• Title/Summary/Keyword: Pre-cooling Time

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DYNAMICAL INTERACTION OF SUPERNOVA REMNANT WITH PRE-EXISTING WIND BUBBLE (항성풍 거품 내에서의 초신성 잔해의 동역학적 구조)

  • Choi, Seung-Eon;Cha, Seung-Hun;Gu, Bon-Cheol
    • Publications of The Korean Astronomical Society
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    • v.11 no.1
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    • pp.27-47
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    • 1996
  • We have performed the high resolution computer simulation with 1D spherical hydrodynamic code in order to study the dynamical evolution of supernova ejecta interacting with a pre-existing fast wind structure. The fast wind structure has been calculated with $M_{in}=3{\times}10^{-6}M_{\odot}yr^{-1}$ and ${\upsilon}_{in}=1000km/sec$, which velocity is higher than the critical velocity relating to the initial radiative cooling. The fast wind becomes initially adiabatic. After a shell formation time of ${\sim}4000yrs$, the wind becomes radiative cooling at the shell zone, forming a thin dense radiative shell and an adiabatic wind bubble afterward. When supernova explodes in the wind center at 20,000yrs after the wind evolves, the supernova ejecta, which has a dense distribution of ${\rho}{\propto}r^{-n}$(here we have n = 9), interacts initially with, the understood wind zone, producing forward and reverse shocks. The reverse shock heats the supernova ejecta and its temperature increases. In this study, as the mass of the supernova ejecta is larger than that of the wind shell ($M_{ej}=5M_{\odot}$, $M_{sw}=2M_{\odot}$), we can conform two shell structures: an outer shell by the supernova ejecta and a secondarily shocked wind shell by it. The secondarily shocked wind shell should accelerates in this case to be R-T unstable, consequently producing the knots.

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Study of Pressure Cooling of Agricultural Products Using a Pallet Bin (팔레트 빈(pallet bin)을 이용한 농산물의 차압통풍 냉각 연구)

  • Jeong, Hoon;Yun, Hong-Sun;Lee, Hyun-Dong;Kim, Young-Keun;Lee, Won-Ok
    • Food Science and Preservation
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    • v.15 no.6
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    • pp.847-851
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    • 2008
  • The handling and processing of agricultural products in Korea is done manually. Small plastic boxes, nets, and corrugated cardboard boxes are used as containers during harvesting, sorting and other product handling operations. However, these practices are labor-intensive, time-consuming, require various kinds of packing materials, and are expensive because of high operating costs. To overcome these problems, the use of pallet bins with pre-cooling and storage features for handling and processing bulk farm products was investigated. The airflow resistances through bulk potato, onion and mandarin stocks were measured, and the pallet bins and a pressure pre-cooling device were manufactured. The opening ratio, bed depth and airflow rate through bulk potato, onion and mandarin in the pallet bin were defined with regression equations. The cooling rates of bulk potato, onion and mandarin were 0.8C/h ($21.7{\rightarrow}0C$, 14.5 h), 0.4C/h ($15.4{\rightarrow}.0C$, 32.2 h) and 0.7C/h ($13.7{\rightarrow}C$, 18.8 h), respectively, with the pressure pre-cooling system. Temperature deviances for storage of bulk potato, onion and mandarin were 0.12C, 0.12C and 0.17C, respectively.

Effects on Tensile Strength of Base and Weld Metal of Ti-6Al-4V Alloy in Short Time Exposure to High Temperature (Ti-6Al-4V 합금의 단시간 고온 노출 시 모재 및 용접부의 인장강도 특성)

  • Chae, Byoung-Chan
    • Journal of the Korea Institute of Military Science and Technology
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    • v.17 no.4
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    • pp.413-421
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    • 2014
  • Since the structural temperature of a flight vehicle flying at high speed rises rapidly due to aerodynamic heating, it is necessary for optimum structural design to obtain proper material properties at high temperature by taking into account of its operational environment. For a special alloy, analysis data on strength change due to exposure time to high temperature are very limited, and most of them are for an exposure time longer than 30 minutes for long term operations. In this study, base and weld metal samples of Ti-6Al-4V alloy had been prepared and high temperature tensile tests with induction heating were performed, and then high temperature strength characteristics and strength recovery characteristics through cooling have been analyzed. Pre-tests to determine maximum heating rate were performed, and response characteristics for temperature control were confirmed. As a result, high temperature tensile strength appeared to be lower than that of room temperature, but it was higher than that of high temperature of 30 minite exposure listed in MMPDS. In strength recovery through cooling Ti-6Al-4V alloy has shown higher recovery rate compared with other alloys.

Calculation of Jominy Hardenability Curve of Low Alloy Steels from TTT/CCT data (TTT/CCT 데이터를 이용한 저합금강의 죠미니 경화능 곡선 계산)

  • Jung, Minsu;Son, YoonHo
    • Journal of the Korean Society for Heat Treatment
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    • v.32 no.1
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    • pp.17-28
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    • 2019
  • Jominy hardenability curves of low alloy steel containing less than 5 wt.% of alloying elements in total were calculated by applying Scheil's rule of additivity to pre-calculated isothermal transformation curve. Isothermal transformation curve for each phase in steel was approximated as a simple mathematical equation by using Kirkaldy's approach and all coefficients in the equation were estimated from experimental temperature-time-transformation (TTT) and/or continuous cooling transformation (CCT) data in the literature. Then jominy test with simple boundary conditions was performed in computer by applying the finite difference scheme. The resultant cooling curves at each location along a longitudinal direction of Jominy bar were applied to calculate phase fractions as well as mechanical properties such as micro Vickers hardness. The simulated results were compared with experimental CCT data and Jominy curves in the literature.

The Effect of Pre-strain on Cyclic Deformation Characteristic of Ti-Ni Alloy (Ti-Ni합금의 반복변형특성에 미치는 pre-strain의 효과)

  • 박영철;조용배;허선철
    • Journal of Ocean Engineering and Technology
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    • v.9 no.1
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    • pp.101-110
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    • 1995
  • In SMA(Shape Memory Alloy), the degradation by fatigue is one of the most important problems to be overcome, when SMA is used for robot-actuator materials. The actuator is operated repetitively for long time and its repeating operation develops the fatigue degradation of SMA. The fatigue degradation changes the transformation temperature and deformation behavior and results in inaccurate operation and deformation which results form repeating operation is to be investigated in advance and the scheme to resolve those problems have to be made for the design of actuator. In this paper, for the improvement of the fatigue degradation by repetive movement and better control of the correct movement by the stability of martensite transformation in the development of Robots actuator, Pre-strain(0, 1.5, 5, 8%) are loaded in the specimens and fatigue testing were carried out by the method of heating and cooling in direct condition. From the results of these experiments, the effect on pre-strain which affect the transformation characteristic and fatigue degradation phenomena were correctly investigated.

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Performance Analysis of an Inert Gas Generator for Fire Extinguishing

  • Kim, Su-Yong;Arkadiy F. Slitenko
    • 연구논문집
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    • s.29
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    • pp.5-15
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    • 1999
  • Present study deals with performance analysis of an inert gas generator (IGG) which is to be used as an effective mean to suppress the fire. The IGG uses a turbo jet cycle gas turbine engine to generate inert gas for fire extinguishing. It is generally known that a lesser degree of oxygen content in the product of combustion will increase the effectiveness of fire suppressing. An inert gas generator system with water injection will bring advantages of suffocating and cooling effects which are considered as vital factors for fire extinguishing. As the inert gas is injected to the burning site, it lowers the oxygen content of the air surrounding the flame as well as reduces the temperature around the fire as the vapour in the inert gas evaporates during the time of spreading. Some important aspects of influencing parameters, such as, air excess coefficient. $\alpha$, compressor pressure ratio, $ pi_c$, air temperature before combustion chamber, $T_2$, gas temperature after combustion chamber, $T_3$, mass flow rate of water injection, $M_w$, etc., on the performance of IGG system are investigated. Calculations of total amount of water needed to reduce the turbine exit temperature to pre-set nozzle exit temperature employing a heat exchanger were made to compare the economics of the system. A heat exchanger with two step cooling by water and steam is considered to be better than water cooling only. Computer programs were developed to perform the cycle analysis of the IGG system and heat exchanger considered in the present study.

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Analysis of the Molten Metal Direct Rolling for Magnesium Considering Thermal Flow Phenomena (열 유동 현상을 고려한 마그네슘 용탕 직접 압연공정 해석)

  • Bae J.W.;Kang C.G.;Kang S.B.
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2005.10a
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    • pp.786-789
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    • 2005
  • The proper parameters in a twin roll strip casting are important to obtain the stabilization of the Mg sheet. What is examined in this paper is the quantitative relationships of the important control parameters such as the roll speed, height of pool region, outlet size of nozzle, solidification profile and the final point of solidification in a twin roll strip casting Unsteady conservation equations were used for transport phenomena in the pool region of a twin roll strip casting in order to predict a velocity, temperature distributions of fields and a solidification process of molten magnesium. The energy equation of cooling roll Is solved simultaneously with the conservation equations of molten magnesium In order to consider the heat transfer through the cooling roil. The finite difference method (2-D) and the finite element method (2-D) are used in the analysis of pool region and cooling roil to reduce computing time and to improve the accuracy of calculation respectively.

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Crystallinity and Mechanical Properties of Glass Fiber Reinforced Thermoplastic Composites by Rapid Press Consolidation Technique (Consolidation 방법에 의해 제작된 유리섬유강화 복합재료의 결정성과 기계적성질에 관한 연구)

  • Shin, Ick-Jae;Kim, Dong-Young;Lee, Dong-Joo
    • Proceedings of the KSME Conference
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    • 2000.04a
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    • pp.91-96
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    • 2000
  • Glass fiber reinforced thermoplastic composites were manufactured by Rapid Press Consolidation Technique(RPCT) as functions of temperature, pressure and time in pre-heating, consolidation and solidification sections during the manufacturing processing. It was found that the material property is greatly affected by pre-heating temperature under vacuum, mold temperature and molding pressure. Among them, the temperature In the mold was the most critical factor in determining the mechanical properties and the molded conditions of specimen. The crystallinity of PET matrix was also investigated by differential scanning calorimetry(DSC) measurements for various processing conditions. The level of crystallinity($X_c$) depended strongly on the mold temperature, cooling rate and the type of composite. The difference in $X_c$ is believed to be one of important factors in characterizing the mechanical properties.

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A Study on Effect of Various Cooling Methods in Motion of High-Precision Ball Screw (고속 고정밀 볼 스크류 구동에 따른 강제 냉각방식의 효과에 관한 연구)

  • Kim, Su-Sang;Xu, Zhe-Zhu;Kim, Hyun-Koo;Lyu, Sung-Ki
    • Journal of the Korean Society for Precision Engineering
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    • v.30 no.3
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    • pp.254-259
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    • 2013
  • Ball screw system is widely used as a precision mechanical linear actuator that translates rotational motion to linear motion for its high efficiency, great stiffness and long life. Recently, according to the requirements of high accuracy and stiffness, the pre-load on the ball screw which means of remove the backlash in the ball screw is usually used. Because of the preload which means the frictional resistance between the screw and nut, becomes a dominating heat source and it generates thermal deformation of ball screw which is the reason for low accuracy of the positioning decision. There are several methods to solve the problem that includes temperature control, thermal stable design and error compensation. In the past years, researchers focused on the error compensation technique for its ability to correct ball screw error effectively rather than the capabilities of careful machine design and manufacturing. Significant amounts of researches have been done to real-time error compensation. But in this paper, we developed a series of cooling methods to get thermal equilibrium in the ball screw system. So we find the optimum cooling type for improving positioning error which caused by thermal deformation in the ball screw system.

The Magnetic Characteristics and Microstructure of Mn-A1 System Alloys(1st Report) -Focused on the Mn-A1 Alloys- (Mn-Al계 합금의 열처리에 따른 미세조직 변화와 지기적 특성(제1보) -Mn-Al-Cu 합금을 중심으로-)

  • Pang, Man-Gyu;Yang, Hyun-Soo;Kwak, Chang-Sup
    • Journal of the Korean Society for Precision Engineering
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    • v.5 no.4
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    • pp.48-58
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    • 1988
  • This study was undertaken to observe the formation behavior of ferro- magnetic phase in Mn-Al-Cu Alloys. The alloy selected for this investigation was 70% Mn-29% Al-1% Cu. This pre-allyed pig was prepared to the cylinderical castings using an Induction furnace after homogenizing at $1100^{\circ}C$ for 2hr, the specimens were cooled by cooling methods. Subwequent isothermal heat treatments were followed at $550^{\circ}C$ for various periods of time at predetermined(1-1000min). The formation behavior of ferromagnetic phase was investigated by measurements of magnetic properties of the specimens at each stage of heat treatment, and optical microscopic esamination and X-Ray diffraction analyses were also employed. By this basic experimental results, the conclusions are as follows 1) In order to obtain much amount of ferromagnetic phase, the optimum average cooling rate was about 7.35-$16.4^{\circ}C$/sec($1100^{\circ}C$-$600^{\circ}C$). 2) We verified the decomposition of {\tau} phase to {\beta} -Mn and {\gamma} , as the specimens were homogenized at $1100^{\circ}C$ for 12hr, then heat-treased at $550^{\circ}C$ for 1-1000min. 3) A condition of optimum heat treatments in Mn-Al-Cu permanent mag-netic alloys showed that after homogenizing at $1100^{\circ}C$ for 2hr, the speciments were cooled in air or furnace(A) and subsequent heat treatments at $550^{\circ}C$ for 1-30min. The maximum magnetic properties were measured as follows: Air cooling; Br=1200(Gause), bHc=100(oe), (BH)max=0.07(MGOe) Furnace cooling(A);Br=950(Gauss), bhe=80(Oe), (BH)max=0.05(MGOe)

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