Heat Transport in Liquid Filled Tubes

Abstract

When heat is applied to a liquid filled tube, the liquid moves under buoyancy forces which arise from density variations. In long thin tubes, inclined at. an angle to the horizontal, two counter-flowing streams of liquid are observed which extend over virtually the whole length. A simple one-dimensional model is developed in which an analysis of heat flows into and between the two streams is made. This is used to predict the temperature in the system and the average fluid velocities at any point in the tube. The results of the model are in good agreement with experimental measurements on these tubular systems, and on a planar convection cell. Systems such as this can exhibit very large effective thermal conductances, and may be useful as a heat extraction device in evacuated tubular solar collectors.