• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2008년도 추계학술대회B
• /
• pp.1996-2000
• /
• 2008

In autothermal reforming reaction, oxygen to carbon ratio (OCR) and steam to carbon ratio (SCR) are significant factors, which control temperature and carbon deposition into the reactor. The OCR is more sensitive than the SCR to affect the temperature distribution and reforming efficiency. In conventional operation, hydrocarbon fuel, steam, and oxygen was homogeneously mixed and injected into the reactor in order to get hydrogen-rich gas. The temperature was abruptly raised due to fast oxidation reaction in the former part of the reactor. Deactivation of packed catalysts can be accelerated there. In the present study, therefore, the effect of the oxygen distribution is introduced and investigated to suppress the carbon deposition and to maintain the reactor in the mild operating temperature (e.g., $700{\sim}800^{\circ}C$). In order to investigate the effect numerically, the following models are adopted; heterogeneous reaction model and two-medium model for heat balance.

• 전력전자학회논문지
• /
• 제27권6호
• /
• pp.535-540
• /
• 2022

DC-link capacitors are reliability-critical components in a photovoltaic (PV) inverter. Typically, the lifetime of a DC-link capacitor is evaluated by considering the voltage and hot-spot temperature of the capacitor under the specific operating condition of the PV inverter. However, the output of the PV inverter is determined by solar irradiation and ambient temperature, which vary with the seasons; accordingly, the hot-spot temperature of the capacitor also changes. Therefore, the mission profile of the PV system should be considered to effectively evaluate the reliability of the DC-link capacitor. In this study, the reliability of the DC-link capacitor of a three-level NPC inverter is comparatively analyzed with and without considering the mission profiles of the PV system, where two mission profiles recorded in Arizona and Iza are considered. The accumulated damage of the DC-link capacitor is calculated based on the lifetime model by analyzing its thermal loading. Afterward, a reliability evaluation of the DC-link capacitor is performed at the component level and then at the system level by considering all capacitors by means of Monte Carlo analysis. Results reveal the importance of performing a mission-profile-based reliability evaluation during the design of high-reliability PV inverters to achieve the target reliability performance.

• Journal of Advanced Marine Engineering and Technology
• /
• 제18권1호
• /
• pp.114-122
• /
• 1994

A cold temperature control system for the BAF(batch annealing furnace) has been established in order to reduce energy consumption to imrpove productivity and stabilize the properties of products. Therefore we confirmed a relation between annealing cycle time and atmospheric gas, changing annealing cycle time according to BAF temperature with time during heating and actual temperature measurements cold spot during soaking. The results of the temperature variation effect on the batch annealing are as follows. 1) Cooling rate is increasing gradually with increasing atmospheric gas flow, but heating rate is hardly increasing without atmospheric gas component. Heating time is reduced to one half with increasing atmospheric gas flow rate and changing of atmospheric gas component from HNx to Ax gas and annealing cycle time is reduce to 2.7 times. 2) With enlarging the difference between furnace temperature and soaking temperature at the HNx BAF, heating time becomes short, but cooling time is indifferent. 3) If temperature difference of 300.deg. C in the temperature change of cold spot according to the annealing cycle control temperature, Hi-CON/H2BAF is interchanging at each other at 26hours, but HNxBAF at 50 hours. 4) Soaking time at batch annealing cycle determination is made a decision by the input coil width, and soaking time for quality homogenization of 1219 mm width coil must be 2.5 hours longer then that of 914mm width coil for the same coil weight at Hi-CON/H2BAF. But, it is necessary to make 2 hours longer at HNxBAF.

• International Journal of Automotive Technology
• /
• 제7권6호
• /
• pp.697-702
• /
• 2006

The change in the critical speed due to surface temperature of automotive disk brakes may be analyzed both theoretically as well as experimentally. Juddering of disk brakes is closely related to its critical speed. In analyzing the critical speed, if $\sigma$ is positive, Disk develops TEI(Thermo-Elastic Instability) resulting in juddering in disk brakes. And $\sigma$ is affected not only by the critical speed but also by the initial temperature of disk surface. As the initial temperature of the disk surface rises, the critical speed decreases and juddering is developed more easily. Also, when hot spots are developed by TEI, they show large temperature difference in small local range.

• 한국윤활학회:학술대회논문집
• /
• 한국윤활학회 1992년도 제16회 학술강연회초록집
• /
• pp.50-56
• /
• 1992

공업재료의 표면은 수많은 돌기들로 구성되어 있으며 이러한 돌기들의 접촉으로 진실접촉이 이루어진다. 그러므로 마찰은 겉보기 접촉면적과는 무관하며 진실접촉면에서 일어난다. 표면의 한 돌기가 접촉면과 상대운동을 함으로 인하여 마찰열이 발생된다. 이러한 마찰에너지 발산의 결과로서 진실접촉면적 주위의 국부적인 표면 온도가 상승되며 따라서 표면의 평균온도가 상승된다. 이러한 표면온도를 결정하기 위한 이론적 및 실험적인 방법이 많이 제시되어왔다. 정적상태에서의 표면온도는 Block(1937)과 Jaeger(1942)에 의해 이론적으로 소개하였다. Jaeger는 열원의 위치와 상대적인 접촉운동 그리고 크기 및 경계조건 등의 특정한 조건 하에서 진실접촉점의 온도를 계산하였다. 이에 Bany와 Baber(1984)는 그들의 경계조건이 잘목 정의되었음을 지적하고 더욱 세분화된 경계조건으로 온도분포를 유도한 바 있다. Ling(1969)은 접촉점에서의 온도가 주변의 겉보기 접촉면적의 온도보다 훨씬 높다는 것을 수치해석으로 밝혀냈다. 본 연구는 고속정밀촬영기를 이용하여 진실접촉점에서 발생하는 Hot spot의 온도분포를 실험을 통하여 규명하고 그 결과를 Geoim과 Winer의 이론식에 적용하므로 식의 유용성을 검증하는데 그 목적이 있다.

• 한국주조공학회지
• /
• 제5권2호
• /
• pp.109-117
• /
• 1985

A two dimensional analysis of the solidification phenomena has been simulated by IAD (Implicit Alternating Direction)method for L-shaped castings with external chills. The effect of chills has been studied with the variation of chill size, shape, and their materials, and also with the variation of the pouring temperature. Three kinds of cross-sectional shapes of chills such as triangle, square, and L-shape were chosen, and graphite, cast iron, and copper for their materials. It has been shown by the computation that the hot spot at the junction of L-shaped castings can not be removed by external chills, and that the distance between the inner corner and the hot spot on the line of symmetry, as well as the solidification time of castings depend only on VHC (Volumetric Heat Capacity).

• 대한원격탐사학회지
• /
• 제33권6_2호
• /
• pp.1101-1118
• /
• 2017

급격한 도시화와 이상기후의 증가로 도시의 기온이 꾸준히 올라가고 있으며, 한 도시 안에서도 열분포 양상이 지역마다 다르게 나타나고 있어 상세한 도시 열환경 분석이 요구된다. 최근에는 위성자료를 이용한 열환경 분석이 수행되고 있으나, 위성자료는 시 공간해상도의 Trade-off 관계로 인해 정밀한 분석에 어려움이 따른다. 이 연구는 2012년부터 2016년의 대구광역시 여름철 열환경 분석을 위해, MODIS(Moderate Resolution Imaging Spectroradiometer) 1 km 공간해상도의 낮과 밤 지표면온도(낮$LST_{1km}$, 밤$LST_{1km}$)를 250 m 공간해상도(낮$LST_{250m}$, 밤$LST_{250m}$)로 상세화 시켰다. 상세화에는 기계학습 기법인 랜덤 포레스트(Random Forest)가 이용되었다. 향상된 $LST_{250m}$는 기존의 $LST_{1km}$에 비해, 대구광역시 행정동 기준 불투수면적 비율과 지표면온도가 높은 상관관계를 보여주었다. 다음으로, 상세화 된 낮과 밤$LST_{250m}$를 이용하여 Hot Spot 분석을 수행하였다. 대구광역시 행정동 중 낮과 밤 지표면온도가 Hot Spot으로 군집화된 영역을 비교하고, 토지피복도를 이용하여 그 원인을 분석했다. 낮에는 공업 및 상업지역의 비율이 높은 영역에서, 밤의 경우 주거지역의 비율이 높은 영역에서 높은 Hot Spot이 군집 되었다. 본 연구의 열환경 분석 접근은 향후 도시정책 수립 및 국민안전에 큰 기여를 할 수 있을 것으로 기대된다.

• 한국농림기상학회:학술대회논문집
• /
• 한국농림기상학회 2016년도 추계 학술발표논문집
• /
• pp.181-183
• /
• 2016

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2008년도 춘계학술대회논문집
• /
• pp.648-651
• /
• 2008

Numerical calculations are performed to simulate the film cooling effect of turbine blade tip with squealer rim. Because of high temperature of inside rim, squealer rim is damaged easily. Therefore many various cooling systems were used. The calculations are based on 100,000 Reynolds number in linear cascade model. A blade has 2% tip clearance and 8.4% rim height. The axial chord length and turning angle is 237mm, 126$^{\circ}$. Numerical calculations are performed without and with film cooling. In a film cooling in the cavity, hot spots of cavity were cooled effectively. However hot spots of suction side rim still remains. The CFD results show that the circulation flow in cavity of squealer tip affects the temperature rise of squealer rim. To maintain the blade integrity and avoid the excessive hot spot of blade, rearrangement of cooling hole is needed.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2003년도 추계학술대회 논문집 Vol.16
• /
• pp.216-219
• /
• 2003

This paper presents the analyzing method for surface temperature distribution of a cast-resin transformer. For the study, the surface temperature of the transformer winding was measured and analyzed by a infrared thermography system. Alternating voltages were applied to simulate deterioration of the specimen transformer, and the hot-spot on the transformer surface was measured to analyze the condition for the winding. The hot line condition measured to the changes in surface temperature using infrared thermography camera and was set up the based of diagnostic method of the electric power apparatus. The results ould show the possibility of remote diagnosis using internet.