Tribological Performance of the R1233zd Refrigerant in Extreme Confinement at the Nanoasperity Level: A Molecular Dynamics Study Using an ab Initio-Based Force Field

S Tromp and L Joly and M Cobian and N Fillot, TRIBOLOGY LETTERS, 67 (2019).

DOI: 10.1007/s11249-019-1180-9

The tribological performance of the R1233zd refrigerant in extreme confinement between two hematite Fe2O3 (01 (1) over bar2) surfaces is studied thanks to large-scale molecular dynamics simulations based on a force field previously parametrized from ab initio calculations. With atomically smooth surfaces, and a refrigerant film thickness as small as 2 nm, adsorbed layers of R1233zd molecules on Fe2O3 surfaces resist to high pressures and high sliding velocities. In ultra-confined systems, friction behaves non-monotonously, reaching a global maximum when a single saturated layer is formed. Moreover, sliding simulations with a rough surface reveal total film breakdown for a local pressure around 13 GPa. Interestingly, the addition of a sliding velocity enhances the performance through a hydrodynamic lift-like mechanism: the higher the sliding, the higher the chance for refrigerant molecules to be entrained into the asperity contact.

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