A new LED-based extinction tomography method for measurement of aerosol surface area

A light-emitting-diode (LED) based optical technique is developed to measure the surface area per unit volume of particles in aerosols and liquid sprays. The technique uses path-integrated measurements of transmittance, T, from two angles to produce a tomographic reconstruction of the local extinction coefficients, K, in the region of interest, using the Beer-Lambert law and a deconvolution algorithm. When the particles in the flow have sufficiently large diameters (existing in the Mie scattering regime), these extinction coefficients can be related to the surface area per unit volume of the particles. The technique has the potential to be applied to a wide range of two-phase flows. In the present study, it is applied to flows through a pharmaceutical inhaler device, where two powders with different particle size distributions are considered.