• Title/Summary/Keyword: Heat Increment

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Design Study of a Korean Mars Mission

  • Lee, Eun-Seok;Chang, Keun-Shik;Park, Chul
    • International Journal of Aeronautical and Space Sciences
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    • v.5 no.2
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    • pp.54-61
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    • 2004
  • In this paper we carried out a design study for an unmanned Mars missionsuitable for Republic of Korea. The mission will use a KSLV series launch system,which is to place a one tonne payload into the LEO. We calculated the velocityincrements(AV) required for departure from Earth and insertion into the orbitaround Mars based on the mission opportunity data provided by NASA. Two typesof Mars modules - entry type and orbiter type - were considered in this studyWe calculated the mass of TPS(therma1 protection system) for the entry tvpe Marsmodule based on the heat transfer rate and heat load from the Mars atmosphere tothe surface of the TPS. The heat transfer rate and heat load were obtained throughan entry trajectory calculation. For the orbiter type Mars module, we calcuIated themass breakdown of the additional spacecraft which is to insert the Mars moduleinto the orbit around Mars. Other mass items were determined by proportioningfrom the existing Mars modules. This paper finally proposes the payload capacitiesfor each types of Mars modules.

Influence of SiC Content and Heat Treatments on Strength of Al2O3 Ceramics ($Al_2O_3$ 세라믹스의 강도에 미치는 소결 첨가제 SiC의 함량과 열처리의 영향)

  • Kim, G.U.;Moon, C.K.;Yoon, H.K.;Kim, B.A.
    • Journal of Power System Engineering
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    • v.15 no.6
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    • pp.67-72
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    • 2011
  • In the present study, crack healing effect and residual stress of $Al_2O_3$ ceramics were investigated by changing the sintering temperature and heat treatment conditions. And also it was investigated that the influence of different filler loadings of nano-sized SiC particles on the crack healing behavior of $Al_2O_3$ ceramics. The test samples were characterized by three point bend flexural tests to evaluate their mechanical properties. The morphological changes were studied by FE-SEM and EDS. The test results indicated that the $Al_2O_3$ with nano-sized SiC ceramics sintered at $1800^{\circ}C$ were showed highest density. Sintering temperature at $1800^{\circ}C$, the bending strength of heat treatment in air atmosphere specimens showed about 42 % increment in comparison to the un-heat treated specimens. The cracked specimens can be healed by heat treatment in vacuum atmosphere but the crack healing effect of $Al_2O_3$ ceramics, which is heat treated in air atmosphere was higher than that of heat treated in vacuum atmosphere. $Al_2O_3$ with 30 wt% of SiC ceramics indicated higher crack healing ability than that with 15 wt% of SiC ceramics. The FE-SEM images showed that the median cracks and pores were disappeared after heat treatment in air.

Thermal Analysis of a Radial Heat Sink with Radiation and Natural Convection (복사 열전달을 고려한 자연대류 원형 히트싱크 열전달 해석)

  • Yu, Seung-Hwan;Jang, Dae-Seok;Lee, Kwan-Soo
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.36 no.4
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    • pp.385-390
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    • 2012
  • A radial heat sink, adopted to LED(light emitting diode) downlight, was optimized. Discrete transfer radiation model (DTRM) was used to calculate radiation heat transfer, and numerical model was verified with experimental results. The effects of number of fin, long fin length and middle fin length on overall thermal resistance and radiation heat transfer were analyzed. As the emissivity increased, thermal resistance decreased due to the increment of radiation heat transfer. The radial heat sink was optimized and optimum number of long fins is 19~28, optimum length of long fin is about half of radius of heat fink and optimum fin ratio is 0.4~0.7.

Effect of Post Deposition Annealing Temperature on the Structural, Optical and Electrical Properties of GZO Films Prepared by RF Magnetron Sputtering (RF 마그네트론 스퍼터링으로 증착 된 GZO 박막의 진공 열처리온도에 따른 구조적, 광학적, 전기적 특성 연구)

  • Kim, Daeil
    • Journal of the Korean Society for Heat Treatment
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    • v.24 no.4
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    • pp.199-202
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    • 2011
  • Ga doped ZnO thin films were deposited with RF magnetron sputtering on glass substrate without intentional substrate heating and then the effect of post deposition annealing temperature on the structural, optical and electrical properties of the films was investigated. The post deposition annealing process was conducted for 30 minutes in a vacuum of $1{\times}10^{-3}$ Torr and the vacuum annealing temperatures were 150 and $300^{\circ}C$, respectively. As increase annealing temperature, GZO films show the increment of the prefer orientation of ZnO (002) diffraction peak in the XRD pattern and the optical transmittance in a visible wave region was also increased, while the electrical sheet resistance was decreased. The figure of merit obtained in this study means that GZO films which vacuum annealed at $300^{\circ}C$ have the highest optoelectrical performance in this study.

The Studies on the Prediction of Residual Stresses by Thermal Elasto-Plastic Analysis and its Effect for Circumferential Welded Cylinder (열탄소성 해석에 의한 원주용접 원통관의 잔류응력 예측과 그 영향에 대한 연구)

  • 류기열;엄동석
    • Journal of Welding and Joining
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    • v.15 no.5
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    • pp.115-123
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    • 1997
  • The buckling strength, fatigue strength, stress corrosion cracking are considerably effected on one of initial imperfections, the residual stresses produced by a circumferential weld between axisymmetric cylinders. Therefore, we study the residual stresses, plastic strain and temperature distribution with using thermal elasto-plastic analysis which are generated by a circumferential weld between axisymmetric cylinders. It is investigated that welding residual stresses have an effect on the strength of cylinder for inner and outer shell under external pressure.

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The Variation of Mechanical Properties by Thermomechanical Treatment in Fe-30%Ni-0.1 %C Alloy (가공열처리에 의한 Fe-30% Ni-0.1%C 합금의 기계적성질 변화)

  • Ahn, H.K.;Kim, H.S.
    • Journal of the Korean Society for Heat Treatment
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    • v.7 no.2
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    • pp.88-95
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    • 1994
  • In order to compare mechanical properties of ausformed martensite with those of marformed martemsite in Fe-30%Ni-0.1%C alloy and to investigate their strengthening mechanisms, ausformed martensite and marformed martensite were prepared by ausforming treatment and marforming treatment respectively. The microstructures were observed and the quantities of retained austenite, hardness, yield strength, ultimate tensile strength and elongation were examined. The strength of ausformed martensite was mainly increased because of the lattice defects inherited from austenite. The ductility of ausformed martensite was constant at the rate of 7-8% by ductile matrix formation of the retained austenite in spite of the increase in strength. The strength of marformed martensite was increased by the increment in dislocation density, the crossing of transformation twin with deformation twin and the mutual crossing of deformation twin. The ductility of mar formed martensite was slightly lower than that of ausformed martensite, but the strength of mar formed martensite was prominently higher.

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A Study on the Improvement of a Cooling System by the Increment of Room Humidity without Reheating Process (실내 습도 증가를 이용한 무재열 냉방시스템 개선에 관한 연구)

  • Lee Hung Joo;Kim Yong Ku
    • The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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    • v.16 no.6
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    • pp.613-619
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    • 1987
  • In a room air conditioning cooling system, if the room-sensible-heat-factor as plotted on a Psychrometric Chart intersects the saturation curve below the apparatus leaving air dewpoint, reheat must be used to maintain the design room air conditions. However, if the design room humidity is permitted to be raised to some degree, the cooling system will not require reheat as a new room-sensible-heat-factor line is developed between the apparatus leaving air dew-Point and the adjusted design room air conddition point. The advantages to this are the cost of reheat equipment and operation can be avoided. The cycle of this system can be shown on a Psychrometric Chart to plot the design condition points.

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Aerodynamic control capability of a wing-flap in hypersonic, rarefied regime: Part II

  • Zuppardi, Gennaro;Vangone, Daniele
    • Advances in aircraft and spacecraft science
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    • v.4 no.5
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    • pp.503-514
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    • 2017
  • The attitude control of an aircraft is usually fulfilled by means of thrusters at high altitudes. Therefore, the possibility of using also aerodynamic surfaces would produce the advantage of reducing the amount of fuel for the thrusters to be loaded on board. For this purpose, Zuppardi already considered some aerodynamic problems linked to the use of a wing flap in a previous paper. A NACA 0010 airfoil with a trailing edge flap of 35% of the chord, in the range of angle of attack 0-40 deg and flap deflections up to 30 deg was investigated. Computer tests were carried out in hypersonic, rarefied flow by a direct simulation Monte Carlo code at the altitudes of 65 and 85 km of Earth Atmosphere. The present work continues this subject, considering the same airfoil and free stream conditions but two flap extensions of 45% and 25% of the chord and two flap deflections of 15 and 30 deg. The main purpose is to compare the influence of the flap dimension with that of the flap deflection. The present analysis is carried out in terms of: 1) percentage variation of the global aerodynamic coefficients with respect to the no-flap configuration, 2) increment of pressure and heat flux on the airfoil lower surface due to the Shock Wave-Shock Wave Interaction (SWSWI) with respect to the same quantities with no SWSWI or in no-flap configuration, 3) flap hinge moment. Issues 2) and 3) are important for the design of the mechanical and thermal protection system and of the flap actuator, respectively. Under the above mentioned test and geometrical conditions, the flap deflection is aerodynamically more effective than the flap extension, because it involves higher variation of the aerodynamic coefficients. However, tests verify that a smaller deflection angle involves the advantage of a smaller increment of pressure and heat flux on the airfoil lower surface, due to SWSWI, as well as a smaller hinge moment.

A Study of the Effects of Small Amount of Eu Impurities in α-Fe2O3 (α-Fe2O3 에 첨가한 미소량 EU 불순물의 효과에 대한 연구)

  • 오창헌
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.16 no.6
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    • pp.532-537
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    • 2003
  • Crystallographic, electric, magnetic and heat transition properties of $\alpha$-Fe$_2$O$_3$ have been studied with a small addition of Eu impurities. Hematite($\alpha$-Fe$_2$O$_3$) is a basic ferromagnetic material having rhombohedral structure, which is similar to perovskites structure. Eu is a rare earth element that has an electric configuration of 4f$^{7}$ 6s$^2$. X-ray diffraction pattern of Fe$_{1-x}$ Eu$_{x}$O$_3$ (x = 0.00, 0.04, 0.06) shows an increament of a value when the amount of Eu impurities increased. The VSM data show an increment of magnetization by increasing the amount of Eu impurity. The one with x=0.06 shows the largest increment of magnetic remanence. The magnetic remanence varied from 0.49$\times$10$^{-3}$ emu/g to 0.62$\times$10$^{-3}$ emu/g when Eu impurity is increased by 2 %. Coercivity is decreased as Eu impurity is increased. Resistances is reduced significantly by Eu impurity. There is a clear difference in temperature-dependent resistance depending on the amount of Eu impurities. Especially, there are cusps between 150 K to 175 K. It indicates the change of electronic quantum states inside the atoms by rare earth impurities in rhombohedral structure. Temperature-dependent heat capacity shows that the most effective amount of Eu impurities is 6 %. %.

Effects of Root Gap on Residual Stresses and Deformation in the Multi-Pass Weld of Thick Plates for Steel Bridge (교량용 후판 다층용접시 잔류응력과 변형에 미치는 루트간격의 영향)

  • 장경복;김하근;강성수
    • Journal of Welding and Joining
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    • v.17 no.1
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    • pp.88-96
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    • 1999
  • The effects of root gap on welding residual stress and deformation are dealt with the multi-pass weldment with three kinds(0, 6, 30mm) of root gap by F.E.M common code, and then compared with experiment data. In this analysis, an 100% ramp heat input model was used to avoid numerical convergence problem due to an instantaneous increase in temperature near the fusion zone, and the effect of a moving arc in a two dimensional plane was also included. During the analysis, a small time increment was applied in a period with instantaneous temperature fluctuation while a large time increment was used in the rest period. The residual stress is distributed as symmetric types and maximum value is also equivalent when the weldment with 0mm and 6mm root gap is welded. In the case of 30mm root gap welding, the distribution of the residual stress extends over a wide range as asymmetric types due to the built-up weld, and most of the residual stress is biased in the side of a built-up weld part. In case of 0mm gap welding and 6mm gap welding, a little angular distortion occurs, but the level of deformation is small. When the weldment with 30mm root gap is welded, the angular deformation of the asymmetric types, however, occurs larger than the other specimens. The experimental and the analytic results show good coincidence and indicate that the welding residual stress and deformation distribution of 30 mm root gap specimen may be asymmetric and the amplitude is larger than those of root gap specimen under standard.

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