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

Abstract

A diffusion multilayer model is introduced which allows time-dependent simulations of heat and mass transfer for photoacoustic experiments on aerosol particles (MHM-PA model). It provides spatial and temporal information on the particle temperature, composition, and size during photoacoustic modulation cycles, and thus, enables accurate simulations of the photoacoustic amplitude and phase at different modulation frequencies. Simulations for micrometer-sized, mixed water-tetraethylene glycol droplets at different relative humidity and at different modulation frequencies between 4 kHz and 100 kHz reveal a substantial loss of the information content of the photoacoustic signal above approximately 30 kHz. The photoacoustic amplitude reduces by two orders of magnitude, causing sensitivity issues. The photoacoustic phase converges to the same constant value for all droplet sizes and humidities, meaning that useful information on heat and mass transfer is essentially lost in the phase.