Non-selective evaporation mechanism of binary aerosol generating agent on porous atomizer and its experimental verification

TL;DR

This study investigates the non-selective evaporation mechanism of binary aerosol agents in porous atomizers, combining theoretical analysis and experiments to explain the similarity in aerosol and liquid composition despite differing boiling points.

Contribution

It introduces a novel mechanistic understanding of non-selective evaporation involving evaporation layers and capillary effects, validated through comprehensive experiments.

Findings

Non-selective evaporation caused by liquid convection obstruction in capillaries.

Evaporation temperature aligns with dew point, not bubble point.

Surface heating and mass transfer resistance influence evaporation behavior.

Abstract

To explain the similarity between e-cigarette aerosol and e-liquid composition despite differing component boiling points, a non-selective evaporation mechanism for binary aerosol generating agents was investigated using phase diagrams and capillary evaporation theory. Experiments including evaporation temperature measurement, airflow heating, and capillary evaporation observation validated the non-selective evaporation process. Key findings: 1) Non-selective evaporation occurs due to liquid convection obstruction in capillaries, forming an evaporation layer with a composition distinct from the main liquid phase. Stable non-selective evaporation arises when the gas-phase composition matches the liquid-phase components transferred to the evaporation layer. 2) Evaporation temperature (T) deviated significantly from the bubble point temperature (Tb) and aligned closely with the dew point temperature (Tc), indicating a stable evaporation layer with a unique composition. 3) Surface heating and porous material experiments demonstrated significant deviations from ideal selective evaporation in water/methanol, water/propylene glycol, and propylene glycol/glycerol systems, highlighting the roles of "surface heating" and "mass transfer resistance" in non-selective evaporation. 4) A two-stage capillary evaporation experiment revealed a transition in evaporation rate, confirming a shift in the evaporation layer's composition during stable non-selective evaporation. 5) Particle tracing confirmed unidirectional liquid flow in capillaries, with micro-convection near the meniscus, further supporting the "evaporation layer" concept. These findings provide a mechanistic understanding of non-selective evaporation in e-cigarette aerosols.