BT-11 Film Breakdown in Falling Film Evaporation of Ethylene Glycol/Water and Ethylene Glycol/Water/I-Propanol Solutions, Preliminary Evaluation

J. W. Palen

HTRI Report BT-10 documents HTRI sponsored research on falling film evaporation of glycol/water solutions at Lehigh University during the period 1986 - 1988. In that document it was reported that evaporating films composed of mixtures of ethylene glycol and water break down at much lower heat fluxes for a given flow rate than would be expected for evaporation of pure fluids. No additional data were available in the literature on mixtures of this type. It was suspected, as reported in BT-10, that the reason for the early breakdown was the surface tension gradients in the film which were set up by the preferential vaporization of water molecules from mixture. However, even a qualitative theory could not be constructed at that time.

This report reviews some preliminary data obtained from the first ternary falling film experiments at Lehigh. The addition of i-propanol to the glycol/water mixture drastically altered the physical properties of the mixture and extended the observations sufficiently so that a qualitative theory could be envisioned. A preliminary curve fit of the data is presented, and implications of the proposed theory on design are discussed.