Drying kinetics and nucleation in evaporating sodium nitrate aerosols

Abstract

A quantitative understanding of the evaporative drying kinetics and nucleation rates of aqueous based aerosol droplets is important for a wide range of applications, from atmospheric aerosols to industrial processes such as spray drying. Here, we introduce a numerical model for interpreting measurements of the evaporation rate and phase change of drying free droplets made using a single particle approach. We explore the evaporation of aqueous sodium chloride and sodium nitrate solution droplets. Although the chloride salt is observed to reproducibly crystallise at all drying rates, the nitrate salt solution can lose virtually all of its water content without crystallising. The latter phenomenon has implications for our understanding of the competition between the drying rate and nucleation kinetics in these two systems. The nucleation model is used in combination with the measurements of crystallisation events to infer nucleation rates at varying equilibrium state points, showing that classical nucleation theory provides a good description of the crystallisation of the chloride salt but not the nitrate salt solution droplets. The reasons for this difference are considered.

High time resolution measurements of droplet evaporation kinetics and particle crystallisation

“…However, single droplet evaporation experiments can provide an empirical route to resolving this information. [25][26][27] To investigate the interplay of drying rate, final particle morphology and aerodynamic size, a suitable instrument would allow observation of the evolving particle morphology throughout the drying process with parallel measurements of geometric diameter and aerodynamic diameter. Finally, sampling of the dry particles produced would allow detailed analysis of the relationship between drying conditions and final dry particle morphology providing a direct comparison to the dry particles produced in industrial applications.…”

Isomorphs in nanoconfined liquids

“…1,2 This simplification is, however, hard to achieve in experiments, and most liquids in nature are in contact with, or confined by, one or several surfaces. [3][4][5][6][7][8][9][10][11][12][13][14] Recent experiments on levitation of metallic liquids using electrostatic or magnetic fields, [15][16][17][18] ionic solution droplets in optical tweezers, 19 and especially colloids 20 come closer to the simplification of standard computer simulations, [15][16][17][18] but still have ''free surfaces'' that may affect the probed quantities. Significantly, the added complexity induced by the walls has made fundamental theories of nanoconfined liquids slower to develop, in particular for the dynamics.…”

Water evaporation from solute-containing aerosol droplets: Effects of internal concentration and diffusivity profiles and onset of crust formation

“…Handscomb et al 52 proposed a numerical model consisting of a set of advection–diffusion equations coupled to ordinary differential equations describing the particle size and temperature to simulate the drying of droplets that contain solid particles prior to crust formation. Solute nucleation and crust formation in drying free droplets were numerically modeled by Robinson et al 53 using a single-particle approach based on the diffusion equation. Diffusion through atmospheric aerosols has been numerically simulated using core–shell multilayer models such as the KM-GAP model proposed by Shiraiwa et al 54 based on the PRA (Poschl-Rudich-Ammann) framework, 55 the model proposed by Fowler et al 56 based on the Maxwell–Stefan diffusion framework, and the Fi-PaD model proposed by O'Meara et al 57 based on the Fickian diffusion framework.…”