Abstract
Natural convection heat transfer on the outside of an inclined helical coil was investigated experimentally. For a single turn helical coil laid on the horizontal plane, the heat transfer rate was very close to that of a horizontal cylinder. The heat transfer rate decreased when the coil was tilted. For inclined helical coils with higher numbers of turns, the heat transfer rates were influenced by plumes from the lower turns, exhibiting preheating, velocity, and chimney effects. For very small pitches, the preheating effect was dominant. For moderate pitches, the velocity and chimney effects became dominant. For larger pitches, the plume effect disappeared. The angle of inclination affects the physical arrangement of the helical coil and influences the heat transfer. The study was performed using very high Pr of 2014. An empirical correlation was proposed based on the experiments.
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Abbreviations
- C b :
-
Cupric ion concentration in the bulk (mol/m3)
- D :
-
Diameter of the helical coil (m)
- D m :
-
Mass diffusivity (m2/s)
- F :
-
Faraday constant, 96,485 (C/mol)
- g :
-
Gravitational acceleration, 9.8 (m/s2)
- H :
-
Height of the helical coil (m)
- h h :
-
Heat transfer coefficient (W/m2K)
- h m :
-
Mass transfer coefficient (m/s)
- I lim :
-
Limiting current (A)
- k :
-
Thermal conductivity (W/mK)
- L :
-
Total length of the helical coil (m)
- N :
-
Number of turns of the helical coil
- n :
-
Number of electrons in charge transfer reaction
- Nu D :
-
Nusselt number based on the diameter (hhD/k)
- P :
-
Pitch of the helical coil (m)
- Pr :
-
Prandtl number (ν/α)
- R :
-
Winding radius of the helical coil (m)
- Ra D :
-
Rayleigh number based on the diameter (gβΔTD3/αν)
- Sh D :
-
Sherwood number based on the diameter (hmD/Dm)
- T :
-
Temperature (K)
- t n :
-
Transference number
- U x :
-
Uncertainty of x
- α :
-
Thermal diffusivity (m2/s)
- β :
-
Volume expansion coefficient (1/K)
- γ :
-
Dispersion coefficient
- θ :
-
Angular position of cylinder (°)
- μ :
-
Viscosity (kg/m s)
- ν :
-
Kinematic viscosity (m2/s)
- ρ :
-
Density (kg/m3)
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Acknowledgments
This study was sponsored by the Ministry of Science, ICT & Future Planning (MSIP) and was supported by Nuclear Research & Development program grant funded by the National Research Foundation (NRF) (Grant code: 2014M2A8A1030777).
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Moon, JY., Heo, JH. & Chung, BJ. Natural convection experiments on the outer surface of an inclined helical coil. Heat Mass Transfer 51, 1229–1236 (2015). https://doi.org/10.1007/s00231-015-1495-5
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DOI: https://doi.org/10.1007/s00231-015-1495-5