• 제목/요약/키워드: Heat density

검색결과 1,935건 처리시간 0.025초

Effect of Mg content on the density and critical properties of in-situ reacted MgB2 bulk superconductor

  • Jun, Byung-Hyuk;Kim, Dan-Bi;Park, Soon-Dong;Kim, Chan-Joong
    • 한국초전도ㆍ저온공학회논문지
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    • 제16권1호
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    • pp.19-22
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    • 2014
  • The effects of Mg content on the pore formation, density and critical properties were investigated in in-situ reacted $MgB_2$ superconductors. The $Mg_{1+x}B_2$, (x=-0.2, 0.0, 0.05, 0.3, 1.0) bulk samples with different Mg contents were heat-treated at $900^{\circ}C$ for 1 h in an Ar atmosphere. The dimensional changes of a pellet's mass and volume after heat-treatment were measured. After heat-treatment process, the sample mass was decreased by Mg evaporation, but the sample volume was expanded by pore formation at the Mg site; therefore, the apparent density was decreased. Spherical pores the same as Mg particles were developed after heat-treatment in all samples, and the pore density was increased with increasing Mg content. As the x of Mg content was increased to 1.0, the apparent density of $Mg_{1+x}B_2$ samples was decreased due to a relatively larger reduction in a mass change. The critical current density of Mg excessive sample of x=0.05 showed the highest values over the applied magnetic fields because the excessive Mg may compensate Mg loss and enhance grain connectivity.

핀-관 열교환기의 착상 거동에 대한 표면 접촉각의 영향 (The effect of surface contact angle on the behavior of frost formation in a fin-tube heat exchanger)

  • 이관수;지성;이동욱
    • 설비공학논문집
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    • 제12권1호
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    • pp.95-101
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    • 2000
  • The effect of surface contact angle on the behavior of frost formation in a fin-tube heat exchanger is investigated experimentally. It is shown that both heat exchangers with hydrophilic and hydrophobic surfaces appear to have a better thermal performance than bare aluminium heat exchanger, but the improvements are very small. There is a little increase in the amount of the frost deposited onto the heat exchanger with both hydrophilic and hydrophobic surface. However, the effect of contact angle on the frost density is observed ; the frost with high density forms on the heat exchanger with hydrophilic surface ; and the frost with low density is deposited onto the heat exchanger with hydrophobic surface when compared with the frost deposited onto the heat exchanger with bare aluminium surface. This may be attributed to the fact that the shape of water droplets which condense on the surface of heat exchanger at the early stage of frosting varies with contact angle, and thus makes a difference on the structure of frost formation. From the experiments with different relative humidity of inlet air, it is shown that the variations of operating parameter make no influence on the effect of surface contact angle on the frosting behavior in the heat exchanger.

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고에너지밀도용접 과정에서의 2차원 열유동에 대한 수치해석적 연구 (Numerical Study on the Two-Dimensional Heat Flow in High-Power Density Welding Process)

  • 박건중;장경천;김찬중
    • 대한기계학회논문집B
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    • 제24권9호
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    • pp.1166-1174
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    • 2000
  • This work presents a two-dimensional quasi-steady state model to study the fluid flow and heat transfer in high-power density welding process of thin AISI-304 stainless steel plates. The enthalpy method and the finite volume method were used for a numerical analysis of the mushy region phase change as well as the heat flow at the weld pool and the heat-affected zone. The results show that the mushy region distributed around the weld pool becomes wider downstream and the surface heat losses by convection and radiation can be significant factors in welding process especially when a welding speed is relatively low.

고밀도, 등방성 탄소의 제조에 관한 연구 (Preparation of Isotropic Carbon with High Density)

  • 오종기;이선우;박광원
    • 한국세라믹학회지
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    • 제28권11호
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    • pp.908-916
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    • 1991
  • The characteristics of the carbonized and calcined products made from coal tar pitch coke and coal tar pitch, were investigated in the aspect of the manufacture of isotropic graphite with high density. The mesophase from the pitch was rapidly formed at higher heat-treatment temperature between 410$^{\circ}C$ and 450$^{\circ}C$, where the insolubes in the pitch accelerated the rate of nucleation and growth of the mesophase. The benzene insolubles and the quinoline insolubes were increased as the heat treatment temperature and the heat-treatment time increased. The ratio of benzene insolubles and quinoline solubles (BI/QS) was decreased as the heat-treatment temperature was higher and maintained to be nearly constant regardless of heat-treatment time at fixed heat treatment temperature. The bulk density of the calcined carbon was linearly proportional to the ratio of quinoline solubes to volatile matter in the green coke. Anisotropic ratio of electrical resistance was measured to be between 0.98 and 1.10.

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발포 금속을 사용하는 채널의 열전달 특성 실험 및 해석 (Experiment and Analysis on the Heat Transfer Characteristics of a Channel Filled with Metal Form)

  • 손영석;신지영;조영일
    • 설비공학논문집
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    • 제22권7호
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    • pp.448-453
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    • 2010
  • Porous media containing complex fluid passage have especially large surface area per unit volume. This study is aimed to identify the heat transfer characteristics of high-porosity metal foams in a horizontal channel. Experiment is performed under various heat flux, velocity and pore density. Nusselt number decreases with higher pore density. Metal foams shows higher heat transfer coefficients than pin-fin structure with the same porosity. This is due to the more complex flow passage and larger heat transfer area based on the structure of the metal foams. The analysis on the pin-fin structure may not be suitable to the metal foam structure but should be identified extensively through further study.

AN ENERGY DENSITY ESTIMATE OF HEAT EQUATION FOR HARMONIC MAP

  • Kim, Hyun-Jung
    • 한국수학교육학회지시리즈B:순수및응용수학
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    • 제18권1호
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    • pp.79-86
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    • 2011
  • Suppose that (M,g) is a complete and noncompact Riemannian mani-fold with Ricci curvature bounded below by $-K{\leq}0$ and (N, $\bar{g}$) is a complete Riemannian manifold with nonpositive sectional curvature. Let u : $M{\times}[0,{\infty}){\rightarrow}N$ be the solution of a heat equation for harmonic map with a bounded image. We estimate the energy density of u.

충돌공기제트에서의 다공성 방열기의 열전달 특성 (Heat Transfer from a Porous Heat Sink by Air Jet Impingement)

  • 백진욱;김서영;강병하
    • 설비공학논문집
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    • 제13권2호
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    • pp.73-79
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    • 2001
  • Experiment were carried out to investigate the heat transfer characteristics of an aluminum foam block as a porous heat sink on a heat source by a vertical air jet impingement that can be applied for electronics cooling. The performance of the aluminum foam heat sink was evaluated by the convective heat transfer coefficient on the heat source. At a fixed porosity, pore density ($\beta$) of the foam and Reynolds number Re were varied in the range of $\beta$a=10, 20, 40 PPI(Pore Per Inch) and $850\leqRe\leq25000$. A nozzle diameter and the nozzle-to-plate spacing were also varied. It was found that the convective heat transfer was enhanced by the aluminum foam heat sink with lower pore density due to relatively intensified flow through the foam block. The aluminum foam block with much reduced weight shows slightly better performance with larger Nusselt number, compared with the convectional heat sink.

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낮은 핀을 가진 수평관의 응축액 억류에 관한 연구 (A Study on the condensate Retention at Horizontal Integral-Fin tubes)

  • 한규일;조동현
    • 설비공학논문집
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    • 제8권1호
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    • pp.151-165
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    • 1996
  • Relation between condensate retention and heat transfer performance is studied for condensation of CFC-11 on horizontal integral-fin tubes. Eight tubes with trapezoidally shaped integral fin density from 738fpm to 1654fpm and 10, 30 grooves are tested. The liquid retention angles are measured by the height gauge, and each tube is tested under static(non-condensing) condition (CFC-11, water) and under dynamic(condensing) condition (CFC-11). The analytical model predicts the amount of liquid retention on a horizontal integral-fin tubes within+10 percent over most of the data. Average retention angle increases as both surface tension-to-density ratio($\sigma/\rho$) and fin density(fpm) increase, The tube having a fin density of 1299~1654fpm has the best heat transfer performance. The amount of surface flooding must keep below of 40 percent for best heat transfer performance at condensation. The tube having low number of fin density must be used for fluids having high values of $\sigma/\rho$(water, (TEX)$NH_3$, ect.) and the tube having high number of fin density must be used for the fluid having low values of $\sigma/\rho$(R-11, R-22, etc.)

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고체-고체-기체 화학 열펌프 시스템의 반응기 설계에 관한 연구 (A Study on the Reactor Design of Solid-Solid-Gas Chemical Heat Pump System)

  • 김성준;이태희;;최홍규;이종호
    • 설비공학논문집
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    • 제6권4호
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    • pp.406-416
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    • 1994
  • In this study the reactor design procedure and method of solid-solid-gas chemical heat pump system using STELF technology were investigated. For manufacturing IMPEX block which is the kernel of reactor, proper salt pair should be selected, and equilibrium temperature drop and COP should be examined for selected salt pair. Moreover, apparent density, residual porosity, and graphite ratio should be calculated to give minimum block volume and mass, and maximum energy density without causing heat and mass transfer problems. Since heat exchange area can be changed with operating condition, reactor diameter, length, and stainless steel thickness should be decided for desired specifications. These procedure and method were applied to the case study of 6kW cold production and 8 hours storage capacity reactor.

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더블라셀파일 원단의 열처리조건에 따른 물리적 특성 변화에 관한 연구 (A Study on the Physical Properties of Double Raschel Pile Fabric according to Heat Treatment)

  • 손은종;박홍원;황영구
    • 한국염색가공학회지
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    • 제31권4호
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    • pp.288-297
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    • 2019
  • The specimens were heat treated at 180℃, 190℃, 200℃, 210℃ and 220℃ to observe the change of the physical properties of the double raschel pile fabric. The density, tensile strength, weight, elongation, dyeing characteristics, fabric surface morphology and cross sectional shape were observed by heat treatment temperature. Compared with untreated samples, weight, density and tensile strength were increased with increasing heat treatment temperature. No increase was observed at 220℃. In the case of elongation, it increased to 190℃ but thereafter it could not be observed. In the case of uprightness of brushed hair, it was observed that the gap between the yarns was narrowed and the density was increased and the straightness of the yarn and pile yarn was improved by widening the heat treatment temperature. As a result, it was observed that the uprightness was remarkably improved and the bulky properties was increased. It was also observed that the increase of the dyeability was observed with increasing the heat treatment temperature.