Heat transfer and pressure drop characteristics during the in-tube cooling process of carbon dioxide in the supercritical region

This paper presents the experimental data for the heat transfer and pressure drop characteristics obtained during the gas cooling process of carbon dioxide in a horizontal tube. The tubes in which carbon dioxide flows are made of copper with an inner diameter of 7.73 mm. Experiments were conducted for various mass fluxes and inlet pressures of carbon dioxide. Mass fluxes are controlled at 225, 337 and 450 kg m^-2 s^-1 by a variable speed gear pump, and the inlet pressures are adjusted from 7.5 to 8.8 MPa. The experimental results in this study are compared with the existing correlations for the supercritical heat transfer coefficient, which generally under-predict the measured data. Pressure drop data agree very well with those calculated by Blasius' equation. Using the measured data, a new empirical correlation to predict the near-critical heat transfer coefficient has been developed. Most of the experimental data can be predicted by the new correlation within a relative deviation of ±20%.