• Proceedings of the KAIS Fall Conference
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• 2010.05b
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• pp.1237-1240
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• 2010

본 연구에서는 유동층반응기를 이용하여 왕겨의 탄화반응을 수행하였다. 탄화반응은 내경 40mm, 높이 1.8m의 유동층을 사용하였으며, 분산판은 다공성 스테인레스스틸을 사용하였다. 탄화반응은 질소를 이용하여 수행하였다. 왕겨 주입입자 크기는 직경 2.0mm, 0.715mm, 0.359mm, 0.194mm를 각각 사용하였으며, 유동층의 온도는 $400^{\circ}C$, $500^{\circ}C$, $600^{\circ}C$, $700^{\circ}C$에서 탄화특성을 측정하였다. 또한 유동층의 매질로는 직경 1.0mm의 Co-Mo-Fe/$Al_2O_3$ 촉매를 사용하였으며, 탄화물은 유동층상부에 설치된 사이크론에 의하여 포집분리되었다. 탄화시 유동층 내부의 현상을 압력요동을 이용하여 해석하였으며, 압력신호로부터 평균압력, 압력요동의 표준편차, 주진동수, power spectrum density function을 계산하여 층내현상을 해석하였다. 층내온도, 유동화속도, 공급 입자크기에 따른 층내현상을 압력요동특성치를 이용하여 해석할 수 있었다.

• Korean Chemical Engineering Research
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• v.46 no.4
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• pp.707-713
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• 2008

Characteristics of minimum fluidization velocity and pressure fluctuations were investigated in an annular fluidized bed whose diameter was 0.102 m and 2.0 m in height. Effects of gas velocity, particle size and bed temperature on the minimum fluidization velocity and pressure fluctuations were examined. The values of minimum fluidization velocity obtained by means of three different methods were very similar each other. The correlation dimension could be a quantitative parameter for expression the resultant complex behavior of gas and solid mixture in the annular fluidized bed. The value of correlation dimension increased with increasing gas velocity, fluidized particle size and temperature in the bed. The minimum fluidization velocity could be determined by means of correlation dimension of pressure fluctuations as well as pressure drop in the bed and standard deviation of pressure fluctuations. The minimum fluidization velocity increased with increasing particle size but decreased with increasing bed temperature in annular fluidized beds. The minimum fluidization velocity was well correlated in therms of correlation dimension as well as operating variables within experimented conditions of this study.

• Proceedings of the Korean Nuclear Society Conference
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• 2004.05a
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• pp.97.1-97.1
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• 2004

• The KSFM Journal of Fluid Machinery
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• v.10 no.5
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• pp.9-19
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• 2007

Fluid temperature fluctuations in a mixing tee pipe were numerically analyzed by LES model in order to clarify internal turbulent flows and to develope an evaluation method for high-cycle thermal fatigue. Hot and cold water with an temperature difference $40^{\circ}C$ were supplied to the mixing tee. Fluid temperature fluctuations in a mixing tee pipe is analysed by using the computational fluid dynamics code, FLUENT, Temperature fluctuations of the fluid and pipe wall measured as the velocity ratio of the flow in the branch pipe to that in the main pipe was varied from 0.05 to 5.0. The power spectrum method was used to evaluate the heat transfer coefficient. The fluid temperature characteristics were dependent on the velocity ratio, rather than the absolute value of the flow velocity. Large fluid temperature fluctuations were occurred near the mixing tee, and the fluctuation temperature frequency was random. The ratios of the measured heat transfer coefficient to that evaluated by Dittus-Boelter's empirical equation were independent of the velocity ratio, The multiplier ratios were about from 4 to 6.

• Korean Chemical Engineering Research
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• v.46 no.1
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• pp.56-62
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• 2008

Characteristics of heat transfer were investigated in a three-phase swirling fluidized bed whose diameter was 0.102 m and 2.5 m in height. Effects of gas and liquid velocities, particle size and liquid swirling ratio ($R_S$) on the immersed heater-to-bed overall heat transfer coefficient were examined. The heat transfer characteristics between the immersed heater and the bed was well analyzed by means of phase space portraits and Kolmogorov entropy(K) of the time series of temperature difference fluctuations. The phase space portraits of temperature difference fluctuations became stable and periodic and the value of Kolmogorov entropy tended to decrease with increasing the value of liquid swirling ratio from 0.1 to 0.4. The value of Kolmogorov entropy exhibited its minimum with increasing liquid swirling ratio. The value of overall heat transfer coefficient (h) showed its maximum with the variation of liquid velocity, bed porosity or liquid swirling ratio, but it increased with increasing gas velocity and particle size. The value of K exhibited its maximum at the liquid velocity at which the h value attained its maximum. The overall heat transfer coefficient and Kolmogorov entropy were well correlated in terms of dimensionless groups and operating variables.

• Journal of the Korean Vacuum Society
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• v.13 no.2
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• pp.54-58
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• 2004

Three hot cathode ionization gauges (HCIG) were used to study their responses of pressure measurements at the stainless steel high vacuum (HV) chamber around room temperatures. The pressure variations of HV measured by the three HCIGs between $20 ^{\circ}C$ and $26 ^{\circ}C$ were 5.0 %, 5.3 %, and 10.3 %, respectively. However, pressure differences between $21.5 ^{\circ}C$ and $22.5^{\circ}C$ were lower than the gauges uncertainty limits. The pressure variations of the HCIGs at the HV chamber was not directly affected by gauge characteristics, but pressure changes due to room temperatures.

• Journal of the Korean Vacuum Society
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• v.3 no.1
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• pp.33-38
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• 1994

-Hot-wall epitaxy 방법에 의하여 GaAs(100) 기판위에 CdTe(100)박막을 성장하였다. 박막을 성 장하는 동안 기판의 온도는 28$0^{\circ}C$ 증발원의 온도는 $430^{\circ}C$로 유지하였고 성장률은 $2mu$m/h이었다. 박막의 두께가 증가함에 따라 격자상수와 2결정 X-선 요동곡선의 반폭치가 감소하였다. CdTe (100) 박막의 광 전류 스펙트럼으로부터 에너지 띠간격의 광전류 봉우리는 가전자대 8 에 있는 전자가 광흡수에 의해 전도대 6 전이한 것이며 에너지 띠간격의 온도의존성을 구한 결과 온도계수 a=-2.3~-3.5 x 10-4 ev/k.

• Journal of the Korean Magnetics Society
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• v.12 no.1
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• pp.14-19
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• 2002

The iron-doped perovskite La$_{0.67}$Sr$_{0.33}$Mn$_{0.99}$$^{57}$Fe$_{0.01}$O$_3$compound has been studied by x-ray diffraction, Mossbauer spectroscopy, and vibrating sample magnetometry. The single phase of the polycrystalline La$_{0.67}$Sr$_{0.33}$Mn$_{0.99}$$^{57}$Fe$_{0.01}$O$_3$powder has been prepared by a waterbased solgel method. Crystalline La$_{0.67}$Sr$_{0.33}$Mn$_{0.99}$$^{57}$Fe$_{0.01}$O$_3$was a rombohedral structure with lattice parameters a$_{0}$=5.480 $AA$, $alpha$=60.259$^{circ}$. Mossbauer spectra of La$_{0.67}$Sr$_{0.3}$/Mn$_{0.99}$$^{57}$Fe$_{0.01}$O$_3$have been taken at various temperatures ranging from 20 to 400 K. As the temperature increases toward the Curie temperature, T$_{c}$=375 K, the Mossbauer spectra show line broadening and the difference between the 1,6 and 3,4 linewidths is caused by the anisotropic hyperfine field fluctuation. The anisotropic field fluctuation of +H (P$_{+}$=0.80) is greater than -H (P$_{-}$=0.20). We calculated that the anisotropy energy was 124.01 erg/cm$^3$for T=150 K which is associated with the large line broadening.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.7 no.4
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• pp.44-50
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• 2011

Turbulent mixing of hot and cold coolants is one of the possible causes of high cycle thermal fatigue in piping systems of nuclear power plants. A typical situation for such mixing appears in turbulent flow through a T-junction. Since the high cycle thermal fatigue caused by thermal striping was not considered in the piping fatigue design in several nuclear power plants, it is very important to evaluate the effect of thermal striping on the integrity of mixing tees. In the present work, before conducting detailed evaluation, three thermal striping evaluation methodology suggested by EPRI, JSME and NESC are analyzed. Then, a by-pass pipe connected to the shutdown cooling system heat exchanger is investigated by using these evaluation methodology. Consequently, the resulting thermal stresses and the fatigue life of the mixing tee are reviewed and compared to each other. Futhermore, the limitation of each methodology are also presented in this paper.

• Korean Chemical Engineering Research
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• v.50 no.3
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• pp.499-504
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• 2012

Characteristics of overall heat transfer were investigated in a three-phase slurry bubble column with relatively low surface tension media, which has been frequently encountered in the fields of industry. The heat transfer phenomena was examined in the system which was composed of a coaxial vertical heater and a proper of bubble column. The heat transfer coefficient was estimated from the measured mean value of temperature difference between the heater surface and the column proper at the steady state condition. Effects of gas velocity ($U_G$), solid fraction in the slurry phase ($C_S$) and surface tension (${\sigma}_L$) of continuous liquid media on the overall heat transfer coefficient (h) in the bubble column were determined. The mean value of temperature difference was estimated from the data of temperature difference fluctuations with a variation of time. The amplitude and mean value of temperature difference fluctuations with respect to the elasped time appeared to decrease with decreasing the surface tension of liquid phase. The overall heat transfer coefficient between the immersed heated and the bubble column increased with an increase in the gas velocity or solid fraction in the slurry phase, but it decreased with an increase in the surface tension of continuous liquid media. The overall heat coefficient in the slurry bubble column with relatively low surface tension media was well correlated in term of operating variables and dimensionless groups within this experimental conditions.