Experimental Investigation of Free Convection in a Liquid Metal in Long Tubes

Abstract

This paper reports an extension of a previously published investigation into the natural convection process in a liquid metal (4), using circular tubes closed at their lower ends, operating on the thermosyphon principle of heat transfer. In this work longer tubes were used than previously and two distinct regimes of flow were observed. At low heating rates the non-dimensional heat transfer coefficient was found to be a linear function of the temperature difference, and the fluid at the lower end of the tube appeared to be stagnant, contributing negligibly to the overall heat transfer process.

At higher heat transfer rates, the data followed the general trends of the previously observed flows in a liquid metal, although The Heat Transfer Rates Were At Least 17 Per Cent Less Than With Normal Boundary Layer Flow, and More Dependent Upon The Surface Geometry. This Was Due To Interference Between The Heated Boundary Layer and The Core of Cooler Fluid, and This Caused Violent Oscillations In The Temperature of The System Which Persisted Throughout The Entire Test Programme.