• Elastomers and Composites
• /
• 제56권2호
• /
• pp.72-78
• /
• 2021

A phase-change material (PCM) is a material that has the ability to delay heat transfer by absorbing heat from its environment or releasing heat to its environment while its phase changes from solid to liquid or liquid to solid at a specific temperature. As it is applied, it can contribute to environmental conservation such as energy savings and carbon dioxide emission reduction. In order for a PCM to store and release heat, the volume change during its phase transition should be large, and thus a phase transition space is required. When a PCM is used as a polymer additive, it is confined within the polymer, and there is no phase transition space; thus, its ability to absorb and release heat is significantly reduced. Therefore, in this study, porous silica was used to provide EVA/PCM compounds with sufficient space for their phase transition, and to improve the compatibility between the EVA and PCM, modified silica is used: surface-modified 5 wt% silica with 3-methacryloxypropyltrimethoxysilane. The compound was prepared and compared with the silica compound. The presence or absence of the modified silica surface modification was confirmed using Fourier-transform infrared spectroscopy and thermogravimetric analysis, the heat capacity of the compound was evaluated based on a differential scanning calorimetry analysis, and its mechanical strength and morphology were determined using scanning electron microscopy.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 추계학술대회
• /
• pp.1122-1127
• /
• 2004

an isolated droplet combustion exposed to pressure perturbations in stagnant gaseous environment is numerically conducted. Governing equations are solved for flow parameters at gas and liquid phases separately and thermodynamic parameters at the interfacial boundary are matched for problem closure. For high-pressure effects, vapor-liquid interfacial thermodynamics is rigorously treated. A series of parametric calculations in terms of mean pressure level and wave frequencies are carried out employing a n-pentane droplet in stagnant gaseous air. Results show that the operating pressure and driving frequency have an important role in determining the amplitude and phase lag of a combustion response. Mass evaporation rate responding to pressure waves is amplified with increase in pressure due to substantial reduction in latent heat of vaporization. Phase difference between pressure and evaporation rate decreases due to the reduced thermal inertia at high pressure. In addition to this, augmentation of perturbation frequency also enhances amplification of vaporization rate because the time period for the pressure oscillation is much smaller than the liquid thermal inertia time. The phase of evaporation rate shifts backward due to the elevated thermal inertia at high acoustic frequency.

• 한국분말재료학회지
• /
• 제7권4호
• /
• pp.218-227
• /
• 2000

It is well known that the Cu-Cr alloys are very difficult to be made by conventional sintering methods. This difficulty originates both from limited solubility of Cr in the Cu matrix and from limited sintering temperature due to high vapor pressures of Cr and Cu components at the high temperature. Densification of Cu-50%Cr Powder compacts by conventional Powder metallurgy Process has been studied. Three kinds of sintering methods were tested in order to obtain high-density sintered compacts. Completely densified Cu-Cr compacts could be obtained neither by solid state sintering method nor by liquid phase sintering method. Both low degree of shrinkage and evolution of large pores in the Cu matrix during the solid state sintering are attributed to the anchoring effect of large Cr particles, which inhibits homogeneous densification of Cu matrix and induces pore generation in the Cu matrix. In addition, the effect of undiffusible gas coming from the reduction of Cu-oxide and Cr-oxide was observed during liquid phase sintering. A two-step sintering method, solid state sintering followed by liquid phase sintering, was proved to have beneficial effect on the fabrication of high-dendsity Cu-Cr sintered compacts. The sintered compacts have properties similar to those of commercial products.

• Journal of the Korean Wood Science and Technology
• /
• 제43권4호
• /
• pp.429-437
• /
• 2015

아세틸화처리는 목재의 치수안정성을 높이는 방법으로 알려졌다. 기상처리보다는 액상처리가 중량증가율이 높기 때문에 더 많이 사용된다. 국내산 소나무재와 잣나무재를 액상 아세틸화처리하여 밀도, 휨강도, 치수안정성 등 물리적 성질에 미치는 효과를 조사하였다. 아세틸화처리에 의한 소나무와 잣나무 시편의 중량은 각각 평균 10.4%와 9.2% 증가하였으며, 전건밀도는 각각 평균 6.9%와 4.6% 증가하였다. 소나무와 잣나무 모두 휨파괴계수(MOR)와 휨탄성계수(MOE), 동탄성계수(DMOE)의 변화는 없었다. 아세틸화처리 후 목재시료의 평균 항흡습률(PRH)은 소나무와 잣나무가 각각 20.6%와 13.8% 이었다. 평균 항흡수율(PRA)은 소나무와 잣나무가 각각 20.0%와 8.5%였다. 따라서 아세틸화처리에 의해 소나무의 치수안정성이 향상된 결과를 얻었다.

• 한국분말재료학회지
• /
• 제22권4호
• /
• pp.266-270
• /
• 2015

The synthesis of NiTi alloy powders by hydrogen reduction and dehydrogenation process of NiO and $TiH_2$ powder mixtures is investigated. Mixtures of NiO and $TiH_2$ powders are prepared by simple mixing for 1 h or ball milling for 24 h. Simple-mixed mixture shows that fine NiO particles are homogeneously coated on the surface of $TiH_2$ powders, whereas ball milled one exhibits the morphology with mixing of fine NiO and $TiH_2$ particles. Thermogravimetric analysis in hydrogen atmosphere reveals that the NiO and $TiH_2$ phase are changed to metallic Ni and Ti in the temperature range of 260 to $290^{\circ}C$ and 553 to $639^{\circ}C$, respectively. In the simple-mixed powders by heat-up to $700^{\circ}C$, agglomerates with solid particles and solidified liquid phase are observed, and the size of agglomerates is increased at $1000^{\circ}C$. From the XRD analysis, the presence of liquid phase is explained by the formation and melting of $NiTi_2$ inter-metallic compound due to an exothermic reaction between Ni and Ti. The simple-mixed powders, heated to $1000^{\circ}C$, lead to the formation of NiTi phase but additional Ni-, Ti-rich and Ti-oxide phases. In contrast, the microstructure of ball-milled powders is characterized by the neck-grown particles, forming $Ni_3Ti$, Ti-oxide and unreacted Ni phase.

• 한국분무공학회지
• /
• 제2권3호
• /
• pp.17-24
• /
• 1997

A simplified experiment was performed to figure out the atomization characteristics of rice-bran oil which it is highly viscous liquid by applying ultrasonic energy. A spray system, an ultrasonic system, and three kinds of hole-type nozzles(hole diameter: 0.31, 0.34, 0.37mm) were manufactured. To investigate the effects of ultrasonic energy on the atomization of a highly viscous liquid, a phase doppler particle analyzer was used for measurement and calculation of spray droplets data. Nozzle opening pressures were chosen of 3 levels, i.e, 16, 20, and 24MPa. As a result, it could be concluded that the ultrasonic energy was effective to improve the spray atomization when it applied to the fuel by means of 3 different nozzles because of the effects of the liquid fuel cavitation and relaxation between molecules caused by ultrasonic energy. The improvement rate of the spray atomization by the ultrasonic method compared with the conventional spray increased about 15% in the case of hole type nozzles. By increasing of the nozzle opening pressure and decreasing of the hole diameter, the atomization of spray droplets was improved.

• 한국분무공학회지
• /
• 제10권4호
• /
• pp.8-15
• /
• 2005

The use of clean gaseous fuels for the purpose of high efficiency and low emission in automotive engines has tendency to increase in order to meet the reinforcing emission regulations and to efficiently utilize limited natural resources. Automotive companies developed and commercialized a LPG liquid injection system, which is mounted on LPLi(Liquid Phase LPG Injection) engines and vehicles based on this research trend. This research examines the biggest problem in LPLi engine, that is, the leakage characteristics of low viscosity LPG fuel according to the injector design variables. This study is also aimed to improve the performance of fuel-leakage in LPLi engine through the addition of a lubrication improver in HFRR(High Frequency Reciprocating Rig) facility. The needle displacement and the spring displacement of an LPLi injector are found to be already optimized. The possibility of a maximum of 70% leakage reduction compared to a conventional case, is verified when 1000ppm of a lubrication improvement material is added and 40% increase of a injector spring constant (K) is applied.

• 한국분말재료학회지
• /
• 제19권6호
• /
• pp.393-397
• /
• 2012

$AgNO_3$ has the characteristic is controlling the inhibition or promotion of particle growth by adsorbing onto specific facets of platinum nanoparticles. Therefore, in this study, $AgNO_3$ was added to control the shape of platinum nanoparticles during the liquid phase reduction process. Consequently, platinum cubes were synthesized when $AgNO_3$ of 1.1 mol% (with respect to the Pt concentration) was added into the solution. Platinum octahedrons were synthesized when 32 mol% (with respect to the Pt concentration) was added into the solution. These results demonstrate that the metal salt $AgNO_3$, effectively controlled the relative growth rates of each facet of Pt nano particles.

• 한국분말재료학회지
• /
• 제19권1호
• /
• pp.60-66
• /
• 2012

In this study, Platinum(Pt) nanoparticles were synthesized by using polyol process which is one of the liquid phase reduction methods. Dihydrogen hexachloroplatinate (IV) hexahydrate $(H_2PtCl_6{\cdot}6H_2O)$, as a precursor, was dissolved in ethylene glycol and silver nitrate ($AgNO_3$) was added as metal salt for shape control of Pt particle. Also, polyvinylpyrrolidone (PVP), as capping agent, was added to reduce the size of particle and to separate the particles. The size of Pt nanoparticles was evaluated particle size analyzer (PSA). The size and morphology of Pt nanoparticles were observed by transmission electron microscopy (TEM) and high resolution TEM (HRTEM). Synthesized Pt nanoparticles were studied with varying time and temperature of polyol process. Pt nanoparticles have been successfully synthesized with controlled sizes in the range 5-10 and 20-40 nm with cube and multiple-cube shapes.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 춘계학술대회
• /
• pp.1286-1291
• /
• 2004

In order for studying pressure-coupled dynamic responses of droplet vaporization, open-loop experiment of an isolated droplet vaporization exposed to pressure perturbations in stagnant gaseous environment is numerically conducted. Governing equations are solved for flow parameters at gas and liquid phases separately and thermodynamic parameters at the interfacial boundary are matched for problem closure. For high-pressure effects, vapor-liquid interfacial thermodynamics is rigorously treated. A series of parametric calculations in terms of mean pressure level and wave frequencies are carried out employing a n-pentane droplet in stagnant gaseous nitrogen. Results show that wave instability in view of pressure-coupled vaporization response seems more susceptible at higher pressures and higher wave frequencies. Mass evaporation rate responding to pressure waves is amplified with increase in pressure due to substantial reduction in latent heat of vaporization. Augmentation of perturbation frequency also enhances amplification due to the reduction of phase differences between pressure perturbation and surface temperature fluctuation.