Comprehensive evaluation on the thermal-hydraulic performance of supercritical CO2/R41 in a micro-fin tube

Abstract

A 3-D flow and heat transfer theoretical model was established for a 5 mm micro-fin tube to explore the heat transfer and flow characteristics of supercritical CO2/R41 therein under different pressures, mass fluxes, and components. The research attempts to provide reference for selecting components of working media and setting the pressure and mass flux in different application scenarios. Results show that the closer the temperature of the working medium to the critical temperature, the larger the local convective heat transfer coefficient (CHTC). The CHTC at the critical temperature is 8 to 16 times higher compared with that at the non-critical temperature. The maximum CHTC is greater and the temperature corresponding to the maximum CHTC is lower when the mixed working medium is at a pressure closer to the critical pressure. The maximum CHTC under 7.0 MPa is twice that at 8.0 MPa. As the mass flux increases from 400 to 800 kg/m2s, the CHTC at the non-critical temperature increases by 1.7 times, while the comprehensive evaluation results of heat transfer and pressure drop decrease significantly. When the CO2 fraction increases from 20.5% to 75%, the maximum CHTC is increased by 2.6 times.