Progress in Superconductivity and Cryogenics (한국초전도ㆍ저온공학회논문지)

The Korean Society of Superconductivity and Cryogenics (한국초전도저온학회)
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Friction factor and Nusselt number correlations for rectangular helical flow in stacks-in-conduit conductors

  • Received : 2025.09.05
  • Accepted : 2025.09.29
  • Published : 2025.09.30
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Abstract

Engineering correlations are derived to estimate the friction factor and Nusselt number of rectangular helical flow in stacks-in-conduit conductors (SICC). The SICCs are under current development at KFE (Korea Institute of Fusion Energy) towards the realization of HTS (high-temperature superconductor) fusion system. A copper band is helically wound around the outer wall of a rectangular bundle of stacked REBCO (rare-earth barium copper oxide) tapes, and the space between the bundle and the external jacket serves as a cooling channel for helium gas flow. Key geometric parameters are identified for the SICC structure, and three-dimensional numerical analyses are performed with ANSYS FLUENT and real thermo-physical properties of materials and fluids at 20-30 K. The analysis domain consists of (1) the REBCO bundle, (2) the copper band, and (3) the helium gas flow. A special attention is paid to the role of helix angle of copper band (and helium flow), significantly affecting not only the hydraulic diameter and flow length of cooling channel, but also the flow pattern of cooling gas established by the centrifugal force in curved flow passage. The thermo-hydraulic data are simplified with the typical method of dimensional analysis, and it is successfully verified that the dimensionless friction factor and Nusselt number can be expressed in terms of well-known Dean number (composed of inertial, centrifugal, and viscous forces), in a similar way with the helical tube flow. The derived correlations are directly applicable to the ongoing design and manufacturing of SICC, and eventually to the development of forced-flow gas-cooled HTS magnets.

Keywords

Acknowledgement

This research was supported by R&D Program of "Fusion HTS Magnet Fabrication Process Development (code No. CN2504)" through the Korea Institute of Fusion Energy (KFE) funded by the Government funds, Republic of Korea.

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