• Title/Summary/Keyword: CHANGE OF TEMPERATURE

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Effects of decay heat and cooling condition on the reactor pool natural circulation under RVACS operation in a water 2-D slab model

  • Min Ho Lee ;Dong Wook Jerng ;In Cheol Bang
    • Nuclear Engineering and Technology
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    • v.55 no.5
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    • pp.1821-1829
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    • 2023
  • The temperature distribution of the reactor pool under natural circulation induced by the RVACS operation was experimentally studied. According to the Bo' based similarity law, which could reproduce the temperature distribution of the working fluid under natural circulation, SINCRO-2D facility was designed based on the PGSFR. It was reduced to 1 : 25 in length scale, having water as a simulant of the sodium, which is the original working fluid. In general, temperature was stratified, however, effect of the natural circulation flow could be observed by the entrainment of the stratified temperature. Relative cooling contribution of the upper plenum (narrow gap) and lower plenum was approximately 0.2 and 0.8, respectively. In the range of decay heat from 0.2% to 1.0%, only the magnitude of the temperature was changed, while the normalized temperature maintained. Boundary temperature distribution change made a global temperature offset of the pool, without a significant local change. Therefore, the decay heat and cooling boundary condition had no significant effect on temperature distribution characteristics of the pool within the given range of the decay heat and boundary temperature distribution.

A Study on the Effects of Heat Pump Using Standing Column Well on Soil and Groundwater Microorganisms (스탠딩컬럼웰을 적용한 지열히트펌프의 토양 및 지하수 미생물에 대한 영향 연구)

  • Jun, Jungeui;Park, Sisam;Na, Sangmin;Rhee, Keonjoong;Park, Jaewoo
    • Journal of the Korean GEO-environmental Society
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    • v.10 no.7
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    • pp.93-101
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    • 2009
  • Standing column well (SCW) heat pump system produces geothermal energy by the heat exchange of the groundwater. If SCW system changed the temperature of soil and groundwater, it could also change species or population of microorganisms. Therefore it is needed to research about the effect of temperature change on microorganisms to use eco-friendly geothermal energy. We produced the simulative heat pump system (SHPS) and observed the change of the soil temperature in SHPS. Characteristic analysis of microorganisms isolated from soil was performed and groundwater temperature variation was evaluated. Also the bleeding effect in SHPS was investigated and the results are included. As the results, the population of microorganisms was increased about 90%, as the groundwater temperature increased 2-3 celsius degree. However the species of microorganism was little influenced by the temperature change of the soil.

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Climate Change and Coping with Vulnerability of Agricultural Productivity (기후변화와 농업생산의 전망과 대책)

  • 윤성호;임정남;이정택;심교문;황규홍
    • Korean Journal of Agricultural and Forest Meteorology
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    • v.3 no.4
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    • pp.220-237
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    • 2001
  • Over the 20th century global temperature increase has been 0.6$^{\circ}C$. The globally averaged surface temperature is projected to increase by 1.4 to 5.8$^{\circ}C$ over the period 1990 to 2100. Nearly all land areas will have higher maximum temperature and minimum temperature, and fewer cold days and frost days. More intense precipitation events will take plate over many areas. Over most mid-latitude continental interiors will have increased summer continental drying and associated risk of drought. By 2100, if the annual surface temperature increase is 3.5$^{\circ}C$, we will have 15.9$^{\circ}C$ from 12.4$^{\circ}C$ at present. Also the annual precipitation will range 1,118-2,447 mm from 972-1,841 mm at present in Korea. Consequently the average crop periods for summer crops will be 250 days that prolonged 32 days than at present. In the case of gradual increase of global warming, an annual crop can be adapted to the changing climate through the selection of filial generations in breeding process. The perennial crops such as an apple should be shifted the chief producing place to northern or high latitude areas where below 13.5$^{\circ}C$ of the annual surface temperature. If global warming happens suddenly over the threshold atmospheric greenhouse gases, then all ecosystems will have tremendous disturbance. Agricultural land-use plan, which state that farmers decide what to plant, based on their climate-based advantages. Therefore, farmers will mitigate possible negative imparts associated with the climate change. The farmers will have application to use agricultural meteorological information system, and agricultural long-range weather forecast system for their agroecosystems management. The ideal types of crops under $CO_2$ increase and climate change conditions are considered that ecological characteristics need indispensable to accomplish the sustainable agriculture as the diversification of genetic resources from yield-oriented to biomass-oriented characteristics with higher potential of $CO_2$ absorption and primary production. In addition, a heat-and-cold tolerance, a pest resistance, an environmental adaptability, and production stability should be also incorporated collectively into integrated agroecosystem.

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Effect of Annealing Temperature on the Operation of Phase-Change Memory (상변화 메모리 소자 동작 특성에 미치는 열처리 온도 효과)

  • Lee, Seung-Yun;Park, Young-Sam
    • Journal of the Korean Vacuum Society
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    • v.19 no.2
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    • pp.155-160
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    • 2010
  • The effect of process temperature of a final annealing step in the fabrication of phase change memory (PCM) devices was investigated. Discrete PCM devices employing $Ge_2Sb_2Te_5$ (GST) films as an active element were made in a pore-style configuration, and they were annealed at various temperatures ranging from 160 to $300^{\circ}C$. The behaviors of cell resistance change from SET resistance to RESET resistance were totally different according to the annealing temperatures. There was a critical annealing temperature for the fabrication of normal PCM devices and abnormal operations were observed in some devices annealed at temperatures lower or higher than the critical temperature. Those influences of annealing temperature seem closely related to the thermal stability of a top electrode/GST/heating layer multilayer structure in the PCM devices.

Double magnetic entropy change peaks and high refrigerant capacity in Gd1-xHoxNi compounds in the melt-spun form

  • Jiang, Jun-fan;Ying, Hao;Feng, Tang-fu;Sun, Ren-bing;Li, Xie;Wang, Fang
    • Current Applied Physics
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    • v.18 no.12
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    • pp.1605-1608
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    • 2018
  • $Gd_{1-x}Ho_xNi$ melt-spun ribbons were fabricated by a single-roller melt spinning method. All the compounds crystallize in an orthorhombic CrB-type structure. The Curie temperature ($T_C$) was tuned between 46 and 99 K by varying the concentration of Gd and Ho. A spin reorientation (SRO) transition is observed around 13 K. Different from $T_C$, the SRO transition temperature is almost invariable for all compounds. Two peaks of magnetic entropy change (${\Delta}S_M$) were found. One at the higher temperature range was originated from the paramagnet-ferromagnet phase transition and the other at the lower temperature range was caused by the SRO transition. The maximum of ${\Delta}S_M$ around $T_C$ is almost same. The other maximum of ${\Delta}S_M$ around SRO transition, however, had significantly positive relationship with x. It reached a maximum about $8.2J\;kg^{-1}\;K^{-1}$ for x = 0.8. Thus double large ${\Delta}S_M$ peaks were obtained in $Gd_{1-x}Ho_xNi$ melt-spun ribbons with the high Ho concentration. And the refrigerant capacity power reached a maximum of $622J\;kg^{-1}$ for x = 0.6. $Gd_{1-x}Ho_xNi$ ribbons could be good candidate for magnetic refrigerant working in the low temperature especially near the liquid nitrogen temperature range.

Estimation of Characteristics Change on Transverse Mode PZT Vibrator Under Space Environment (우주환경하에서 횡진동 모드 PZT진동자의 특성변화 예측)

  • Lee, Sang Hoon;Moon, Guee Won;Yoo, Seong Yeon;Kim, Jung Soon;Kim, Moo Joon
    • The Journal of the Acoustical Society of Korea
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    • v.31 no.8
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    • pp.514-522
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    • 2012
  • The temperature dependence of the characteristics in a PZT-5 piezoelectric ceramic vibrator with the transverse mode was investigated in the range of $-100^{\circ}C$ to $90^{\circ}C$ using a thermal vacuum chamber to utilize the vibrator in aerospace industries. As the results, at room temperature, the resonant and anti-resonant frequencies had the minimum value, whereas, the dielectric constant increased linearly from about 2500 to 7500 in the given temperature range. The mechanical loss decreased linearly from 0.08 to 0.03. Through the regression analysis, the temperature dependence functions of the characteristics were derived to linear and square regression functions. Applying the functions, the input admittance characteristics of the piezoelectric vibrator were calculated, and the results showed good agreement with measured ones. It can be confirmed that this method is useful to estimate the characteristics change of the piezoelectric vibrator caused by the temperature change under the space environment.

Developing Models for Patterns of Road Surface Temperature Change using Road and Weather Conditions (도로 및 기상조건을 고려한 노면온도변화 패턴 추정 모형 개발)

  • Kim, Jin Guk;Yang, Choong Heon;Kim, Seoung Bum;Yun, Duk Geun;Park, Jae Hong
    • International Journal of Highway Engineering
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    • v.20 no.2
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    • pp.127-135
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    • 2018
  • PURPOSES : This study develops various models that can estimate the pattern of road surface temperature changes using machine learning methods. METHODS : Both a thermal mapping system and weather forecast information were employed in order to collect data for developing the models. In previous studies, the authors defined road surface temperature data as a response, while vehicular ambient temperature, air temperature, and humidity were considered as predictors. In this research, two additional factors-road type and weather forecasts-were considered for the estimation of the road surface temperature change pattern. Finally, a total of six models for estimating the pattern of road surface temperature changes were developed using the MATLAB program, which provides the classification learner as a machine learning tool. RESULTS : Model 5 was considered the most superior owing to its high accuracy. It was seen that the accuracy of the model could increase when weather forecasts (e.g., Sky Status) were applied. A comparison between Models 4 and 5 showed that the influence of humidity on road surface temperature changes is negligible. CONCLUSIONS : Even though Models 4, 5, and 6 demonstrated the same performance in terms of average absolute error (AAE), Model 5 can be considered the optimal one from the point of view of accuracy.

Analysis of Road Surface Temperature Change Patterns using Machine Learning Algorithms (기계학습을 이용한 노면온도변화 패턴 분석)

  • Yang, Choong Heon;Kim, Seoung Bum;Yoon, Chun Joo;Kim, Jin Guk;Park, Jae Hong;Yun, Duk Geun
    • International Journal of Highway Engineering
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    • v.19 no.2
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    • pp.35-44
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    • 2017
  • PURPOSES: This study suggests a specific methodology for the prediction of road surface temperature using vehicular ambient temperature sensors. In addition, four kind of models is developed based on machine learning algorithms. METHODS : Thermal Mapping System is employed to collect road surface and vehicular ambient temperature data on the defined survey route in 2015 and 2016 year, respectively. For modelling, all types of collected temperature data should be classified into response and predictor before applying a machine learning tool such as MATLAB. In this study, collected road surface temperature are considered as response while vehicular ambient temperatures defied as predictor. Through data learning using machine learning tool, models were developed and finally compared predicted and actual temperature based on average absolute error. RESULTS : According to comparison results, model enables to estimate actual road surface temperature variation pattern along the roads very well. Model III is slightly better than the rest of models in terms of estimation performance. CONCLUSIONS : When correlation between response and predictor is high, when plenty of historical data exists, and when a lot of predictors are available, estimation performance of would be much better.