A new correlation of flow boiling heat transfer coefficients for carbon dioxide

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.