Simulation of Excited Molecule Propagation to Determine Plasma Sterilization Effectiveness in Lumens

Sterilizing or disinfecting medical narrow-lumen instruments such as endoscopes is a highly difficult process. Although plasma sterilization is effective against a broad spectrum of microorganisms, its effectiveness is dependent on the density of plasma-generated, excited particles that attack the microorganisms. The lifetime of the excited particles is not long, and their survival is a function of operating condition and geometry. The current study employs a numerical method to investigate the propagation and density of the excited nitrogen molecules in a narrow lumen and to identify the conditions where the plasma sterilization is effective. The plasma gas properties are calculated using the gas kinetic theory, and different lifetimes are assumed for excited molecules. The simulation results show that the survival of excited particles in a lumen increases more than 10 times when the pressure is reduced by a factor of 10. Thus, it is highly recommended that the plasma be operated at lower pressure to increase the sterilization efficiency of narrow lumen devices.