Flow boiling heat transfer and pressure drop characteristics of CO 2 in horizontal tube of 4.57-mm inner diameter

Abstract

Abstract This paper presents the flow boiling heat transfer and pressure drop of CO 2 (R744) in a horizontal tube. The test tube had an inner diameter of 4.57 mm, with a 0.89-mm wall thickness and length of 4.2 m. Experiments were carried out for heat fluxes ranging from 10 to 40 kW/m 2 K, mass fluxes ranging from 200 to 1000 kg/m 2 s, and saturation temperatures ranging from 0 to 40 °C. The boiling heat transfer of CO 2 has a greater effect on nucleate boiling than convective boiling and highly depends on the vapor quality, heat flux, and saturation temperature. The boiling heat transfer coefficient of CO 2 increases with a decrease in the inner tube diameter. In a comparison to previous boiling heat transfer correlations, the correlation of Cheng et al. showed fairly good agreement with the experimental data for CO 2 . The boiling pressure drop of CO 2 increased with an increase in the mass flux and decreased with an increase in the saturation temperature. None of the empirical correlations from the existing literature were able to predict the pressure drop of CO 2 in good agreement with the experimental data. Therefore, it is necessary to develop a reliable and accurate prediction for estimating the boiling pressure drop of CO 2 .