13 research outputs found
Cavitation Bubble Measurement in Tribological Contacts Using Digital Holographic Microscopy
Hydrodynamic friction of viscosity-modified oils in a journal bearing machine
The friction properties of a range of viscosity modifier-containing oils in an engine bearing have been studied in the hydrodynamic regime using a combined experimental and modelling approach. The viscometric properties of these oils were previously measured and single equations derived to describe how their viscosities vary with temperature and shear rate (Marx et al. Tribol Lett 66:92, 2018). A journal bearing machine has been used to measure the friction properties of the test oils at various oil supply temperatures, while simultaneously measuring bearing temperature using an embedded thermocouple. This shows the importance of taking account of thermal response in journal bearings since the operating oil film temperature is often considerably higher than the oil supply temperature. For Newtonian oils, friction coefficient measurements made over a wide range of speeds, loads and oil supply temperatures collapse onto a single Stribeck curve when the viscosity used in determining the Stribeck number is based on an effective oil film temperature. Journal bearing machine measurements on VM-containing oils show that these give lower friction than a Newtonian reference oil. A thermo-hydrodynamic model incorporating shear thinning has been used to explore further the frictional properties of the VM-containing oils. These confirm the findings of the journal bearing experiments and show that two key factors determine the friction of the engine bearing; (i) the low shear rate viscosity of the oil at the effective bearing temperature and (ii) the extent to which the blend shear thins at the high shear rate present in the bearing
Recommended from our members
Droplet manipulation of hierarchical steel surfaces using femtosecond laser fabrication
© 2020 Femtosecond laser irradiation is one of the most promising treatments to fabricate liquid repellent surfaces, attracting substantial scientific and industrial attention. So far, the focus has been on hierarchical interfacial structures at micro- and nanoscales, however, this has yet to be used in combination with macro-sized features. We present a strategy of femtosecond laser irradiation to create macro-micro-nano hierarchical surfaces for liquid droplet manipulation. These three-level hierarchical surfaces are shown to successfully split and gyrate impacting droplets. Our work is believed to be the first demonstration of femtosecond-laser-structured macro-micro-nano hierarchical surfaces to artificially design droplet impact, paving the way for aircraft anti-icing and energy harvesting.This work was supported by China Postdoctoral Science Foundation (2019T120340, 2017M621458), National Natural Science Foundation of China (11572192, 11632011), and Engineering and Physical Sciences Research Council (EP/N025954/1)