• Title/Summary/Keyword: Excess Temperature

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Polymorphic Phase Transition and Temperature Coefficient of Capacitance of Alkaline Niobate Based Ceramics

  • Bae, Seon-Gi;Shin, Hyea-Gyiung;Sohn, Eun-Young;Im, In-Ho
    • Transactions on Electrical and Electronic Materials
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    • v.14 no.2
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    • pp.78-81
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    • 2013
  • $0.95(Na_{0.5}K_{0.5})NbO_3-0.05BaTiO_3+0.2wt%\;Ag_2O$ (hereafter, No excess NKN) ceramics and $0.95(Na_{0.5}K_{0.5})NbO_3-0.05BaTiO_3+0.2wt%\;Ag_2O$ with excess $(Na_{0.5}K_{0.5})NbO_3$ (hereafter, Excess NKN) were fabricated by the conventional solid state sintering method, and their phase transition properties and dielectric properties were investigated. The crystalline structure of No excess NKN ceramics and Excess NKN ceramics were shown characteristics of polymorphic phase transition (hereafter, PPT), especially shift from the orthorhombic to tetragonal phase by increasing sintering temperature range from $1,100^{\circ}C$ to $1,200^{\circ}C$. Also, the temperature coefficient of capacitance (hereafter, TCC) of No excess NKN ceramics and Excess NKN ceramics from $-40^{\circ}C$ to $100^{\circ}C$ was measured to evaluate temperature stability for applications in cold regions. The TCC of No excess NKN and Excess NKN ceramics showed positive TCC characteristics at a temperature range from $-40^{\circ}C$ to $100^{\circ}C$. Especially, Excess NKN showed a smaller TCC gradient than those of Excess NKN ceramics in range from $-40^{\circ}C$ to $100^{\circ}C$. Therefore, NKN piezoelectric ceramics combined with temperature compensated capacitor having negative temperature characteristics is desired for usage in cold regions.

An Analytical Investigation on the Build-up of the Temperature Field due to a Point Heat Source in Shallow Coastal Water with Oscillatory Alongshore-flow

  • Jung, Kyung-Tae;Kim, Chong-Hak;Jang, Chan-Joo;Lee, Ho-Jin;Kang, Sok-Kuh;Yjm, Ki-Dai
    • Ocean and Polar Research
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    • v.25 no.1
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    • pp.63-74
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    • 2003
  • The build-up of the heat field in shallow coastal water due to a point source has been investigated using an analytical solution of a time-integral form derived by extending the solutions by Holley(1969) and also presented in Harleman (1971). The uniform water depth is assumed with non-isotropic turbulent dispersion. The alongshore-flow is assumed to be uni-directional, spatially uniform and oscillatory. Due to the presence of the oscillatory alongshore-flow, the heat build-up occurs in an oscillatory manner, and the excess temperature thereby fluctuates in that course and even in the quasi-steady state. A series of calculations reveal that proper choices of the decay coefficient as well as dispersion coefficients are critical to the reliable prediction of the excess temperature field. The dispersion coefficients determine the absolute values of the excess temperature and characterize the shoreline profile, particularly within the tidal excursion distance, while the decay coefficient determines the absolute value of the excess temperature and the convergence rate to that of the quasi-steady state. Within the e-folding time scale $1/k_d$ (where $k_d$ is the heat decay coefficient), heat build-up occurs more than 90% of the quasi-steady state values in a region within a tidal excursion distance (L), while occurs increasingly less the farther we go to the downstream direction (about 80% at 1.25L, and 70% at 1.5L). Calculations with onshore and offshore discharges indicate that thermal spreading in the direction of the shoreline is reduced as the shoreline constraint which controls the lateral mixing is reduced. The importance of collecting long-term records of in situ meteorological conditions and clarifying the definition of the heat loss coefficient is addressed. Interactive use of analytical and numerical modeling is recommended as a desirable way to obtain a reliable estimate of the far-field excess temperature along with extensive field measurements.

The Effect of Feeding Characteristics on the Temperature Distribution of Rotary Kiln (로타리 킬른의 장입 특성이 온도분포에 미치는 영향)

  • Park, Jong-Seok;Chun, Chul-Kyun
    • Journal of the Korean Society of Combustion
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    • v.12 no.3
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    • pp.24-32
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    • 2007
  • A theoretical model was developed for rotary kiln and computational study was conducted to find the effect of feeding characteristics. One dimensional model with the variations of heating distribution, length of heating zone, excess air ratio and revolution was considered. The comparison of parallel-flow rotary kiln with that of counter-flow was conducted. For parallel-flow type, it is found that the variation of temperature of solid is not great for the zone that is following flame-heating zone. This zone is good to take the special treatment because thermal deviation is small and contacting time is enough for another treatment. Increase of excess air ratio have the effect of decreasing solid temperature. But this effect of decreasing solid temperature goes small for the great excess air ratio. The heating is efficient for the flame which has the maximum heating at the central region of the full length.

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A SEARCH FOR MOLECULAR CLOUDS AT HIGH GALACTIC LATITUDE

  • Chi Seung-Youp;Park Yong-Sun
    • Journal of The Korean Astronomical Society
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    • v.39 no.1
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    • pp.19-24
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    • 2006
  • We carried out CO survey toward IR-excess clouds using SRAO 6-m telescope in search of molecular $H_2$. These clouds, which show far-infrared excess over what is expected from HI column density, are considered to be candidates of molecular clouds. In order to find new high Galactic latitude clouds, we made mapping observations for 14 IR-excess clouds selected from Reach et al.(1998) in $^{12}CO$ J = 1 - 0 line, supplementing the similar survey in southern hemisphere (Onishi et al. 2001). $^{12}CO$ emission is detected from three IR-excess clouds among 14 objects. Three newly detected clouds exhibit somewhat clumpy morphology and column densities amount to ${\sim}10^{21}\;cm^{-2}$. One of three clouds, DIR120-28, show discrepancy between IR-excess center and CO emission center. It seems that IR-excess may not be an effective tracer of molecular gas. Instead, optical depth$(\tau)$ excess, i.e., IR-excess corrected for temperature dependence, may be more effective tracer of molecular clouds, since, by combining statistics from both hemispheres, we found that the detection rate is higher for IR-excess clouds with lower dust temperature.

Densities, Viscosities and Excess Properties of 2-Bromopropane - Methanol Binary Mixtures at Temperature from (298.15 to 318.15) K (298.15~318.15 K 에서 2-브로모프로판-메탄올 이성분 혼합물의 밀도, 점성도, 여분 성질)

  • Li, Hua;Zhang, Zhen;Zhao, Lei
    • Journal of the Korean Chemical Society
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    • v.54 no.1
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    • pp.71-76
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    • 2010
  • The densities and viscosities of 2-bromopropane-methanol binary mixtures had been determined using an digital vibrating U-tube densimeter and Ubbelohde capillary viscometer respectively from (298.15 to 318.15) K. The dependence of densities and viscosities on temperature and concentration had been correlated. The excess molar volume and the excess viscosity of the binary system were calculated from the experimental density and viscosity data. The excess molar volumes were related to compositions by polynomial regression and regression parameters and total RMSD deviations were obtained; the excess viscosities was related to compositions by Redlich-Kister equation and regression coefficients and total RMSD deviation of the excess viscosity for 2-bromopropane and methanol binary system were obtained. The results showed that the model agreed very well with the experimental data.

Experimental study on combustion characteristics of high efficiency oxy-fuel burner (고효율 순산소 버너의 연소 특성에 관한 실험적 연구)

  • Kim, Se-Won;Ahn, Jae-Hyun;Kim, Min-Soo
    • 한국연소학회:학술대회논문집
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    • 2002.11a
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    • pp.57-64
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    • 2002
  • This paper describes the results of a series of experiments executed by using two pilot-scale oxv-fuel burners are designed for maximum capacity of 50,000 kacl/hr, 300,000 kcal/hr and installed in the test furnace. The effects of turn-down ratio, excess oxygen ratio, nozzle exit velocity, injection angle, swirl vane angle and inlet oxygen temperature on the combustion characteristic are investigated. Temperature distributions are measured using R-type and Molybdenum sheathed C-type thermocouple. The results showed that maximum temperature and mean temperature increase with the increase of turn-down ratio and inlet oxygen temperature. The maximum flame temperature was increased about 35% compared to the case of equivalent air operated condition. In addition, Optimum excess oxygen ratio and nozzle characteristics are obtained for this oxy-fuel glass melting furnace.

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Effects of Excess PbO and Ball-Milling on the Microstructure, Sintering Behavior and Mechanical Properties of PZT Ceramics (과잉 PbO 첨가 및 미분쇄에 의한 PZT 압전세라믹스의 미세구조제어와 소결특성 및 기계적 성질)

  • 전봉관;남효덕;김상태
    • Journal of the Korean Ceramic Society
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    • v.32 no.6
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    • pp.726-734
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    • 1995
  • Pb(Zr0.53Ti0.47)O3 (PZT) ceramics having different microstructures were fabricated at low temperatures using calcined PZT powders with addition of excess PbO powder and/or ball milling. The effects of excess PbO and ball milling time on the microstructure, the sintering characteristic, and the mechanical properties of these ceramics were studied. Fine powders with average particle size of 0.38㎛ could be obtained by ball milling with 2.5 mm Ф zirconia balls for 120 hours. By the addition of 2mol% of excess PbO to these powders, it was possible to obtain well-densitified PZT ceramics at low sintering temperature of 980℃. Densification behavior of PZT was affected by the addition of excess PbO powder, while, grain growth was hardly affected by PbO addition. It was observed that Vicker's hardness decreased and fracture toughness increased with the increasing amount of PbO. At 1mol% excess PbO, it was shown that the minimum values of hardness and maximum fracture toughness were achieved. In addition, with increasing sintering time, the fracture toughness decreased and the hardness increased.

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Effect of a Reductant on Production and Characteristics of Tantalum Powder (탄탈륨 분말제조시 분말특성에 미치는 환원제의 영향)

  • Yun, Jae-Sik;Park, Hyeong-Ho;Bae, In-Seong;Lee, Sang-Baek;Yun, Dong-Ju;Kim, Byeong-Il
    • Korean Journal of Materials Research
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    • v.11 no.12
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    • pp.1047-1051
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    • 2001
  • Purity tantalum powder has been produced by sodium reduction of potassium tantalum fluoride($K_2TaF_7$)in a stainless steel bomb. The influence of experimental variable, such as excess of reductant and temperature of reduction on the yield and quality of the Ta powder has been studied. The excesses of reductant were varied from -20%, -10%, 0%, 5%, 10%, 20%. When -20% excess of sodium was used, the un-reacted sodium remained in the reacted product. The yield of 81% of Ta powder has been achieved by reducing 50g of$K_TaF_7$with 5% sodium in excess of stoichiometric amount in presence of 16.8g of sodium chloride in the charge at a reduction temperature of$905{\circ}C$. The proportion of fine fraction(~325mesh) decreased appreciably with the increase of sodium excess, and the yield of tantalum powder improved from 65% to 94%. The average particle size of Ta Powder is improved from 3 microns to 4 microns in the 5% excess sodium.

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Local Adaptation Plan to Climate Change Impact in Seoul: Focused on Heat Wave Effects (서울시 기후변화 영향평가 및 적응대책 수립: 폭염영향을 중심으로)

  • Kim, Eunyoung;Jeon, Seong-Woo;Lee, Jung-Won;Park, Yong-Ha;Lee, Dong-Kun
    • Journal of Environmental Impact Assessment
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    • v.21 no.1
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    • pp.71-80
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    • 2012
  • Against the backdrop of the clear impact of climate change, it has become essential to analyze the influence of climate change and relevant vulnerabilities. This research involved evaluating the impact of heat waves in Seoul, from among many local autonomous bodies that are responsible for implementing measures on adapting to climate change. To carry out the evaluation, the A1B scenario was used to forecast future temperature levels. Future climate scenario results were downscaled to $1km{\times}1km$ to result in the incorporation of regional characteristics. In assessing the influence of heat waves on people-especially the excess mortality-we analyzed critical temperature levels that affect excess mortality and came up with the excess mortality. Results of this evaluation on the impact of climate change and vulnerabilities indicate that the number of days on which the daily average temperature reaches $28.1^{\circ}C$-the critical temperature for excess mortality-in Seoul will sharply increase in the 2050s and 2090s. The highest level of impact will be in the month of August. The most affected areas in the summer will be Songpa-gu, Gangnam-gu, and Yeongdeungpo-gu. These areas have a high concentration of residences which means that heat island effects are one of the reasons for the high level of impact. The excess mortality from heat waves is expected to be at least five times the current figure in 2090. Adaptation plan needs to be made on drawing up long-term adaptation measures as well as implementing short-term measures to minimize or adapt the impact of climate change.

An Analytical Model for Predicting Heat Transport due to a Point Source in Coastal Water under a Spring-Neap Modulation of Tidal Currents (조류의 대.소조 변동이 존재하는 연안역에서의 점열원에 의한 열오염의 이동 예측을 위한 해석해 모형)

  • 이호진;김종학
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.16 no.2
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    • pp.92-102
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    • 2004
  • In this paper, an analytical solution of calculating the excess temperature field due to a point heat source is presented in the presence of spring-neap modulation of convective alongshore flow. The basic form of the solution is identical to that given by Jung et al. (2003) but the convective term in the exponential kernel function is extended and a spring-neap variation in the horizontal eddy diffusivity is newly introduced. A set of calculations have been performed to examine the sensitivity of the heat build-up to the change in current fields and turbulent dispersion. Results indicate that the excess temperature field is confined within the tidal excursion distance, while the excess temperature field beyond the distance is mainly controlled by the horizontal diffusion. The heat build-up within the distance is considerably affected by the spring-neap variation in the horizontal eddy diffusivity; the relatively high excess temperature more than 1$^{\circ}C$ is extended further when the eddy diffusivity has spring-neap modulation.