A multilayer heat and mass transfer model for photoacoustics of aerosol particles (MHM-PA)

Unexpected concentration dependence of the mass accommodation coefficient of water on aqueous triethylene glycol droplets

“…[37][38][39][40][41] For the determination of a M , we combined our newly developed Photothermal Single-Particle Spectroscopy (PSPS) 7,30,[42][43][44][45][46] with our recently developed multilayer heat and mass flux model for photoacoustic spectroscopy on single aerosol particles (MHM-PA). 47 PSPS consists of an optical trap (not shown in Fig. 1) that immobilises a single droplet in a gas environment of controlled gas composition, relative humidity, pressure and temperature.…”

“…For the simulation of the MMS signals, we combined Mie theory for light scattering with Fourier's law of thermal conduction and Fick's first law of diffusion to describe heat and mass flux, respectively. External fluxes according to eqn (4) and (5) (heat and water mass exchange of the liquid surface of the particles with the surrounding gas phase) and internal diffusion of heat and water according to eqn (7) were calculated as a function of time t during photothermal cycles using our recently reported multi-layer heat and mass transfer model MHM-PA. 47 MHM-PA is a numerical approach to solve Fick's first law of diffusion, and hence allows us to simulate heat and mass flux away from and towards the droplet and the temporal evolution of the water concentration and temperature inside the droplet at conditions close to equilibrium. In contrast to the multi-layer model reported by Shiraiwa et al, 21,54 we do neither assume a sorption layer nor a quasi-static surface layer to model the cyclic heat and water exchange with the ambient gas phase.…”

“…56,57,59,60 Consistently with our previous work and other authors, we set a T = 0.97. 47,49,56 The MHM-PA model does not explicitly treat surface and bulk mass accommodation separately. This is consistent with the fact that the experimental data do not provide any information on the individual processes, but only on the entire process.…”

“…Consistent with the experimental information we have, we thus incorporate the mass transfer process into the model via the transition regime correction factor b M (eqn (6)). 7,47,[55][56][57] This approach works well for the measurements presented here because TREG particles even when they are dry remain moderately viscous (o0.049 Pa s 50 ). Hence the viscosity is not limiting the mass accommodation of water in our droplets, unlike what has been observed with highly viscous particles.…”

“…The simulation parameters used here are listed in the ESI, † and more detailed information about the simulations are given in ref. 47 .…”