학
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• 제12권4호
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• pp.267-273
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• 2003

Emulsion 연료는 연료절감과 오염방지특성에 의하여 많은 관심을 끌고 있다. 본 연구에서는 B-C유와 Emulsion 연료(B-C유와 폐수를 혼합하여 만든 연료)의 연소효율을 비교 분석하였다. 보일러의 양쪽에 R-Type Thermocouple과 광학온도계를 설치하였고, 연소가스배출구에 연소측정기를 설치하여 B-C유와 Emulsion 연료의 연소시 화염의 온도, 연소율 및 배기가스 농도를 측정 비교하였다. 이에 대한 실험 결과로서, 보일러 전$.$후반부의 화염온도는 B-C유의 화염온도보다 약 5$0^{\circ}C$ 낮았고, 이러한 온도차이의 원인은 Emulsion 연료의 폐수 속 수분 잠열로 인한 것으로 사료되어진다. 또한 Emulsion연료를 사용하였을 때 배출가스의 분석 결과는 오염물질의 같소 및 CO 농도 또한 매우 낮게 측정되어짐을 나타내고 있다. 3-C유와 Emulsion 연료의 연소 효율은 각각 85.5%와 84.8%이다.

• 대한기계학회논문집B
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• 제36권8호
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• pp.821-828
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• 2012

CPU의 발열량 증가는 서버를 통과하는 배출공기와 유입공기와의 상당한 온도차를 발생시키고 이로 인해 배출공기의 재순환 현상과 유입공기의 바이패스 현상이 발생한다. 이는 데이터센터 냉각시스템의 효율저하를 발생시킨다. 따라서 CRAC의 제어를 통해 유입공기와 배출공기를 분리하는 것이 데이터센터 냉각시스템의 중요한 목표이다. 본 연구에서는 CFD 해석 코드인 ICEPAK을 이용하여 데이터센터에 대한 수치해석을 진행하였다. 실내부로 유입되는 공기유량의 변화에 따른 CPU의 온도와 실 전체의 온도분포를 분석하였다. 이를 통해 CPU의 발열량에 따른 최적 유입유량을 선정하였다. CPU 발열량이 100, 120, 140 W인 경우 유입유량이 $0.15m^3/s$인 지점에서 발열제거와 온도분배가 가장 잘 이루어졌다. RTI 성능지표를 이용하여 해석결과를 검증하였고 RTI 값이 81인 경우 가장 안정적인 결과를 보였다.

• 설비공학논문집
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• 제25권3호
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• pp.150-155
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• 2013

Usually, a window tends to have a lower thermal performance, than that of an ordinary wall. This study analyzes the enhancement of thermal performance of a window, when a Thermal Insulation Shutter is installed. The analyses were conducted at the laboratory, and with a full-scale mockup house, and the U-factor and heating load were examined. The laboratory results show that the U-factor increased by approximately 28%, when a Thermal Insulation Shutter was installed. The temperature difference was about $5^{\circ}C$, and this shows that the Thermal Insulation Shutter enhances the thermal performance of the window, when installed. The mockup house was used to calculate the heating load; the heating load was reduced by more than 41%, and shows that the installation of a Thermal Insulation Shutter is an effective way to reduce heating energy consumption.

• 설비공학논문집
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• 제28권2호
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• pp.75-80
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• 2016

There are three types of dehumidification systems : refrigeration dehumidification method, desiccant dehumidification method and hybrid dehumidification method. The first method involves removing moisture by condensation below the dew point, the second method involves absorption by a desiccant material and the last is an integration method. However, the refrigeration dehumidification system consumes too much power and controlling the humidity ratio is difficult. The desiccant dehumidification system uses less power but it has problems of environmental pollution. The hybrid dehumidification system has the disadvantage of a high initial cost. On the other hand, the energy consumption of the membrane based dehumidification system is lower than for the refrigeration dehumidification system. Also, it is an environmentally friendly technology. In this study, the performance parameters are evaluated for the dehumidification system using a hollow fiber membrane. Available area, duct side dry-bulb temperature, sweep gas flux (flow rate) and LMPD (Log Mean Pressure Difference) were used as the performance parameters.