Effect of Lubricant Concentration, Miscibility, and Viscosity on R134a Pool Boiling.
Effect of Lubricant Concentration, Miscibility, and
Viscosity on R134a Pool Boiling.
Kedzierski, M. A.
NISTIR 6450; 61 p. January 2000.
International Journal of Refrigeration, Vol. 24,
Available from: National Technical Information Service
(NTIS), Technology Administration, U.S. Department of
Commerce, Springfield, VA 22161.
1-800-553-6847 or 703-605-6000;
Order number: PB2000-103297
refrigerants; lubricants; heat transfer; surfactants;
This paper presents pool boiling heat transfer data for
twelve different R134/lubricant mixtures and pure R134a
on a Turbo-BII-HP surface. The mixtures were designed to
examine the effects of lubricant mass fraction,
viscosity, and miscibility on the heat transfer
performance of R134a. The magnitude of the effect of
each parameter on the heat transfer was quantified with
a regression analysis. The mechanistic cause of each
effect was given based on new theoretical interpretation
and/or one from the literature. The model illustrates
that large improvements over pure R134a heat transfer
can be obtained for R134a/lubricant mixtures with small
lubricant mass fraction, high lubricant viscosity, and a
large critical solution temperature (CST). The ratio of
the heat flux of the R134a/lubricant mixture to that of
the pure R134a for fixed wall superheat was given as a
function of pure R134a heat flux for all twelve
mixtures. The lubricant that had the largest CST with
R134a exhibited the greatest heat transfer: 100% + 20%
greater than that of pure R134a. By contrast, the heat
transfer of the mixture with the lubricant that had the
smallest viscosity and the smallest CST with R134a was
55% + 9% of that of pure R134a. High-speed films of the
pure and mixture pool boiling were taken to observe the
effect of the lubricant on the nucleate boiling.