• Title/Summary/Keyword: temperature cycles

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Characteristics of Flame Hardening Process for 12Cr Steels (12Cr 강의 이동 화염경화 공정 특성)

  • Kim Gwang-Ho;Lee Min-Ku;Kim Kyeong-Ho;Kim Whung-Whoe;Rhee Chang-Kyu;Kim Gil-Mu
    • Journal of the Korean institute of surface engineering
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    • v.39 no.2
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    • pp.49-56
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    • 2006
  • In this study, the movable flame hardening process of 12Cr steel for a uniform hardness and desirable residual stress have been investigated. For this, the temperature cycles have been controlled accurately as a function of the three processing variables, the flame intensity $I_f$, the scanning velocity $V_s$, and the initial flame holding time $t_h$, where the standard surface temperature $T_{s,\;max}$, was maintained at $960^{\circ}C$. The optimized conditions were $V_s=0.68mn/s\;and\;t_h=67sec$ for the $C_3H_8:O_2\;=\;5:20l/min,\;V_s=0.80mm/s$ and $t_h=56sec$ for the $C_3H_8:O_2=6:24l/min,\;V_s=1.01mm/s\;and\;t_h=48sec$ for the $C_3H_8:O_2=7:28l/min,\;and\;V_s=1.15mm/s$ and $t_h=39sec$ for the $C_3H_8:O_2$=8:32 l/min. The optimally flame-hardened surface exhibited uniform distributions of the hardness and residual compressive stress over the treated area with moderate levels of $470{\sim}490HV_{0.2}$in hardness and $-300{\sim}-450MPa$ in residual stress, which were acceptable on the basis of the acceptance criteria of Siemens AG-KWU and GE Power Generation Engineering.

Fatigue Strength in Aged Turbine Rotor Steel (시효 열화시킨 터빈 로터강의 피로강도에 관한 연구)

  • 서창민;허정훈;이해무;서덕영
    • Journal of Ocean Engineering and Technology
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    • v.10 no.2
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    • pp.77-87
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    • 1996
  • The estimation of the remaining life for the aged components in power plant as well as chemical and peroleum plants has been recently coberned. The raw materials used in this syudy are the 1Cr-1Mo-0.25V rotor steel which intensified P and S compositions along with the nominal compositions of ASTM A470 standard. Five kinds of specimens with the different degradation levels were prepared by isothermal aging teat treatment at $630^{\circ}C$ The mechanical properties and fatigue strength of virgin and aged 1Cr-1Mo-0.25V rotor steel have been inbestigated through the hardness, tensile, fatigue test, SEM fractograph and EDS analysis at room temperature. Thus, the data of aged specimens were compared with those of virgin specimen to evaluate the aging effects. The main results obtained in this study are as follows; The decrease of the hardness due to degradation was distinguished until 50, 000hrs simulated service time. And is was confirmed that the considerable amount of P, Mn, Cr and S was precipitated at the grain boundary of aged material through the SEM and EDS analysis. The fatigue strength of 25, 000, 50, 000, 75, 000 and 100, 000hrs aged material was decreased 29.5%, 24.4%, 28.6%, 35.7% than that of virgin material at $10^7$ cycles of room temperature. The major cracks of virgin and aged materials initiated at the inclusions including Si, P and Mn compositions which were located at the outer periphery of the specimen.

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Construction of Microbial Fuel Cells Using Thermophilic Microorganisms, Bacillus licheniformis and Bacillus thermoglucosidasius

  • Choi, Young-Jin;Jung, Eun-Kyoung;Park, Hyun-Joo;Paik, Seung R.;Jung, Seun-Ho;Kim, Sung-Hyun
    • Bulletin of the Korean Chemical Society
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    • v.25 no.6
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    • pp.813-818
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    • 2004
  • A systematic study of microbial fuel cells comprised of thermophilic Bacillus licheniformis and Bacillus thermoglucosidasius has been carried out under various operating conditions. Substantial amount of electricity was generated when a redox mediator was used. Being affected by operation temperature, the maximum efficiency was obtained at 50$^{\circ}C$ with an open circuit voltage of ca. 0.7 V. While a small change around the optimum temperature did not make much effect on the cell performance, the rapid decrease in performance was observed above 70$^{\circ}C$. It was noticeable that fuel cell efficiency and discharge pattern strongly depended on the kind of carbon sources used in the initial culture medium. In the case of B. thermoglucosidasius, glucose alone was utilized constitutively as a substrate in the microbial fuel cell irrespective of used carbons sources. When B. licheniformis was cultivated with lactose as a carbon source, best charging characteristics were recorded. Trehalose, in particular, showed 41.2% coulombic efficiency when B. thermoglucosidasius was cultured in a starch-containing medium. Relatively good repetitive operation was possible with B. thermoglucosidasius cells up to 12 cycles using glucose as a carbon source, when they were cultured with lactose as an initial carbon source. This study demonstrates that highly efficient thermophilic microbial fuel cells can be constructed by a pertinent modulation of the operating conditions and by carefully selecting carbon sources used in the initial culture medium.

Stretchable Characteristics and Power Generation Properties of a Stretchable Thermoelectric Module Filled with PDMS (PDMS로 충진된 신축열전모듈의 신축특성과 발전특성)

  • Han, Kee Sun;Oh, Tae Sung
    • Journal of the Microelectronics and Packaging Society
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    • v.26 no.4
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    • pp.149-156
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    • 2019
  • A stretchable thermoelectric module consisting of 5 pairs of Bi2Te3-based hot-pressed p-n thermoelectric legs was processed by filling the module inside with polydimethylsiloxane (PDMS) and removing the top and bottom substrates. Its stretchable characteristics and power generation properties were measured. The integrity of the module was kept well even after 10 strain cycles ranging from 0 to 0.1. With increasing the tensile strain to 0.2, the module circuitry became open because of joint failure between Cu electrodes and thermoelectric legs. The stretchable thermoelectric module exhibited an open circuit voltage of 4.6 mV with a temperature difference of 2.2K across both ends of thermoelectric legs, and changes in its open circuit voltage were below 5% for tensile strains of 0~0.1. Being elongated for a strain of 0.1, it exhibited the maximum output power of 18.5 ㎼ with the temperature difference of 2.2K across its both ends.

Synthesis of Sub-Micron MgH2 using Hydriding Thermal Chemical Vapor Synthesis (수소화기상증착공정을 이용한 마그네슘하이드라이드 미세분말 합성)

  • Kang, Taehee;Kim, Jinho;Han, Kyusung;Kim, Byunggoan
    • Transactions of the Korean hydrogen and new energy society
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    • v.23 no.5
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    • pp.455-460
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    • 2012
  • This work describes the hydriding chemical vapor synthesis (HCVS) of the $MgH_2$ in a hydrogen atmosphere and the product's hydriding-dehydridng properties. Mg powder was used as a starting material to synthesize $MgH_2$ and uniformly heated to a temperature of $600^{\circ}C$ for Mg vaporization. The effects of hydrogen pressure on the morphology and the composition of HCVS-$MgH_2$ were examined by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). It is clearly seen that after the HCVS process, the particle size of synthesized $MgH_2$ was drastically reduced to the submicron or micrometer-scale and these showed different shapes (needle-like nanofibers and angulated plate) depending on the hydrogen pressure. It was found that after the HCVS process, the $H_2$ desorption temperature of HCVS-$MgH_2$ decreased from 380 to $410^{\circ}C$, and the minimum hydrogen desorption tempreature of HCVS-$MgH_2$ powder with needle-like shape can be obtained. In addition, the enhanced hydrogen storage performance for needle-like $MgH_2$ was achieved during subsequent hydriding-dehydriding cycles.

The Freezing Temperature of Chemical Admixtures for Concrete and the Quality Vareation of Concrete Using the Frozen Admixtures (콘크리트용 혼화제의 동결온도 및 동결된 혼화제의 사용에 따른 콘크리트의 품질변화)

  • 한천구;한경익;이건철
    • Magazine of the Korea Concrete Institute
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    • v.10 no.4
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    • pp.205-212
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    • 1998
  • Frost damage of a storage tank for chemical admixtures caused by a low temperature in winter and quality deterioration of chemical admixtures have been often reported. However, there have been few regulations and researches related to the frost damage of chemical admixtures and facilities. Therefore, this paper is intend to investigate not only, the freezing points of chemical admixtures such as AE admixtures and water-reducing AE admixtures, etc., but also the quality variation of concrete used with chemical admixtures before freezing and after freeze-thaw cycles. According to the results of experiments, most chemical admixtures except anti-freezing agent and accelerating water-reducing AE admixtures should be kept from being frozen in low winter temperatures. However, full agitation of frozen chemical admixtures dose not cause the problems of concrete related to the quality of chemical admixtures.

A Study on the Actual Conditionis and Improvement Plan of Interior Landscape in the Subway Stations (지하철역내의 실내조경현황과 개선방안에 관한 연구)

  • 방광자;주진희;박혜경;박성은
    • Journal of the Korean Institute of Landscape Architecture
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    • v.26 no.3
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    • pp.258-266
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    • 1998
  • The purpose of this study is to investigate the actual conditions, to find problems, and to present an improvement plan of interior landscape in the subway stationis. Moreoiver, it will presume the possibilties to develop the subway and ways to utilie underground space effectively. The results are summarized as follows A light intensity was recorded 0-100 Lux as the lowest light and 500 Lux below as the highest in 61 subway stations. An average temperature of 12 $^{\circ}C$and an air humidity of 38% were recorded over a 4 month period from January to April, but includes a drastic variaton between -8.5$^{\circ}C$ and 21.5$^{\circ}C$. Soil acidity of pH 7 below and soil moisture of 1-2 wet degree were apeared in subway stations mostly. Plant forms consisted of artificial flower & flower. Plant species were recorded at a total of 54 species and appeared in the order of Araucaria heteropylla, Ophiophogon jaburan, Aspidistra elatior cv. 'Asahi' and Hedera helix. Plant height was, for the most part, below 0.5m. Plant species that was fined of conditions were Palm, Camellia japonica, Araucaria heterophylla as a high plant, dracaena fragrans, dracaena deremensis cv. Wakneckii as a middle plant, and Ophiopogon jaburan, Hedra helix, ytomium falcatum, Aspidistra elatior cv. Asahi as a low plant. It used to water materials such as small pool, small cascade, water cycles and natural materials such as natural rock, small rock, sand, bark and animal materials such as squirrels, birds, goldfish as an object for plants in the subway stations. From these actual conditions, First of all, It must make up physical environments such as light, temperature humidity, soil for plant growth, and is important to chooce suitable indoor plants and draw up systematic management in the subway environments. Also, it change plants frequently and uses variable objects for subway stationi individuatism, Moreover, indoor plants with strong environmental adaptation abities such as shade tolerance, drought tolerance and cold tolerance need to develope variable species possibly. If these improvements occur, utilization and amenity of subway stationis will increase, according to the use of interior landscape.

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Experimental Study on Heating Performance by Operation Combination of Heat Pump with 3 Indoor-Units (3실 열펌프의 운전조합에 대한 난방성능 실험연구)

  • Kim, Ju-Hyung;Kim, Ki-Young;Kwon, Young-Chul;Park, Seung-Chul
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.14 no.9
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    • pp.4197-4203
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    • 2013
  • In order to investigate the heating performance of multi-heat pump applying an inverter compressor, the experiment on heat pump with 3 indoor units was performed under the heating standard and heating low-temperature conditions. The performance data of heat pump with 3 indoor units were measured by the multi-psychrometric calorimeter. The operation characteristics and the behavior of the refrigerant cycle of the heat pump with 3 indoor units were understood from the heating capacity, heating COP, and P-h diagram by indoor-unit combination. The present experimental results show that the operating load and performance of the multi-heat pump depends on the indoor-unit combination. The heating capacity and heating COP of the low temperature condition were smaller than those of the standard one. Also the refrigerant cycles on indoor-unit combination were analyzed by using P-h diagram.

Evaluation of Composite Laminates for Aircraft Primary-Structure Applications Using Non-Linear Parameter of Ultrasonic Guided Wave (유도초음파의 비선형 파라미터를 이용한 항공기 구조체의 복합재료 적층판 열화 평가)

  • Cho, Youn-Ho;Kim, Do-Youn;Choi, Heung-Soap;Lee, Joon-Hyun
    • Journal of the Korean Society for Nondestructive Testing
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    • v.30 no.2
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    • pp.126-131
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    • 2010
  • The purpose of this study is to assess the condition of composites used in aircraft under varying temperature environment with ultrasound guided wave technique. Investigation of crucial influential factor on the composite health monitoring related to aircraft operational environments such as the number of thermal cycles and temperature deviation between ground level and flight altitude has been of a great concern for aircraft safety issue. In this study, ultrasonic guided wave health monitoring scheme is proposed to evaluate composite specimens damaged with the thermal fatigue simulating aircraft operational condition. Guided wave dispersion curves are used to select right modes which show a promising sensitivity to each different thermal fatigue damage level. The present approach can be also implemented as one of on-lines health monitoring tools for aircraft.

Reliability Evaluation of Fiber Optic Sensors Exposed to Cyclic Thermal Load (주기적인 반복 열하중에 노출된 광섬유 센서의 신뢰성 평가)

  • Kim, Heon-Young;Kang, Donghoon;Kim, Dae-Hyun
    • Journal of the Korean Society for Nondestructive Testing
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    • v.36 no.3
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    • pp.225-230
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    • 2016
  • Fiber Bragg grating (FBG) sensors are currently the most prevalent sensors because of their unique advantages such as ease of multiplexing and capability of performing absolute measurements. They are applied to various structures for structural health monitoring (SHM). The signal characteristics of FBG sensors under thermal loading should be investigated to enhance the reliability of these sensors, because they are exposed to certain cyclic thermal loads due to temperature changes resulting from change of seasons, when they are applied to structures for SHM. In this study, tests on specimens are conducted in a thermal chamber with temperature changes from -$20^{\circ}C$ to $60^{\circ}C$ for 300 cycles. For the specimens, two types of base materials and adhesives that are normally used in the manufacture of packaged FBG sensors are selected. From the test results, it is confirmed that the FBG sensors undergo some degree of compressive strain under cyclic thermal load; this can lead to measurement errors. Hence, a pre-calibration is necessary before applying these sensors to structures for long-term SHM.