Slip length of branched hydrocarbon oils confined between iron surfaces

Mehrnia, Seyedmajid; Pelz, Peter F.

doi:10.1016/j.molliq.2021.116589

Cited by 10 publications

(26 citation statements)

References 29 publications

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“…Hence, both viscosity and slip length decrease with increasing temperature, consistent with the experimental findings in this paper and the Tolstoi model. This decrease of slip length with increasing temperature is also a result of recent MD simulations by Mehrnia & Pelz (2021). Hénot et al (2018) measured slip length as a function of shear rate for three polymers of different molecular weights utilising a velocimetry technique based on photobleaching.…”

Section: Temperature Dependence Of Wall Slipmentioning

confidence: 52%

“…The experiments can be performed either in a controlled laboratory environment (cf. this paper) or 'in silico' using MD simulations (Mehrnia & Pelz 2021). In either case, the determined viscometric constants for both shear, i.e.…”

Section: Wall Slip In Nanofluidicsmentioning

confidence: 99%

“…Hence, we have μ = f λ for the relation of viscosity μ, friction factor f and slip length λ. Recent results from molecular dynamics (MD) simulations by Mehrnia & Pelz (2021) showed that the apparent viscosity for (non-polar) hydrocarbon alpha-olefin (PAO 6) is shear rate independent up to an apparent shear rate of γc = 10 8 s −1 (see figure 10). Hence, the relaxation time for those typical lubricant with mean molar mass M = 600 u is approximately 10 ns (inverse of the critical shear rate) at ambient temperature.…”

Section: Boundary Conditions At the Solid-fluid Interface For Newtoni...mentioning

confidence: 99%

“…However, the statement λ ∼ a is only valid for h a, which is always assumed in this work. Mehrnia & Pelz (2021) considered also the complementary case h → a by analysing the Couette flow between two plates (gap height h, tangential speed U) using MD methods. The simulation results show λ → ∞ for h → a.…”

Section: Boundary Conditions At the Solid-fluid Interface For Newtoni...mentioning

confidence: 99%

“…The former used to be called bias error, the latter random error (Abernethy, Benedict & Dowdell 1985). Today, the terms systematic and stochastic uncertainty are common (Joint Committee for Guides in Metrology 2008; Kamke 2010; Bailer-Jones 2017; Pelz et al 2021). The term systematic uncertainty is used for all reproducible measurement errors that can be attributed to a measurement set-up with individually selected sensors and corresponding calibration curves, whereas the term stochastic uncertainty is used for all data that show a probability distribution when performing different measurement runs with the particular measurement set-up.…”

Section: Strategies To Minimise Stochastic and Systematic Uncertainty...mentioning

confidence: 99%

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Temperature-dependent wall slip of Newtonian lubricants

Pelz

Corneli²,

Mehrnia³

et al. 2022

J. Fluid Mech.

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We discuss (i) the measurement, (ii) interpretation and (iii) technical impact of temperature-dependent wall slip and its activation energy for polar and non-polar hydrocarbon Newtonian fluids moving relative to machined metal surfaces. A newly developed apparatus, the slip length tribometer (SLT), overcomes the drawbacks of existing measurement devices in terms of characterising relevant rough surfaces by measuring the slip length at different temperatures over a sufficiently large wetted area. The experimental data show that the bulk viscosity and slip length at the fluid–metal interface is independent of the shear rate up to $10^5\,\mathrm {s}^{-1}$ , being consistent with recent results from molecular dynamics simulations by Mehrnia & Pelz (J. Mol. Liq., vol. 336, 2021, 116589). Furthermore, the activation energies for wall slip and bulk shear determined by means of the SLT differ by a factor of two, i.e. $E_{\lambda }\approx 0.5 E_\mu$ for non-polar hydrocarbon molecules sliding relative to metal walls. This difference is explained by a generalised Eyring model applied to wall slip. The paper closes with the impact of wall slip on Sommerfeld's similarity theory of tribology and the resulting Stribeck curve (Sommerfeld, Z. Math. Phys., vol. 50, 1904, pp. 97–155; Z. Tech. Phys., vol. 2. Jahrg., 1921; Mechanik der deformierbaren Medien, 1944, Akademische Verlagsgesellschaft Becker & Erler). For this purpose, Reynolds’ equation generalised for wall slip is solved in combination with the experimentally determined constitutive relations for bulk shear and wall slip to predict typical characteristics of journal bearings. The results show that, for a typical journal bearing, where the ratio of slip length to average bearing clearance is of the order of $10^{-2}$ , the influence of wall slip on both load-carrying capacity and dissipation is not negligible. This work combines nanofluidics and tribology in order to provide methods and knowledge for e.g. tailor-made fluids and interfaces.

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Section: Temperature Dependence Of Wall Slipmentioning

confidence: 52%

Section: Wall Slip In Nanofluidicsmentioning

confidence: 99%

Section: Boundary Conditions At the Solid-fluid Interface For Newtoni...mentioning

confidence: 99%

Section: Boundary Conditions At the Solid-fluid Interface For Newtoni...mentioning

confidence: 99%

Section: Strategies To Minimise Stochastic and Systematic Uncertainty...mentioning

confidence: 99%

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Temperature-dependent wall slip of Newtonian lubricants

Pelz

Corneli²,

Mehrnia³

et al. 2022

J. Fluid Mech.

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Tribological Design by Molecular Dynamics Simulation: Influence of the Molecular Structure on Wall Slip and Bulk Shear

Mehrnia

Pelz

2022

Chem Eng & Technol

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The tribological properties of a complex branched‐hydrocarbon oil under shear in a gap between smooth iron atom surfaces were studied by large‐scale molecular dynamics (MD) simulation. The liquid was a nonpolar lubricant, i.e. a polyalphaolefin (PAO) oil mixture of 1‐decane dimer, trimer, and tetramer molecules. The rheological characteristics of the lubricant, including the shear stress and viscosity as well as the relaxation time of the liquid molecule, were calculated. The results show that, as the number of branches of the liquid molecule increases, the shear stresses and the wall slip increase. However, for a mixture fluid containing three different branched molecules, the wall slip decreases in comparison to a liquid consisting of only one kind of branched molecule.

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MHD flow between electromagnetically coupled concentric cylinders with slipping walls

Senel

2022

European Journal of Mechanics - B/Fluids

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Slip length of branched hydrocarbon oils confined between iron surfaces

Cited by 10 publications

References 29 publications

Temperature-dependent wall slip of Newtonian lubricants

Temperature-dependent wall slip of Newtonian lubricants

Tribological Design by Molecular Dynamics Simulation: Influence of the Molecular Structure on Wall Slip and Bulk Shear

MHD flow between electromagnetically coupled concentric cylinders with slipping walls

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