Optimal combination of converging and diverging minichannels in PCHE as precooler under diverse operating conditions of supercritical CO₂

The performance of printed circuit heat exchangers (PCHEs) has been studied extensively in supercritical CO₂ power cycles. However, no clear analysis has been conducted to investigate the impacts of converging and diverging flow path patterns on thermal and hydraulic characteristics of supercritical CO₂ flowing inside PCHEs, particularly under the precooler operating conditions. Accordingly, 3D numerical simulations coupled with a segmental-averaged discretization technique are carried out and validated to cover the existing research gap and scrutinize the corresponding effects on the performance of water precoolers. All the proposed cases are examined under three different operating conditions of the supercritical CO₂, namely far-, near, and trans-critical (F–C, N–C, and T-C). The findings approve that converging the cold side (H₂O) minichannel and diverging the hot side (CO₂) minichannel offer a great number of advantages in terms of increasing the thermal performance of precoolers. The pressure drop for the CO₂ flow could be alleviated by about 60% through diverging the hot side minichannel along with converging the cold side minichannel. Meanwhile, this combination leads to the lowest CO₂ outlet temperatures of the precooler, being about 310.2 K, 299.9 K, and 291.6 K under the F–C, N–C, and T-C operating conditions, respectively.