HEAT TRANSFER ENHANCEMENT FOR GRAVITY CONTROLLED CONDENSATION ON A HORIZONTAL TUBE BY COILING WIRES.

A device for enhancing condensation heat transfer coefficient by means of protrusions on a tube surface was proposed by Gregorig, where the film thickness at the top of the protrusion is thinned by the effect of surface tension. The idea of Gregorig is to thin the film thickness at the top parts of the protrusions, while that of Thomas is to thin the film thickness at the area between protrusions. The use of wire coiled tubes is also effective for horizontal tube bundles. Thomas reported that the heat transfer coefficient was about two times the value predicted by the Nusselt's expression for a smooth tube in an ammonia condenser. Marto and Wanniarachchi found significant reduction of the effect of condensate inundation in a steam condenser with large tube bundles. However, the selection of the most effective wire diameter and pitch is still uncertain even for a single condenser tube. To clarify this problem is the objective of this paper.