Gas-Vapor Mixture Temperature in the Near-Surface Layer of a Rapidly-Evaporating Water Droplet.

Pavel Strizhak,Dmitry Antonov,Roman Volkov

doi:10.3390/e21080803

Abstract

Mathematical modeling of the heat and mass transfer processes in the evaporating droplet–high-temperature gas medium system is difficult due to the need to describe the dynamics of the formation of the quasi-steady temperature field of evaporating droplets, as well as of a gas-vapor buffer layer around them and in their trace during evaporation in high-temperature gas flows. We used planar laser-induced fluorescence (PLIF) and laser-induced phosphorescence (LIP). The experiments were conducted with water droplets (initial radius 1–2 mm) heated in a hot air flow (temperature 20–500 °C, velocity 0.5–6 m/s). Unsteady temperature fields of water droplets and the gas-vapor mixture around them were recorded. High inhomogeneity of temperature fields under study has been validated. To determine the temperature in the so called dead zones, we solved the problem of heat transfer, in which the temperature in boundary conditions was set on the basis of experimental values.

Highlights

Today, there are quite a lot of studies looking into the processes of evaporation and combustion of liquid fuel droplets [1,2,3,4]
Since the optical measurement techniques planar laser-induced fluorescence (PLIF) and laser-induced phosphorescence (LIP) have some limitations of the observation area sizes near the media interface, it is reasonable to make additional calculations using the model of high-temperature water droplet evaporation [22] and taking into account the dependence of vaporization rate on temperature, obtained in study [21]
There we showed that accounting for a holder will make it possible to correct the heating and evaporation times of water droplets by no more than

Summary

Introduction

There are quite a lot of studies looking into the processes of evaporation and combustion of liquid fuel droplets [1,2,3,4]. The main consistent patterns of heat and mass transfer processes, when single droplets of liquid fuels and their aerosol flows of different particle sizes are heated and evaporate, were established by the results of theoretical and experimental research, generalized in study [5]. The influence of the temperature difference along the spherical fuel droplet radius on the intensity of heat exchange with the external gas medium was studied in papers [6,7,8,9]. The influence of the convective and radiative components of the heat flux on the intensity of heat and mass transfer when heating a fuel droplet in the gas medium was evaluated in study [11]. The application fields of the evaporation processes of a large group of liquid, emulsion, and slurry droplets in gas media cover much higher temperatures (e.g., in extinguishing fires with water fog, water curtain, and water mist systems) [17]

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