Modelling of a post-discharge reactor used for plasma sterilization

Abstract

A three-dimensional hydrodynamic model is developed to simulate a post-discharge reactor placed downstream from a flowing microwave discharge in N2–O2 used for plasma sterilization. The temperature distribution and the density distributions of NO(B 2Π) molecules and O(3P) atoms, which are known to play a central role in the sterilization process, are obtained in the reactor in the case of discharges at 915 and 2450 MHz, pressure range 1–8 Torr and N2–xO2 mixture composition, with x = 0.2–2%. Excluding the flow direction, sufficiently low temperatures ideal for sterilization have been found in most parts of the reactor. The highest NO(B) and O(3P) concentrations at the reactor entrance are achieved at the highest pressure values investigated here. However, these larger densities rapidly decrease within a few centimetres below the values obtained at lower pressure. On the contrary, at low pressure the density distributions of NO(B) and O(3P) are quasi-homogeneous in most of the horizontal planes. At 8 Torr the densities increase orders of magnitude in the reactor as the gas flow increases from 1 × 103 to 4 × 103 sccm, while at 2 Torr this increase does not reach even one order of magnitude. In agreement with the experiment, the densities of NO(B) and O(3P) have been found to increase at 2 Torr as the O2 percentage increases in the discharge gas mixture, whereas at 8 Torr the density of NO(B) decreases with O2 percentage and the O(3P) density presents only minor changes.