The Influence of the Inclination Angle on the Performance of a Closed Two-Phase Thermosyphon

Abstract

An experimental investigation mas performed in order to observe the effect of the inclination angle on the transport behaviour of a closed two-phase thermosyphon. A vertical or inclined steel pipe was used; this was electrically heated at the lower part (“heating zone”), and it was cooled by water at constant temperature along the upper part (“cooling zone”). Between these two zones there was the well insulated “transport zone”. As working fluid refrigerant R 115 was used. The quantity of fluid in the tube was taken so that the critical specific volume VCRIT was obtained. Thus, a mean thermodynamical critical state can be reached. The heating zone was always flooded. The electric heat input and the inclination angle ϕ towards the vertical position were varied in steps. The maximum heat flow rate in the tube proved to depend upon the inclination, with a largest value of QMAX = 2850 W at ϕ = 40°. An effective thermal conductivity Λeff of the thermosyphon can be determined depending strongly on inclination and heat flow rate; roughly speaking: The steeper the tube and the larger the heat flow rate, the higher is the effective conductivity. Separate consideration of the transport regimes in the various zones showed their individual influence upon the overall behaviour. The condensation in the cooling zone exhibits the largest transport resistance. The heat transfer with boiling in the heating zone shows large local differences and depends strongly on inclination.