Abstract
Heat transfer characteristics of supercritical CO 2 cooled inside a small internally grooved tube were investigated. The mean inner diameter (ID) and helix angle of this tube were 2 mm and 6.3°, respectively. Experiments were conducted in the pressure range of 8–10 MPa and mass flux range of 400–1200 kg m −2 s −1. The effect of PAG-type lubricating oil on the heat transfer characteristics was investigated by changing the oil concentration from 0% to 5%. The drop in the heat transfer coefficient was 30–50% and 50–70% at oil concentrations of 1% and 3%, respectively. The heat transfer coefficient of CO 2 in the grooved tube was higher than that in the smooth tube at all oil concentrations tested. The experimental results indicated that the grooved tube has a large heat transfer area and facilitates the breaking up of the oil film.
Published Version
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