Optimisation of a thermophoretic personal sampler for nanoparticle exposure studies

A new Thermal Precipitator (TP) was developed as a personal sampler for nanoparticle exposure studies. Two parallel 20-mm-long plates with different but uniform temperatures were introduced into the TP with an appropriate gap distance, to achieve a uniform temperature gradient along the length of the plates. Particles are thermophoretically deposited on the colder plate in the TP which acts as the substrate. Analytical calculations were carried out to determine an optimal plate gap distance and temperature gradient in the TP. A simulation grid was created from the resulting geometry which was used for numerical modelling with a CFD Software. Results from the simulations showed a uniform deposition of particles up to the size range of about 300 nm for a temperature gradient of 15 K/mm and a 1-mm gap distance, independent of the orientation of the TP during sampling. In contrast to the old TP where up to 32 SEM images of its non-uniform particle deposition had to be evaluated to obtain an average particle size distribution, an evaluation of the uniform deposition with the new TP is much more simplified, remarkably reducing the time and cost of the evaluation, while providing more accurate results.