An experimental study on the characteristics of evaporation heat transfer of carbon dioxide flowing upward in an inclined smooth tube

The ozone layer depletion and global warming has driven us to develop new alternative refrigerants. As the carbon dioxide is believed as a good alternative, evaporation heat transfer characteristics of carbon dioxide flowing upward in an inclined smooth tube(45? have been investigated by experiment. A pre-heater is installed to adjust the inlet quality of the refrigerant to get a desired value before the test section. An inclined smooth tube(45? with outer diameter of 5 mm and length of 1.44 m was selected as a test tube. The test was conducted at mass fluxes of 318 to 530 kg/m2s, saturation temperatures of -5 to 20 .deg. C, and heat fluxes of 15 to 45 kW/m2. As the vapor quality increases, the heat transfer coefficients of carbon dioxide are slightly decreased, and the heat transfer coefficients increase with the heat fluxes and saturation temperatures elevated