Local heating at convection fronts and moving contact lines on hygroscopic fluids

A temperature rise on the order of tenths of a degree is observed as one fluid spreads over a hygroscopic fluid. While this behavior is only exhibited with hygroscopic fluids, it is independent of the properties of the spreading fluid. The spreading induces a ‘rolling’ motion in the subphase which brings ‘fresh’ fluid to the surface, exposing it to the water vapor in the air. As water is absorbed into the hygroscopic liquid, heat is released. The same behavior is observed whether the spreading fluid has a spreading monolayer that drives a convection front or is a spreading lens with a moving three-phase contact line.

The temperature rise from oleic acid spreading on glycerol. The color code identifies the temperature differences. Figure optionsDownload as PowerPoint slideHighlights
► A temperature rise is observed for liquids spreading on hygroscopic fluids.
► This temperature rise is observed for both convection fronts and moving contact lines.
► The heat generated is a result of atmospheric water being absorbed into the hygroscopic fluid.