Numerical Simulation of Evaporation of Ethanol–Water Mixture Droplets on Isothermal and Heated Substrates

Abstract

In many printing technologies involving multicomponent liquids, the deposition and printing quality depend on the small-scale transport processes present. For liquids with dispersed particles, the internal flow within the droplet and the evaporation process control the structure of the deposition pattern on the substrate. In many situations, the velocity field inside microdroplets is often subject to either thermal or solutal Marangoni convection. Therefore, to achieve more uniform material deposition, the surface tension-driven flow should be controlled and the effect of different fluid and chemical parameters should be identified. Here, we employ an axisymmetric numerical model to study droplet spreading and evaporation on isothermal and heated substrates. For ethanol–water droplets, the effects of the initial contact angle and initial ethanol concentration inside the droplet (solutal Marangoni number) have been studied. We explore the role of the initial ethanol concentration on the magnitude and structure of the internal flows for binary mixture droplets. In addition, we show that certain combinations of initial contact angle and initial ethanol concentration can lead to a more uniform deposition of dispersed particles after all of the liquid has been evaporated.

Comparative Study of Sample Carriers for the Identification of Volatile Compounds in Biological Fluids Using Raman Spectroscopy

“…Thus, the spot (C) of the droplet is the optimum position to focus when the Raman spectrum is acquired, as the ratio of the peak intensities (ethanol to urine) is maximum. This is the outcome of the non-uniformity of ethanol concentration inside the droplet and can be attributed to mass and thermal convection phenomena [ 50 ]. Higher evaporation flux near the contact line leads to minimal ethanol concentration at the edge of the droplet (spot A).…”

“…Higher evaporation flux near the contact line leads to minimal ethanol concentration at the edge of the droplet (spot A). On the contrary, many ethanol molecules are trapped in the center near the top of the droplet where concentration is maximized [ 50 ].…”

Optical Fiber Sensor for Monitoring the Evaporation of Ethanol–Water Mixtures

“…This is an indication that the remaining solution still contains ethanol molecules that did not evaporate. The reason behind this behavior is still not fully understood, though it is believed that it can be associated to the hydrophobic hydration effect [ 26 , 27 ] and to ethanol diffusion inside the droplet to the interface [ 6 , 28 ].…”

“…For solutions with a higher ethanol concentration, the droplet will spread over the substrate. This is due to the increased wettability and decreased water surface tension with higher ethanol concentrations [ 5 , 28 ]. For the water sample, a spherical cap-shape is formed, a characteristic that is associated with the high roughness and wettability of the substrate [ 30 ].…”

Evaporation-Based Low-Cost Method for the Detection of Adulterant in Milk

“…The evaporation dynamics of a liquid mixture involving a nonvolatile solute, colloids, and a volatile solvent is a complex phenomenon due to the coupled effects of hydrodynamics, heat and mass transfer, and contact-line dynamics. ,− The evaporative deposition pattern is highly sensitive to the surface tension, surface tension gradient of the liquid, wettability and roughness of the underlying substrate, and nature of the solute. − While there have been several works on the evaporative deposition of colloidal particles on different wettability substrates, the effect of dissolved solute on the deposition pattern is rather limited. ,, In aqueous saline drops, the salt crystallizes when the concentration exceeds the saturation concentration during evaporation. , The evaporative deposition is further affected by the presence of multiple components (evaporation of fuel, ouzo droplets, and surfactant in a binary mixture). Recently, the differences in drying patterns of sessile droplets of blood have been reported as a means to detect diseases. , Milk is a complex fluid that contains nonvolatile milk solids (fats, protein, salt) and volatile (water-enriched material, ketones, alcohols, hydrocarbons, esters, etc …”