Method to improve classification of particles in a gas stream by reducing thermal convective instabilities

摘要

A method to improve classification in particle classifiers, such as an aerosol particle mass analyser, a centrifugal particle mass analyser or an aerodynamic aerosol classifier, utilises a classification force of which a centrifugal force is a component. A temperature gradient is maintained across the classification region 3 of sufficient magnitude and direction to reduce or eliminate thermal convective instabilities which could otherwise adversely affect the classification performance. The centrifugal force may be provided by rotating the classification region 3. An electrical force may be provided, with the classification region 3 bounded by an inner electrode 8 and an outer electrode 9. The inner electrode 8 may rotate less quickly than the outer electrode 9. The outer electrode 9 may be cooled to maintain the temperature gradient. A cooling tube may be provided around the outer electrode 9. The inner electrode 8 may be heated. The Rayleigh-Benard effect is used to calculate the Rayleigh number which determines the maximum temperature difference.