Design and development of an Monodisperse Aerosol Generator

Abstract

A study has been carried out at the Department of Chemical Engineering, Loughborough University of Technology (UK), to design and characterise a condensation type monodisperse aerosol generator. The design of this new generator was based on an already existing design, the MAGE (Monodisperse Aerosol GEnerator). The new generator has been shown to be very good at generating aerosol of 1-4 µm diameter. A system to change the particle diameter using a condensation nuclei filter was developed and tested. Filtering the condensation nuclei is a very good method of increasing the size of aerosol particle produced. Measurements employing the nuclei filtration system showed a 100% efficiency of the fliter and the expected theoretical linear correlation between cube root of the particle diameter and condensation nuclei concentration. The effect of a reheater on the aerosol size distribution was also studied. It was found that using heating tape as a reheater can improve aerosol monodispersity. This heating tape is used to maintain a high temperature in the tube carrying the seed aerosol and stearic acid vapour from the furnace to the first couple of centimetres of the condenser tube. Vapour liquid bubbler efficiencies at various gas flow rates and temperatures were also calculated. Measurements and computer simulation of the preheater showed that the preheater doesn’t heat the incoming nitrogen to the furnace temperature before it reaches the bubbler. It is therefore important to measure, and subsequently control, the temperature in the bubbler instead of in the furnace. Different gas flow and liquid heights in the bubbler will then not affect the size of aerosol produced at a given temperature.