• Title, Summary, Keyword: Stratification

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Comparison of DME HCCI Operating Ranges for the Thermal Stratification and Fuel Stratification based on a Multi-zone Modeling (Multi-zone 모델링을 통한 온도성층화와 농도성층화가 존재하는 DME HCCI 엔진의 운전영역에 관한 수치해석연구)

  • Jeong, Dong-Won;Lim, Ock-Taeck
    • Transactions of the Korean Society of Automotive Engineers
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    • v.19 no.2
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    • pp.35-41
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    • 2011
  • This work investigates the potential of in-cylinder thermal stratification and fuel stratification for extending the operating ranges in HCCI engines, and the coupling between thermal stratification and fuel stratification. Computational results areemployed. The computations were conducted using both a custom multi-zone version and the standard single-zone version of the Senkin application of the CHEMKINII kinetics rate code, and kinetic mechanism for di-methyl ether (DME). This study shows that the potential of thermal stratification and fuels stratification for extending the high-load operating limit by a staged combustion event with reduced pressure-rise rates is very large. It was also found that those stratification offers good potential to extend low-load limit by a same mechanism in high-load. However, a combination of thermal stratification and fuel stratification is not more effective than above stratification techniques for extending the operating ranges showing similar results of fuel stratification. Sufficient condition for combustion (enough temperature for) turns misfire in low-load limit to operate engines, which also leads to knock in high-load limit abruptly due to the too high temperature with high. DME shows a potential for maximizing effect of stratification to lower pressure-rise rate due to the characteristics of low-temperature heat release.

Enhancement of Seed Germination by Aging, Cold-stratification, and Light Quality during Desiccation in Burcucumber (Sicyos Angulatus L.)

  • Kang, Jin-Ho;Jeon, Byong-Sam;Lee, Sang-Woo;Choe, Zhin-Ryong;Shim, Sang-In
    • KOREAN JOURNAL OF CROP SCIENCE
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    • v.48 no.1
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    • pp.13-16
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    • 2003
  • Seeds of burcucumber were treated with accelerated aging, cold-stratification, and light quality illuminated during desiccation to enhance their germination and seedling emergence. The germination was increased by aging and cold-stratification although the latter treatment showed greater effectiveness than the former one. In the combined treatment of aging 6 days at $45^{\circ}C$ and cold-stratification, the germination was promoted under longer period of cold-stratification to reach nearly 100% in 3 week cold-stratification on the ninth day from sowing. In the sequentially combined treatment of aging, cold-stratification, and light quality during 24 hour desiccation at $35^{\circ}C$, no-stratified seeds showed the highest rate in red light treatment but the lowest in far-red light. This implies that the phytochrome action run during the desiccation of imbibed seeds. The red light exposure during drying for the cold-stratified seeds after aging accelerated the germination even more than the dark treatment and germinated 100% on the next day of sowing. It is concluded that the sequential treatment of aging, cold-stratification, and red light illumination during desiccation can highly promote percentage and speed of burcucumber seed germination.

Multivariate Stratification Method for the Multipurpose Sample Survey : A Case Study of the Sample Design for Fisher Production Survey (다목적 표본조사를 위한 다변량 층화 : 어업비계통생산량조사를 위한 표본설계 사례)

  • Park, Jin-Woo;Kim, Young-Won;Lee, Seok-Hoon;Shin, Ji-Eun
    • Survey Research
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    • v.9 no.1
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    • pp.69-85
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    • 2008
  • Stratification is a feature of the majority of field sample design. This paper considers the multivariate stratification strategy for multipurpose sample survey with several auxiliary variables. In a multipurpose survey, stratification procedure is very complicated because we have to simultaneously consider the efficiencies of stratification for several variables of interest. We propose stratification strategy based on factor analysis and cluster analysis using several stratification variables. To improve the efficiency of stratification, we first select the stratification variables by factor analysis, and then apply the K-means clustering algorithm to the formation of strata. An application of the stratification strategy in the sampling design for the Fisher Production Survey is discussed, and it turns out that the variances of estimators are significantly less than those obtained by simple random sampling.

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Experimental Study on Axial Stratification Process and Its Effects (I) - Stratification in Engine -

  • Ohm, In-Yong;Park, Chan-Jun
    • Journal of Mechanical Science and Technology
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    • v.16 no.11
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    • pp.1457-1469
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    • 2002
  • This paper is the first of several companion papers, which investigate axial stratification process and its effects in an Sl engine. The axial stratification is very sophisticate phenomenon, which results from combination of fuel injection, port and in-cylinder flow and mixing. Because of the inherent unsteady condition in the reciprocating engine, it Is impossible to understand the mechanism through the analytical method. In this paper, the ports were characterized by swir and tumble number in steady flow bench test. After this, lean misfire limit of the engines, which had different port characteristic, were investigated as a function of swirl ratio and injection timing for confirming the existence of stratification. In addition, gas fuel was used for verifying whether this phenomenon depends on bulk air motion of cylinder or on evaporation of fuel. High-speed gas sampling and analysis was also performed to estimate stratification charging effect. The results show that the AFR at the spark plug and LML are very closely related and the AFR is the results of bulk air motion.

A Numerical Analysis on Thermal Stratification Phenomenon by In-Leakage in a Branch Piping

  • Park Jong-Il
    • Journal of Mechanical Science and Technology
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    • v.19 no.12
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    • pp.2245-2252
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    • 2005
  • Thermal stratification in the branch piping of power plants can be generated by turbulent penetration or by valve leakage. In this study, a numerical analysis was performed to estimate the thermal stratification phenomenon by in-leakage in the SIS branch piping of nuclear power plant. Leakage rate, leakage area and leakage location were selected as evaluation factors to investigate the thermal stratification effect. As a result of the thermal stratification effect according to leakage rate, the maximum temperature difference between top and bottom of the horizontal piping was evaluated to be about 185K when the valve leakage rate was about 10 times as much as the allowed leakage rate. For leakage rate more than 10 times the allowed leakage rate, the temperature difference was rapidly decreased due to the increased mixing effect. In the result according to leakage area, the magnitude of temperature difference was shown in order of $3\%,\;1\%\;and\;5\%$ leakage area of the total disk area. In the thermal stratification effect, according to the leakage location, temperature difference when leakage occurred in the lower disk was considerably higher than that of when leakage occurred in the upper disk.

The Effect of Turbulence Penetration on the Thermal Stratification Phenomenon Caused by Leaking Flow in a T-Branch of Square Cross-Section (난류침투가 사각단면 T분기관 내 누설유동에 의해 발생한 열성층 현상에 미치는 영향)

  • 홍석우;최영돈;박민수
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.15 no.3
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    • pp.239-245
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    • 2003
  • In the nuclear power plant, emergency core coolant system (ECCS) is furnished at reactor coolant system (RCS) in order to cool down high temperature water in case of emergency. However, in this coolant system, thermal stratification phenomenon can occur due to coolant leaking in the check valve. The thermal stratification produces excessive thermal stresses at the pipe wall so as to yield thermal fatigue crack (TFC) accident. In the present study, effects of turbulence penetration on the thermal stratification into T-branches with square cross-section in the modeled ECCS are analysed numerically. $textsc{k}$-$\varepsilon$ model is employed to calculate the Reynolds stresses in momentum equations. Results show that the length and strength of thermal stratification are primarily affected by the leak flow rate of coolant and the Reynolds number of the main flow in the duct. Turbulence penetration into the T-branch of ECCS shows two counteracting effects on the thermal stratification. Heat transport by turbulence penetration from the main duct to leaking flow region may enhance thermal stratification while the turbulent diffusion may weaken it.

The Effect of Turbulence Penetration on the Thermal Stratification Phenomenon Caused by Coolant Leaking in a T-Branch of Square Cross-Section

  • Choi, Young-Don;Hong, Seok-Woo;Park, Min-Soo
    • International Journal of Air-Conditioning and Refrigeration
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    • v.11 no.2
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    • pp.51-60
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    • 2003
  • In the nuclear power plant, emergency core coolant system (ECCS) is furnished at reactor coolant system (RCS) in order to cool down high temperature water in case of emergency. However, in this coolant system, thermal stratification phenomenon can occur due to coolant leaking in the check valve. The thermal stratification produces excessive thermal stresses at the pipe wall so as to yield thermal fatigue crack (TFC) accident. In the present study, effects of turbulence penetration on the thermal stratification into T-branches with square cross-section in the modeled ECCS are analysed numerically. Standard k-$\varepsilon$ model is employed to calculate the Reynolds stresses in momentum equations. Results show that the length and strength of thermal stratification are primarily affected by the leak flow rate of coolant and the Reynolds number of duct. Turbulence penetration into the T-branch of ECCS shows two counteracting effects on the thermal stratification. Heat transport by turbulence penetration from main duct to leaking flow region may enhance thermal stratification while the turbulent diffusion may weaken it.

SIMULATION OF THERMAL STRATIFICATION IN INLET NOZZLE OF STEAM GENERATOR

  • Ji, Joon-Suk;Youn, Bum-Su;Jeong, Hyun-Chul;Kim, Sang-Nyung
    • Nuclear Engineering and Technology
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    • v.41 no.3
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    • pp.287-294
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    • 2009
  • Due to thermal hydraulics phenomena, such as thermal stratification, various events occur to the parts of a nuclear power plant during their lifetimes: e.g. cracked and dislocated pipes and thermally fatigued, bent, and damaged supports. Due to the operational characteristics of the parts of the steam generator feedwater inlet horizontal pipe, thermal stratification takes place particularly frequently. However, the thermal stress due to thermal stratification at the steam generator feedwater inlet horizontal pipe was not reflected in the design stage of old plants(Kori Unit No.1, 2, 3 and 4, Yeonggwang Unit No. 1 and 2, and Uljin Unit No. 1 and 2; referred to as old-style power plants hereinafter). Accordingly, a verification experiment was performed for thermal stratification in the horizontal inlet nozzle steam generator of old-style plants. If thermal stratification occurred in the horizontal pipe of an old-style power plant, numerical analysis of the temperature distribution of the pipes and fluids was conducted. The temperature distributions were compared at the curved part of the pipe and the horizontal pipe before and after the installation of the improved thermal sleeves designed to alleviate thermal stress due to thermal stratification. The thermal stress reduction measure was proven effective at the steam generator inlet horizontal pipe and the curved part of the pipe.

Seasonal Variations and Characteristics of the Stratification Depth and Strength in the Seas Near the Korea Peninsular using the Relative Potential Energy Anomaly (한반도 근해의 상대적 위치에너지 편차 변화를 이용한 성층화의 특성과 계절별 변화에 대한 연구)

  • Cho, Chang-Bong;Kim, Young-Gyu;Chang, Kyung-Il
    • Journal of the Korea Institute of Military Science and Technology
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    • v.14 no.2
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    • pp.205-212
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    • 2011
  • In this paper, we have proposed a method for quantization of the stratification strength in the sea water and analysing the distributions of the maximum stratification depths calculated by the method at the seas near the Korean peninsular. For calculating the stratification strength, modified and applied the potential energy anomaly formular which was suggested by Simpson in 1977. The data had been collected by NFRDI from 1971 to 2008 were used to determine the maximum vertical density gradient depth and the relative potential energy anomaly at that depth. In the East Sea, the stratification depth has become deepened about 20m in February and April since 1971. In Yellow-South Sea, the maximum density gradient depth has been deepened about 10m only in December during the same period and the difference of the stratification depth between summer and winter has been enlarged. These trends of variation of stratification strength and depth near the Korean peninsular should be investigated more carefully and continuously. And the results of these studies could be adopted for the more efficient operation of underwater weapon and detection systems.

Optimal Harvesting Time of Ginseng Seeds and Effect of Gibberellic Acid (GA3) Treatment for improving Stratification Rate of Ginseng (Panax ginseng C. A. Meyer) Seeds (인삼 종자의 개갑률 향상을 위한 적정 수확시기 및 GA3 처리 효과)

  • Kim, Young Chang;Kim, Young Bae;Park, Hong Woo;Bang, Kyong Hwan;Kim, Jang Uk;Jo, Ick Hyun;Kim, Kee Hong;Song, Beom Heon;Kim, Dong Hwi
    • Korean Journal of Medicinal Crop Science
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    • v.22 no.6
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    • pp.423-428
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    • 2014
  • This study was performed to identify optimal harvesting time of ginseng seeds and to examine the effect of $GA_3$ treatment for improvement of seed stratification rate. Ginseng seeds harvested from Land race, Chunpoong and Yunpoong cultivar in July 20 were tested for stratification rate. It was shown that stratification rates of land race, Yunpoong and Chunpoong cultivar were 94.1%, 93.1%, and 82.6%, respectively. Seeds of Chunpoong cultivar harvested 10-15 days later showed a comparable stratification rate to that of Land race, indicating that late harvest of Chunpoong seeds is beneficial for the increase of stratification rate. The higher stratification rate was found in mature seeds (92.3%) than immature seeds (37.8%), both of which were harvested in July 20. Stratification rate of mature seeds harvested in July 15 was 87.5%, demonstrating optimal harvesting time of ginseng seeds with higher stratification rate is after mid-July. An exponential growth of endosperms of ginseng seeds was observed from early June to mid-June and then slow growth was observed. There was no obvious growth of embryos from fertilization to mid-August. After the this time, embryos quickly grew until late October. Thus, appropriate stratification control is essential during the period (from early September to late October) in order to optimize embryo growth and development. While no increase of stratification rate was observed in seeds treated with 50 ppm of $GA_3$, significant increases were observed in seeds treated with 100 ppm of $GA_3$. At this concentration of $GA_3$, the stratification rate of Land race, Chunpoong and Yunpoong cultivar was 95.0%, 95.3%, and 96.5%, respectively.