• Title/Summary/Keyword: Controlled Cooling Rate

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Development of Aluminium Alloy for Piston of Air Compressor (공기 압축기의 피스톤용 알루미늄 합금 소재 개발)

  • Kim, Soon-Kyung;Kim, Moon-Kyung
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.7 no.1
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    • pp.9-16
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    • 2008
  • It is important not only to reduce the casting defects of piston but also to improvement in the mechanical properties(hardness) of piston for the air compressor. The blow hole is typical casting defects in the conventional cast of aluminium alloy(AC8A-T6) piston. Because of the heat treatment method, mechanical properties of the aluminium alloy for piston was decided on the heat treatment method and cycle. Therefore, we tested on the development of mechanical properties and on the casting defects of piston for the air compressor in accordance with the heat treatment and casting condition. After the heat treatment and casting was carried out as several times, and was compared with the imported piston. As a result of several investigations; microstructure, hardness and casting defects of piston was changed under the influence of the heat treatment and casting method. When the cooling rate was controlled and the uni-cast method used, it bas the same mechanical properties and microstructure.

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Development of Asynchronus High Speed Turbo Blower with Gas Bearing Supports (비동기형 고속모터를 사용한 공기부양식 터보블로워의개발)

  • Park, Ki-Cheol;Yoon, Ju-Shik;Lee, Ki-Ho;Kim, Kyung-Soo;Kim, Dong-Kwon;Kim, Seung-Woo
    • 유체기계공업학회:학술대회논문집
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    • 2003.12a
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    • pp.324-329
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    • 2003
  • Asynchronus high speed turbo blower of 100HP class with gas bearing supports is developed. The high speed motor is cooled by air and it's RPM is controlled by high frequency inverter to adjust inlet flow rate. Product family is ranged from 50 to 200HP and covered by three frames. Highly efficient impeller is designed and proved by performance test on system. Overall measured system efficiency is 82% including motor and inverter. The motor efficiency is about 95%. It is designed to guarantee to operate at ambient temperature of 35 Deg.C and max 45 DegC. Gas bearing with high load capacity is developed to support heavy rotor on low rotational speed.

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An Experimental Study on the Effect of Ventilation Velocity on the Burning Rate in Longitudinal Ventilation Tunnel Fires (종류식 배연 터널 화재시 배연속도가 연소율에 미치는 영향에 대한 실험적 연구)

  • Yang Seung-Shin;Ryou Hong-Sun;Choi Young-Ki;Kim Dong-Hyeon
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.17 no.10
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    • pp.914-921
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    • 2005
  • In this study, the 1/20 reduced-scale experiment using Froude scaling were conducted to investigate the effect of longitudinal ventilation velocity on the burning rate in tunnel fires. The methanol pool fires with heat release rate ranging from 2.02 kW to 6.15 kW and the n-heptane pool fires with heat release rate ranging from 2.23 kW to 15.6 kW were used. The burning rate of fuel was obtained by measuring the fuel mass at the load cell. The temperature distributions were observed by K-type thermocouples in order to investigate smoke movement. The ventilation velocity in the tested tunnel was controlled by inverter of the wind tunnel. In methanol pool fire, the increase in ventilation velocity reduces the burning rate. On the contrary in n-heptane pool fire, the increase in ventilation velocity induces large burning rate. The reason for above conflicting phenomena lies on the difference of burning rate. In methanol pool fire, the cooling effect outweighs the supply effect of oxygen to fire plume, and in n-heptane pool vice versa.

An Experimental Study on the Effect of Longitudinal Ventilation on the Variation of Burning Rate in Tunnel Fires (터널 화재시 종류식 환기가 연소율 변화에 미치는 영향에 관한 실험적 연구)

  • Yang Seung Shin;Kim Sung Chan;Ryou Hong Sun
    • Tunnel and Underground Space
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    • v.15 no.1 s.54
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    • pp.55-60
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    • 2005
  • In this study, the 1/20 reduced-scale experiments using Froude scaling were conducted to investigate the effect of longitudinal ventilation on the variation of burning rate in tunnel fires. The methanol square pool fires with heat release rate ranging from 3.57 kW to 10.95 kW were used. The burning rate of fuel was obtained by measured mass using load cell and temperature distribution were measured by K-type theomocouples in order to investigate smoke movement. The wind tunnel was connected with one side of the tested tunnel, and logitudinal ventilation velocity in the tested tunnel was controlled by power of the wind tunnel. In methanol fire case, the increase in ventilation velocity decreased the turning rate due to the direct cooling of fire plume. For the same dimensionless velocity(V), homing rate decreased as the size of pool fire increased.

Controlled Growth of Large-area Mono-, Bi-, and Few-layer Graphene by Chemical Vapor Deposition on Copper Substrate

  • Kim, Yooseok;Lee, Su-il;Jung, Dae Sung;Cha, Myoung-Jun;Kim, Ji Sun;Park, Seung-Ho;Park, Chong-Yun
    • Proceedings of the Korean Vacuum Society Conference
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    • 2014.02a
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    • pp.380.2-380.2
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    • 2014
  • Direct synthesis of graphene using a chemical vapor deposition (CVD) has been considered a facile way to produce large-area and uniform graphene film, which is an accessible method from an application standpoint. Hence, their fundamental understanding is highly required. Unfortunately, the CVD growth mechanism of graphene on Cu remains elusive and controversial. Here, we present the effect of graphene growth parameters on the number of graphene layers were systematically studied and growth mechanism on copper substrate was proposed. Parameters that could affect the thickness of graphene growth include the pressure in the system, gas flow rate, growth pressure, growth temperature, and cooling rate. We hypothesis that the partial pressure of both the carbon sources and hydrogen gas in the growth process, which is set by the total pressure and the mole fraction of the feedstock, could be the factor that controls the thickness of the graphene. The graphene on Cu was grown by the diffusion and precipitation mode not by the surface adsorption mode, because similar results were observed in graphene/Ni system. The carbon-diffused Cu layer was also observed after graphene growth under high CH4 pressure. Our findings may facilitate both the large-area synthesis of well-controlled graphene features and wide range of applications of graphene.

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Carbon Nanotube Oscillator Operated by Thermal Expansion of Encapsulated Gases (삽입 가스의 부피 팽창을 이용한 탄소나노튜브 진동기)

  • Kwon, Oh-Keun
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.18 no.12
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    • pp.1092-1100
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    • 2005
  • We investigated a carbon nanotube (CNT) oscillator controlled by the thermal gas expansion using classical molecular dynamics simulations. When the temperature rapidly increased, the force on the CNT oscillator induced by the thermal gas expansion rapidly increased and pushed out the CNT oscillator. As the CNT oscillator extruded from the outer nanotube, the suction force on the CNT oscillator increased by the excess van der Waals(vdW) energy. When the CNT oscillator reached at the maximum extrusion point, the CNT oscillator was encapsulated into the outer nanotube by the suction force. Therefore, the CNT oscillator could be oscillated by both the gas expansion and the excess vdW interaction. As the temperature increased, the amplitude of the CNT oscillator increased. At the high temperatures, the CNT oscillator escaped from the outer nanotube, because the force on the CNT oscillator due to the thermal gas expansion was higher than the suction force due to the excess vdW energy. By the appropriate temperature controls, such as the maximum temperature, the heating rate, and the cooling rate, the CNT oscillator could be operated.

Study on the Regenerating Performance of Liquid Desiccant in the Cooling/Dehumidification System able to use a Solar Water Heater in Summer(On the Analysis of Source Effect by the Design of Experiments) (여름철 냉방/제습시스템 중 태양열 온수기를 적용할 수 있는 액체흡수제의 재생성능에 관한 연구(실험계획법에 의한 요인효과 분석에 관하여))

  • Choi, K.H.;Kim, B.C.;Kim, B.J.
    • Journal of the Korean Solar Energy Society
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    • v.22 no.1
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    • pp.1-8
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    • 2002
  • With the possibility of hot water being able to be used as a heating source in a liquid desiccant system, an experimental apparatus for regeneration of the liquid desiccant was set up and series of experiments were conducted in a climate-controlled chamber. This study was performed to ascertain the influences of experimental factors on regenerating performance and to suggest the optimal combination of factors affecting regeneration rate. Furthermore. in order to figure out the contribution ratio of the factors on regenerating performance, a multi-way factorial design among the design of experiments was adopted. According to experimental results, the most influential factor on regenerating performance was temperature of the liquid desiccant and its contribution ratio was about 79.4%. In addition. the optimal operating combination was as follows; $60^{\circ}C$ of solution temperature, $14\ell$/min of solution flow rate, and 190m3/h of air volume.

Nd:YAG laser firmware Design under RTOS operation (RTOS(Real Time Operation System) 환경하의 Nd:YAG 레이저 Firmware 설계)

  • Kim, B.G.;Kim, W.Y.;Park, G.R.;Moon, D.S.;Hong, J.H.;Kim, H.J.;Cho, J.S.
    • Proceedings of the KIEE Conference
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    • 2000.07c
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    • pp.2107-2109
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    • 2000
  • A pulsed Nd:YAG laser is used widely for materials processing and medical instrument. It's very important to control the laser energy density in those fields using a pulsed Nd:YAG laser. A pulse repetition rate and a pulse width are regarded as the most dominant factors to control the energy density of laser beam. In this paper, the alternating charge and discharge system was designed to adjust a pulse repetition rate This system is controlled by microprocessor and allows to replace an expensive condenser for high frequency to cheap one for low frequency. In addition, The microcontroller monitors the flow of cooling water, short circuit. and miss firing and so on. We designed Nd:YAG laser firmware with smart microcontroller, and want to explain general matters about the firmware from now.

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Artificial Insemination in Poultry (가금의 인공수정)

  • Howarth, Birkett
    • Korean Journal of Animal Reproduction
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    • v.7 no.2
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    • pp.57-71
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    • 1983
  • 1. Diluted chicken semen can be preserved at 2 to 5$^{\circ}C$ for 24 to 48 hr with resultant fertility of greater than 90% of that of fresh semen. Turkey semen can be preserved at 10 to 15$^{\circ}C$ for 6 to 24 hr and provide economical fertility. 2. Frozen chicken semen has given variable results; a 21 to 93% fertility ranges as compared to 92 to 94% expected with fresh semen. Highest fertility levels obtained with frozen turkey semen intravaginally inseminated have been 61 and 63% using DMSO and glycerol, respectively, as cryoprotectants. 3. The use of glycerol as a cryoprotectant reauires that its concentration in semen be reduced to less than 2% either by dialysis or centrifugation after thawing and before intravaginal insemination if optimal fertility is to be obtained. 4. The temperature at which cryoprotectants are added to semen and the time allowed for equilibration are important for subsequent fertility pre- and post-freezing. 5. The type of container used for packaging the semen, freeze or cooling rates, thaw rates and level of cryoprotectant all interact in affecting cell survival. 6. Plastic freeze straws as a packaging device for semen offers the following advantages: easy to handle, require minimal storage space, offer a wide range of freeze and thaw rates, and insemination can be made directly from them upon thawing. 7. Controlled slow cooling rates of 1 to 8$^{\circ}C$/min have thus far provided the best results for cooling chicken semen throught the transition phase change (liquid to solid) or critical temperature range of +5 to -20 or -35$^{\circ}C$. 8. Highest fertilities have been achieved with frozen chicken semen where a slow thaw rate (2。 to 5$^{\circ}C$) has been used regardless of the freeze rate. 9. To maintain a constant high level of fertility throughout a breeding season with frozen semen, a higher absolute number of spermatozoa must be inseminated (2 to 3 times as many) as compared to fresh semen since a, pp.oximately 50% are destroyed during processing and freezing. 10. The quality of semen may vary with season and age of the male. Such changes in sperm quality could be accentuated by storage effects. Thus, the correct number of spermatozoa may very well vary during the course of a breeding period. 11. As to time of insemination, it is best to avoid inseminating chicken hens within 1-2 hr after or 3-5 hr before oviposition; and turkey hens during or 7-10 hr before oviposition. 12. The physiological receptiveness of the oviduct at the time of insemination is a very important biological factor influencing fertility levels throughout the breeding season.

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Estimation of Soil Cooling Load in the Root Zone of Greenhouses (온실내 근권부의 지중냉각부하 추정)

  • 남상운
    • Journal of Bio-Environment Control
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    • v.11 no.4
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    • pp.151-156
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    • 2002
  • Root zone cooling, such as soil or nutrient solution cooling, is less expensive than air cooling in the whole greenhouse and is effective in promoting root activity, improving water absorption rate, decreasing plant temperature, and reducing high temperature stress. The heat transfer of a soil cooling system in a plastic greenhouse was analyzed to estimate cooling loads. The thermal conductivity of soil, calculated by measured heat fluxes in the soil, showed the positive correlation with the soil water content. It ranged from 0.83 to 0.96 W.m$^{[-10]}$ .$^{\circ}C$$^{[-10]}$ at 19 to 36% of soil water contents. As the indoor solar radiation increased, the temperature difference between soil surface and indoor air linearly increased. At 300 to 800 W.m$^{-2}$ of indoor solar radiations, the soil surface temperature rose from 3.5 to 7.$0^{\circ}C$ in bare ground and 1.0 to 2.5$^{\circ}C$ under the canopy. Cooling loads in the root zone soil were estimated with solar radiation, soil water content, and temperature difference between air and soil. At 300 to 600 W.m$^{-2}$ of indoor solar radiations and 20 to 40% of soil water contents,46 to 59 W.m$^{-2}$ of soil cooling loads are required to maintain the temperature difference of 1$0^{\circ}C$ between indoor air and root zone soil.