Simultaneous Visual and Calorimetric Measurements of R11, R123, and R123/Alkylbenzene Nucleate Flow Boiling.
Simultaneous Visual and Calorimetric Measurements of
R11, R123, and R123/Alkylbenzene Nucleate Flow Boiling.
Kedzierski, M. A.
NISTIR 4948; 54 p. October 1992.
American Society of Mechanical Engineers (ASME). Heat
Transfer With Alternate Refrigerants. HTD-Vol. 243.
1993, 27-33 pp, 1992.
Sponsor:Department of Energy, Washington, DC
Available from: National Technical Information Service
Order number: PB93-120756
refrigerants; alkylbenzene; alternative refrigerants;
boiling; bubble parameters; building technology;
calorimetric; chemistry; dichlorotrifluoroethane;
Bubble formation during horizontal flow boiling of
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.