Horizontal Nucleate Flow Boiling Heat Transfer Coefficient Measurements and Visual Observations for R12, R134a, and R134a/Ester Lubricant Mixtures.
Horizontal Nucleate Flow Boiling Heat Transfer
Coefficient Measurements and Visual Observations for
R12, R134a, and R134a/Ester Lubricant Mixtures.
Kedzierski, M. A.; Kaul, M. P.
NISTIR 5144; 31 p. March 1993.
Korean Society of Mechanical Engineers. Symposium on
Transport Phenomena (ISTP-6) in Thermal Engineering, 6th
International. Volume 1. May 9-13, 1993, Seoul, Korea,
Lee, J. S.; Chung, S. H.; Kim, K. H., Editor(s)(s),
111-116 pp, 1993.
Sponsor:Department of Energy, Washington, DC
Available from: National Technical Information Service
Order number: PB93-178598
heat transfer; lubricants; building technology; boiling;
The heat transfer characteristics of horizontal nucleate
flow boiling of R12, R134a, and R134a/Ester Lubricant
mixtures were investigated both visually and
calorimetrically. The effect of two different ester
lubricants on the boiling characteristics of R134a were
investigated. The test refrigerant entered a roughened
quartz tube test section slightly above the saturated
state. Both the heat flux and the Reynolds number were
varied in order to investigate their effect on the heat
transfer coefficient. The heat transfer increased
nearly proportionally with an increase in the heat flux.
An increase in the Reynolds number caused a marginal
increase in the heat transfer coefficient. Locally
measured heat transfer coefficients were taken
simultaneously with high speed motion picture images of
the boiling process. The motion pictures were used to
obtain a descriptive behavior of the boiling which was
compared directly to the measured heat transfer
coefficients. The rate of bubble production for pure
R134a was 38% greater than that of R12. This is the most
likely reason that the R134a heat trasfer coefficient
was approximately 20% greater than that of R12. The
addition of lubricant to R134a caused a drastic
reduction in the diameter of the bubbles. In fact, for
one R134a/lubricant mixture, the bubbles were emitted
from the of a mist. The addition of the low viscosity
lubricant to R134a enhanced the heat transfer of R134a.
For Reynolds numbers above 8000, the addition of the
high viscosity lubricant degraded the heat transfer as
compared to that of the pure component. A mechanistic
explanation for the observed R134a/lubricant boiling is