Experimental Study on Small Scale Printed Circuit Heat Exchanger with Zigzag Channels

Printed circuit heat exchanger (PCHE) is a promising candidate of coolers used for SCO₂ Brayton cycle. The thermal-hydraulic performance of SCO₂ in a PCHE depends on the PCHE structure as well as the operating conditions of SCO₂ due to its dramatic variation of thermal physical properties near the pseudo-critical point. This work experimentally investigated the thermal-hydraulic characteristics of zigzag-channel PCHEs between SCO₂ and water at pressures that ranged from 8.0 to 11.0 MPa. Results showed that increasing the flow rate of SCO₂ might affect the PCHE more pronouncedly in comparison with changing the flow rate of water, indicating that the major convective thermal resistance is on the SCO₂ side. When increasing the operating pressure from 8.0 MPa to 11.0 MPa, the Nusselt numbers of PCHEs with zigzag angles of 0°, 15°, and 25° averagely decrease by 63.3%, 62.1%, and 54.0%, and the friction factors averagely decrease by 28.6%, 27.4%, and 21.0% respectively. Meanwhile, it is found that the buoyancy force is non-negligible during SCO₂ cooling process in PCHEs. In this regard, Nusselt number and friction factor correlations considering the buoyancy effect are proposed with applicable ranges.