Predictive Determination of the Integral Characteristics of Evaporation of Water Droplets in Gas Media with a Varying Temperature

The possibility of using three heat-transfer models based on ordinary differential equations (ODEs) has been analyzed with account taken of the relevant endothermic phase transformations to predict the integral characteristics of evaporation of liquid droplets (with the example of water) in gas media with a varying temperature. The existing formulations with "diffusive" and "kinetic" approximations to the description of the process of evaporation have been considered, and a new model has been developed according to approximations obtained from the results of conducted experiments (with the use of high-speed cameras and cross-correlation software and hardware systems). Two integral characteristics of the process of evaporation were monitored: the mass rate of vaporization and the lifetime (time of complete evaporation) of a droplet. A comparison of simulation results and experimental data allowed us to draw the conclusion on the expediency of use of ODE-based "diffusive" and "phase-transition" models in a limited temperature range (to 600 K). At high gas temperatures (particularly, higher than 1000 K), a satisfactory correlation with experimental data can be provided by a model that takes account of the substantially nonlinear dependence of the vaporization rate on temperature, the formation of a buffer (steam) layer between the droplet and the gas medium, and the basic mechanisms of heat transfer in the liquid and in the gas medium.