学术文献库

Optical investigations on the dynamics of dense suspensions are challenging due to reduced optical accessibility. Furthermore, the suspension particle image size can strongly deviate from the optimal particle image size for PIV measurements. Optical accessibility can be achieved by refractive index matching of surface labelled suspension particles. This results in particle images that are transparent in the particle image center, but fluoresce at the particle image rim, resulting in ring-shaped particle images. In the present study the influence of particle image size of such ring-shaped particle images is compared with Gaussian and plateau-shaped particle images. Particles of Gaussian image shape result from fully labelled particles with small image diameters and are commonly used in PIV measurements. Such particles are also utilized for the determination of the continuous phase velocities in the experimental part of the present study. Monte Carlo simulations show that ring-shaped particle images have a superior behavior, i.e. they assume a reduced displacement estimation error for noisy as well as for noise-free image data, compared to Gaussian and plateau-shaped particle images. This is also true for large particle image diameters when particle images are intersected at interrogation window borders. Measurements are performed on a suspension containing 5 Vol.-% surface labelled, refractive index matched 60$μ$m PMMA particles. Simultaneously, $μ$PIV measurements of the carrier liquid flow are performed utilizing 1.19$μ$m fluorescent PS particles. Overall, the present study demonstrates theoretically and experimentally that the usage of suspension particles with ring-shaped images is suitable for $μ$PIV measurements to gain detailed insights into suspension bulk dynamics.