Review of correlations of flow boiling heat transfer coefficients for carbon dioxide

• Evaluates 34 correlations of flow boiling heat transfer with 2956 data of CO2.
• Provides a guideline to choose the best correlation for engineering design.
• Proposes new criterion for channel transition of CO2 flow boiling heat transfer.
• Identifies the importance of dryout effects on CO2 flow boiling heat transfer.
• Pointes out several topics worthy of attention for future studies.

Carbon dioxide (CO2) has quite different flow boiling heat transfer characteristics from conventional refrigerants due to its much higher reduced pressures that make its thermodynamic and transport properties very different. There were some studies evaluating the correlations of flow boiling heat transfer coefficient for CO2. However, either the number of correlations covered or the number of data used was limited, resulting in inconsistent conclusions. This work presents a comparative review of existing correlations for flow boiling heat transfer coefficient of CO2. There are 34 correlations analyzed and evaluated using 2956 experimental data points of CO2 flow boiling heat transfer from 10 independent laboratories. The Fang (2013) correlation performs best with a mean absolute deviation of 15.5%. The evaluation analysis sets a channel transition criterion for flow boiling heat transfer of CO2. Several topics worthy of attention for future studies are identified.