Supplementary Material: Temperature-dependent wall slip of Newtonian lubricants

Repository containing the data included in "Pelz, P., Corneli, T., Mehrnia, S., & Kuhr, M. (2022). Temperature-dependent wall slip of Newtonian lubricants. Journal of Fluid Mechanics, 948, A8. doi:10.1017/jfm.2022.629". In the paper, (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 is discussed. 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 s−1, being consistent with recent results from molecular dynamics simulations by Mehrnia & Pelz. Furthermore, the activation energies for wall slip and bulk shear determined by means of the SLT differ by a factor of two, 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. 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.

本数据集仓库收录了来自论文《Pelz, P., Corneli, T., Mehrnia, S., & Kuhr, M. (2022). 牛顿润滑剂的温度依赖性壁面滑移（Temperature-dependent wall slip of Newtonian lubricants）. 流体力学杂志（Journal of Fluid Mechanics）, 948, A8. doi:10.1017/jfm.2022.629》的全部相关实验数据。该论文围绕三项核心内容展开讨论：其一为极性与非极性烃类牛顿流体在经机械加工的金属表面相对运动时，温度依赖的壁面滑移（wall slip）现象及其活化能的测量；其二为该现象的阐释；其三为其技术影响。研究团队开发的新型测试装置——滑移长度摩擦计（slip length tribometer, SLT），可在足够大的润湿面积下测量不同温度下的滑移长度，从而克服了现有测量设备在表征相关粗糙表面时的固有局限。实验数据表明，在10^5 s⁻¹的剪切速率范围内，流体-金属界面的本体黏度与滑移长度不受剪切速率影响，这与Mehrnia与Pelz近期的分子动力学模拟（molecular dynamics simulations）结果一致。此外，针对在金属壁面相对滑动的非极性烃类分子，通过SLT测得的壁面滑移活化能与本体剪切活化能相差一倍，该差异可通过应用于壁面滑移的广义艾林模型（Eyring model）得到合理解释。该论文最后探讨了壁面滑移对摩擦学（tribology）中索末菲相似性理论的影响，以及由此衍生的斯特里贝克曲线（Stribeck curve）。为此，研究人员将适用于壁面滑移的广义雷诺方程（Reynolds’ equation）与实验测得的本体剪切及壁面滑移本构关系相结合，以预测径向滑动轴承（journal bearing）的典型特性。结果显示，对于滑移长度与轴承平均间隙之比约为10^−2的典型径向滑动轴承，壁面滑移对其承载能力与功耗损耗的影响均不可忽略。本研究结合了纳米流体学（nanofluidics）与摩擦学，旨在为定制化流体与界面设计等场景提供方法与理论支撑。