Tribology of engineering and coated materials in the presence of environmentally friendly refrigerant

In recent years, considerable effort has been devoted towards finding of alternative refrigerants due to environmental issues related to high global warming potential (GWP). Specifically, developing a system-compatible alternative refrigerant is of prime concern in order to reduce costs associated with design modifications. Among the candidate refrigerants, newly developed HFO-1234yf is considered as a direct substitution for the current R-134a refrigerant for possessing similar thermo -physical properties. However, in an actual system, a refrigerant circulates through different tribo-components where it interacts with the interfacial components (such as surface materials and lubricants), altering their tribological behavior. Therefore, the tribological performance of a refrigerant must be evaluated prior to widely used in refrigeration/ air-conditioning systems. Along this line, we have investigated the tribological performance of HFO-1234yf refrigerant under aggressive boundary lubrication conditions. Specifically, we have performed controlled tribo-experiments, simulating actual automotive air-conditioning compressor systems, to measure in-situ friction and near-contact temperature. Interestingly, we have observed a run-in instability in the frictional behavior for the case of HFO-1234yf refrigerant, unlike R-134a refrigerant. This intermediate instability is associated with decomposition of the reactive HFO-1234yf refrigerant at the contact interface under specific loading conditions. However, beneficial anti-wear tribofilms were shown to evolve throughout this process as revealed via Scanning Electron Microscopic (SEM) analysis. Energy Dispersive Spectroscopy (EDS) in conjunction with X-ray Photoelectron Spectroscopic (XPS) analysis identified the existence of Fluorine on these boundary films, attributing the fluorinated interaction at the contact zone. This fluorination, thus, facilitates formation of FeF3- enriched tribofilms over the cast iron based interface. In addition, we have demonstrated the influence of the loading conditions and state-or-art lubricants on the tribological compatibility of HFO-123yf refrigerant. Finally, the tribological performance of newly synthesized aromatic thermosetting polyester (ATSP), blended with 5% polytetrafluoroethylene (PTFE), namely ATSP/PTFE, has been evaluated under unlubricated and boundary lubricated conditions. Current state-of-art polymeric coatings have also been considered for comparative purposes. Tribological and morphological investigations revealed superior tribological performance for ATSP/PTFE. The better performance is attributed to segregated surface morphology associated with ATSP/PTFE

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• Akram, Mohammad

Contributors dc:contributor

• Polycarpou, Andreas A.
• Economy, James
• Bellon, Pascal
• Jasiuk, Iwona
• Dunn, Alison

• Aromatic Thermosetting Poyester (ATSP)
• Polymeric Coatings
• Tribofilm
• Boundary Lubrication
• Tribology
• Hydrofluoroolefins (HFO-1234yf)
• Environmentally Friendly Refrigerant

Statement dc:rights

• Copyright 2015 Mohammad Akram

Handle dc:identifier

http://hdl.handle.net/2142/78320

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/78320