On thermal inactivation of pathogens in aerosolized droplets through electromagnetic heating
2021
A simple model describing the most significant impact of electromagnetic heating on pathogen-containing aerosols is presented. While the physics of ohmic heating are well understood, the connection between the unsteady temperature increase with net pathogen inactivation in an aerosolized electrolyte solution over a range of frequencies is not clear. The model is composed of two parts: a thermal model of electromagnetic heating of the droplets and a survival model describing the active pathogen population as a function of time. The droplets of saline solution, whose electrical conductivity depends on salt concentration and carrier frequency, are assumed to be small enough so that ambient air flows are sufficient to counter gravity, and the droplets are assumed to be equally spaced. As the droplets move with the ambient air, energy transport is limited to conduction, and within an adiabatic system, the mean spatial mode dominates the thermal transients of the air-droplet system. The kill rate of the pathogen depends on temperature, and the result of our thermal model informs the pathogen population through the Arrhenius kill rate. The model shows strong qualitative agreement with microwave inactivation of MS2 bacteriophages in aerosolized droplets. Inactivation is improved with larger electric field amplitudes, even for small duty cycles. We show that for a range of viruses with known activation energy, the thermal inactivation mechanism is more reliable for viruses with larger activation energy.
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