Design of a Laboratory Turbulence Tank for the Investigation of Bio-filmed Microplastics

Open Access
- Author:
- Morales, Luna
- Area of Honors:
- Mechanical Engineering
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Margaret Louise Byron, Thesis Supervisor
Daniel Humberto Cortes Correales, Thesis Honors Advisor - Keywords:
- synthetic jet
turbulence
microplastics
Particle Image Velocimetry
design
actuator - Abstract:
- Microplastics are small fragments of plastics that range from 5mm to a few microns in diameter. Because of their small size, they can easily enter the environment which may pose health risks to many living organisms. Toxic chemicals (like BPA) can concentrate on plastic surfaces, which can then be ingested by animals. Despite the growing concern over this plastic pollution problem, very little is known about how they move through aquatic systems. Microplastics can be observed through field studies, however, environmental factors can be difficult to control. A laboratory facility provides a controlled environment for studies to be conducted so we can more directly test the effects of specific variables. Of the existing microplastic studies in a controlled setting, much of the focus has been on still-water conditions. However, this does not accurately reflect environmental flows which are generally turbulent. In this thesis, we present a design for a laboratory apparatus that can be used to generate homogenous and isotropic turbulence, intended for the study of microplastic transport. Our focus is on simplifying the design of an actuator that is used to generate a synthetic jet and quantifying the resulting flow. Our primary goal was to determine how to optimize the turbulence generated by the actuator by changing the geometry of the actuator design. The actuator consisted of a subwoofer speaker attached to a pipe/nozzle with varying degrees of interior taper; the speaker diaphragm drove flow through a set of small orifices in the far end of the pipe, creating a synthetic jet. We studied three actuator designs (no taper, full taper, and partial taper). Based on our results, we estimate that tapering through the full length of the nozzle at small angles creates a synthetic jet with stronger turbulent fluctuations in the axial direction, but weaker fluctuations in the jet-normal direction compared to the zero-taper case. Larger tapers resulted in a smaller amount of kinetic energy entering the tank. We hypothesize that separation and turbulence within the nozzle increased flow resistance, ultimately resulting in less mass displacement from the speaker diaphragm. We conclude that the interior tapering characteristics of the nozzle play a role in the characteristics of the resulting synthetic jet. This facility will be used in future studies to observe microplastics in turbulence.