The refrigeration and air conditioning industry has expressed a great interest in the use of carbon dioxide(CO2) as a refrigerant. CO2 is anticipated to replace HFC refrigerants, which are known to have a negative effect onthe environment. The reason behind the interest in CO2 is the fact that it is a natural refrigerant, thusenvironmentally acceptable. Of course, such a replacement raises concerns regarding design criteria andperformance due to the different thermodynamic properties of CO2 and the very different range of pressures requiredfor the CO2 refrigeration cycle.So far, work related to CO2 has been done from a thermodynamics point of view and researchers havemade significant progress developing automotive and portable air-conditioning systems that use the environmentallyfriendly carbon dioxide as a refrigerant. The purpose of this work is to develop an understanding of how CO2 playsa role from a tribology standpoint. More specifically, the goal of this work is to gain an understanding on how CO2influences friction, lubrication, wear and scuffing of tribological pairs used in compressors.Work in the area of tribology related to CO2 is very limited. Preliminary work by Cusano and coworkersshowed that consistent data for tests using CO2 could not be acquired nor could a satisfactory explanation be offeredfor the inconsistency. Their results triggered the initiation of the work presented here. In this first attempt tounderstand the tribological behavior of CO2 several problems were encountered. During this work we noted that itsbehavior, unlike conventional refrigerants, could not always be predicted. We believe that this can be attributed tothe thermodynamic properties of CO2, which cannot be ignored when studying its tribological behavior.Thermodynamic Properties such as miscibility are very important when tribological testing is performed. A limitingfactor with our tester was that it was not designed for CO2 testing, but for other conventional refrigerants andtherefore made previously developed testing protocols non-applicable with CO2. Through a different approach andsome modifications to our tester we were able to establish a protocol for testing under the presence of CO2. CO2was then compared to R134a and the experimental results showed that it performs equally well.
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