• Title/Summary/Keyword: Surface phase change

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Hydrogen Formation by Photo-splitting of Water on Ilmenite (일메나이트 상에서 물의 광분해에 의한 수소의 생성)

  • Choi, Im-Kyu;Ha, Baik-Hyun
    • Solar Energy
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    • v.8 no.1
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    • pp.49-56
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    • 1988
  • Thermally treated Korean ilmenite was characterized and used for water splitting to obtain hydrogen by photo-catalytic reaction. Experiments on specific surface area, X-ray diffraction and EDS showed that the formation of FeO, $Fe_2O_3$ and $TiO_2$ ilmenite crystal surface increased the specific surface area with maximum value, phase change of $TiO_2$ at $600^{\circ}C$ and hetrogeneity. The hydrogen evolved in caustic soda solution on these ilmenites indicated that there was a maximum yield point at about $600^{\circ}C$. This point was explained with the change of the surface area due to sintering of newly formed FeO, $Fe_2O_3$ and $TiO_2$, as well as crystal phase change of anatase to rutile at $600^{\circ}C$. Produced hydrogen increased also as the concentration of caustic soda, but become constant at the near 1N solution.

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The characteristics of microencapsulated phase-change materials (상전이 마이크로캡슐 재료의 축열특성)

  • 임대우
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 2003.04a
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    • pp.53-56
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    • 2003
  • The objective of this research is to investigate the thermal behavior of microencapsulated phase-change materials(MEPCM), and a shell of melamine-formaldehyde. These PCM materials were tested using DSC and thermal data station. Fabrics with enhanced thermal properties were prepared by padding the fabrics with the microcapsules containing PCM and acryl binder. The rate of temperature increase was significantly decreased as the amount of MEPCM added on the surface of the fabrics increased.

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A Study on Two Dimensional Phase Change Problem (상변화 축열계의 비정상 해석)

  • Won, Sung-Pil;Ro, Sung-Tack
    • The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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    • v.10 no.1
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    • pp.12-21
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    • 1981
  • The Enthalpy Model was verified in order to analyze two- dimensional phase change problems. By using the Enthalpy Model, interface locations, frozen fraction rates, heat flux distribution rut cooled surfaces, and surface-integrated heat flux were purely numerically calculated in rectangular thermal storage units, whose initial condition was saturated liquid and phase change material was cooled on its boundaries by convective heat transfer. The calculations were performed for various Stefan numbers and Biot numbers. The effect on those dimensionless numbers were explained.

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An Algorithm for Discontinuous Surface Profile Measurement using Wavelength Scanning Interferometer (파장 주사 간섭계를 이용한 불연속면의 표면 형상 측정 알고리즘)

  • 우현구;강철무;조형석
    • Journal of Institute of Control, Robotics and Systems
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    • v.9 no.7
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    • pp.507-514
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    • 2003
  • Inspection and shape measurement of three-dimensional objects are widely needed in industries for quality monitoring and control. Recently the shape measurement using interferometric principle is found to be a successful methodology among other visual or optical technologies. Especially, the measuring method using wavelength scanning interferometer(WSI) has a great advantage in comparison with other conventional jnterferometric methods in that the absolute distance from the reference surface can be directly obtained from the amount of jnterferometric phase change. However, the measurement methods using WSI proposed by other researchers have low measurement resolution so far because they can't measure fractional phase change. To avoid this shortcoming we propose a new algorithm in this paper, which can obtain a small amount of even fractional phase change by sinusoidal function fitting. To evaluate the effectiveness of the proposed sinusoidal function fitting algorithm, a series of measuring experiments are conducted for discontinuously shaped specimens which have various height. The proposed algorithm shows much more enhanced measurement resolution than other existing conventional algorithms such as zero crossing algorithm and Fourier transform algorithm.

Effect of Capsule Shape on Heat Storage (캡슐 형상이 축열에 미치는 영향)

  • 정재동
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.14 no.11
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    • pp.964-971
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    • 2002
  • A numerical investigation of the constrained melting of phase change materials within spherical-like capsule is presented. A single-domain enthalpy formulation is used for simulation of the phase change phenomenon. The solution methodology is verified with the melting process inside an isothermal spherical capsule. Especially, the effect of capsule shape on the heat storage is emphasized. Two shape parameters are considered from the real capsule shape showing good characteristics of heat storage and the effect of these parameters is examined. Early during the melting process, the conduction mode of heat transfer is dominant. Thus the capsule shape with large surface area is desirable. However, the capsule shape with large surface area plays negative role on the strength of buoyancy-driven convection that becomes more important as melting continues.

Effects of Phase Change Material Floor Heating Systems using Direct Solar Gain on Cooling Load (직달일사를 이용한 잠열축열식 바닥난방 시스템이 냉방부하에 미치는 영향에 대한 검토)

  • Kim, Soo-Kyung
    • Journal of the Korean Solar Energy Society
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    • v.33 no.3
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    • pp.9-16
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    • 2013
  • In this research, the effect of a heating system, which is powered by direct solar energy accumulated in phase change material (PCM) as heat storage material installed on the floor surface, on the cooling load was studied. Cooling load of a test building designed for this research was measured with fan coil unit and factors affecting it were also estimated. Experiments were performed with and without PCM installed on the building floor to understand the effect of the PCM on the cooling load. Additionally, to confirm the experiments results, the prediction calculation formula by average outside temperature and integrated solar radiation was composed using multivariate regression model. The results suggested that the heating system with PCM on the floor surface has the potential to shift electric power peak by radiating heat, stored during the daytime in it, at night, not increasing the total cooling load much.

Effect of GaGe Sputtering Power on Ga Doping in Phase Change Memory Materials (상 변화 메모리 재료 내의 Ga 주입에 미치는 GaGe 스퍼터링 전력의 영향)

  • Jung, Soon-Won;Lee, Seung-Yun
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.28 no.5
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    • pp.285-290
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    • 2015
  • The phase change memory material is an active element in phase change memory and exhibits reversible phase transition behavior by thermal energy input. The doping of the phase change memory material with Ga leads to the increase of its crystallization temperature and the improvement of its amorphous stability. In this study, we investigated the effect of GaGe sputtering power on the formation of the phase change memory material including Ga. The deposition rate linearly increased to a maximum of 127 nm and the surface roughness remained uniform as the GaGe sputtering power increased in the range from 0 to 75 W. The Ga concentration in the thin film material abruptly increased at the critical sputtering power of 60 W. This influence of GaGe sputtering power was confirmed to result from a combined sputtering-evaporation process of Ga occurring due to the low melting point of Ga ($29.77^{\circ}C$).

Thermal characteristic of PRAM with top electrode (상부전극에 따른 상변화 메모리의 발열 특성)

  • Choi, Hong-Kyw;Jang, Nak-Won;Kim, Hong-Seung;Lee, Seong-Hwan;Mah, Suk-Bum
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2007.11a
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    • pp.97-98
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    • 2007
  • In this paper, we analyzed the reset current variation of PRAM device with top electrode using the 3-D finite element analysis tool. As thickness of phase change material thin film decreased, reset current caused by phase transition highly increased. Joule's heat which was generated at the contact surface of phase change material and bottom electrode of PRAM was given off through top electrode to which was transferred phase change material. As thermal conductivity of top electrode decreased, heating temperate was increased.

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Interannual Variabilities of Sea Surface Temperature and Sea Level Anomaly related to ENSO in the Tropical and North Pacific Ocean System (열대 및 북태평양에서 ENSO와 관련된 표층수온과 해면고도의 경년 변동성)

  • Kim, Eung;Jeon, Dong-Chull
    • Ocean and Polar Research
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    • v.30 no.3
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    • pp.313-324
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    • 2008
  • In order to understand the variation of ENSO-related oceanic environments in the tropical and North Pacific Ocean, spatio-temporal variations of sea surface temperature anomaly (SSTA) and sea surface height anomaly (SSHA) are analyzed from distributions of complex empirical orthogonal functions (CEOF). Correlations among warm pool variation, southern oscillation index, and ocean surface currents were also examined with respect to interannual variability of the warm pool in western tropical Pacific. Spatio-temporal distributions of the first CEOF modes for SSTA and SSHA indicate that their variabilities are associated with ENSO events, which have a variance over 30% in the North Pacific. The primary reasons for their variabilities are different; SST is predominantly influenced by the change of barrier layer thickness, while SSH fluctuates with the same phase as propagation of an ENSO episode in the zonal direction. Horizontal boundary of warm pool area, which normally centered around $149^{\circ}E$ in the tropics, seemed to be expanded to the middle and eastern tropical regions by strong zonal currents through the mature phase of an ENSO episode.

Design of Dynamically Focus-switchable Fresnel Zone Plates Based on Plasmonic Phase-change VO2 Metafilm Absorbers

  • Kyuho Kim;Changhyun Kim;Sun-Je Kim;Byoungho Lee
    • Current Optics and Photonics
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    • v.7 no.3
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    • pp.254-262
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    • 2023
  • Novel thermo-optically focus-switchable Fresnel zone plates based on phase-change metafilms are designed and analyzed at a visible wavelength (660 nm). By virtue of the large thermo-optic response of vanadium dioxide (VO2) thin film, a phase-change material, four different plasmonic phase-change absorbers are numerically designed as actively tunable Gires-Tournois Al-VO2 metafilms in two and three dimensions. The designed phase-change metafilm unit cells are used as the building blocks of actively focus-switchable Fresnel zone plates with strong focus switching contrast (40%, 83%) and high numerical apertures (1.52, 1.70). The Fresnel zone plates designed in two and three dimensions work as cylindrical and spherical lenses in reflection type, respectively. The coupling between the thermo-optic effect of VO2 and localized plasmonic resonances in the Al nanostructures offer a large degree of freedom in design and high-contrast focus-switching performance based on largely tunable absorption resonances. The proposed method may have great potential in photothermal and electrothermal active optical devices for nonlinear optics, microscopy, 3D scanning, optical trapping, and holographic displays over a wide spectral range including the visible and infrared regimes.