• 제목/요약/키워드: Critical Temperature

검색결과 2,706건 처리시간 0.037초

산소농도 변화에 따른 입상활성탄의 자연발화에 관한 연구 (A Study on the Autoignition of Granulated Activated Carbon with Change of Oxygen Concentration)

  • 목연수;최재욱;류동현;최일곤;김상렬
    • 한국안전학회지
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    • 제10권2호
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    • pp.84-91
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    • 1995
  • The characteristics of critical spontaneous ignition of granulated activated carbon were investigated In atmospheres of differing oxygen concentration. At the same concentration the larger vessels yielded the lower critical spontaneous ignition temperature. At the same vessel, as the concentration of oxygen was reduced, Ignition occurred later and at higher ambient temperature, and critical spontaneous ignition temperature increased. The apparent activation energy calculated from the Frank-Kamenetskii's ignition theory appeared to be the slight different value respectively and the mean apparent activation energy was 19850㎈/㏖.

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저온 주사 레이저 현미경(LTSLM)을 이용한 YBCO 초전도 선재의 불균질성 연구 (A study on inhomogeneity of YBCO Coated Conductors using Low-temperature Scanning Laser Microscopy (LTSLM))

  • 박상국;김종만;이상봉;김상훈;김가영;이형철
    • Progress in Superconductivity
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    • 제11권1호
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    • pp.72-77
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    • 2009
  • Low temperature scanning laser microscopy (LTSLM) can be used for a two-dimensional display of bolometric response arising from the localized excitation of a sample by the focused laser beam. In this study, the distribution of critical temperature ($T_c$) and critical current density ($J_c$) in YBCO coated conductor were analyzed using LTSLM. For improving the temperature stability, we have modified the system into a double-shielding type. Through the modification, the temperature stability was successfully improved from ${\pm}10mK\;to\;{\pm}2mK$. The superconducting properties of YBCO coated conductors were measured for the sample of a narrow bridge type using wet etching process. The spatial non-uniformity of the ac voltage response, ${\delta}V(x)$, which is proportional to ${\partial}\rho(x,J_B)/{\partial}T$ in the transition temperature region could be observed and displayed in a two-dimensional image.

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室溫時效 및 變形時效가 微小 疲勞크랙의 開口變位에 미치는 影響 (Influence of Room Temperature and Strain Aging on the COD for a Small Fatigue Crack)

  • 김민건
    • 대한기계학회논문집
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    • 제19권2호
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    • pp.402-407
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    • 1995
  • The effects of room temperature and strain aging treatment are discussed on the critical condition for the onset of growth of non-propagating cracks on 0.15% C low carbon steel, with special emphasis on the length of the critical non-propagating crack and on the crack opening displacement(COD) at the crack tip. It is found from the experimental analysis that room temperature and strain aging of a fatigue pre-cracked specimen introduced the closure of a crack tip of the pre-crack and the reduction of crack opening displacement at the wake of crack, together with an improvement in crack growth resistance of the microstructure. This may cause an increase in the endurance limit of the specimen, through the enhancement of effective stress for the onset of growth of the critical non-propagating crack.

The Effect of Deformation Stress-strain and Temperature on the $I_c$ Degradation of Bi-2223/Ag Tapes

  • Ha, Hong-Soo;Kim, Sang-Cheol;Ha, Dong-Woo;Oh, Sang-Soo;Joo, Jin-Ho
    • 한국분말야금학회:학술대회논문집
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    • 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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    • pp.1251-1252
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    • 2006
  • In order to investigate 95% retained critical current of Bi-2223/Ag tapes under various stress-strain conditions, load cell attached tension and bending apparatus was used. The critical current of stress-strained tape was degraded below 95% retained critical current when tension and bending was simultaneously applied together. But only one of this tension or bending did not degrade the tape below 95% retained critical current. Deformation temperature was important to maintain the 95% retained Ic of Bi-2223/Ag tapes after bending or tension deformation because mechanical strength of tapes can be changed drastically between room temperature and 77 K.

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A Numerical Study on the Laminar Flow Field and Heat Transfer Coefficient Distribution for Supercritical Water in a Tube

  • Lee Sang-Ho
    • International Journal of Air-Conditioning and Refrigeration
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    • 제13권4호
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    • pp.206-216
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    • 2005
  • Numerical analysis has been carried out to investigate laminar convective heat transfer at zero gravity in a tube for supercritical water near the thermodynamic critical point. Fluid flow and heat transfer are strongly coupled due to large variation of thermodynamic and transport properties such as density, specific heat, viscosity, and thermal conductivity near the critical point. Heat transfer characteristics in the developing region of the tube show transition behavior between liquid-like and gas-like phases with a peak in heat transfer coefficient distribution near the pseudo critical point. The peak of the heat transfer coefficient depends on pressure and wall heat flux rather than inlet temperature and Reynolds number. Results of the modeling provide convective heat transfer characteristics including velocity vectors, temperature, and the properties as well as the heat transfer coefficient. The effect of proximity on the critical point is considered and a heat transfer correlation is suggested for the peak of Nusselt number in the tube.

저온공조용 취출구의 선정 (Selection of Diffuser for Lower Temperature Air Distribution System)

  • 박성규;유호준;최명신
    • 대한설비공학회:학술대회논문집
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    • 대한설비공학회 2008년도 하계학술발표대회 논문집
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    • pp.484-492
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    • 2008
  • Air Discharge pattern and even temperature distribution is critical for a successful lower temperature air distribution system, which would supply lower temperature air than normal HAVC system. Selection of appropriate diffuser is the most critical element in completing lower temperature system.

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유전자 알고리즘에서 볼쯔만 선택방법의 개선 (The improvement of genetic algorithm using Boltzmann selection)

  • 윤기석;김태형;김유신
    • 대한전자공학회:학술대회논문집
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    • 대한전자공학회 1999년도 하계종합학술대회 논문집
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    • pp.429-432
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    • 1999
  • In this paper, we propose a method to improve Genetic Algorithm using Boltzmann selection which Michael has suggested. But Michael uses temperature schedule(the initial temperature, the cooling rate), which can be applicable only to the limited range of problems. We propose a new method to find the critical temperature and the cooling rate as parameters of the temperature schedule. The critical temperature can be derived from the distribution of each individual's fitness. Through the application of the island model where each island has differing cooling rate, it is proved that it is unnecessary to find the optimal cooling rate. The simulation on the TSP's with various city sizes proves the proposed critical temperature correct.

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Acclimation temperature influences the critical thermal maxima (CTmax) of red-spotted grouper

  • Rahman, Md Mofizur;Lee, Young-Don;Baek, Hea Ja
    • Fisheries and Aquatic Sciences
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    • 제24권7호
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    • pp.235-242
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    • 2021
  • The present study investigated the critical thermal maxima (CTmax) of red-spotted grouper, Epinephelus akaara under different acclimation temperatures (Tacc). Fish were acclimated at 24℃, 28℃, and 32℃ water temperature for 2 weeks. Water temperature was increased at a rate of 1℃/h and CTmax level was measured following the critical thermal methodology (Paladino et al., 1980). The results showed that CTmax values of E. akaara were 35.61℃, 36.83℃, and 37.65℃ for fish acclimated at 24℃, 28℃, and 32℃, respectively. The acclimation response ratio (ARR) was 0.26. The CTmax values were significantly correlated with body size. Collectively, it is said that the CTmax value of red-spotted grouper can be affected by different adaptation temperature (24℃, 28℃, and 32℃) and the fish acclimated to a higher temperature has a higher CTmax level. Besides, the CTmax value of 35.61℃-37.65℃ indicating the upper thermal tolerance limit for E. akaara under different Tacc (24℃, 28℃, and 32℃). Understanding the thermal tolerance of E. akaara is of ecological importance in the conservation of this species.

비전도 반평판 사이에서 미끄럼 운동하는 평판 층의 열탄성 불안정성 (Thermoelastic Instability of the Layer Sliding between Two Non-conducting Half-planes)

  • 하태원;조용구;김흥섭;이정윤;오재응
    • 한국소음진동공학회:학술대회논문집
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    • 한국소음진동공학회 2003년도 춘계학술대회논문집
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    • pp.483-488
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    • 2003
  • Frictional heating in brakes causes thermoelastic distortion of the contacting bodies and hence affects the contact pressure distribution. The resulting thermo-mechanical coupling can cause thermoelastic instability (TEI) if the sliding speed is sufficiently high, leading to non-uniform heating called hot spots and low frequency vibration known as hot judder. The vibration of brakes to the known phenomenon of frictionally-excited thermoelastic instability is estimated studying the interface temperature and pressure evolution with time. A simple model has been considered where a layer with half-thickness ${\alpha}$ slides with speed V between two half-planes which are rigid and non-conducting. The advantage of this properly simple model permits us to deduce analytically the critical conditions for the onset of instability, which is the relation between the critical speed and the growth rate of the interface temperature and pressure. Symmetrical component of pressure and temperature distribution at the layer interfaces can be more unstable than antisymmetrical component. As the thickness ${\alpha}$ reduces, the system becomes more apt to thermoelastic instability. Moreover, the evolution of the system beyond the critical conditions has shown that even if low frequency perturbations are associated with low critical speed, it might be less critical than high frequency perturbations if the working sliding speed is much larger than the actual critical speed of the system.

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Bi2212/Ag 선재의 초전도 특성에 대한 열처리의 영향 (Effect of Heat Treatment on Superconducting Properties on Bi2212/Ag Wire)

  • 김상철;하동우;송규정;오상수;이남진;한일용;오재근;손호상
    • Progress in Superconductivity
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    • 제8권1호
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    • pp.54-58
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    • 2006
  • We have fabricated double stacked 385 filamentary Bi2212/Ag round wires which have different Ag ratios. The wires have been heat-treated at the maximum temperature($T_{max}$) of $882{\sim}896^{\circ}C$ for 0.5 h. Effect of heat treatment on critical current density and critical temperature on Bi2212/Ag round wires has been studied. Critical current density of the wire heat -treated at $890^{\circ}C$ showed 206,250 $A/cm^2$ at 4.2 K, 0 T and critical temperature of the wire was 83 K. Microstructure of the wires also has been studied via optical microscopy and SEM.

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