• Journal of Hydrogen and New Energy
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• v.30 no.6
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• pp.490-498
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• 2019

The intermittent electric power supply of renewable energy can have extremely negative effect on power grid, so long-term and large-scale storage for energy released from renewable energy source is required for ensuring a stable supply of electric power. Power to gas which can convert and store the surplus electric power as hydrogen through water electrolysis is being actively studied in response to increasing supply of renewable energy. In this paper, we proposed the novel concept of hydrogen liquefaction process combined with pre-cooling process using the liquid air. It is that hydrogen converted from surplus electric power of renewable energy was liquefied through the hydrogen liquefaction process and vaporization heat of liquid hydrogen was conversely recovered to liquid air from ambient air. Moreover, Comparisons of specific energy consumption (kWh/kg) saved for using the liquid air pre-cooling was quantitatively conducted through the performance analysis. Consequently, about 12% of specific energy consumption of hydrogen liquefaction process was reduced with introducing liquid air for pre-cooling and optimal design point of helium Brayton cycle was identified by sensitivity analysis on change of compression/expansion ratio.

• Economic and Environmental Geology
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• v.44 no.6
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• pp.513-523
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• 2011

We estimated geothermal power generation potential in Korea through Enhanced Geothermal System (EGS) technology following the recently proposed protocol which was endorsed by international organizations. Input thermal and physical data for estimation are density, specific heat and thermal conductivity measurements from 1,516 outcrop samples, 180 heat production, 352 heat flow, and 52 mean surface temperature data. Inland area was digitized into 34,742 grids of $1'{\times}1'$ size and temperature distribution and available heat were calculated for 1 km depth interval from 3 km down to 10 km. Thus estimated theoretical potential reached 6,975 GW which is 92 times total generation capacity of Korea in 2010. Technical potential down to 6.5 km and considering land accessibility, thermal recovery ratio of 0.14 and temperature drawdown factor of $10^{\circ}C$ was 19.6 GW. If we disregard temperature drawdown factor, which can be considered in estimating economic potential, the technical potential increases up to 56 GW.

• Asian-Australasian Journal of Animal Sciences
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• v.28 no.2
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• pp.207-214
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• 2015

The effects of high carbohydrate diet on growth, serum physiological response, and hepatic heat shock protein 70 expression in Wuchang bream were determined at $25^{\circ}C$ and $30^{\circ}C$. At each temperature, the fish fed the control diet (31% CHO) had significantly higher weight gain, specific growth rate, protein efficiency ratio and hepatic glucose-6-phosphatase activities, lower feed conversion ratio and hepatosomatic index (HSI), whole crude lipid, serum glucose, hepatic glucokinase (GK) activity than those fed the high-carbohydrate diet (47% CHO) (p<0.05). The fish reared at $25^{\circ}C$ had significantly higher whole body crude protein and ash, serum cholesterol and triglyceride, hepatic G-6-Pase activity, lower glycogen content and relative levels of hepatic growth hormone (GH) gene expression than those reared at $30^{\circ}C$ (p<0.05). Significant interaction between temperature and diet was found for HSI, condition factor, hepatic GK activity and the relative levels of hepatic GH gene expression (p<0.05).

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.05a
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• pp.155-160
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• 2002

Metal matrix composites had generated a lot of interest in recent times because of significant in specific properties. It was also highlighted as the materials of frontier industry because strength, heat-resistant, corrosion-resistant, wear-resistant were superiored. In this study the strength properties of $Al_{18}B_4O_{33}/AC4CH$ were represented mixing the binder of $Al_2O_3$ and $TiO_2$. It was also fabricated by squeeze casting. $Al_{18}B_4O_{33}/AC4CH$ was fabricated at the melt temperature of $760^{\circ}C$ the perform temperature of $700^{\circ}C$ and mold temperature of $200^{\circ}C$ under the pressure of 83.4MPa and observed SEM. Fatigue crack growth rate tests on compact tension specimen(half-size) of thickness 12.5mm were conducted by using sinusoidal waveform. Compact tension specimens(half-size) were used and fatigue crack growth rate da/dN and stress intensity factor range ${\Delta}K$ were analyzed concerning to the R value of 0.1 and 0.05. In order to find out the value of ${\Delta}K$, load amplitude constant method was applied by the standard fatigue testing method describes in ASTM E647-95a. As the results of this study, Fatigue crack growth rate increased with in creasing the load ratio, Consequently, At equivalent stress intensity factors, the fatigue crack growth rates in MMC were faster than those of AC4CH alloy. then the fatigue life and the fatigue crack growth rate was investigated using scanning election microscopy(SEM)

• 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.

• Journal of the Korean Society of Combustion
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• v.20 no.4
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• pp.34-41
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• 2015

Oxy-methane nonpremixed flames diluted with $CO_2$ were investigated to clarify impact of radiation heat loss and chemical effects of additional $CO_2$ to oxidizer stream on flame extinction. Flame stability maps were presented with functional dependencies of critical diluents mole fraction upon global strain rate at several oxidizer stream temperatures in $CH_4-O_2/N_2$, $CH_4-O_2/CO_2$, and $CH_4-O_2/CO_2/N_2$ counterflow flames. The effects of radiation heat loss on the critical diluent mole fractions for flame extinction are not significant even at low strain rate in nonpremixed $CH_4-O_2/N_2$ diffusion flame, whereas those are significant at low strain rate and are negligible at high strain rate (> $200s^{-1}$) in $CH_4-O_2/CO_2$ and $CH_4-O_2/CO_2/N_2$ counterflow flames. Chemical effects of additional $CO_2$ to oxidizer stream on the flame extinction curves were appreciable in both $CH_4-O_2/CO_2$ and $CH_4-O_2/CO_2/N_2$ flames. A scaling analysis based on asymptotic solution of stretched flame extinction was applied. A specific radical index, which could reflect the OH population in main reaction zone via controlling the mixture composition in the oxidizer stream, was identified to quantify the chemical kinetic contribution to flame extinction. A good correlation of predicted extinction limits to those calculated numerically were obtained via the ratio between radical indices and oxidizer Lewis numbers for the target and baseline flames. This offered an effective approach to estimate extinction strain rate of nonpremixed oxy-methane flames permitting air infiltration when the baseline flame was taken to nonpremixed $CH_4-O_2/N_2$ flame.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.1A
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• pp.53-59
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• 2010

Recently, NDTs (Non-Destructive Techniques) using infrared camera are widely studied for detection of damage and void in RC (reinforced concrete) structures and they are also considered as an effective techniques for maintenance of infrastructures. The temperature on concrete surface depends on material and thermal properties such as specific heat, thermal conductivity, and thermal diffusion coefficient. Different porosity on cement mortar due to different mixture proportions can show different heat behavior in cooling stage. The porosity can affect physical and durability properties like strength and chloride diffusion coefficient as well. In this paper, active thermography which uses flash for heat induction is utilized and thermal characteristics on surface are evaluated. Samples of cement mortar with W/C (water to cement ratio) of 0.55 and 0.65 are prepared and physical properties like porosity, compressive strength, and chloride diffusion coefficient are evaluated. Then infrared thermography technique is carried out in a constant room condition (temperature $20{\sim}22^{\circ}C$ and relative humidity 55-60%). The mortar samples with higher porosity shows higher residual temperature at the cooling stage and also shows reduced critical time which shows constant temperature due to back wall effect. Furthermore, simple equation for critical time of back wall effect is suggested with porosity and experimental constants. These characteristics indicate the applicability of infrared thermography as an NDT for quality assessment of cement based composite like concrete. Physical properties and thermal behavior in cement mortar with different porosity are analyzed in discussed in this paper.

• Journal of Radiation Protection and Research
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• v.24 no.4
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• pp.187-193
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• 1999

The specific radioactivity concentrations in the coal fly ash obtained from heat producing stations in Korea were analyzed and its radiological hazard for reuse in construction purpose was evaluated. The concentrations of uranium isotopes in the real fly ash measured by TBP solvent extraction method and $\alpha$-spectrometer were found to be about 116.1 Bq $kg^{-1}$ for $^{238}U$, 5.01 Bq $kg^{-1}$ for $^{235}U$, and 121.2 Bq $kg^{-1}$ for $^{234}U$, respectively. The activity ratio of $^{234}U/^{238}U$, in the coal fly ash was in $1.04\;{\pm}\;0.03$, which is similar to that of uncontaminated Korean soil in natural conditions (1.14). The specific radioactivities of $^{226}Ra,\;^{232}Th,\;and\;^{40}K$ in the coal fly ash were also determined using $\gamma$-spectrometer with a HPGe detector The results showed that $^{226}Ra,\;^{232}Th,\;and\;^{40}K$ in the coal fly ash were in concentrations of $101.7{\sim}113.9$, $39.5{\sim}54.2\;and\;315.0{\sim}990.6$ Bq $kg^{-1}$, respectively. With the specific radioactivities obtained from $\gamma$-spectrometric measurements of the coal fly ash, its radiological hazard for reuse was evaluated. The result showed that the radioactivity of the coal fly ash was in permissible level.

• Korean Journal of Heritage: History & Science
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• v.53 no.1
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• pp.24-33
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• 2020

In excavated bronze artifacts, corrosion products of various shapes and colors are observed due to multiple corrosion factors coexisting in the burial environment, and these corrosion products can constitute important data not only in terms of long-term corrosion-related information, but also in connection with preservation of artifacts. As such, scientific analysis is being carried out on the corrosion layer and corrosion products of bronze artifacts, and the corrosion mechanism and the characteristics of corrosion products elucidated, which is essential for interpreting the exposed burial environment and its association with corrosion factors inside the burial environment. In this study, after classifying excavated bronze artifacts according to alloy ratio and fabrication technique, comprehensive analysis of the surface of corrosion artifacts, corrosion layer, and corrosion products was carried out to investigate the corrosion mechanism, formation process of the corrosion layer, and characteristics of corrosion products. The study designated two groups according to alloy ratio and fabrication technique. In Group 1, which involved a Cu-Sn-Pb alloy and had no heat treatment, the surface was rough and external corrosion layers were formed on a part, or both sides, of the inside and the outside, and the surface was observed as being green or blue. α+δ phase selection corrosion was found in the metal and some were found to be concentrated in an empty space with a purity of 95 percent or more after α+δ phase corrosion. The Cu-Sn alloy and heat-treated Group 2 formed a smooth surface with no external corrosion layer, and a dark yellow surface was observed. In addition, no external corrosion layer was observed, unlike Group 1, and α corrosion was found inside the metal. In conclusion, it can be seen that the bronze artifacts excavated from the same site differ in various aspects, including the formation of the corrosion layer, the shape and color of the corrosion products, and the metal ion migration path, depending on the alloy ratio and fabrication technique. They also exhibited different corrosion characteristics in the same material, which means that different forms of corrosion can occur depending on the exposure environment in the burial setting. Therefore, even bronze artifacts excavated from the same site will have different corrosion characteristics depending on alloy ratio, fabrication technique, and exposure environment. The study shows one aspect of corrosion characteristics in specific areas and objects; further study of corrosion mechanisms in accordance with burial conditions will be required through analysis of the corrosive layer and corrosive product characteristics of bronze artifacts from various regions.

• Journal of the Korean Ceramic Society
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• v.41 no.3
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• pp.221-228
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• 2004

Basic properties of artificial lightweight aggregate by using waste dusts and strength properties of LWA concrete were studied. Bulk specific gravity and water absorption of artificial lightweight aggregates varied from 1.4 to 1.7 and 13 to 16%, respectively. Crushing ratio of artificial lightweight aggregate was above 10% higher than that of crushed stone or gravel. As a result of TCLP leaching test, the leaching amount of tested heavy metal element was below the leaching standard of hazardous material. Slump, compressive strength and stress-strain properties of LWA concrete made of artificial lightweight aggregate were tested. Concrete samples derived from LWA substitution ratio of 30 vol% and W/C ratio of 45 wt% showed the best properties overall. Thermal insulation and sound insulation characteristics of light weight concrete panel with the optimum concrete proportion were tested. Average overall heat transmission of 3.293W/㎡$^{\circ}C$ was observed. It was higher by about 15% than those of normal concrete made by crushed stone. Sound transmission loss of 50.9 ㏈ in frequency of 500 ㎐ was observed. It was higher by about 13% than standard transmission loss.