Using mixtures of the zeotropic refrigerant mixture R-22/R-142b, a series of experiments was performed to determine the sectional and average heat transfer coefficients. Experiments were also conducted to compare three different heat transfer enhancement methods to that of smooth tubes. They were microfins, twisted tapes, and high fins. Measurements at different mass fluxes were obtained at six refrigerant mass fractions from 100 percent R-22 up to a 50 percent/50 percent mixture of R-22/R-142b. All condensation measurements were conducted at an isobaric inlet pressure of 2.43 MPa. This pressure corresponds to a saturation temperature of 60°C for R-22. The measurements were taken in 9.53 mm outer diameter smooth tubes and microfin tubes with lengths of 1603 mm. The heat transfer coefficients were determined with the Log Mean Temperature Difference equations. It was found that microfins were more suitable as an enhancement method than twisted tubes or high fins. Also, that the heat transfer coefficients and pressure drops decrease as the mass fraction of R-142b increases.
Issue Section:
Heat Transfer Enhancement
Keywords:
Condensation,
Enhancement,
Finned Surfaces,
Refrigeration,
Tubes,
heat transfer,
condensation,
pipe flow,
two-phase flow
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.Copyright © 2002
by ASME
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