Tag Archives: microplastics

Microplastics pollution and fibers in turbulence

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Microplastics pollution represents a major global problem: tiny plastic particles ending up in oceans and accumulating in living organisms may disrupt entire ecosystems. How tiny particles behave in turbulent flows is challenging to predict, especially in case of thin fibers, which represent more than half of microplastic contamination in marine life-forms.

At TU Wien we have now succeeded in characterizing the behavior of such microplastic fibers in channel flow experiments and with the help of high-speed cameras. This should now form the basis for new models that can be used to predict the spread of microplastics globally. The results have been published in Physical Review Letters.

Experimental apparatus employed at TU Wien
Microplastic fibres in channel flow turbulence

Vlad Giurgiu, Giuseppe Caridi, Alfredo Soldati and I, investigated the rotational dynamics of elongated plastic fibers. Through optical experiments, we revealed unprecedented insights into the three-dimensional orientation of these particles.

A reconstructed fiber (dark gray voxels), its fitted polynomial (yellow line), the fiber-fixed axes, and its center of mass G (black dot) are shown. Spinning (ωs) and tumbling rate components (ω2, ω3) around these axes are noted.
Main panel: Mean square tumbling and spinning rates normalized by the viscous timescale over the wall-normal coordinate. Inset: ratio of the mean squared spinning to mean squared tumbling rate over the wall-normal coordinate.

Our findings establish a universal behavior in the rotation rates, which is independent of the turbulent flow configuration. This achievement, together with the first spinning measurements performed in this configuration, not only opens new paths in microplastic research, but also introduces a novel approach to understand and mitigate the environmental impact of these pollutants.

We thank the Austrian Science Fund (FWF) and TU Wien for the generous funding. The manuscript and the data are freely available for download.

Link to the article and the data: Physical Review Letters and arxiv
See also the Focus story Measuring the Rotation of Polluting Plastic Particles

Processed images of fibres and tracers.

How to study the behaviour of microplastics?

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Microplastics are plastic fragments smaller than 5 mm originated from human activities, and have been found everywhere, also in the remotest places of the Earth. Measuring their position and velocity in turbulent flows, such as ocean, rivers and lakes, is crucial to better understand their behaviour and make physical models that describe their paths. To this aim, we designed a new facility, the TU Wien turbulent Water Channel, which we recently presented in paper published on Review in Scientific Instrument. This project is funded by FWF (Austrian Science Fund).

The TU Wien Turbulent Water Channel (main figure). Cameras may be arranged in different configurations to investigate the behaviour of microplastics (bottom right figure).

The TU Wien Turbulent Water Channel is a 3000 litres volume and 10 meters long flow loop designed for 3D and time-resolved measurements of anisotropic particles dynamics. We developed a novel approach to track microplastics, since they are usually anisotropic and techniques developed for spherical particles are not suitable to track such objects. In addition, in this work, we provide guidelines to design turbulent water ducts, and we also compare against existing facilities.

The data and the paper (Open Access) are freely available for download.

Would you like to perform experiments in the TU Wien Turbulent Water Channel? Contact us!

This work has been selected for the Kudos Research Showcase.