An experimental study on condensation of R744 in a multi-port extruded tube

In the present study, the condensation process of R744 in a horizontal multi-port extruded tube was investigated experimentally. The test tube is made of aluminum alloy, and has 22 rectangular channels of 0.36 mm in hydraulic diameter. Experiments were carried out in the mass velocity range of 470 to 950 kg m^-2s^-1 at 5, 6 and 7 MPa in pressure, respectively. The pressure drop characteristics were measured at the both ends of the test section of approximately 730 mm in length. The local heat transfer characteristics were also measured in eight subsections of 75 mm in effective heat transfer length using heat flux sensors. The measured pressure drop increases as the mass velocity increases and the refrigerant pressure level decreases. These data were compared with several previous correlations. The measured local heat transfer coefficient decreases as the liquid quality increases, while it increases with increase of mass velocity. These data were compared with several correlations. The high quality data agree relatively with correlations of Moser et al. and Cavallini et al., while those of low quality do not agree with any correlations well. Therefore, new heat transfer correlation considering effects of vapor sheared stress and surface tension is developed.