Abstract
<title>Abstract</title> <p>The paper considers the evaporation of droplets consisting of a mixture of liquids with different boiling points. The change in the component concentration in a solution over time is a process that takes place in many technological applications. This paper presents the results of direct measurements of the average concentration in suspended droplets using a capacitance method over a wide range of surrounding airflow temperatures and velocities. To measure the dielectric permittivity (and, consequently, the concentration) of a binary liquid, a coaxial capacitor probe connected to a high-frequency generator was used. A change in the droplet composition leads to a change in the capacitance of the probe and the frequency of the generator, which allows real-time registration of concentration. Drawing on the example of aqueous solutions of acetone, methanol, and ethanol, it is shown that under similar environmental conditions, the evaporation processes are identical and independent of their past history. The study has been conducted jointly with an analysis of the variation in droplet diameter, which has provided an opportunity to evaluate the mass loss from the droplet surface and to establish a criterial correlation dependent on the Nusselt number. To generalize experimental data with differing airflow temperatures, it is necessary to use a combination of dimensionless criteria including Reynolds, Prandtl, Fourier, and Kutateladze numbers. Within a wide range of temperature and airflow velocity parameters, sufficiently accurate generalizing correlations have been obtained, although different for acetone and the two types of alcohol. For complete data generalization, one must consider not only the environmental parameters but also the processes occurring inside the droplet. One of criterion, which determines the relative role of molecular momentum transfer and mass transfer of the impurity in the droplet volume under consideration, is the Schmidt number. The introduction of this number into the previously used complex has allowed reaching a good generalization of all experimental data.</p>