• Title/Summary/Keyword: Thermal diffusion equation

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A comparison on the heat load of HTS current leads with respect to uniform and non-uniform cross-sectional areas

  • Han, Seunghak;Nam, Seokho;Lee, Jeyull;Song, Seunghyun;Jeon, Haeryong;Baek, Geonwoo;Kang, Hyoungku;Ko, Tae Kuk
    • Progress in Superconductivity and Cryogenics
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    • v.19 no.3
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    • pp.44-48
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    • 2017
  • Current lead is a device that connects the power supply and superconducting magnets. High temperature superconductor (HTS) has lower thermal conductivity and higher current density than normal metal. For these reasons, the heat load can be reduced by replacing the normal metal of the current lead with the HTS. Conventional HTS current lead has same cross-sectional area in the axial direction. However, this is over-designed at the cold-end (4.2 K) in terms of current. The heat load can be reduced by reducing this part because the heat load is proportional to the cross-sectional area. Therefore, in this paper, heat load was calculated from the heat diffusion equation of HTS current leads with uniform and non-uniform cross-sectional areas. The cross-sectional area of the warm-end (65K) is designed considering burnout time when cooling system failure occurs. In cold-end, Joule heat and heat load due to current conduction occurs at the same time, so the cross-sectional area where the sum of the two heat is minimum is obtained. As a result of simulation, current leads for KSTAR TF coils with uniform and non-uniform cross-sectional areas were designed, and it was confirmed that the non-uniform cross-sectional areas could further reduce the heat load.

Numerical Analysis of Thermal and Flow affected by the variation of rib interval and Pressure drop Characteristics (리브 간격 변화에 따른 열.유동 수치해석 및 압력 저하 특성)

  • Chung, Han-Shik;Lee, Gyeong-Wan;Shin, Yong-Han;Choi, Soon-Ho;Jeong, Hyo-Min
    • Journal of Advanced Marine Engineering and Technology
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    • v.35 no.5
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    • pp.616-624
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    • 2011
  • The flow characteristics and heat transfer augment on the periodically arranged semi-circular ribs in a rectangular channel for turbulent flow has been investigated numerically. The aspect ratio of the rectangular channel was AR=5, the rib height to hydraulic diameter ratio were 0.07 and rib height to channel height ratio was set as e/H=0.117 for various PR(rib pitch-to-rib height rate) between 8~14, respectively. The SST k-${\omega}$ turbulence model and v2-f turbulence model were used to find out the heat transfer and the flow characteristics of near the wall which are suited to obtain realistic phenomena. The numerical analysis results show turbulent flow characteristics, heat transfer enhancement and friction factor as observed experimentally. The results predict that turbulent kinetic energy(k) is closely relative to the diffusion of recirculation flow. and v2-f turbulence model simulation results have a good agreement with experimental values.

Dynamic Characteristics Analysis of the Cryogenic Nitrogen Injection of Swirl Injector using POD and DMD (POD와 DMD를 이용한 와류형 분사기의 극저온 질소 분무 동적 특성 분석)

  • Kang, Jeongseok;Sung, Hong-Gye;Sohn, Chae Hoon
    • Journal of the Korean Society of Propulsion Engineers
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    • v.21 no.5
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    • pp.1-9
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    • 2017
  • The cryogenic nitrogen spray of a swirl injector has been numerically investigated using three dimensional LES turbulence model to analyze the dynamic characteristics under supercritical condition. To predict the precise nitrogen properties under supercritical condition, SRK equation of state, Chung's method for viscosity and thermal conductivity and Takahashi's correlation based on Fuller's theory for diffusion coefficient are implemented. The complex flow structures due to interaction between flow field and acoustic field are observed inside and outside the injector under supercritical condition. FFT, POD, and DMD techniques are employed to understand the coherent structures. By implementing the FFT, the dominant frequencies are identified inside and outside the injector. The coherent flow structures related to the dominant frequencies are visualized using the POD and DMD techniques. In addition, the DMD provides the damping coefficient which is related with the instability prediction.

COMPUTATION OF LAMINAR NATURAL CONVECTION OF NANOFLUID USING BUONGIORNO'S NONHOMOGENEOUS MODEL (Buongiorno의 비균질 모델을 사용한 나노유체의 층류 자연대류 해석)

  • Choi, S.K.;Kim, S.O.;Lee, T.H.
    • Journal of computational fluids engineering
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    • v.18 no.4
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    • pp.25-34
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    • 2013
  • A numerical study of a laminar natural convection of the CuO-water nanofluid in a square cavity using the Buongiorno's nonhomogeneous model is presented. All the governing equations including the volume fraction equation are discretized on a cell-centered, non-uniform grid employing the finite-volume method with a primitive variable formulation. Calculations are performed over a range of Rayleigh numbers and volume fractions of the nanopartile. From the computed results, it is shown that both the homogeneous and nonhomogeneous models predict the deterioration of the natural convection heat transfer well with an increase of the volume fraction of nanoparticle at the same Rayleigh number, which was observed in the previous experimental studies. It is also shown that the differences in the computed results of the average Nusselt number at the wall between the homogeneous and nonhomogeneous models are very small, and this indicates that the slip mechanism of the Brown diffusion and thermophoresis effects are negligible in the laminar natural convection of the nanofluid. The degradation of the heat transfer with an increase of the volume fraction of the nanoparticle in the natural convection of nanofluid is due to the increase of the viscosity and the decrease of the thermal expansion coefficient and the specific heat. It is clarified in the present study that the previous controversies between the numerical and experimental studies are owing to the different definitions of the Nusselt number.