Lubricants Enter New Refrigerant Equation

August 30, 2010
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Purdue University was host for three concurrent conferences dealing with a range of refrigeration and air conditioning applications.

WEST LAFAYETTE, Ind. - If an industry with HCFCs, HFCs, HFOs, and HCs wasn’t complex enough, consider the oil aspect. There are mineral oils, POEs, ABs, and the latest entry, PVEs. The issue then becomes - what refrigerants with what oils?

That was a topic that occupied about two hours of paper presentations at the 13th International Refrigeration and Air-Conditioning Conference at Purdue University this summer.



PVE

During the session, the most specific lubricant research came from Idemitsu with Polyvinylethe (PVE) as a lubricant with HFC refrigerants. “PVE is being examined as lubricants for air conditioning systems which use alternative refrigerants such as HFC refrigerants instead of HCFC-22.”

In noting that “since 1998, most of Japanese OEMs have already started to supply air conditioning systems with HFC refrigerants and PVE,” the report said. “PVE is the most suitable refrigeration lubricant for air conditioning systems with HFC refrigerants.”

Its pluses, the report said, relate to “the chemical and physical properties (solubility, thermal stability, lubricity, volume resistivity).”

R-1234

The most talked about refrigerants at the conference were HFO-1234yf and HFO-1234ze(E), being looked at as beyond-HFC refrigerants with HFCs facing a possible phase down. HFOs are already planned for use in automotive air conditioning in Europe and research is now underway for HFOs in stationary applications. In the case of stationary, much research remains to be done.

For example, in a paper on 1234yf from Catholic University of America in Washington, D.C., and the University of Padova, Italy, it was noted, “This paper critically reviews the best publically available data and property models for R-1234yf for the normal boiling point temperature, the critical state temperature, pressure and density, vapor pressure, liquid density, specific heat at constant pressure, liquid dynamic viscosity, and surface tension. The paper presents new property correlations for vapor pressure, liquid density, and liquid dynamic viscosity, which provide better fits of the publically available data than any of the other available correlations.”

It then went on to note, “However, thermodynamic and transport property data, and associated Equations of State (EoS), have only begun appearing in the open literature since approximately mid-year 2009.”

When it came to ze(E), researchers at the National Institute of Standards, in its paper, noted the refrigerant was a work in progress.

“In this work, we present measurements of the thermodynamic properties of R1234ze(E). These data were used to develop a fundamental equation of state that is valid over the entire fluid surface and that can be used to calculate all of the thermodynamic properties. Our data are compared to the very limited literature data available for this fluid.”

After its research, the NIS report said, “The EoS based on these data, together with selected literature data, is the best currently available for this fluid and the best that is feasible given the currently available data. The EoS is entirely adequate to evaluate this fluid in typical refrigeration applications. Further measurements would be warranted, especially if R1234ze(E) becomes widely used.”

A report that did look at ze(E)’s thermodynamic properties as part of a mixture within HFC-32, isobutene and difluoromethane, came from Sangyo University in Japan and looks at the blend as an alternative to HFCs. For the purposes of the paper, the intent was to “predict properties such as densities and heat capacities with satisfactory accuracies” to “allow a reliable analysis of refrigeration systems using the mixtures.”

HCs

A study from Universita Politecnica Delle Marche, Italy, looked at methane, ethane, and propane thermal conductivity along the saturation line. The intent was to conduct research to be used in further studies of the refrigerants.

“In this paper a formula for the calculation of thermal conductivity of organic liquids along the saturation line is presented and tested on a database of more than 40 refrigerants belonging to the series of methane, ethane and propane. Almost all the refrigerants present in ASHRAE Standard 34 have been considered, thus covering most of the substances in use in the refrigeration industry at the moment.”

Publication date: 08/30/2010

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