On the Influence of Low-power Laser Source on the Evaporation of Single Droplets: Experimental and Numerical Approaches

This work investigates the influence of laser power on an evaporating single droplet made from an H2O and NaCl mixture. Heat and mass transfer of a single droplet with the presence of a low-power laser source (as He-Ne laser) is studied both numerically and experimentally in this article. A new model is presented to simulate water droplet evaporation. The model is robust enough to be applied for various initial concentrations and conditions of the droplet, ambient conditions, and dissolved media properties. Moreover, laser energy is taken into consideration as a source term which is a function of the wave length of the source beam and refractive index of the droplet. Considering the involved parameters, the model is implemented in a MATLAB code and validated using experimental data obtained in this study on top of those already available in the literature. Experimental data were collected for droplets with an initial radius of 500μm at room temperature for three initial concentrations of 3%, 5%, and 10% (by mass) of NaCl in water as well as pure water droplet to provide a comprehensive validation dataset. It is shown that low-power laser source significantly increases the evaporation rate (2.7 to 5.64 for 0% and 10% initial concentration of salt, respectively) which must be taken into consideration while using laser based measurement techniques.