Heat Transfer in an Open Thermosyphon

Abstract

In this report two sorts of experimental studies of free convection heat transfer in an open thermosyphon tube are described : One is carried out using an apparatus with a rectangular passage for observation of the flow pattern, and the other gives the exact heat transfer data, including the turbulent region using two sorts of apparatus with a circular passage. On the basis of such studies, the heat transfer mechanism of thermosyphon in both laminar and turbulent regions are explained. In the laminar region experimental data agree closely with analytical solution. As for the occurrence of turbulence, however, it may be probably originated at a boundary between up-flow and down-flow, where only the down-flow is disturbed at first, and there the heat transfer data are little different from those in the laminar region. When a turbulence occurs under the impeded flow regime, however, it spreads to all over the tube at once, affecting heat transfer data considerably, but they can be correlated by using Prandtl number and length-radius ratio as parameters. Finally the correlating equation for the heat transfer in an open thermosyphon tube is derived.