Flow condensation heat transfer of CO2 in a horizontal tube at low temperatures

This study presents experimental data of CO2 flow condensation heat transfer for mass fluxes ranging from 100 to 500 kg/m2-s inside a 4.73 mm inside diameter, smooth horizontal copper tube, at saturation temperatures between −10 and 0 °C under a wide range of vapour quality conditions. Experimental data were obtained from an open-loop test rig which discharged high-pressure CO2 liquid from bottles to the atmosphere. Experimental results showed that when the test mass flux was greater than or equal to 300 kg/m2-s, for vapour qualities greater than 0.4, the rate of heat transfer increased with increasing mass flux and vapour quality, and increased with decreasing saturation temperature. The flow regimes under these working conditions were predicted as annular from the values of the Soliman Froude number (Frso > 14). Three recently proposed CO2 flow condensation models from the open literature were evaluated against the data from the current experiment. Overall, the model of Li and Norris (2016) gave the most accurate predictions, but under-predicted the low Nusselt number heat transfer rates. This model was modified using the current data, and then re-evaluated against experimental data from the current and other experiments, and was found to have a mean absolute percentage deviation of 7%.