Experimental Study of Thermal Convection in a Vertical Cylinder of Mercury Heated from Below

Abstract

Very precise temperature measurements have been made on a vertical circular column of liquid mercury, and also a mercury-zinc alloy, heated from below. In both pure mercury and the alloy, two types of temperature oscillations, indicating two modes of time-dependent fluid flow, were observed. The first oscillatory mode appeared at a Rayleigh number 10% higher than the critical Rayleigh number for the onset of fluid flow predicted by linear stability theory. At higher Rayleigh numbers this mode disappeared and the second oscillatory mode, having a shorter period, began at Rayleigh numbers 30% above the critical value. Both types of temperature oscillations are consistent with a pulsed mode of fluid flow. Attempts to detect the predicted, steady, antisymmetric flow at the onset of fluid motion by means of lateral temperature measurements were unsuccessful.