Evaporation-Induced Temperature Gradient in a Foam Column

Various parameters affect 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 liquid loss but 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 a 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 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 spans over a length scale comparable to the tube radius.