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oai:www.ideals.illinois.edu:2142/78320 2023-07-11 col_2142_5131 col_2142_14787 com_2142_5130 com_2142_9630 com_2142_234

Polycarpou, Andreas A. Polycarpou, Andreas A. Economy, James Bellon, Pascal Jasiuk, Iwona Dunn, Alison Akram, Mohammad 2015-07-22T22:15:59Z 2015-07-22T22:15:59Z 2015-05 2015-03-10 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 Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2015-07-22 without embargo terms The student, Mohammad Akram, accepted the attached license on 2015-02-27 at 22:21. The student, Mohammad Akram, submitted this Dissertation for approval on 2015-02-27 at 22:36. This Dissertation was approved for publication on 2015-03-10 at 16:12. DSpace SAF Submission Ingestion Package generated from Vireo submission #7730 on 2015-07-22 at 10:30:14 Made available in DSpace on 2015-07-22T22:15:59Z (GMT). No. of bitstreams: 2 Akram_Mohammad1.pdf: 7005983 bytes, checksum: ea68e4c0b965b77aa129b4fe67c77e98 (MD5) license.txt: 4063 bytes, checksum: ed0f456ce856d3b4086e73e66b2d08e8 (MD5) Previous issue date: 2015-03-10 application/pdf http://hdl.handle.net/2142/78320 Copyright 2015 Mohammad Akram Aromatic Thermosetting Poyester (ATSP) Polymeric Coatings Tribofilm Boundary Lubrication Tribology Hydrofluoroolefins (HFO-1234yf) Environmentally Friendly Refrigerant Tribology of engineering and coated materials in the presence of environmentally friendly refrigerant text text 2015-5 Mechanical Sci & Engineering Mechanical Engineering University of Illinois at Urbana-Champaign Dissertation Ph.D.