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New Insitu Technique for Measuring the Concentration of Lubricant on a Boiling Heat Transfer Surface.


pdf icon New Insitu Technique for Measuring the Concentration of Lubricant on a Boiling Heat Transfer Surface. (4737 K)
Kedzierski, M. A.; Bruno, T. J.; O'Neill, M. B.

NISTIR 6110; 43 p. January 1998.

Sponsor:

Department of Energy, Washington, DC

Available from:

National Technical Information Service
Order number: PB98-124837

Keywords:

lubricants; refrigerants; absorption; alternative refrigerants; boiling; enhanced; fluorescence; heat transfer; refrigerant/lubricant mixtures; reflected harmonic; alternative refrigerants

Abstract:

This paper presents a technique for using the fluorescent properties and/or the harmonic focusing properties of several commercial lubricants to measure the concentration of lubricant on an aluminum vignetting target. The measurement method is being developed to determine the concentration of lubricant insitu on a boiling heat transfer surface. The heat transfer performance of a boiling surface is a strong function of both the type of lubricant and its concentration in the refrigerant. In general, severe boiling performance degradations may occur for higher concentrations of lubricant on the surface. The lubricant is preferentially drawn out of the bulk refrigerant/lubricant mixture by the boiling process and accumulates on the surface in excess of the bulk concentration. However, different lubricants accumulate on the heat transfer surface by different amounts for the same bulk concentration. The excess lubricant resides in a very thin layer on the surface. Accordingly, the ability to measure the lubricant concentration on the heat transfer surface would lead to a fundamental understanding of the mechanism by which lubricants can degrade or improve boiling performance. The lubricant concentration on a vignetting target was found to be linear with respect to the fluorescence intensity and the reflected harmonic from the surface. Consequently, the results of this study have shown that it is feasible to use the fluorescence and reflected harmonic measured from a boiling heat transfer surface to obtain the concentration of lubricant on the surface.