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Free convective heat-transfer performance of a two-dimensional open thermosyphon with heat sources of cavity dotted along vertical wall

Wärmeübertragungsverhalten bei freier Konvektion eines zweidimensionalen, offenen Thermosyphons mit längs der vertikalen Wand verteilten Hohlräume als Wärmequellen

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Abstract

This paper is concerned with the heat-transfer characteristics in a vertical two-dimensional open thermosyphon whose heat sources are the heated cavities dotted along the vertical wall. Air is utilized for the measurement of heat transfer, while transformer oil for the observation of the flow patterns. Attention is particularly focussed on the effects of the depth of cavity and the clearance for main fluid-flow on the behavior of free convective heat transfer in the present open thermosyphon. Environmental temperature is maintained at 10°C, while temperature of the bottom-surface of cavity and the clearance of main fluid-flow are parametrically varied, as Rayleigh number ranging from 1.2×101 to 3.8×106.

It is found that the effect of the clearance on the heat-transfer characteristics in the two-dimensional open thermosyphon is unexpectedly large. Experimental results are finally given as plots of Nusselt number versus Rayleigh number. An experimental correlation is given for the Nusselt number as a function of the Rayleigh number and the clearance/length ratio of the open thermosyphon.

Zusammenfassung

Der Bericht befaßt sich mit dem Wärmeübertragungsverhalten in einem vertikalen, zweidimensionalen offenen Thermosyphon mit längs der vertikalen Wand verteilten, beheizten Hohlräumen als Wärmequellen. Zur Messung des Wärmeüberganges wird Luft, zur Strömungsbeobachtung Transformatorenöl verwendet. Besonderes Interesse gilt den Einflüssen der Hohlraumtiefe und der lichten Weite für den Hauptstrom auf das Verhalten des Wärmeüberganges bei freier Konvektion. Die Umgebungstemperatur wird auf 10°C gehalten, während die Hohlraumbodentemperatur und die lichte Weite für den Hauptstrom variiert werden mit Rayleigh-Zahlen zwischen 1.2×101 und 3.8×106.

Es wird festgestellt, daß der Einfluß der lichten Weite auf das Wärmeübertragungsverhalten unerwartet groß ist. Die experimentellen Ergebnisse werden in Diagrammen der Nusselt-Zahl über der Rayleigh-Zahl dargestellt. Ein Zusammenhang für die Nusselt-Zahl als Funktion von der Rayleigh-Zahl und dem Verhältnis von lichte Weite zu Länge wird gegeben.

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Abbreviations

B :

distance between heated wall and opposing insulation wall,W+D

d i :

diameter of inner tube

d 0 :

diameter of outer heated tube

D :

depth of cavity along vertical wall, 0, 25, and 50 mm

g :

gravitational acceleration

H :

length of heated or un-heated wall, 100 mm

L :

length of thermosyphon, 500 mm for two-, 700 mm for three-, and 1100 mm for five-dotted heat sources

Nu B :

Nusselt number based on B as reference length

Nu x :

Nusselt number, defined in Eq. (1)

Pr :

Prandtl number, defined in Eq. (3)

q :

heat flux from heated wall

r :

equivalent heat-transfer radius

Ra B :

Rayleigh number based on B as reference length

Ra x :

Rayleigh number, defined in Eq. (2)

T e :

temperature of entrance-fluid

T w :

temperature of heated wall

ΔT :

temperature difference between heated wall and entrance-fluid,T w -T e

W:

clearance for main fluid-flow

x :

reference length

X :

distance from bottom of thermosyphon

β :

coefficient of volumetric expansion

χ :

thermal diffusivity

λ :

thermal conductivity

ν :

kinematic viscosity

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Authors and Affiliations

  1. Department of Mechanical Engineering Faculty of Engineering, Hokkaido University, 060, Sapporo, Japan

    S. Fukusako (Ass. Prof.), N. Seki (Prof.) & A. Yamaguchi (Graduate Student)

Authors
  1. S. Fukusako
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  2. N. Seki
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  3. A. Yamaguchi
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Fukusako, S., Seki, N. & Yamaguchi, A. Free convective heat-transfer performance of a two-dimensional open thermosyphon with heat sources of cavity dotted along vertical wall. Wärme- und Stoffubertragung 18, 9–15 (1984). https://doi.org/10.1007/BF01461485

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