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Investigation of the Condensing and Expansion Behaviors of Alternative Refrigerants

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Title: Investigation of the Condensing and Expansion Behaviors of Alternative Refrigerants
Author(s): Meyer, J.J.; Dunn, W.E.
Subject(s): heat transfer pressure drop R-22 alternatives R-502 alternatives
Abstract: This study examines the heat transfer and pressure drop performance of R22 and R502 alternatives, most of which are mixtures of two or three refrigerants, while condensing in an enhanced tube and while expanding in a capillary tube. The condensation study includes data for four mass fluxes ranging from 111.6 klbm/ft2-hr to 595.7 klbm/ft2-hr (151.7 kg/m2-s to 809.0 kg/m2-s), heat fluxes from 700 Btu/ft2-hr to 16,000 Btu/ft2-hr, and oil concentrations of 0%, 1 %, and 3%. A total of 1080 unique data sets were obtained, each of which contains nine local data points. The capillary tube study examined the mass flow rate of refrigerants while expanding, with an emphasis on the nature of the metastable region for both single component refrigerants and mixtures. We found that the pressure drop of the helically enhanced tube is best predicted by using a friction factor set equal to a constant multiplied by the friction factor of a smooth tube, not a constant roughness. Also, the addition of oil has a pressure lowering effect for low qualities, where most of the flow is liquid, and a pressure raising effect at high qualities, where most of the flow is vapor in contact with a liquid oil film. When adjusting the two-phase pressure-temperature relationship for the presence of oil, it was noticed that for each mixture there was a consistent deviation between the expected condensing temperature and the measured value. This discrepancy results from errors in the model used to predict the two-phase properties of the blends, and has been accounted for in the reduction of the data. We found that oil has a significant effect on heat transfer coefficients at qualities above about 0.7, but very little effect at lower qualities. Also, the performance of mixtures increases more rapidly than that of a single component refrigerant as the mass flux is increased. The metastable region of a capillary tube was found to be much more predictable than previously thought. A new and revealing data taking technique, which takes the history of the system into account, allowed for the discovery of a hysteresis effect in the mass flow rate as the level of inlet subcooling is increased and decreased. This finding may have a profound impact on the future of capillary tube data acquisition and modeling.
Issue Date: 1996-08
Publisher: Air Conditioning and Refrigeration Center. College of Engineering. University of Illinois at Urbana-Champaign.
Series/Report: Air Conditioning and Refrigeration Center CR-06
Genre: Technical Report
Type: Text
Language: English
URI: http://hdl.handle.net/2142/13182
Date Available in IDEALS: 2009-07-27
Identifier in Online Catalog: 4036144
 

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