Abstract
The paper reports a finite difference solution for the natural counterflow generated in a horizontal adiabatic duct with different end-temperatures. Ducts with circular and rectangular cross-section are considered. The natural counterflow is modeled as fully-developed. The numerical results demonstrate that the flow consists of a strong axial counterflow superimposed on four secondary eddies situated in the four quadrants of the cross-section. The paper documents the temperature variation around the wall of a pipe, in a moderate Rayleigh number range not documented previously. The use of the wall temperature information in thermal stress analysis is discussed. The numerical results are also used to assess the applicability of analytical predictions for the flow field in ducts with rectangular cross-section.
Zusammenfassung
Die Arbeit berichtet über eine Lösung mit finiten Differenzen der natürlichen Gegenströmung in einem horizontalen adiabaten Kanal mit kreisförmigem oder rechteckigem Querschnitt bei ungleichen Endtemperaturen. Die natürliche Gegenströmung soll voll ausgebildet sein. Das Ergebnis zeigt, daß die Strömung aus einer starken axialen Gegenströmung und vier überlagerten sekundären Wirbeln in den vier Quadranten des Querschnitts besteht. Man erhält auch die Temperaturänderung längs der Rohrwand, wie sie für mäßige Rayleigh-Zahlen bisher nicht mitgeteilt wurde. Die Verwendung der berechneten Wandtemperatur bei Untersuchungen über thermischen Spannungen wird diskutiert. Die numerischen Ergebnisse wurden auch verwendet, um die Anwendbarkeit analytischer Voraussagen über das Strömungsfeld in rechteckigen Kanälen abzuschätzen.
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Abbreviations
- A:
-
aspect ratio, b/h
- b:
-
horizontal dimension of rectangular crosssection
- g:
-
gravitational acceleration
- Gr:
-
Grashof number
- h:
-
vertical dimension of rectangular crosssection
- P:
-
pressure
- r:
-
radial position
- r0 :
-
pipe radius
- Ra:
-
Rayleigh number
- T:
-
temperature
- ΔT/L:
-
longitudinal temperature gradient
- u:
-
transversal velocity component (Fig.1)
- v:
-
transversal velocity component (Fig.l)
- w:
-
longitudinal velocity
- x:
-
horizontal transversal position
- y:
-
vertical transversal position
- Y:
-
circumferential temperature distribution
- z:
-
longitudinal position
- ()* :
-
dimensional quantity
- α:
-
thermal diffusivity
- β:
-
coefficient of thermal expansion
- θ:
-
angular position
- ν :
-
kinematic viscosity
- ρ:
-
density
- ψ:
-
streamfunction
- ω :
-
vorticity function
- r0 :
-
refers to Gr and Ha based on pipe radians
- h:
-
refers to Gr and Ra based on h of rectangular cross-section
References
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Kimura, S., Bejan, A. Numerische Berechnung der natürlichen Konvektion in einem waagerechten Kanal mit ungleichen Endtemperaturen. Warme- und Stoffubertragung 14, 269–280 (1980). https://doi.org/10.1007/BF01618358
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DOI: https://doi.org/10.1007/BF01618358