Aseptic Zero Discharge Fluid Dynamic Gauging for Measuring the Thickness of Soft Layers on Surfaces

Abstract

A bench-top device that can be used to perform fluid dynamic gauging measurements of soft solid layers with zero net liquid discharge and potentially under aseptic (closed system) conditions is demonstrated. Testing results are presented for Newtonian liquids with a range of viscosities: deionised water, 8 wt% and 10 wt% sucrose solutions, 18 wt% glycerol/water solutions and a paraffin oil (1.12-1000 mPa s). The experimental data for discharge coefficient, C d , against clearance/nozzle throat diameter, h/d t , gave good agreement with CFD simulations and the correlation presented by Tuladhar et al. [1]. The influence of surface roughness was studied by making measurements on a series of commercial sandpapers. The rough surfaces gave rise to systematic differences in C d from those obtained with smooth substrates which could not be corrected for using the height of the asperity peaks and careful calibration is therefore required when gauging rough surfaces. Ein Laboranalysemethode zur Messung der Schichtdicke von weichen Feststoffablagerungen mit Hilfe des Fluid Dynamic Gauging wird vorgestellt. Dabei wird im Gegensatz zu bisherigen Anwendungen kein Fluid aus dem System entnommen, was einen aseptischen Betrieb ermöglicht. Erste Ergebnisse werden gezeigt für Newtonische Flüssigkeiten in einem weiten Viskositätsbereich: entionisiertes Wasser, 8 Gew.-% and 10 Gew.-% Zuckerlösung, 18 Gew.-% Glyzerin/Wasser-Lösung und ein Paraffinöl (1,12-1000 mPa s). Die experimentellen Daten für die Abhängigkeit des dimensionslosen Massenstrom C d vom Verhältnis Abstand/Düsendurchmesser h/d t , zeigen eine gute Übereinstimmung mit CFD-Simulationen und der von Tuladhar et al. [1] präsentierten Korrelation.

Fluid‐dynamic gauging for studying the initial swelling of soft solid layers

“…The effect of cracking is discussed briefly. FDG measurements assume a smooth interface whereas the CMS layer is rough and features cracks of depth δ o : Wang et al 3 investigated the impact of surface roughness experimentally and showed that surface roughness leads to C d being overestimated so that δ is therefore underestimated. The cracks in the CMS layers, moreover, present flow channels and allow more liquid to pass than a uniform surface would (or give a lower pressure drop for a given flow rate).…”

“…where δ ∞ is the equilibrium thickness, 3 chains. 28 At high pH, PVAc undergoes hydrolysis to give poly(vinyl alcohol; PVA) and acetic acid.…”

“…While the accuracy of measurement by some noncontact methods like tomography is high, these are often expensive and may not be feasible. 3 The technique of fluid dynamic gauging (FDG), first reported by Tuladhar et al, 4 was developed to make real-time measurement of the thickness of soft solid layers in situ. Next, the nozzle is located near the layer at some clearance h. The pressure drop across the nozzle, P = P − P 0 , and mass flow rate are measured as liquid is withdrawn and/or ejected.…”

“…The forces exerted by the FDG flow on the surface of the layer can then be calculated with some confidence from computational fluid dynamics (CFD) modeling. 3,[5][6][7]9,12,13 Chew et al 12 poly(vinyl acetate), PVAc; and a complex model food soil containing starches, proteins, and fats which is known to present challenges in cleaning. 14…”

Development of zero discharge net flow fluid dynamic gauging for studying biofilm and spore removal

“…By using syringe pumps to introduce or withdraw fluid at a fixed or adjustable rate in an alternating sequence, the total volume of solution does not change, thereby achieving zero net flow (giving ZFDG, see Yang et al, 2014). This enables aseptic operation, as well as supporting testing with solutions of high value or significant safety risk (Wang et al, 2016). The photograph in Figure 1(b) shows the ZFDG unit used in the work on biofilms reported here.…”