Heat exchange of an evaporating water droplet in a high-temperature environment

Abstract

In this research, we present the results of experiments capturing the characteristics of high-temperature heating and evaporation of water droplets. The experimental parameters are as follows: initial droplet radius 1–2.5 mm, temperature 20–1100 °C, air flow velocity 0–5 m/s. We use two schemes of water droplet fixation in the heated air flow. In the experiments, we record the heating and evaporation of free-falling droplets so that the holder does not interfere with the experimental results. Typical water droplet heating rates range from 0.4 to 92.4 °C/s and evaporation rates from 0.003 to 0.178 kg/(m2s). Criterial processing of our experimental data is based on the classical equations formulated by Ranz and Marshall and equations proposed by a set of research groups and scientists. We determine the variation ranges of the Reynolds numbers, in which one can only use a limited set of Nu(Re,Pr) correlations. Adjustment coefficients are proposed to take into account the droplet surface temperatures and evaporation rates as functions of the gas medium temperature. Finally, we hypothesize as to how modern mathematical models can be modified to bring the simulation results closer to the experimental data in droplet heating and evaporation rates during fast heat supply.