Nusselt number analysis of printed circuit heat exchangers with straight and zigzag channels

Abstract

Printed Circuit Heat Exchangers (PCHEs) are applied in processes involving high temperatures and working pressures, such as the supercritical CO2 Brayton cycle. These devices are typically designed with semi-circular channels and zigzag paths to enhance thermal performance. In recent years, several Nusselt number correlations for zigzag channels have been proposed to estimate the thermal performance. However, under similar operating conditions and zigzag angles, these correlations yield divergent results for supercritical and non-supercritical condition. No study has compared these correlations to identify the most accurate one. Therefore, this research performed a thermal analysis of PCHEs operating with straight and zigzag channels, using fluids in normal and supercritical conditions. Additionally, it was evaluated existing Nusselt number correlations to determine which ones presents the best result. This study examined 37 Nusselt number correlations, analyzed four experimental studies available in the literature and evaluated a total of 374 experimental data. For straight channels, the error ranged from 3% to 27%, whereas for zigzag channels, the error varied between 3% and 84%. This demonstrates how correlations developed for the same application can lead to discrepant results.