Single image corrections to facilitate planar imaging of particle concentration in particle-laden fluids

Abstract

Planar Nephelometry is a laser-based technique capable of providing instantaneous planar local number density measurements of particles in fluid systems. This technique records laser light scattered from particles to obtain information regarding particle concentration. Planar Nephelometry does not need to resolve particles individually, thus enabling large image viewing areas. However, when particle loadings are sufficiently high, attenuation of the incident laser beam becomes significant. As Planar Nephelometry infers particle concentration from incident laser intensity, attenuation can result in erroneous concentration measurements. Planar Nephelometry measurements under these conditions must thus be corrected for laser attenuation to ensure accurate concentration measurements. Experiments were conducted on suspensions of neutral density spherical particles in water at various homogeneous concentrations. The attenuation correction method implemented is a ray-based extinction model which incorporates the use of scattered light from a polymer strip at a down-beam location. This method is suitable for highly turbulent flows requiring instantaneous planar information since single shot images are used in the post-processing work. The derived correction method provides an alternative to Beer-Lambert’s law for attenuation corrections in laser diagnostics techniques. The proposed method is validated experimentally using non-homogenous particle distributions in fluid suspensions.