• 설비공학논문집
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• 제7권4호
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• pp.547-555
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• 1995

Melting process of ice in a rectangular cavity with different temperature walls has been studied experimentally. Front shape of ice and melting rate were affected by initial temperature of ice and variation of temperature distribution and density gradient. When the hot wall temperature was below $8^{\circ}C$, the melting rates were higher at the bottom than those of at the top due to the density inversion, but with increasing the hot wall temperature the melting rates at the top were affected by hot wall and were higher than those of at the bottom. When the initial temperature of ice was low, melting rates were low, but with increasing the time melting rates were almost the same with those of each initial temperature of ice.

• 설비공학논문집
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• 제12권8호
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• pp.745-754
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• 2000

An experimental study has been carried out in order to investigate the heat storage characteristics for a latent heat storage tank with horizontal shell and tube type. The heat storage tank consists of cylindrical capsules with a staggered tube bank. The effects of flow rates and initial temperature differences on the melting time and heat storage rates are examined. It is found that the melting time decreases with increase of the flow rates and initial temperature differences. Results also show that the time-averaged overall heat transfer coefficients increase in proportion to the increase of flow rates and initial temperature differences.

• Ocean and Polar Research
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• 제37권2호
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• pp.141-147
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• 2015

Snow albedo can be decreased if there are any impurities on the snow surface other than the snow itself. Due to the decrease of snow albedo, melting rates of surface snow can increase, which is very crucial in climate change and hydrogeology in many parts of the world. Anthropogenic black carbons caused by the incomplete combustion of fossil fuel affect snow and tephra particles generated by geologic volcanic activities reduce snow albedo. In this study, we investigated isotopic compositions for snow covered by tephra particles and compared with this with clean snow. Isotopic compositions of snow with tephra statistically show more enriched than those of clean snow (p<0.02). This can be explained by the fact that snow becomes enriched in $^{18}O$ or D relative to meltwater as melting rates are increased. In addition, the slopes of the linear regression between oxygen and hydrogen for snow with tephra and clean snow are 6.7 and 8, respectively, and the latter is similar to that of the global meteoric water line of 8. Therefore, we can conclude that snow impurities control the isotopic compositions of snow, which is very crucial in the study of climate change and hydrogeology. To quantitatively explain these observations, melting experiments and numerical approaches are required.

• 설비공학논문집
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• 제19권12호
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• pp.883-888
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• 2007

As a starting point of investigating what molecular dynamic simulations can reveal about the nature of atomic level of heating and cooling process, argon described by the LJ potential is considered. Stepwise heating and cooling of constant rates are simulated in the NPT (constant number, pressure and temperature) ensemble. Hysteresis is found due to the superheating and supercooling. Drastic change of volume and energy is involved with phase change, but the melting point can not be obtained by simply observing the changes of these quantities. Since liquid and solid phases can co-exist at the same temperature, Gibbs free energy should be calculated to find the temperature where the Gibbs free energy of liquid is equal to that of the solid since the equilibrium state is the state of minimum Gibbs free energy. The obtained melting temperature, $T^*=0.685$, is close to that of the experiment with only 2% error.

• 소성∙가공
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• 제22권8호
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• pp.456-462
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• 2013

Compression tests were conducted at the various temperatures and strain rates to investigate void formation and microstructures behavior of a 1.9wt%C ultrahigh carbon steel used in forged workrolls. The microstructure, grain size and volume fraction of cementite were determined using specimens deformed in the temperature range from 800 to $1150^{\circ}C$ and strain rates from 0.01 to 10/s. It was found from the microstructural analysis that the grain size is larger at higher temperatures and lower strain rate deformation conditions. In addition, a higher volume fraction of cementite was measured at lower temperatures. The brittle blocky cementite was fractured at $800^{\circ}C$ and $900^{\circ}C$ regardless of strain rate. As a result, numerous new micro voids were formed in the fragmented blocky cementite. It was also found that local melting can occur at temperatures of more than $1130^{\circ}C$. Therefore, the forging temperature should be controlled between $900^{\circ}C$ and $1120^{\circ}C$. The temperature rise, which depends on the anvil stroke and velocity, was estimated through cogging simulation to find the appropriate forging temperature and to prevent local melting due to plastic work.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제50권1호
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• pp.1-5
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• 2001

P(VDF/TrFE) copolymer thin films with 70/30 and 80/20 mol% VDF (polyvinylidene fluoride) and TrFE (trifluoroethylene) rates were prepared by using a vapor deposition method, During thin films were prepared, the substrate temperatures were maintained at 30 $^{\circ}C$ and 120 $^{\circ}C$, and the heating source temperature was fixed at 350 $^{\circ}C$. Contary to PVDF homopolymer, P(VDF/TrFE) copolymers showed the Curie point(Tc) below the melting point. The Curie point (Tc) and the melting point of the P(VDF/TrFE) copolymers were changed as a function of substrate temperature and the VDF mol%. The Curie point and the melting point of P(VDF/TreFE) thin films decreased and increased with increasing substrate temperature, respectively. Also with increasing VDF mol%, the melting point decreased slightly, however the Curie point increased.

• 자원리싸이클링
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• 제20권2호
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• pp.74-81
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• 2011

자동차 폐촉매로부터 폐촉매 중에 함유되어 있는 백금족 금속(Pt, Rh, Pd)를 회수하는 방법으로는 크게 건식법과 습식법이 현재 이용되고 있다. 본 연구에서는 건식 용융법으로 폐촉매로부터 백금족 금속 회수하기 위한 기초 실험으로 포집금속으로 Fe와 Cu을 사용하여 폐촉매를 용융하였을 때 각각의 농도 변화를 비교함으로써 용융 조건과 적정 포집금속으로 찾는 것을 목적으로 하였다. 본 실험으로 얻어진 결과를 요약하면 Fe을 포집금속으로 히는 것이 Cu을 포집금속으로 사용하는 것보다 회수율 측면에서 유리하였으며, 용융 처리 온도는 $1,500^{\circ}C$에 비교하여 $1,600^{\circ}C$ 용융 하였을 때 슬래그 중 잔류하는 백금족 금속의 농도 변화율이 크게 향상되었다. 용융 온도 $1,600^{\circ}C$의 경우 처리 후 슬래그 중 백금족 원소인 Rh, Pd, Pt의 평균 농도는 각각 6.21 ppm, 5.98 ppm, 6.97ppm으로, 이는 용융 온도 $1,500^{\circ}C$시 보다도 슬래그 백금족 원소 중 Rh와 Pd는 농도변화율 측면에서 각각 50.58%, 55.31%향상되었다. 그러나 폐촉매 중의 Pt의 초기농도가 12.9 ppm으로 낮아 용융처리 후 농도변화율의 비교가 어려웠다.

• 설비공학논문집
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• 제8권3호
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• pp.437-450
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• 1996

A set of stability equations is formulated for natural convection flows adjacent to a vertical isothermal surface melting in cold pure water. It takes account of the nonparallelism of the base flows. The melting rate is regarded as a blowing velocity at the ice surface. The numerical solutions of the linear stability equations which constitute a two-point boundary value problem are accurately obtained for various values of the density extremum parameter $R=(T_m-T_{\infty})/(T_0-T_{\infty})$ in the range $0.3{\leq}R{\leq}0.6$, by using a computer code COLNEW. The blowing effects on the base flow becomes more significant as ambient temperature ($T_{\infty}$) increases to $T_{\infty}=10^{\circ}C$. The maximum decrease of heat transfer rate is about 6.4 percent. The stability results show that the melting at surface causes the critical Grashof number $G^*$ and the maximum frequency of disturbances to decrease. In comparision with the results for the conventional parallel flow model, the nonparallel flow model has a higher critical Grashof number but has lower amplification rates of disturbances than does the parallel flow model. The spatial amplification contours exhibit that the selective frequency $B_0$ of the nonparallel flow model is higher than that of the parallel flow model and that the effects of melting are rather small. The present study also indicates that the selective frequency $B_0$ can be easily predicted by the value of the frequency parameter $B^*$ at $G^*$, which comes from the neutral stability results of the nonparallel flow model.

• 미생물학회지
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• 제28권1호
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• pp.19-26
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• 1990

To examine the effects of sequence variations near the transcriptional start site on the rate of formation of the open complexes at bacteriophage $\lambda P_{R}$ promoter, two mutant promoters were created by site-specific mutagenesis using synthetic oligonucleotides. Mutant I coatains changes at positions -3 and -4 from TT to CC, thus having a 6-bp long G/C stretch between -10 region and transciptional start site (+1). Mutant II has changes at positions -5 and -6 from GG to AA, thereby having a 9-bp long A/T stretch between positions -11 and -3. Selective filter binding assays were performed to measure the rate of formation of the open complexes between the wild-type or two mutant $P_{R}$ promoters on 664 bp fragments and E. coli RNA polymerase at two temperatures. At 37.deg.C, the wild-type and two mutants showed similar rates for the formation of open complex. The second order rate constant $k_{a}$ and $\tau _{int}$, as determined from the .tau.-plot analysis, were $(6.0\pm0.4)\times10^{6}M^{-1}sec^{-1}$ and $11\pm5$sec, respectively. At 18.deg.C, however, the wild-type and two mutant promoters showed differences in the kinetic parameters. k for the wild-type promoter was (2.2$\pm$0.1)\times 10^{6}M^{-1}sec^{-1}$ and $\tau _{int}$ was 76$\pm$sec. Mutant I and II exhibited differences mainly in the rate of isomerization ($\tau_{int,I}=91\pm$10 sec, int,II=34$\pm$ sec), whereas the second order rate constant $k_{a}$ was similar to the wild type value. This result implies that at $18^{\circ}C$, the isomerization rate is determined by both protein conformational change and DNA melting, which are separable kinetically according to the 3-step mechanism of Roe et al.(1984,1985), and that the base changes affected mainly the rate of DNA melting as predicted.lting as predicted.

• 한국결정성장학회지
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• 제7권4호
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• pp.528-535
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• 1997

Halogen type floating zone system을 이용하여 직경 6 mm, 길이가 20 mm인 조화용융조성(congruently melting composition)의 $LiTaO_3$(LT) 단결정을 성장시켰다. 최적의 분말합성조건, 원료봉의 소결조건, 결정 성장조건을 확립하였다. 공기나 질소분위기에서는 결정성장이 불가능하였으나 아르곤 분위기에서는 안정한 형태의 용융대를 형성 및 유지할 수 있어서 결정성장이 용이하게 진행될 수 있었다. 성장된 결정으로 Laue back reflection pattern, 전이온도, 굴절율분포, 투과율을 측정하여 성장된 결정의 물성을 평가하였다. 성장된 결정의 부분별(top, body, tail) 전이온도 차가 $1^{\circ}C$로 측정되어 floating zone(FZ)법으로 성장된 LT결정이 조성적으로 균일함을 확인할 수 있었다.