The Effect of Natural Impurities Film on Temperature Distribution in Near-Surface Layer of Water

In any water, except deionized, there are natural impurities present on the surface. Even in trace amount, they form a film, which should be taken into account to model the heat and mass transfer between water and air. This film can be broken if the surface is perturbed, but then it is quickly restored by adsorption from the bulk or by advection along the surface. In the present study, the process of water cooling is considered, during which the natural impurities film persists. Also, cooling of ethanol, which does not form surface film, is considered. New modification of the nonintrusive Background Oriented Schlieren technique, used in this study, enabled us to obtain the path-averaged water temperature fields and the mean vertical profiles of temperature with the step about 0.025–0.035 mm and to analyze the field of temperature fluctuations. The difference between the thermal structure of the boundary layer in water and in ethanol is demonstrated. 2D and 3D numerical simulations are performed using Comsol Multiphysics 6.2 software with different boundary conditions specified at the surface of water and ethanol, and the results are compared with experimental data. In water, in contrast to ethanol, linear variation of temperature is observed near the surface, which confirms the molecular mechanism of the heat transfer near the interface.