Scuffing and wear of engineering materials under different lubrication regimes in the presence of environmentally friendly refrigerants

In recent years, the air-conditioning industry has been focusing on alternative refrigerants for the replacement of hydrofluorocarbons (HFCs) due to environmental regulations. HFCs refrigerants have been widely used in the refrigeration industry since the early 1990’s as replacement to chlorofluorocarbon (CFCs) refrigerants that were non-flammable and non-toxic, but posses a high ozone depletion potential (ODP). Despite the fact that HFCs have zero ODP, they were found to have a high global warming potential (GWP) being considered one of the green house substances to be banned by the Kyoto agreement. The interest for long term solutions has been towards natural refrigerants. Among different natural refrigerants such as water, air, and ammonia, carbon dioxide (CO2, R744) is an attractive and possibly the most viable candidate. Although, CO2 is a non-flammable and non toxic natural refrigerant (being not the case for Hydrocarbons and Ammonia), one of the main drawbacks related to its implementation as a refrigerant in air-conditioning compressors has to do with the high operating working pressures. These working pressures can be around 5 to 6 times higher compared to HFCs systems. One of the important aspects in the design of an air-conditioning compressor is the understanding of the miscibility and solubility of the lubricant and the refrigerant. The incomplete miscibility and solubility of CO2 with commonly used lubricants in the vapor compression cycle affects the way the lubricant is transported out of the refrigeration circuit. Also, when miscibility and solubility is incomplete, the lubricant accumulates in the system causing pressure drops (especially in the evaporator). Appropriate lubrication of the critical components of the compressor becomes important as the demands for higher efficiency increases. Control of the wear of these components has to be ensured in order to guarantee appropriate operation of the compressor over a prolonged period of time. Scuffing is another important aspect to be addressed in the design of compressors. This is considered a severe adhesive type of failure that renders the tribocontacts non functional. Interaction of the lubricant, refrigerant, and materials, plays an important role on the scuffing performance since tribochemical reactions might improve or lower the wear resistance at the sliding interfaces. Studies on CO2 as an alternative refrigerant for air-conditioning systems has been mainly focused on the thermodynamical aspects to ensure that the efficiency and cost will make it suitable as a replacement to HFCs. However, research on the tribological aspects of CO2 with lubricants and engineering materials is scarce. The aforementioned drawbacks related to the circulation of lubricant and refrigerant in the refrigeration circuit has raised the possibility of design and development of oil-less compressors. In this direction, it is imperative to design advanced materials able to withstand aggressive sliding conditions in the absence of lubricant. This research focuses on the study of the friction and wear behavior of different materials and lubricants in the presence of CO2 for air-conditioning and refrigeration compressors. Bare materials and soft polymeric type of coatings were studied in the presence of lubricants and environmentally friendly refrigerants to understand the role of tribochemistry by using a range of analytical tools that provide answers of the scientific aspects during the characterization of friction and wear.

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

2011

Author dc:creator

• Escobar Nunez, Emerson

Contributors dc:contributor

• Polycarpou, Andreas A.
• Conry, Thomas F.
• Tseregounis, Spyros I.
• Bellon, Pascal

• Polymer coatings
• Tribolayers
• Carbon dioxide
• Global Warming Potential (GWP)
• ozone depletion potential (ODP)
• Friction
• Wear
• x-ray photoelectron spectroscopy (XPS)
• scanning electron microscope (SEM)
• energy dispersive spectroscopy (EDS)
• x-ray diffraction (XRD)
• time of flight (ToF-SIMS)

Statement dc:rights

• Copyright 2010 Emerson Escobar Nunez

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/18411

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/18411