Convective instabilities in a closed vertical cylinder heated from below. Part 1. Monocomponent gases

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Abstract
Kr, Xe and SiCI4have been investigated for convective instabilities in closed vertical cylinders with conductive walls heated from below. Critical Rayleigh numbersNiRafor the onset of various convective modes (including the onset of marginally stable and periodic flow) have been determined with a high resolution differential temperature sensing method. Flow patterns were deduced from a multiple sensor arrangement. For the three lowest modes (i= 1, 2, 3) good quantitative agreement with linear stability theory is found. Stable oscillatory modes (periodic fluctuations of the mean flow) with a period of approximately 5 s are found for a relatively narrow range ofNRa. The critical Rayleigh numberNoscRafor the onset of oscillatory temperature fluctuations is 1348 ± 50 for an aspect ratio (height/radius) of 6.