Invitation: PhD Proposal Defense of Emily Kruszon
Hello ME Community,
You are invited to join the PhD Proposal Defense of Emily Kruszon, on Wednesday, November 18, beginning at 2:00pm. The defense will be presented in person in the Engineering Building room 210-I (the Mechanical Engineering Conference room)
Co-Advisors: Dr. Sayantan Bhattacharya and Dr. Charles Eggleton
Title: Shear Stress Quantification on a Coupon Surface in a CDC Biofilm Reactor: Effects of Varying Rotational Speeds and Coupon Materials
Abstract:
Biofilms are communities of microorganisms that attach to biotic or abiotic surfaces and work together to survive, mature, and spread. They remain a major concern in the food-processing industry, contributing to bacterial contamination and outbreaks. A CDC bioreactor is useful because it allows biofilms to grow on removable coupons under controlled dynamic shear conditions. Experiments conducted in CDC biofilm reactors established correlations between three key parameters—shear stress, surface topography, and turbulent fluctuations—and the processes governing biofilm growth and detachment. However, no previous studies have experimentally quantified these three parameters in a CDC bioreactor under operational conditions. The rotating baffle with multiple coupon holder rods and different coupon disk placements creates a three-dimensional complex flow with periodic vortex shedding and boundary layer interaction. Additionally, limited optical access makes flow observation challenging. To better understand true flow conditions, we developed an experiment to vary the impeller’s rpm and coupon surface roughness independently to observe the change in shear stress and turbulent intensity. With an optimized viewing window, we employed time-resolved Particle Image Velocimetry (PIV) to experimentally quantify the flow velocity field within the CDC Bioreactor. The estimated velocity fields depict shear layer separation, formation of eddies and high mixing, high shear rates near the wall and a periodic variation in flow features for different time points in the impeller cycle near the coupon surface. Specific aim one is focused on measuring shear stress on the surface of the coupons in the biofilm reactor at 100, 200 and 300 RPM. Preliminary testing resulted in these average shear stresses: 0.420, 1.165 and 1.614 Pa. The objective of specific aim two is to study how surface roughness, ranging from 1 - 10 nm, influences shear stress on a coupon's surface at 100, 200 and 300 RPM. For specific aim three, we aim to perform comparable experimentation, analyzing how impeller rpm, 100 - 600 RPM, and surface roughness, 1 - 10 nm, impact turbulence fluctuations. Turbulence kinetic energy will be quantified to establish locations experiencing these turbulent fluctuations. We aim to quantify the shear stress in a CDC bioreactor under different RPMs, coupon surface conditions and hydrodynamic fluctuations, and establish the baseline hydrodynamic conditions that affect biofilm life cycle.