FILM EVAPORATION OF AMMONIA OVER HORIZONTAL ROUND TUBES.

Geoscience has undertaken a fundamental study of film evaporation of ammonia as one task of a three study of heat transfer appropriate to the OTEC evaporator. Three parallel approaches have been employed. The largest part consists of tests in which ammonia films are evaporated over round horizontal tubes with specially-prepared surfaces in an apparatus which allows viewing of the process. The two other parts consist of tests with a simple flow modeling apparatus and analysis of the film evaporation process by mathematical modeling. Data are presented for all of the surfaces tested. It is shown that the mathematical analysis may be used to represent the smooth tube data. It is also shown that properly chosen surface modifications may be used to improve heat transfer conductance or improve lateral liquid distribution by improving both wetting and axial spreading.