Nonisothermal Evaporation of Sessile Drops of Aqueous Solutions with Surfactant

In recent decades, electronic devices have tended towards miniaturization, which necessitates the development of new cooling systems. Droplet cooling on a heated wall is effectively used in power devices with high heat flux densities. The use of a surfactant leads to an increase in the diameter of the wetted spot and the rate of droplet evaporation. Despite the wide interest and numerous works in this area, there are still unexplored questions regarding the influence of surfactant and wall temperature on convection, of nonisothermality, and of the decrease in the partial pressure of vapor with increasing surfactant concentration. This work experimentally studies the effect on the rate of droplet evaporation of wall temperature in the range 20–90 °C and of the concentration of surfactant in an aqueous solution of sodium lauryl sulfate (SLS) from 0 to 10,000 ppm. It is shown for the first time that an inversion of the evaporation rate related to the droplet diameter occurs with increasing wall temperature. The influence of key factors on the evaporation of a water droplet with SLS changes with temperature. Thus, at a slightly heated wall, the growth of the droplet diameter becomes predominant. At high heat flux, the role of nonisothermality is predominant. To determine the individual influence of the surfactant on the partial pressure of water vapor, experiments on the evaporation of a liquid layer were carried out. The obtained results and simplified estimates may be used to develop existing calculation models, as well as to optimize technologies for cooling highly heated surfaces.