Highlighting a Cooling Regime in Liquids under Submillimeter Flows

The shear flow of ordinary liquids is for the first time observed at the submillimeter scale by thermal imaging. We report on microinfrared experiments, showing that liquids as important as water flowing on wetting surfaces produce cooling, while the academic view would foresee heating production. This apparent counterintuitive cooling effect shows that the increase of the internal energy due to the flow can result in different shapes, including a cooling process, before reaching the conventional heating regime at higher shear rates. This unknown property might be interpreted as a transient stretching state of the liquid. Shearing liquids might be a promising alternative compared to conventional endothermic processes (gas expansion or vaporization of a liquid, the Peltier effect, and so forth).