Predicting heat transfer and flow features of supercritical CO₂ in printed circuit heat exchangers with novel wavy minichannels

Printed circuit heat exchangers (PCHEs) are unrivaled choices for heat exchange purposes in power cycles working with natural refrigerants such as carbon dioxide (CO₂). Minichannels play a major role in heat transferring in these devices. They take up more than 95% of PCHEs volume; therefore, increasing the performance or compactness of PCHEs will be realized, provided that novel designs are adopted for the minichannels. In this study, the investigation of non-uniform wavy minichannels applying supercritical carbon dioxide (SCO₂) as working fluid is carried out. To fulfill defined goals, a 3D conjugated model is developed to analyze the performance of novel geometries in both cooling and heating modes by considering the variations of SCO₂'s thermophysical properties. The results demonstrate that the proposed structures for the wavy minichannels create an upsurge in the heat transfer coefficient under the given operating conditions. It is explored that replacing the conventional wavy minichannel with the cases having short wavelengths at the upstream can increase the heat transfer enhancement factor from 36.1 to 51.1% in the cooling mode and from 40.8 to 56.5% in the heating mode. Furthermore, the larger the wave amplitudes at the upstream are, the more superiority it takes. Compared to all the proposed structures, the case with the largest wave amplitude and the smallest wavelength at the upstream attains the best overall performance. This structure of wavy minichannel can be utilized to manufacture highly efficient PCHEs with the capability of improving the overall performance index more than 1.5 times compared to the conventional wavy minichannel.