Comparative analysis of evaporation of isobutane (R600a) and propylene (R1270) in compact smooth and microfinned tubes

Data base for evaporation of flowing isobutane and propylene in compact internally enhanced surfaces is extended by experimental tests in two microfinned tubes and a smooth tube. The outer diameter for all of the test tubes was 5 mm. Heat transfer coefficient and pressure drop were compared for both fluids in all tubes in comparable working conditions. Test conditions were saturation temperatures of 5, 10 and 20 degrees C, heat fluxes ranging between 15 and 34 k W m(-2) and mass fluxes between 200 and 515 kg m(-2) s(-1). Results show that propylene has a higher heat transfer coefficient and lower pressure drop compared to isobutane. Furthermore, propylene is nucleate boiling dominant while convective heat transfer is dominant for isobutane. The tested microfinned tubes tend to have a maximum heat transfer coefficient. While for smooth tube correlations were found to reliably predict both heat transfer coefficient and pressure drop, the accuracy of correlations for microfinned tubes is shown to be greatly dependent on the testing conditions and tubes.