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Two-dimensional convection from heated wires at low Reynolds numbers

Published online by Cambridge University Press:  28 March 2006

D. C. Collis  and
M. J. Williams
D. C. Collis
Affiliation:
Aeronautical Research Laboratories, Australian Defence Scientific Service
M. J. Williams
Affiliation:
Aeronautical Research Laboratories, Australian Defence Scientific Service
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Abstract

Measurements of heat transfer from circular wires placed normal to a horizontal airstream have been made in the Reynolds number range 0·01 to 140. The Nusselt number can be related to the Reynolds number and temperature loading by an expression of the form $N \left(\frac {T_m}{T_\infty} \right)^{-0\cdot 17} = A + BR^n,$

where the values of n, A and B (see table 3) depend on whether the Reynolds number is above or below the value for which a vortex street exists in the wake of the wire. This value of the Reynolds number (R [eDot ] 44) is independent of the intensity and scale of the stream turbulence. The theoretical heat transfer relation based on the Oseen approximation is approached asymptotically as R → 0, provided free convection is negligible.

Free convection effects diminish rapidly with increasing Reynolds number so that the orientation of the wire with respect to the vertical has a negligible influence on heat transfer except at very low velocities. For horizontal wires at very low Reynolds numbers, free convection is significant, when, roughly speaking, the Reynolds number is less than the cube root of the Grashof number.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 6 , Issue 3 , October 1959 , pp. 357 - 384
Copyright
© 1959 Cambridge University Press

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