Experimental study on heat transfer and flow characteristics of supercritical CO2: In-depth analysis of three heat transfer coefficients

Abstract

In the existing experimental research on flow and heat transfer of supercritical carbon dioxide (S-CO₂) in horizontal heated tube, the distinction of inlet temperature states is often neglected. To fill this research gap, this paper conducted a series of extensive experiments and conducted comparative analyses of three different heat transfer coefficients. The results indicate that when inlet temperature is below critical temperature and outlet temperature is below pseudocritical temperature, local heat transfer coefficient increases with the increase of heat flux. For inlet temperature ranging from 282 K to 285 K, average heat transfer coefficient obtained through the method based on average local wall temperature and fluid temperature exhibits a peak as heat flux increases. Notably, there are significant differences in the growth rates of pressure drop in liquid region and supercritical region. Average absolute deviations of three heat transfer correlations are 4.79 %, 3.55 % and 4.44 %, respectively. In heat transfer region where inlet temperature is below 304 K, average absolute errors of flow correlations, without considering wall temperature and with wall temperature taken into account, are 14.61 % and 9.39 % respectively. The work presented in this paper can provide theoretical guidance for design of heat exchangers.