Experimental investigation on comprehensive thermal-hydraulic performance of supercritical CO2 in a NACA 0020 airfoil fin printed circuit heat exchanger

Printed circuit heat exchanger (PCHE) is a promising compact heat exchanger for supercritical CO2 power conversion systems. Among the channel shapes of PCHE, an airfoil fin channel was considered for the high thermal-hydraulic performance of the PCHE. However, quantitative experimental evaluation of the thermal-hydraulic performance between the optimized airfoil fin and the wavy channel (commercially utilized channel shape) has not been performed. Therefore, in this study, to compare the performance according to channel shape, experiments on the optimized arrangement of airfoil fin PCHE (NACA 0020 airfoil fin with non-dimensional arrangement parameters, staggered number 1.0, horizontal number 2.0, and vertical number 1.8) and wavy PCHE (120° bending angle) were conducted. The experimental conditions of supercritical CO2 were temperatures ranging from 70°C (inlet) to 40.5°C (outlet) with pressures varying from 7.5 to 8.5 MPa. To reflect the real etched shape of airfoil fin channel, the real shape of airfoil fin was measured by using optical 3-Dimensional scanner. And hydraulic diameter was calculated based on measured information of real etched airfoil fin shape. The pressure drop of the airfoil fin PCHE was one-fifth of that of the wavy PCHE with the same total heat transfer rate per unit volume. New empirical correlations for the friction factor and Nusselt number of the airfoil fin PCHE were proposed based on the experimental data for the precooler design in the supercritical CO2 Brayton cycle. A friction factor correlation with maximum deviations of ±5.04 % and Nusselt number correlation with maximum deviations of ±14.0 % were proposed.