摘要

Falling film evaporation is frequently used in the chemical, petrochemical, pharmaceutical and food industry due to its favourable characteristics especially for temperature sensitive products. Many of those show viscous flow behaviour and the known experimental database is relatively poor. The present study investigated heat and mass transfer phenomena in thin gravity driven pure liquid films. The focus was on heated falling films, especially surface evaporation but besides that the transition zone to nucleate boiling was studied as well to gain information about the film stability at the maximum wall superheat before nucleate boiling started. The Prandtl number was varied from 1.75 up to 130 with Reynolds numbers varying from 2 to 2000. The overall temperature difference was between 5 K and 40 K. Due to the wide experimental range of Prandtl and Reynolds numbers, resp. it was possible to review known literature models. It was found that they widely deviate from each other at higher Prandtl numbers. In conclusion it was necessary to develop a new correlation for this range and to test it for its applicability. The results presented in this paper significantly extend the database for the evaporation of pure liquids with high Prandtl numbers over previously published data and allow further investigations on a theoretical and practical basis.