Abstract
Spiral tubes are compact and extremely heat-transfer-efficient that are suited for supercritical carbon dioxide (S-CO2) power cycles. Some existing experiments of S-CO2 heating in tubes are mainly conducted in spiral tubes with low ratio of pitch to spiral diameter (p/C<0.5) and straight tubes. In this study, experimental studies are conducted in a high p/C spiral tube with pitch (p) and spiral diameter (C) of 60 mm and 77 mm, diameter (d) and length (L) of 4.57 mm and 1000 mm, and compared with the straight tube of the same size. The results show that the spiral tube can alleviate heat transfer deterioration, with the maximum wall temperature dropping by 47 °C and the average heat transfer coefficient increasing by about 2.6 times from 1437 W·m−2·K − 1 to 3729 W·m−2·K−1 as compared to the straight tube. The wall temperature near the inlet of the spiral tube rises obviously at high q/G. The heat transfer coefficient and uniformity decrease with mass flux decreasing or heat flux increasing, and is little affected by pressure and inlet temperature. The buoyancy effect is analyzed using 1190 and 1260 experimental data points from spiral and straight tubes. The effect of buoyancy on heat transfer in the spiral tube is weakened as compared with the straight tube. A heat transfer correlation is proposed utilizing the experimental data.
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