An experimental investigation of the surface temperature field during evaporative convection

Measurements of the surface temperature field are presented for a water surface undergoing evaporation. These temperature fields were measured using an infrared camera for a range of heat fluxes q″=30–500 W/m2. Experiments were conducted for water surfaces with and without a surfactant monolayer. A statistical analysis of the data is presented which shows the effect of heat flux and surfactants on the root mean square and skewness of the field. The data reveals a linear increase in the rms with increasing heat flux, which is similar for clean and surfactant conditions. In contrast, the skewness is markedly different for the clean and surfactant-covered cases. For clean surface conditions, the skewness attains large, negative values, becoming increasingly negative as q″ increases. When the surface is covered with a surfactant monolayer, however, the skewness exhibits small, negative values which approach zero as the heat flux increases. This behavior is reflected in the pdf which is clearly asymmetric in the clean case and virtually symmetric in the surfactant case. A physical mechanism is presented to explain these results. Temporal power spectra are presented which reveal the role of heat flux and surfactants on the temporal evolution of the surface temperature field.