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Horizontal Nucleate Flow Boiling Heat Transfer Coefficient Measurements and Visual Observations for R12, R134a, and R134a/Ester Lubricant Mixtures.


pdf icon Horizontal Nucleate Flow Boiling Heat Transfer Coefficient Measurements and Visual Observations for R12, R134a, and R134a/Ester Lubricant Mixtures. (3742 K)
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

Keywords:

heat transfer; lubricants; building technology; boiling; dichlorodifluoromethane; 1,1,1,2-tetrafluoroethane; visualization

Abstract:

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 provided.