Direct Simulation of Ionization and Ion Transport for Planar Microscale Ion Generation Devices

The theoretical performance of a planar microscale ion generation device is analysed using the direct simulation Monte Carlo (DSMC) technique. The discrete motion and interactions of electrons and ions are modelled for atmospheric air as represented by N2 and O2 . The ionization threshold of the device in air is found to be 70 V because of the effects of molecular excitations that reduce the energy of the free electrons and the nature of the collision cross sections. Additionally, microscale planar ionization devices are revealed to be inherently inefficient because of the loss of electrons and ions to the dielectric boundary. A multiscale simulation of the electrohydrodynamics is also conducted by extracting the ion–neutral interactions from the DSMC calculations and integrating them into a continuum-scale fluid dynamics model. The multiscale simulations show that the ion–neutral body force distribution for the planar devices is concentrated on the face of the cathode and therefore limits the impact of the force on the flow. A scale analysis confirms that the body force distribution is insufficient to induce high flow rates at this scale