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Free convection in low-temperature gaseous helium

Published online by Cambridge University Press:  29 March 2006

D. C. Threlfall
D. C. Threlfall
Affiliation:
Cavendish Laboratory, University of Cambridge
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Abstract

Free convection has been studied in gaseous helium at low temperatures in a cylindrical vessel of aspect ratio (diameterlheight) 2·5. Compared with measurements in fluids at room temperature the present arrangement has the advantages of small size, a short time constant and improved accuracy. As the Rayleigh number was varied from 60 to 2 × 109, the Nusselt number rose from 1 to 69, obeying the relation Nu = 0·173Ra0·2800±0·0005 over the upper four decades of Ra. The critical Rayleigh number was 1630, but the conditions of the experiment did not allow reliable measurements at such low values of Ra. The very high sensitivity within a given experiment showed the presence of several ‘discrete transitions’, which were often step like and not merely a change of gradient as reported by other workers. The largest of these, at Ra = 3 · 105, involved a drop in heat flux of some 6% and was somewhat hysteretic. The temperature fluctuations increased markedly as the step was crossed.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 67 , Issue 1 , 14 January 1975 , pp. 17 - 28
Copyright
© 1975 Cambridge University Press

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References

Brickwedde, F. G., Van Dijk, H., Durieux, M., Clement, J. R. & Locan, J. K. 1960 J. Res. Nut. Bur. Stand. A 64, 1–17.
Brown, W. 1973 Heat-flux transitions at low Rayleigh number. J. Fluid Mech., 60, 539–559.Google Scholar
Chu, T. Y. & Goldstein, R. J. 1973 Turbulent convection in a horizontal layer of water. J. Fluid Mech., 60, 141–159.Google Scholar
Globe, S. & Dropkin, D. 1959 Natural convection heat transfer in liquids confined by two horizontal plates and heated from below. J. Heat Transfer, 81, 24–28.Google Scholar
Goldstein, R. J. & CHU, T. Y. 1969 Thermal convection in a horizontal layer of air. Prog. Heat Mass Transfer, 2, 55–75.Google Scholar
Hands, B. A. 1972 Oxford Engng Dept. Rep. no. 1046/72.
Hands, B. A. 1973 Heprop. Cryogenics, 13, 423–425.Google Scholar
Hulm, J. K. 1949 Thermal conductivity of superconductors. Ph.D. thesis, University of Cambridge.
Hulm, J. K. 1950 The thermal conductivity of tin, mercury, indium and tantalum at helium temperatures. Proc. Roy. Soc. A 204, 98–123.Google Scholar
Krishnamurti, R. 1970 On transitions to turbulent convection. J. Fluid Mech., 42, 295–308.Google Scholar
Mccarty, R. D. 1972 Thermophysical properties of helium-4 from 2 to 1500K with pressures to 1000 atmospheres. Nat. Bur. Stand. Tech. Note, no. 631.Google Scholar
Malkus, W. V. R. 1954 Discrete transitions in turbulent convection. Proc. Roy. Soc. A 225, 185–212.Google Scholar
Weber, S., Keesom, W. H. & Schmidt, G. 1936 Leiden. Comm. A 246, 1–16.
Willis, G. E. & Deardoref, J. W. 1967 Confirmation and renumbering of the discrete heat flux transitions of Malkus. Phys. Fluids, 10, 1861–1866.Google Scholar