scholarly journals Computational and experimental investigation of biofilm disruption dynamics induced by high velocity gas jet impingement

2019 ◽  
Author(s):  
Lledó Prades ◽  
Stefania Fabbri ◽  
Antonio D. Dorado ◽  
Xavier Gamisans ◽  
Paul Stoodley ◽  
...  
Keyword(s):  
High Speed ◽  
Rational Design ◽  
Shear Thinning ◽  
High Shear ◽  
Shear Rates ◽  
Air Jet ◽  
High Shear Rates ◽  
Applied Forces ◽  
Biofilm Disruption ◽  
The Impact

ABSTRACTExperimental data showed that high-speed micro-sprays can effectively disrupt biofilms on their support substratum, producing a variety of dynamic reactions such as elongation, displacement, ripples formation and fluidization. However, the mechanics underlying the impact of high-speed turbulent flows on biofilm structure is complex in such extreme conditions, since direct measurements of viscosity at these high shear rates are not possible using dynamic testing instruments. Here we used computational fluid dynamics simulations to assess the complex fluid interactions of ripple patterning produced by high-speed turbulent air jets impacting perpendicular to the surface of Streptococcus mutans biofilms, a dental pathogen causing caries, captured by high speed imaging. The numerical model involved a two-phase flow of air over a non-Newtonian biofilm, whose viscosity as a function of shear rate was estimated using the Herschel-Bulkley model. The simulation suggested that inertial, shear and interfacial tension forces governed biofilm disruption by the air jet. Additionally, the high shear rates generated by the jet impacts coupled with shear-thinning biofilm property resulted in rapid liquefaction (within milliseconds) of the biofilm, followed by surface instability and travelling waves from the impact site. Our findings suggest that rapid shear-thinning in the biofilm reproduces dynamics under very high shear flows that elasticity can be neglected under these conditions, behaving the biofilm as a Newtonian fluid. A parametric sensitivity study confirmed that both applied force intensity (i.e. high jet-nozzle air velocity) and biofilm properties (i.e. low viscosity, low air-biofilm surface tension and thickness) intensify biofilm disruption, by generating large interfacial instabilities.IMPORTANCEKnowledge of mechanisms promoting disruption though mechanical forces is essential in optimizing biofilm control strategies which rely on fluid shear. Our results provide insight into how biofilm disruption dynamics is governed by applied forces and fluid properties, revealing a mechanism for ripples formation and fluid-biofilm mixing. These findings have important implications for the rational design of new biofilms cleaning strategies with fluid jets, such as determining optimal parameters (e.g. jet velocity and position) to remove the biofilm from a certain zone (e.g. in dental hygiene or debridement of surgical site infections), or using antimicrobial agents which could increase the interfacial area available for exchange, as well as causing internal mixing within the biofilm matrix, thus disrupting the localized microenvironment which is associated with antimicrobial tolerance. The developed model also has potential application in predicting drag and pressure drop caused by biofilms on bioreactor, pipeline and ship hull surfaces.

scholarly journals Computational and Experimental Investigation of Biofilm Disruption Dynamics Induced by High-Velocity Gas Jet Impingement

mBio ◽  
2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Lledó Prades ◽  
Stefania Fabbri ◽  
Antonio D. Dorado ◽  
Xavier Gamisans ◽  
Paul Stoodley ◽  
...  
Keyword(s):  
High Speed ◽  
Shear Thinning ◽  
High Shear ◽  
Shear Rates ◽  
Ripple Formation ◽  
Air Jet ◽  
High Shear Rates ◽  
Applied Forces ◽  
Biofilm Disruption ◽  
The Impact

ABSTRACT Experimental data showed that high-speed microsprays can effectively disrupt biofilms on their support substratum, producing a variety of dynamic reactions such as elongation, displacement, ripple formation, and fluidization. However, the mechanics underlying the impact of high-speed turbulent flows on biofilm structure is complex under such extreme conditions, since direct measurements of viscosity at these high shear rates are not possible using dynamic testing instruments. Here, we used computational fluid dynamics simulations to assess the complex fluid interactions of ripple patterning produced by high-speed turbulent air jets impacting perpendicular to the surface of Streptococcus mutans biofilms, a dental pathogen causing caries, captured by high-speed imaging. The numerical model involved a two-phase flow of air over a non-Newtonian biofilm, whose viscosity as a function of shear rate was estimated using the Herschel-Bulkley model. The simulation suggested that inertial, shear, and interfacial tension forces governed biofilm disruption by the air jet. Additionally, the high shear rates generated by the jet impacts coupled with shear-thinning biofilm property resulted in rapid liquefaction (within milliseconds) of the biofilm, followed by surface instability and traveling waves from the impact site. Our findings suggest that rapid shear thinning under very high shear flows causes the biofilm to behave like a fluid and elasticity can be neglected. A parametric sensitivity study confirmed that both applied force intensity (i.e., high jet nozzle air velocity) and biofilm properties (i.e., low viscosity and low air-biofilm surface tension and thickness) intensify biofilm disruption by generating large interfacial instabilities. IMPORTANCE Knowledge of mechanisms promoting disruption though mechanical forces is essential in optimizing biofilm control strategies which rely on fluid shear. Our results provide insight into how biofilm disruption dynamics is governed by applied forces and fluid properties, revealing a mechanism for ripple formation and fluid-biofilm mixing. These findings have important implications for the rational design of new biofilm cleaning strategies with fluid jets, such as determining optimal parameters (e.g., jet velocity and position) to remove the biofilm from a certain zone (e.g., in dental hygiene or debridement of surgical site infections) or using antimicrobial agents which could increase the interfacial area available for exchange, as well as causing internal mixing within the biofilm matrix, thus disrupting the localized microenvironment which is associated with antimicrobial tolerance. The developed model also has potential application in predicting drag and pressure drop caused by biofilms on bioreactor, pipeline, and ship hull surfaces.

The Simulation of Aggregated Colloids Under Flow

1992 ◽  
Vol 289 ◽  
Author(s):  
John R. Melrose
Keyword(s):  
Shear Rate ◽  
Large Scale ◽  
Shear Thinning ◽  
High Shear ◽  
Shear Rates ◽  
Rouse Model ◽  
High Shear Rates ◽  
Structural Breakdown ◽  
Large Scale Simulations ◽  
Low Shear

AbstractAn overview is given of theories of aggregates under flow. These generally assume some sort of structural breakdown as the shear rate is increased. Models vary with both the rigidity of the bonding and the level of treatment of hydrodynamics. Results are presented for simulations of a Rouse model of non-rigid, (i.e. central force) weakly bonded aggregates. In large scale simulations different structures are observed at low and high shear rates. The change from one structure to another is associated with a change in the rate of shear thinning. The model captures low shear rate features of real systems absent in previous models: this feature is ascribed to agglomerate deformations. Quantitatively, the model is two orders of magnitude out from experiment but some scaling is possible.

scholarly journals Rheological and Wetting Properties of Environmentally Acceptable Lubricants (EALs) for Application in Stern Tube Seals

Lubricants ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 100 ◽  
Author(s):  
F. Borras ◽  
Matthijn de Rooij ◽  
Dik Schipper
Keyword(s):  
Surface Tension ◽  
Shear Thinning ◽  
Mineral Oil ◽  
Experimental Techniques ◽  
High Shear ◽  
Shear Rates ◽  
Wetting Properties ◽  
High Shear Rates ◽  
Significant Difference ◽  
Newtonian Behavior

The use of Environmentally Acceptable Lubricants (EALs) for stern tube lubrication is increasing. Although the machine components of a sailing vessel are designed to operate together with mineral oil-based lubricants, these are being replaced by the less environmentally harmful EALs. Little is known about the rheological performance of EALs in particular at the high shear rates that occur in stern tube seals. In this study, the viscosity and wetting properties of a set of different EALs is analysed and compared to traditional mineral oil-based lubricants using a set of experimental techniques. Some of the EALs present Newtonian behavior whereas other show shear thinning. No significant difference in surface tension was observed between the different lubricants.

Shear Thinning of Nanometer-Thick Liquid Lubricant Films Measured at High Shear Rates

2014 ◽  
Vol 53 (3) ◽  
pp. 555-567 ◽  
Author(s):  
Shintaro Itoh ◽  
Koki Ishii ◽  
Kenji Fukuzawa ◽  
Hedong Zhang
Keyword(s):  
Shear Thinning ◽  
High Shear ◽  
Shear Rates ◽  
Liquid Lubricant ◽  
High Shear Rates ◽  
Lubricant Films

Shear Thinning and Thickening of Alumina Suspensions

2010 ◽  
Vol 105-106 ◽  
pp. 833-836
Author(s):  
Xiang Yang Lu ◽  
Li Ming Zhang ◽  
Yong Huang
Keyword(s):  
Zeta Potential ◽  
Particle Surface ◽  
Shear Thickening ◽  
Shear Thinning ◽  
High Shear ◽  
Shear Rates ◽  
High Shear Rates ◽  
Stern Potential ◽  
Thickening Behavior ◽  
Alumina Suspensions

The rheological behavior of alumina suspension stabilized with Tri-ammonia citrate (TAC) was studied. It was thought that there would form some particle clusters due to the collisions between particles caused by their relative motion in the suspension, and such particle clusters are classified as thermodynamic clusters and hydrodynamic clusters by their origin. Shear thinning is the result of decomposition of the thermodynamic clusters, while shear thickening is the result of formation of the hydrodynamic clusters. From the view of cluster-forming potential barrier, it was deemed that the viscosities of alumina suspensions at low and high shear rates are respectively determined by zeta potential and Stern potential on the particle surface, and shear thickening behavior can be suppressed with some excessive TAC.

scholarly journals Macroscopic rheology of non-Brownian suspensions at high shear rates: the influence of solid volume fraction and non-Newtonian behaviour of the liquid phase

2021 ◽  
Author(s):  
Patrick Wilms ◽  
Jörg Hinrichs ◽  
Reinhard Kohlus
Keyword(s):  
Liquid Phase ◽  
Shear Rate ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Shear Thinning ◽  
High Shear ◽  
Rate Dependency ◽  
Shear Rates ◽  
Liquid Phases ◽  
High Shear Rates

AbstractModelling the macroscopic rheology of non-Brownian suspensions is complicated by the non-linear behaviour that originates from the interaction between solid particles and the liquid phase. In this contribution, a model is presented that describes suspension rheology as a function of solid volume fraction and shear rate dependency of both the liquid phase, as well as the suspension as a whole. It is experimentally validated using rotational rheometry ($$\varphi$$ φ ≤ 0.40) and capillary rheometry (0.55 ≤ $$\varphi$$ φ  ≤ 0.60) at shear rates > 50 s−1. A modified Krieger-Dougherty relation was used to describe the influence of solid volume fraction on the consistency coefficient, $$K$$ K , and was fitted to suspensions with a shear thinning liquid phase, i.e. having a flow index, $$n$$ n , of 0.50. With the calculated fit parameters, it was possible to predict the consistency coefficients of suspensions with a large variation in the shear rate dependency of the liquid phase ($$n$$ n = 0.20–1.00). With increasing solid volume fraction, the flow indices of the suspensions were found to decrease for Newtonian and mildly shear thinning liquid phases ($$n$$ n ≥0.50), whereas they were found to increase for strongly shear thinning liquid phases ($$n$$ n ≤0.27). It is hypothesized that this is related to interparticle friction and the relative contribution of friction forces to the viscosity of the suspension. The proposed model is a step towards the prediction of the flow curves of concentrated suspensions with non-Newtonian liquid phases at high shear rates.

Normal Stresses at High Shear Rates in a Polymer Solution

1968 ◽  
Vol 90 (3) ◽  
pp. 561-569 ◽  
Author(s):  
L. H. Bernd
Keyword(s):  
Shear Rate ◽  
High Speed ◽  
Width Ratio ◽  
High Shear ◽  
Normal Stresses ◽  
Shear Rates ◽  
Elastic Stresses ◽  
High Shear Rates ◽  
Machine Elements ◽  
High Speed Machine

Based on an examination of the characteristics of shear viscosity versus shear rate, it was postulated that high tensile and compressive stresses might exist in certain liquids at very high shear rates. If obtainable, these stresses could be important as load-bearing mechanisms in high-speed machine elements, and as a sealing mechanism in radial face seals. Such stresses should be evident in a polymer fortified oil, or in a liquid comprised of molecules possessing an appreciable length to width ratio. Therefore, a jet reaction viscometer reaching 107 sec−1 shear rate was developed to explore this possibility. Tests with polyisobutylene dissolved in a kerosene showed that elastic stresses were dominant with respect to viscous stresses at high shear rates. Tensile stresses up to more thn 1000 psi were obtained. However, the life of the polyisobutylene molecule was short. Hence it is concluded that normal stresses of appreciable magnitude can exist in high-speed machine elements under favorable conditions to affect their operation.

ELECTRO-RHEOLOGICAL CATCH/CLUTCH: INERTIAL SIMULATIONS

1994 ◽  
Vol 08 (20n21) ◽  
pp. 2935-2954
Author(s):  
A. R. JOHNSON ◽  
J. MAKIN ◽  
W. A. BULLOUGH
Keyword(s):  
Dynamic Model ◽  
High Speed ◽  
Integrated Approach ◽  
High Yield ◽  
High Shear ◽  
Fully Integrated ◽  
Shear Rates ◽  
High Shear Rates ◽  
General Investigation ◽  
Machinery Design

A high-speed reciprocating mechanism is described in order to provide the basis of a general investigation into the required properties of electro-rheological fluids and associated materials for use in flexible, inertial mechanisms. The dynamic model of this, when run for realistic existing machine requirements clearly illustrates the need for a fully integrated approach to high speed machinery design. The work sets quantified targets and draws attention to the need for the continuing development of improved electro-rheological fluids which will have high yield stresses with acceptable viscosities and the conditions they must operate under: high shear rates, centrifugal loadings and accelerations.

colloid mills, piston homogenizers, rotor/stator mixers, Microfluidizer™ (a registered trademark of Microfluidics International Corp.) technologies, ultrasonic mixers, and hybrid devices. Each uses a unique processing technique to shear a mixture or com-bine the flows of materials in order to form an emulsion or suspensions. Most of the time these devices are not used in a truly continuous process. Rather, after the compo-nents of a dispersed delivery system are combined and blended in a batch vessel, the components in the mixture are passed through the device, and the shearing and mixing that take place inside the device affect particle size reduction, dispersion, and emulsi-fication. 1. Rotor/Stator Mixer Disperser Emulsifiers "All mixers pump and all pumps mix." This is reflected in the earlier-shown power equation, Eq. (3). A type of in-line device that is very similar to a rotor/stator batch mixer is the rotor/stator continuous mixer disperser emulsifier. Indeed, most of the designs of this type of in-line high-shear device are essentially identical to the batch equipment designs of a given manufacturer. Since rotor/stator batch mixers are acting as submerged pumps, a design can be made that places the rotor/stator in a pump hous-ing and allows for product to be pumped through itself (Fig. 27). During the time the product is inside the rotor/stator mixing pump, the droplets and particles are subjected to a wide variety of high shear rates. All pumps of any kind impart some level of shear to the product that passes through the pump. Rotor/stator mixing pumps are designed with fine tolerance rotor/stator gaps that promote the high shear rates and high amounts of shear per pass through. Shear rates in a rotor/stator in-line mixer are equal to those in rotor/stator batch mixers. The maximum shear rates occur in the gap between the high-speed rotating Fig. 27 Rotor/stator in-line mixer disperser emulsifier. (From Ref. 31.)

1998 ◽  
pp. 356-356
Keyword(s):  
High Speed ◽  
Continuous Process ◽  
Processing Technique ◽  
High Shear ◽  
Particle Size Reduction ◽  
Shear Rates ◽  
High Shear Rates ◽  
Pass Through ◽  
Hybrid Devices ◽  
Batch Mixers
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