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Title:Tribology of engineering and coated materials in the presence of environmentally friendly refrigerant
Author(s):Akram, Mohammad
Director of Research:Polycarpou, Andreas A.
Doctoral Committee Chair(s):Polycarpou, Andreas A.
Doctoral Committee Member(s):Economy, James; Bellon, Pascal; Jasiuk, Iwona; Dunn, Alison
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Aromatic Thermosetting Poyester (ATSP)
Polymeric Coatings
Boundary Lubrication
Hydrofluoroolefins (HFO-1234yf)
Environmentally Friendly Refrigerant
Abstract: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
Issue Date:2015-03-10
Rights Information:Copyright 2015 Mohammad Akram
Date Available in IDEALS:2015-07-22
Date Deposited:May 2015

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