On the difficulty of determining the apparent wall slip of highly concentrated suspensions in pressure driven flows The accuracy of indirect methods and best practice

2021 ◽  
pp. 104694
Author(s):  
Patrick Wilms ◽  
Jan Wieringa ◽  
Theo Blijdenstein ◽  
Kees van Malssen ◽  
Jörg Hinrichs ◽  
...  
Keyword(s):  
Best Practice ◽  
Wall Slip ◽  
Concentrated Suspensions ◽  
Indirect Methods ◽  
Apparent Wall Slip ◽  
Pressure Driven

scholarly journals Quantification of shear viscosity and wall slip velocity of highly concentrated suspensions with non-Newtonian matrices in pressure driven flows

2021 ◽  
Author(s):  
Patrick Wilms ◽  
Jan Wieringa ◽  
Theo Blijdenstein ◽  
Kees van Malssen ◽  
Reinhard Kohlus
Keyword(s):  
Shear Stress ◽  
Liquid Phase ◽  
Shear Rate ◽  
Shear Viscosity ◽  
Slip Velocity ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Wall Slip ◽  
Flow Index ◽  
Concentrated Suspensions

AbstractThe rheological characterization of concentrated suspensions is complicated by the heterogeneous nature of their flow. In this contribution, the shear viscosity and wall slip velocity are quantified for highly concentrated suspensions (solid volume fractions of 0.55–0.60, D4,3 ~ 5 µm). The shear viscosity was determined using a high-pressure capillary rheometer equipped with a 3D-printed die that has a grooved surface of the internal flow channel. The wall slip velocity was then calculated from the difference between the apparent shear rates through a rough and smooth die, at identical wall shear stress. The influence of liquid phase rheology on the wall slip velocity was investigated by using different thickeners, resulting in different degrees of shear rate dependency, i.e. the flow indices varied between 0.20 and 1.00. The wall slip velocity scaled with the flow index of the liquid phase at a solid volume fraction of 0.60 and showed increasingly large deviations with decreasing solid volume fraction. It is hypothesized that these deviations are related to shear-induced migration of solids and macromolecules due to the large shear stress and shear rate gradients.

Apparent Wall Slip in Capillary Rheometry of Viscoplastic Liquids

2005 ◽  
Author(s):  
Paulo R. Souza Mendes ◽  
Jose´ R. R. Siffert ◽  
Eduardo S. S. Dutra
Keyword(s):  
Shear Stress ◽  
Yield Stress ◽  
Wall Slip ◽  
Momentum Conservation ◽  
Conservation Equation ◽  
Jump Number ◽  
Capillary Rheometry ◽  
Viscosity Function ◽  
Novel Material ◽  
Apparent Wall Slip

We employ a recently proposed viscosity function (Souza Mendes and Dutra, 2004) to analyze the fully developed flow of yield-stress liquids through tubes. We first show that its dimensionless form gives rise to the so-called jump number, a novel material property that measures the shear rate jump that the material undergoes as the yield stress is reached. We integrate numerically the momentum conservation equation that governs this flow together with the generalized Newtonian Liquid model and the above mentioned viscosity function. We obtain velocity and viscosity profiles for the entire range of the jump number. We show that the friction factor f.Re curves display sharp peaks as the shear stress value at the tube wall approaches the yield stress. Finally, we demonstrate the existence of sharp flow rate increases (or apparent slip) as the wall shear stress is increased in the vicinity of the yield stress.

Diffusion-Layer Theory for Flows Under Apparent Wall Slip

1998 ◽  
Vol 63 (1) ◽  
pp. 132-140 ◽  
Author(s):  
Ondřej Wein
Keyword(s):  
Mass Transfer ◽  
Velocity Profile ◽  
Solid Surface ◽  
Diffusion Layer ◽  
Analytical Formula ◽  
Wall Slip ◽  
Slip Effect ◽  
Local Power ◽  
Overall Mass Transfer Coefficient ◽  
Apparent Wall Slip

An explicit analytical formula is given for the overall mass transfer coefficient between the bulk of flowing microdisperse liquid and a small but finite active part of a solid surface. The apparent wall slip effect inside a diffusion layer is reflected through the local power-law velocity profile, vx(z) = Bzp, and a distribution B = B(x,y) over the solid surface.

Process And Materials Effect In Organic Coating Of Architectural Steels

2020 ◽  
Author(s):  
◽  
Sara L Mugabo
Keyword(s):  
Wall Slip ◽  
Research Programme ◽  
Organic Coating ◽  
Blind Test ◽  
High Speeds ◽  
Apparent Wall Slip ◽  
Solvent Level ◽  
Mature Process ◽  
Coating Line ◽  
Comprehensive Study

Coil roll coating is an industrially mature process to produce pre-coated steels at high speeds.30% sales by revenue for Tata steel colors, UK is attributed to the manufacture of architectural steels which is primarily used for composite panels for cladding systems. A research programme has been carried out which has examined the mechanisms by which the coating is picked up from the coating trough by the roll, with a reference to a defect where an insufficient coating is transferred leading to a defect named paint misses (PMD). A comprehensive study of a pair of coatings, one which demonstrated PMD and one which did not identify that their performance difference could be attributed to differences in rheology. The coating extensional viscosity and elasticity were identified as indicators of the behaviour. The identification of these primary rheological characteristics was corroborated through a blind test of a further pair of coatings where PMD had been observed on the coating line. The ability of the pickup roller to pull the coating from the trough and apparent wall slip (AWS) near the surface were identified as the dominant mechanisms. These mechanisms were also identified in a laboratory-scale simulation of the pickup cylinder rotating in the coating trough. Model PVC coatings were manufactured where the pigment concentration and solvent level was varied independently to develop the further underlying relationship between material rheology and coating pick up. The Mooney analysis method used to examine the slip behaviour was found to be inadequate for describing the behaviour of the liquid coatings. The deviation between idealised and real behaviour increased as polymer and pigment mass fraction increased. The quantity of coating picked up by the roll was found to be difficult to measure accurately due to the presence of the ribbing phenomena, which was particularly evident on the commercial coating systems. Additionally, liquid coating pickup tended to reduce with roll speeds and decreased with increasing pigment fraction (and hence viscosity). The study recommends an updated Quality Control (QC) system for checking the liquid coatings prior to being introduced to the process coating line.

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