Heat Transfer and Flow Instabilities in Ethanol Sessile Drops Under Evaporation

Thanks to a recent increase in space resolution and temperature accuracy of infrared camera device, it’s now possible to perform thermal visualizations of sessile drops under evaporation. Using infrared techniques, we can access local thermal motions inside millimetric drops without perturbing the internal mechanisms. In the full paper, we will provide a literature review of experimental, numerical simulation and theoretical work recently perform on sessile drop evaporation. We will also detail the experimental setup which has been elaborated to realize these thermal observations. Using infrared and visible video recording, we can follow respectively the evolution of the motion inside the drop and the drop shape during evaporation. Using a heat fluxmeter placed below the drop, we can analyze the heat transfer between the substrate and the drop. We will completely describe the evaporation process based on a reference experiment and evidence the existence of several phases during this process. Then, we will dwell on the heat flux transferred to the drop during each step of the evaporation process to obtain very important information about the coupling between flow motion and heat transfer coefficient. Finally, we will present the influence of substrate temperature and drop size on the evaporation process which leads us to build a scaling law and better understand drop evaporation process.