A marine biofilm flow cell for in situ determination of drag, structure and viscoelastic properties

Fabbri, Stefania, Dennington, Simon, Stoodley, Paul and Longyear, Jennifer, Elise (2017) A marine biofilm flow cell for in situ determination of drag, structure and viscoelastic properties. The 5th International Conference on Advanced Model Measurement Technology for The Maritime Industry, , Glasgow. 11 - 13 Oct 2017.

Abstract

It is not straightforward to link biofilm parameters to frictional drag, likely because of the heterogeneous nature of slime. Here we present the design and calibration of a pragmatic, small scale flow-cell in which biofilms can either be cultured under flow or grown statically and then assessed under flow for drag and other properties. The flow cell test section comprised a rectangular channel (870x10x55mm) constructed by sandwiching together rigid opaque PVC panels and side panels of clear acrylic, which allow natural light to enter. A maze-like entry section evened out the inlet flow. Seawater flow rate through the channel was monitored by an in-line digital flowmeter, and pressure drop (ΔP) along the test section was measured using a differential pressure sensor. The friction coefficient (Cf) of the flow cell was found by measuring the ΔP at various flow velocities (u) over the entire pump range (maximum Re ~22,000). Flow cell calibration was carried out using a clean inert marine coating, and various roughness grades (P40, P80 and P120) of waterproof sandpaper sheets, fixed to the wide faces of the channel, to find Cf for each rigid roughness. ΔP was proportional to u2, indicating flow was turbulent in this region (R = 99%). When fouled panels are used as the channel floor and a clear acrylic panel as the ceiling, the flow cell allows for simultaneous measurement of Cf of the lower surface and biofilm physico-mechanical properties (e.g. thickness, roughness, viscoelasticity) by optical coherence tomography (OCT) imaging, which generates depth profiles of translucent samples. Changes to biofilm physico-mechanical properties during flow loading/unloading cycles, determined by image analysis, can be compared to simultaneously collected ΔP measurements scaled to a one-sided sandpaper Cf calibration. Future experiments will assess physico-mechanical and drag properties of marine fouling biofilms in flow using ΔP and OCT.

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Contributors

Author: Paul Stoodley

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