Personal Ultraviolet Respiratory Germ Eliminating Machine (PUR$\diamond$GEM) for COVID-19: Prototype Development

In this article we detail the prototype development of the Personal Ultraviolet Respiratory Germ Eliminating Machine(PUR$\diamond$GEM) to safely, efficiently and economically, continuously disinfect inhaled/exhaled air using Ultraviolet (UV) radiation with possible 99.99% virus elimination. The PUR$\diamond$GEM consists of a series of UV disinfection chambers through which constant airflow is maintained via fans. A minimum air flow rate of $\sim20-30$ L/min is sufficient to keep CO$_2$ levels $\lesssim$ 0.5% in the hood/helmet. We validated that using easily available PTFE wrap, a factor of $\sim 18$ enhancement in UV power can be obtained in our spherical chambers. Detailed analysis is presented for the air travel time distributions through the cavities, and the expectation value for actual pathogen elimination is computed. We provide the scaling of pathogen elimination with the number of cavities in series, reflective enhancement, UV source power, sphere radius and airflow rate. We show that disinfection greater than 4-log is achievable for a series of three or more spheres. We 3D printed our prototype, consisting of two spheres of 10 cm diameter each in series for each direction of disinfection. Using UVC LEDs emitting $\sim$ 40 mW of power each with an airflow rate of 30 L/min, actual SARS-COV2 virus elimination of $\sim$ 98% is expected. While not manually feasible to construct smaller spheres in the lab, smaller cavities can be commercially manufactured, leading to significantly higher actual pathogen elimination, as well as reducing fingerprint and cost of cavity manufacture. Patent pending.