  While facial coverings over the nose and mouth reduce the spread of the virus
SARS-CoV-2 by filtration, masks capable of viral inactivation by heating could
provide a complementary method to limit viral transmission. In this work, we
introduce a new virucidal face mask concept based on a reverse-flow reactor
driven by the oscillatory flow of human breath. The governing heat and mass
transport equation are formulated and solved to analyze designs that evaluate
both viral and CO2 transport during inhalation and exhalation. Given limits
imposed by the volume and frequency of human breath, the kinetics of SARS-CoV-2
thermal inactivation, and human safety and comfort, heated masks may inactivate
SARS-CoV-2 in inflow and outflow to medical grade sterility. We detail one
particular design, with a volume of 300 mL at 90 $^\circ$C, that achieves a
3-log reduction in viral load with minimal viral impedance within the mask
mesh, with partition coefficient around 2. This study is the first quantitative
analysis of virucidal thermal inactivation within a protective face mask and
addresses a pressing need for new approaches for personal protective equipment
during a global pandemic.
