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Wärme - und Stoffübertragung

, Volume 14, Issue 3, pp 189–199 | Cite as

Single-phase heat transfer characteristics of concentric-tube thermosyphon

  • N. Seki
  • S. Fukusako
  • K. Koguchi
Article

Abstract

An experimental study has been conducted to evaluate the influence of the presence of inner tube and the Rayleigh number on free convective heat transfer in an open thermosyphon. Water and fluorocarbon R-11 refrigerant as the working fluids were utilized. Heat transfer results using the concentric geometry were given for modified Rayleigh number from 3.6×102 to 4.1 × 107 which encompasses the regions of similarity, impeded and boundary layer flow conditions. It was found that the presence of the inner tube markedly increases the overall heat transfer coefficient of open thermosyphon by a factor as large as 2 to 10 in the turbulent impeded and boundary layer regimes.

Keywords

Heat Transfer Boundary Layer Heat Transfer Coefficient Rayleigh Number Boundary Layer Flow 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Nomenclature

a

inner radius of heated tube, D/2

Ain

sectional space area of inner tube, πd i 2 /4

Aan

sectional space area of annulus, π(D2-d 0 2 )/4

Cp

specific heat

di

inner diameter of inner tube

d0

outer diameter of inner tube

D

inner diameter of heated tube

g

gravitational acceleration

L

tube length of thermosyphon

Nua

Nusselt number based on inner radius of heated tube

Nur

Nusselt number based on equivalent heattransfer radius

Nux

Nusselt number, defined in equation (1)

Pr

Prandtl number, defined in equation (3)

q

heat flux from heated tube

r

equivalent heat-transfer radius, defined in equation (4)

Raa

modified Rayleigh number based on inner radius of heated tube

Rar

modified Rayleigh number based on equivalent heat-transfer radius

Rax

modified Rayleigh number, defined in equation (2)

Te

temperature of entrance-fluid

Tw

temperature of heated surface

ΔT

temperature difference between heated wall and entrance-fluid, Tw-Te

Greek Symbols

β

coefficient of volumetric expansion

χ

thermal diffusivity

λ

thermal conductivity

μ

viscosity

ν

kinematic viscosity

Wärmeübergang in einem Thermosyphon aus konzentrischem Rohr bei einphasiger Strömung

Zusammenfassung

Es wurde experimentell untersucht, wie der Einbau eines Innenrohres und wie die Rayleigh-Zahl auf die freie Konvektion in einem offenen Thermosyphon, gefüllt mit Wasser oder dem Kältemittel R 11, einwirkt. Der untersuchte Bereich bei konzentrischer Geometrie lag bei modifizierten Rayleigh-Zahlen von 3,6 · 102 bis 4,1 · 107 und umfaßte damit die Regionen der Grenzschichtströmung. Es ergab sich, daß der Einbau eines Innenrohres den Gesamtwärmeübergang eines offenen Thermosyphons im Bereich der behinderten turbulenten Strömungen und Grenzschichtströmungen um den Faktor 2 bis 10 steigert.

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References

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Copyright information

© Springer-Verlag 1980

Authors and Affiliations

  • N. Seki
    • 1
  • S. Fukusako
    • 1
  • K. Koguchi
    • 1
  1. 1.Department of Mechanical Engineering Faculty of EngineeringHokkaido UniversitySapporoJapan

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