High humidity enhances the evaporation of non-aqueous volatile sprays

TL;DR

This study experimentally shows that higher humidity accelerates the evaporation of volatile liquid droplets in turbulent sprays, due to increased water condensation and heat transfer effects, supported by an extended analytical model.

Contribution

It provides the first quantitative analysis of humidity's effect on non-aqueous volatile spray evaporation using controlled experiments and an extended Fick's law model.

Findings

Higher humidity speeds up volatile droplet evaporation.

Increased humidity results in more water condensation on droplets.

An extended Fick's law model accurately predicts evaporation behavior.

Abstract

We experimentally investigate the evaporation of very volatile liquid droplets (Novec 7000 Engineered Fluid) in a turbulent spray. Droplets with diameters of the order of a few micrometers are produced by a spray nozzle and then injected into a purpose-built enclosed dodecahedral chamber, where the ambient temperature and relative humidity in the chamber are carefully controlled. We observe water condensation on the rapidly evaporating droplet, both for the spray and for a single acoustically levitated millimetric Novec 7000 droplet. We further examine the effect of humidity, and reveal that a more humid environment leads to faster evaporation of the volatile liquid, as well as more water condensation. This is explained by the much larger latent heat of water. We extend an analytical model based on Fick's law to quantitatively account for the data.