Measurement of temperature profiles near the liquid–gas interface during evaporation of water and ethanol into air

The article experimentally studies the temperature field of a two-layer liquid–gas system at normal atmospheric pressure for an axisymmetric configuration. Temperature measurements were carried out for a thin layer of water and ethanol about $2$ mm thick with local heating and evaporation into air using a microthermocouple with a flat bead about $3~\mu$m thick, moving across the layers with a step of $48$ nm. A fluoroplastic cuvette with liquid with a diameter of $35$ mm and a heater $($diameter $1.6$ mm$)$ in the center was located inside a box measuring $800 \times 500 \times 350$ mm$^3$, so that evaporation occurs into air with controlled temperature and humidity. The evolution of the temperature profile near the liquid–air interface was obtained with an increase in the heater temperature up to $88^{\circ}$C. Depending on environmental conditions and the type of liquid, the temperature in the gas phase near the interface may be higher or lower than the temperature of the liquid. It is shown that for a volatile liquid (ethanol), the temperature profile is completely different than for a nonvolatile liquid. Namely, the temperature in the gas phase near the liquid–gas interface is higher than in the liquid at the interface throughout the entire temperature range considered, which is explained by convective flow in ethanol.