Heat transfer and fluid flow characteristics of a periodically constricted microchannel heat sink with supercritical carbon-di-oxide (sCO 2 ) as a coolant near its critical point

Microchannel heat sinks have been widely used to minimize surface temperatures of microelectrical components. Apart from mainstream coolants, supercritical carbon dioxide (sCO 2 ) has been introduced as a working fluid in recent studies due to its superior thermophysical characteristics at near-critical points. A numerical study has been conducted in a constricted microchannel with sCO 2 as a working fluid at a constant operating pressure of 8 MPa. Two distinct types of constrictions, namely triangular and rectangular, with three constriction ratios, have been considered while the inlet mass flux and temperature of the coolant vary. A comparative study has been performed for all the simulated cases, and a comprehensive analysis has been reported in terms of thermal and hydraulic parameters. Results indicate that the triangular constricted channel showed significant improvement by boosting the thermal performance 1.5 times compared to the straight channel at low mass flow rates. Higher pressure penalties were recorded in rectangular constricted channels due to prolonged narrow sections. A substantial difference of 43 K in heat sink substrate is generated by reducing the inlet temperature of the sCO 2 from 310 K to 306 K while reducing the constriction ratio cooled the substrate by 8 K. The triangular constricted channel at low inlet temperature and mass flux resulted in highest overall performance index of 1.56 considering the comprehensive thermohydraulic characteristics.