Empirical Shape-Based Estimation of Settling Microplastic Particles Drag Coefficient

Microplastics (MP) are found in nature in various forms. The transport and settling process of MP particles in water streams is highly influenced by particle size and shape. In order to investigate the impact of particle shape, an experimental analysis of settling behavior of flat square particles and 3D cubic particles in flowing water was conducted. The analysis is based on tracking the settling trajectories of particles of various size and using this information for calculating the drag coefficient cd in relation to the Reynolds number Re in the range of 80 to 280 for cubes and 50 to 110 for flat particles. The results were correlated with two shape parameters, sphericity phi and a newly proposed shape descriptor dimensionality delta. The final output is a model for particle shape-based cd estimation, mainly serving as an illustration of the potential of the proposed methodology.