Design and testing of a nanoparticle spectrometer

Abstract

This thesis is concerned with a project to design and test a new Nanoparticle Spectrometer (NPS). The NPS is an instrument designed to make fast measurements of the size distribution and number concentration of aerosol samples containing particles in the size range 5–300nm. The intended application of the NPS is to take time dependant measurements of the aerosols emitted from internal combustion engines. The primary motivation for this work is ultimately the potentially detrimental effects on human health and the environment of combustion generated aerosols.

In common with previous aerosol spectrometers, the Nanoparticle Spectrometer consists of a charger to give particles an electrostatic charge, a classifier, which separates the particles in an aerosol sample according to their electrical mobility (a function of size) and an array of counting devices that count the numbers of particles with different mobilities. The novelty of the NPS is the geometry of the instrument, which, it will be argued, has certain advantages.

The behaviour of particles in the classifier has been modelled numerically and this model has been used to optimise the classifier geometry. Two charger designs were considered, and two analytical charger models developed and compared. The classifier model was combined with the selected charger model to create a simulation of the instrument operation, which predicts the NPS’ output signal for a given aerosol sample size distribution and number concentration.

A prototype NPS was designed, built and tested experimentally. The objective of the experiments was to test the validity of the instrument model and compare the performance of the NPS to an established slow response particulate measuring instrument, the SMPS. The experiments showed good agreement between modelled and measured results, as well as close correlation between the NPS and the SMPS results across most of the instruments range.

The experiments also revealed some areas in which the performance of the NPS could be improved; for instance, the modelling of diffusion in the classifier and of the fluid flow in the particle charger.

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