Heat transfer correlation for sCO2 cooling in a 2 mm tube

Abstract

The heat transfer of carbon dioxide near the critical point cooled in a horizontal tube with 2 mm inner diameter was investigated experimentally. The local heat transfer coefficients (htc) were determined by temperature measurements inside the tube wall along the 1.2 m cooled length. The effects of the CO2 mass fluxes in the range of 400–1300 kg/m2s, CO2 inlet pressures between 77 and 85 bar, CO2 bulk fluid temperatures between 10 and 85 °C and cooling water temperatures between 10 and 40 °C on the heat transfer were examined. The experimental results are compared with existing correlations for sCO2 heat transfer in small diameter tubes. A modified Dittus-Boelter equation was developed to predict the heat transfer coefficients with an accuracy of 20%.