• Title, Summary, Keyword: Melting temperature

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Preparation of Zone-melted NdBaCuO under Low Oxygen Pressure

  • wha, Soh-Dea;guo, Fan-Zhan;ying, Gao-Wei;Jeon Yongwoo
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • pp.85-88
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    • 2001
  • The NdBaCuO superconductor samples were Zone-melted in low oxygen partial pressure (1% O$_2$+99% Ar). The Zone-melting temperature was decreased about 120$^{\circ}C$ from 1060$^{\circ}C$ the zone-melting temperature in air. Thus the loss of liquid phase (BaCuO$_2$ and CuO) was reduced during the zone-melting process. The content of non-superconducting phase Nd422 in zone-melted NdBaCuO samples was clearly decreased, so was the substitution of Nd for Ba. The superconductivity of zone-melted Nd$\sub$1+x/Ba$\sub$2-x/Cu$_3$O$\sub$y/ prepared under low oxygen partial pressure was distinctively improved.

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Study on the Melting Point Depression of Tin Nanoparticles Manufactured by Modified Evaporation Method (수정된 증발법을 이용하여 제작된 주석 나노입자의 녹는점 강하에 관한 연구)

  • Kim, Hyun Jin;Beak, Il Kwon;Kim, Kyu Han;Jang, Seok Pil
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.38 no.8
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    • pp.695-700
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    • 2014
  • In the present study, the melting temperature depression of Sn nanoparticles manufactured using the modified evaporation method was investigated. For this purpose, a modified evaporation method with mass productivity was developed. Using the manufacturing process, Sn nanoparticles of 10 nm size was manufactured in benzyl alcohol solution to prevent oxidation. To examine the morphology and size distribution of the nanonoparticles, a transmission electron microscope was used. The melting temperature of the Sn nanoparticles was measured using a Differential scanning calorimetry (DSC) which can calculate the endothermic energy during the phase changing process and an X-ray photoelectron spectroscopy (XPS) used for observing the manufactured Sn nanoparticle compound. The melting temperature of the Sn nanoparticles was observed to be $129^{\circ}C$, which is $44^{\circ}C$ lower than that of the bulk material. Finally, the melting temperature was compared with the Gibbs Thomson and Lai's equations, which can predict the melting temperature according to the particle size. Based on the experimental results, the melting temperature of the Sn nanoparticles was found to match well with those recommended by the Lai's equation.

Manufacture of Soluble Micro-fiber and Low Melting Polymer for Interior Synthetic Leather (인테리어용 인조가죽을 위한 용출형 극세사와 저온 융착사의 제조)

  • Ahn, Young-Moo
    • Korean Journal of Human Ecology
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    • v.12 no.4
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    • pp.529-537
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    • 2003
  • This study was conducted to manufacture the soluble micro-fiber and to synthesize low melting polymer for the interior fabric not to use the polyurethane resin causing some problems. Low melting polyester for weft yarn was introduced by adding 30-40 mol% ratio of isophthalic acid to a main chain of polyethylene terephthalate to decrease the melting temperature up to heat setting temperature. Micro-fiber for warp yarn consisted of both soluble and insoluble components with multi-layered structure. When the soluble micro-fiber was treated by alkaline hydrolysis with 3-5% concentration of NaOH, it showed the turning point at 28% weight loss since soluble polyester was hydrolyzed approximate five times faster than regular polyester.

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Effect of the Height Change on the Melting Heat Transfer in a Rectangular Enclosure (정사각형 단면을 갖는 용기에서 단면의 크기 변화가 융해 열전달에 미치는 영향)

  • Han, Jin Ho;Ro, Sung Tack
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.2 no.3
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    • pp.208-217
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    • 1990
  • A rectangular test section is devised by assuming two dimensional melting of a solid phase change material heated from two sides which are maintained at constant temperature and allowing a free expansion due to density difference between solid and liquid. The timewise melting shape is recorded photographically by the shadow graph method for several experimental conditions. The analysis shows that the melting process consists of four regimes. At first, the pure conduction heat transfer is dominant, and as time goes by natural convection grows and plays a role greatly. Experiments are carried out varying not only the wall temperature but height of the wall. Each effect of them on the melting process is obtained in the form of combination of dimensionless parameters, $Ste^{0.8}\;FoRa^{0.2}$. An algebraic correlation is suggested, which predicts the melted fraction well.

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An Experimental Study of Accelerating Phase Change Heat Transfer

  • Oh, Yool-Kwon;Park, Seul-Hyun;Cha, Kyung-Ok
    • Journal of Mechanical Science and Technology
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    • v.15 no.12
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    • pp.1882-1891
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    • 2001
  • The present paper investigated the effect of ultrasonic vibrations on the melting process of a phase-change material (PCM). Furthermore, the present study considered constant heat flux boundary conditions unlike many of the previous researches adopted constant wall temperature conditions. Therefore, in the present study, modified dimensionless parameters such as Ste* and Ra* were used. Also, general relationships between melting with ultrasonic vibrations and melting without ultrasonic vibrations were established during the melting of PCM. Experimental observations show that the effect of ultrasonic vibrations on heat transfer is very important throughout the melting process. The results of the present study reveal that ultrasonic vibrations accompany the effects like agitation, acoustic streaming, cavitation, and oscillating fluid motion. Such effects are a prime mechanism in the overall melting process when ultrasonic vibrations are applied. They enhance the melting process as much as 2.5 tildes, compared with the result of natural melting. Also, energy can be saved by applying ultrasonic vibrations to the natural melting. In addition, various time-wise dimensionless numbers provide conclusive evidence of the important role of ultrasonic vibrations on the melting phenomena.

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Assessment of Mass Fraction and Melting Temperature for the Application of Limestone Concrete and Siliceous Concrete to Nuclear Reactor Basemat Considering Molten Coree-Concrete Interaction

  • Lee, Hojae;Cho, Jae-Leon;Yoon, Eui-Sik;Cho, Myungsug;Kim, Do-Gyeum
    • Nuclear Engineering and Technology
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    • v.48 no.2
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    • pp.448-456
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    • 2016
  • Severe accident scenarios in nuclear reactors, such as nuclear meltdown, reveal that an extremely hot molten core may fall into the nuclear reactor cavity and seriously affect the safety of the nuclear containment vessel due to the chain reaction caused by the reaction between the molten core and concrete. This paper reports on research focused on the type and amount of vapor produced during the reaction between a high-temperature molten core and concrete, as well as on the erosion rate of concrete and the heat transfer characteristics at its vicinity. This study identifies themass fraction and melting temperature as the most influential properties of concrete necessary for a safety analysis conducted in relation to the thermal interaction between the molten core and the basemat concrete. The types of concrete that are actually used in nuclear reactor cavities were investigated. The $H_2O$ content in concrete required for the computation of the relative amount of gases generated by the chemical reaction of the vapor, the quantity of $CO_2$ necessary for computing the cooling speed of the molten core, and the melting temperature of concrete are evaluated experimentally for the molten core-concrete interaction analysis.

An Approximate Analytical Solution for the Unsteady Close-Contact Melting on a Flat Surface with Constant Heat Flux (등열유속에 의한 평판위 비정상 접촉융해에 대한 근사적 해석해)

  • Yoo, Hoseon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.22 no.12
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    • pp.1726-1734
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    • 1998
  • This paper focuses on the unsteady close-contact melting phenomenon occurring between a phase change material kept at its melting temperature and a flat surface on which constant heat flux is imposed. Based on the same simplifications and framework of analysis as the case of constant surface temperature, an approximate analytical solution which depends only on the liquid-to-solid density ratio is successfully derived. In order to keep consistency with the known solution procedure, both the dimensionless wall heat flux and the Stefan number are properly redefined. The obtained solution proves to agree quite well with the published numerical data and to be capable of resolving the fundamental features of unsteady close-contact melting, especially in the presence of the solid-liquid density difference. The density ratio directly affects the film growth rate and the initial value of solid descending velocity, thereby controlling the duration of unsteady process. The effects of other parameters can be evaluated readily from the steady solution which is implied in the normalized result. Since the dimensionless surface temperature for the present boundary condition increases from zero to unity along the evolution path of the liquid film thickness, the unsteady process lasts longer than that for the case of isothermal heating.

Dyeability of Low-melting Hybrid Polyester at Low Temperature (저융점 폴리에스테르 복합사의 저온 염색성)

  • Hwang, Ji-Hyun;Kim, Chang-Nam;Ma, Jin-Suk;Oh, Hae-Sun;Yoon, Nam-Sik
    • Textile Coloration and Finishing
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    • v.24 no.2
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    • pp.113-120
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    • 2012
  • Jacquard floor covering could be prepared from low-melting/regular sheath-core hybrid polyester, where the fiber is dyed in yarn state. With regard that the expected high shrinkage of the hybrid polyester in water makes problems in yarn dyeing, low-temperature dyeing properties of the hybrid polyester were studied. The rate of shrinkage of low-melting hybrid polyester exceeds 9% in hot water above $90^{\circ}C$, at such condition, cheese yarn dyeing is very difficult. Although disperse dyes exhaust in a relatively high speed on low-melting hybrid polyester, diffusion of these dyes to the core regular polyester was extremely slow under $90^{\circ}C$. Foron Blue E-BL 150, an anthraquinone E-type disperse dye, showed appreciable diffusion after 48hrs dyeing at $90^{\circ}C$. The fastness to rubbing and drycleaning were improved by one grade after reduction cleaning.

Dyeing and Heat Setting Properties of Low Melting PET Fiber (저온융착사를 이용한 섬유의 염색성 및 열처리 특성)

  • Hwang, Se-Jeong;Choi, Hyun-Seuk;Kim, Dong-Kwon;Chong, In-Sik;Kim, Sung-Gun
    • Textile Coloration and Finishing
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    • v.21 no.3
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    • pp.37-42
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    • 2009
  • The low melting PET yarn has sheath/core structure: sheath portion consists of low melting point PET and core portion is regular PET. Dyeing properties of fabric made from low melting PET yarn were investigated at different dyeing temperatures. It was found that the exhaustion yield on the low melting PET fabric was higher than on regular PET fabric. The total K/S value of the dyed low melting PET fabric increased as heat setting temperature increased above $150^{\circ}C$ because the sheath portion of the low melting yarn melted. Although fastness to light of the low melting PET fabric was similar to regular PET fabric, fastness to washing was inferior to regular PET fabric by 1 grade.

A study on the heat transfer characteristics during outward melting process of ice in a vertical cylinder (수직원통형 빙축열조내 외향용융과정시 열전달특성에 관한 연구 -작동유체의 유동방향 및 축열조 형상비에 따른 열성능 비교-)

  • Kim, D.H.;Kim, D.C.;Kim, I.G.;Kim, Y.K.;Yim, C.S.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.9 no.2
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    • pp.171-179
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    • 1997
  • During the day time in summer, peak of air conditing load, and electric power management system lies under overloaded condition. The reason is the enlarged peak load value of electric power caused by increased air-cooling load in summer. To prevent load concentration during day time and overloaded condition of power management system, some energy storage methods are suggested. One of these methods is ice storage system. Water has some good properties as P.C.M.(Phase Chang Material) : Its melting point is the range of required operation temperature. It has large specific latent heat and is chemically stable compared to other organic or inorganic substances. It is cheap and easy to treat. This study represents experimental results of heat transfer characteristics of P.C.M. under the outward melting process in a vertical cylinder. We experimented with twelve combinations of conditions, i.e., three different inlet temperatures($7^{\circ}C,\;4^{\circ}C\;and\;1^{\circ}C$), two working fluid directions(upward and downward), and two aspect ratios, H/R(4 and 2). At the inlet temperature of $7^{\circ}C$ and $4^{\circ}C$, there was temperature stagnation region where the temperature of P.C.M. remains constant at $4^{\circ}C$ regardless of aspect ratio and direction of working fluid. This temperature stagnation occurs as the water, at its maximum density, flows down to the lower region. The phase change interface formed bell-shaped curve as the melting process continued. With a new set of conditions(4H/R, inlet temperature $4^{\circ}C$ and $1^{\circ}C$, downward/upwerd inlet direction), the movement of phase change interface was faster when the working flued inlet direction was downward. With the same set of conditions, melting rate and total melting energy were larger when the working fluid inlet direction was downward. The results were reversed when the other sets of conditions were applied.

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