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Experiments on the onset of thermal convection in horizontal layers of gases

Published online by Cambridge University Press:  28 March 2006

H. A. Thompson  and
H. H. Sogin
H. A. Thompson
Affiliation:
Department of Mechanical Engineering, Tulane University, New Orleans, Louisiana 70118
H. H. Sogin
Affiliation:
Department of Mechanical Engineering, Tulane University, New Orleans, Louisiana 70118
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Abstract

Precise data are presented on the Rayleigh-Jeffreys instability in air, argon and carbon dioxide at pressures between 0·6 and 6·0 atm in layers of depths 1/8, 1/4, and 3/4in. A new method yields better resolution and repeatability than the methods employed in the past. Here the gas layer is brought through the state of marginal stability by increasing the pressure while both the temperature and the temperature difference are held constant. The onset of convection is detected by means of a type of heat flow meter ascribed to Prof. L. M. K. Boelter. The equipment and procedure are described and analysed in detail.

The experimentally-determined value of the critical Rayleigh number is 1793, repeatable within a probable deviation of 1% due to random errors. Considering in addition the systematic errors of the instrumentation but not the uncertainties of property values, we place the absolute value within 1793 ± 80. The corresponding theoretical value is 1708.

Finite rates of pressure rise inhibit the development of convection. The results achieved at the least rates of pressure rise are in agreement with steady-state determinations.

The approach employed in this investigation shows great promise as a method for measuring the transport properties of gaseous mixtures or of gases at combined high temperature and high pressure.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 24 , Issue 3 , March 1966 , pp. 451 - 479
Copyright
© 1966 Cambridge University Press

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