Abstract
Carbon dioxide (CO2) has remarkable different flow boiling heat transfer characteristics from conventional refrigerants when evaporating at similar temperatures, for which a CO2-specific correlation of evaporative heat transfer coefficients is necessary. A number of correlations for two-phase flow boiling heat transfer coefficients were proposed, among which some are CO2-specific. However, their prediction accuracies for CO2 were not satisfactory. This work proposes a new CO2-specific correlation of flow boiling heat transfer coefficients based on the CO2 database of 2956 experimental data points collected from 13 independent studies. The new correlation incorporates a new dimensionless number and makes great progress in the prediction accuracy. It has a mean absolute deviation of 15.5%, and predicts 72.5% of the entire database within ±20% and 89.1% of the entire database within ±30%, far better than the most influential existing counterpart. The new dimensionless number is associated with the formation and departure of bubbles.
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