Due to the inertial mismatch between dense particles and lighter surrounding gas, aerosol particles in the size range 1 to 10 μm cluster in a flow field. This phenomenon, sometimes referred to as preferential concentration, can increase the particle coagulation rate by as much as two orders of magnitude. Many direct numerical simulation (DNS) studies have been conducted to study preferential concentration and various theoretical models have been proposed to predict the effect of clustering on particle collision rate. However, to date there is very little experimental data available to validate DNS results and theoretical models. In this study, we apply our state-of-the-art holographic imaging system to measure the 3D position of particles in a turbulence chamber. Nearly homogenous isotropic turbulence is generated in the center of the chamber by use of eight fans mounted in the corners. With our holographic imaging system, individual particles can be measured simultaneously and hence we are able to calculate particle radial distribution function (RDF), a statistical measure of particle clustering and a key variable in collision kernel. In this paper we report the first experimental 3D RDF to date. Comparison between our 3D RDF and 2D RDF results shows that significant bias exists in experimental results obtained using 2D experimental techniques.

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