Evaporation-induced temperature gradient in a foam column

TL;DR

This study investigates how evaporation causes a temperature gradient in a foam column, combining theoretical and experimental methods to understand the thermal effects and temperature profiles during evaporation.

Contribution

It provides the first combined theoretical and experimental analysis of temperature profiles caused by evaporation in foam columns, highlighting the balance of heat fluxes involved.

Findings

Temperature at the foam interface is lower than ambient by a few degrees.

Temperature gradient depends on foam thickness and aspect ratio.

Gradient spans over foam thickness or tube radius depending on geometry.

Abstract

Various parameters affect the foam stability: surface and bulk rheology of the solution, gravitational drainage, mechanical vibrations, bubble gas composition, and also evaporation. Evaporation is often considered through the prism of a liquid loss, but it also induces a cooling effect due to the enthalpy of vaporization. In this study, we combine a theoretical and experimental approach to explore the temperature field in a foam column evaporating from the top. We show that a measurable temperature profile exists in this geometry with temperatures at the interface lower than the environmental temperature by few degrees. We demonstrate that the temperature profile is the result of a balance between the enthalpy of vaporization and heat fluxes originating from the thermal conduction of foam and air and the thermal radiation. For small foam thicknesses compared to the radius, we found that the temperature gradient is established over the foam thickness while for large aspect ratios, the gradient is spanning over a lengthscale comparable to the tube radius.