Question

I sometimes like a nice warm bath in the winter. After a while, the bath gets colder. I know there are a few ways that the bath can lose heat, but does a thick layer of bubbles on the top make any significant difference to the heat retention?

Answer 1

Basically you ask this working on the assumption that a layer of bubbles would thermally insulate the top surface of the water, like a bubble wrap would insulate a hot or cold object. This is correct - it will reduce the heat loss through the top surface, both in straight diffusion of heat into the air and in water evaporation, which is a very efficient mechanism of cooling by phase transition. Of course, one has to have very stable long lived bubbles in this form covering the water surface, which can be achieved by the use of good surfactants and salts, although I don't know how good for your health all that would end up being! But my instinct tells me that both of these mechanisms of heat transmission and water evaporation off the top surface, whether insulated or not, are minor in the overall process of a bath cooling down. Let