Simultaneous Visual and Calorimetric Measurements of R11, R123, and R123/Alkylbenzene Nucleate Flow Boiling (NISTIR 4948)
Mark A. Kedzierski
Bubble formation during horizontal flow boiling of trichlorofluoromethane (R11), 1,1-dichloro-2,2,2-trifluoroethane (R123) and two R123/alkylbenzene lubricant mixtures was investigated both visually and calorimetrically. The test fluid was pumped through the inside of a roughened, horizontal, quartz tube which was electrically heated with a metal strip. The refrigerant entered the test section with a quality slightly above the saturated state. Locally measured heat transfer coefficients were taken simultaneously with high speed motion picture images of the boiling process. Predictive equations from the literature yielded acceptable agreement with the measured bubble diameters and contact angles. The addition of lubricant to the R123 increased the size of the contact angle and reduced the size of the bubble. The agreement between existing correlations and the measured bubble frequencies and site densities was within the uncertainty of the measurements. The addition of a small amount (0.5%) of alkylbenzene to R123 increases the number of active nucleation sites by approximately 5 sites/cm2 which corresponds to a 12% to 50% increase in the site density. The increase in the site density contributed to the enhancement of the heat transfer coefficient of the R123/0.5% alkylbenzene mixture over that of the pure R123. Further increase in the amount of alkylbenzene to the R123 reduces the number of active sites to below that of pure R123 to approximately the value for that of R11. Consequently, the 0.5% lubricant mass fraction mixture exhibited a heat transfer coefficient that was larger than that of the 2% lubricant mass fraction mixture. Correspondingly, the lower heat transfer coefficient of R11 as compared to that of R123 was partially due to the lower number of active boiling sites for R11. The dependency of the measured two-phase heat transfer coefficient on the heat flux and Reynolds number was investigated. Increases in both the heat flux and the Reynolds number caused increases in the heat transfer coefficient. The heat flux has a much larger effect on the heat transfer coefficient than the Reynolds number.
Simultaneous Visual and Calorimetric Measurements of R11, R123, and R123/Alkylbenzene Nucleate Flow Boiling (NISTIR 4948), NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD, [online], https://doi.org/10.6028/NIST.IR.4948
(Accessed June 5, 2023)