BK1-9 Enhanced Tubes in Kettle Reboilers

J. W. Palen

This report describes the main results of HTRI/HTFS-sponsored shellside boiling research conducted at the Herlot-Watt University from October 1986 to April 1990. Heat transfer data were taken for a number of pure components and mixtures boiling on a single tube and in a ""slice"" (thin section) of a tube bundle using plain tube surfaces and a number of enhanced surfaces. The main objective of the research was to determine the effectiveness of using enhanced tubes in only the lower rows of a tube bundle.

It was found that all the enhanced surfaces tested greatly improved boiling performance, especially at low temperature differences. Improvement was greater for pure components than for wide-boilinge-range mixtures. Use of enhanced tubes in the bottom rows increased the boiling heat transfer coefficient of the upper rows of plain tubes by a factor of 1.5 to 2 due to increased velocity.

HTRI Design Manual Methods for single tubes, bundles, pure components, and mixtures were evaluated against these data with reasonably good results in most cases. The RKH-2 Computer Program, Mod 0.11, however, will require some updates to permit prediction of these data. Recommendations for improvement are given.

Foaming was a problem for the hydrocarbon mixture data. Characteristics of foaming are discussed and recommendations are made.