A semi-analytical model for assessing nanoparticle collection efficiencies in the partial charging regime

Limiting people’s exposure to fine particles is a critical public health priority. Given that smaller particles have a greater impact, particular attention must be paid to ultrafine particles, i.e., nanoparticles (dp < 100 nm). One way to reduce this exposure is to implement electrostatic filtration, a highly efficient process for removing particles; however, its efficiency is limited for nanoparticles due to their low charge. Efficiency can be optimized by modeling the process; yet, only a few simple models accurately describe the electrostatic precipitator (ESP) collection efficiencies in the partial charging regime. In this context, the present study proposes a collection efficiency model based on calculating the charge distribution and applying simple particle transport considerations (constant velocity, no turbulence, etc.). To validate and assess the mathematical model, a two-stage ESP configuration was selected. An experimental test bench was developed to obtain data for simulation, supplemented by results from the literature. The results showed that the proposed model can capture the various experimental behaviors observed both in the partial charging regime and for larger particle sizes. However, from a qualitative perspective, the velocity law had to be corrected (via a Cunningham number adjustment) to obtain satisfactory simulation results. This approach also confirms that collector optimization alone is insufficient to enhance the collection efficiency of ultrafine particles. Finally, the proposed model enables a straightforward calculation to estimate the boundary of the partial charging regime based on operating conditions and process dimensions.