Experimental study on heat transfer and pressure drop of supercritical CO2 cooled in a large tube

In order to reveal the heat transfer and pressure drop characteristics of supercritical CO2 cooled in the large diameter tube, an experimental system was established. The heat transfer and pressure drop performances of CO2 cooled in horizontal tubes having inner diameters of 4, 6 and 10.7 mm were experimentally investigated. The effects of the CO2 mass flow rate, inlet pressure, mean bulk temperature and tube diameter on the heat transfer coefficient and pressure drop were examined. The results show that the tube diameter significantly affects the heat transfer performance. As a consequence, when the universal heat transfer correlations for the small diameter tube are used to predict the heat transfer coefficient of CO2 in a large diameter tube, the predicted results present obvious deviation compared to the experimental results. Then based on the experimental data, a new heat transfer correlation for the large diameter tube was proposed. The maximum error between the predicted results of the new correlation and the experimental data is ±15%.