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Research Papers: Evaporation, Boiling, and Condensation

Modeling of In-Tube Condensation of Zeotropic Mixtures

[+] Author and Article Information
Malcolm Macdonald

Sustainable Thermal Systems Laboratory,
GWW School of Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30382

Srinivas Garimella

Sustainable Thermal Systems Laboratory,
GWW School of Mechanical Engineering,
Georgia Institute of Technology,
Love Building, Room 340,
801 Ferst Drive,
Atlanta, GA 30332
e-mail: sgarimella@gatech.edu

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received July 4, 2015; final manuscript received March 22, 2016; published online May 17, 2016. Editor: Portonovo S. Ayyaswamy.

J. Heat Transfer 138(9), 091502 (May 17, 2016) (7 pages) Paper No: HT-15-1449; doi: 10.1115/1.4033352 History: Received July 04, 2015; Revised March 22, 2016

Studies in the literature have shown that zeotropic mixture condensation rates are lower than those predicted using a pure-fluid approach. This has been attributed to the decrease in fluid temperature that occurs with zeotropic mixtures and to the development of concentration gradients in the vapor-phase that limit the condensation heat transfer. The decrease in the apparent heat transfer coefficient is not consistent across mass fluxes, tube diameters, fluid combinations, saturation pressures, and concentrations. Several modeling techniques exist, which allow engineers to model the decrease in heat transfer rates. This study provides guidelines on when the mass transfer effects can be neglected and when it is appropriate to apply established models in the literature. A condensation database containing fluid combinations of pairs of hydrocarbons, ammonia and water, and synthetic refrigerants across large changes in operating conditions, tube diameters, and concentrations is used to validate the approach. The proposed framework predicts that the Bell and Ghaly (1973, “An Approximate Generalized Design Method for Multicomponent/Partial Condensers,” AIChE Symp. Ser., 69, pp. 72–79) approach is valid for mid- and high-reduced pressures, i.e., above 0.40, while explicitly accounting for mass transfer is necessary at lower reduced pressures, i.e., below 0.40, where the influence of the temperature glide in the Bell and Ghaly method is weighted too strongly.

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References

Figures

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Fig. 1

Measured apparent heat transfer coefficients for 45% R245fa and 55% n-pentane and equilibrium heat transfer coefficient predictions of the Cavallini et al. correlation

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Fig. 2

Measured apparent heat transfer coefficients for 33% ethane and 67% propane mixture and equilibrium heat transfer coefficient predictions of the Macdonald and Garimella [12] correlation

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Fig. 3

Sample predictions: (a) criterion 1 for the three fluid mixtures in the database and (b) changes in predictions for the ethane and propane mixture at different concentrations and reduced pressures

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Fig. 4

Average deviations of the Colburn and Drew [9] and Bell and Ghaly [8] models using fluid in the database and corresponding values of the Bell and Ghaly correction factor with equivalent reduced pressures

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Fig. 5

Flow chart demonstrating implementation of the criteria outlined

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