The influence of nozzle throat length on the resolution of a low pressure impactor—An experimental and numerical study

This study investigates the effect of the nozzle throat length on the resolution of the low pressure impactor (LPI). Two basic nozzle geometries, rectangular slit and round nozzle with 25 nm cutpoint were investigated both experimentally and by numerical simulation. A new impactor stage with variable nozzle throat length and jet-to-plate distance was designed, built and tested. The impactor was calibrated at four different configurations with monodisperse dioctyl sebacate (DOS) aerosol. A very good agreement between the simulated and the experimental resolutions and cutpoints were found. The main conclusions are that (a) the length of the nozzle is a crucial parameter affecting the resolution and (b) it is possible to achieve a better resolution with a rectangular slit type impactor than with a round nozzle type LPI. The best observed resolution was achieved with the slit type LPI with a nozzle throat length to width ratio of only 0.33. Compared to similar cutpoint impactor stages of commercially available LPIs, the resolution of the new stage is by far the highest.

► The effect of the nozzle throat length on the resolution of an LPI was investigated by experiments and numerical simulations. ► A new LPI stage with 25 nanometer cutpoint and exchangeable nozzle throat length and nozzle shape was designed, built, and tested. ► Rectangular slit with very short nozzle produced the best resolution. ► Resolution of the new stage was by far the highest of the comparable cutpoint stages of well-known LPIs. ► The impaction velocities of particles were found to be very uniform in the new stage.