Enhancing the performance of supercritical CO2-cooled heat sink by converging–diverging minichannels

Abstract

Heat sinks are broadly utilized in micro-electromechanical systems (MEMSs) to optimize their performance and durability. Due to the ongoing rapid development in this realm, miniaturization has been an enviable trend in these systems. As a result of this revolution, the heat flux over the unit area has increased exponentially, necessitating the need for modified geometries and efficient coolants. In this study, heat sinks with eight different structures including convergent and divergent minichannels are proposed, and the heat transfer is analyzed in the turbulent flow of supercritical CO2, being a promising candidate coolant in the considered cases. 3D numerical simulations are carried out based on the finite volume method, and the turbulent flow is simulated by the SST k-ω model. The results illustrate that the CO2 flow in non-uniform minichannels leads to diverse nature of heat transfer and pressure drop due to drastic variation of thermophysical properties of CO2 near its critical point. Converging the minichannels enhances the ratio of the heat transfer coefficient up to 2.37, and diverging the minichannels reduces the ratio of the pressure drop down to 0.31. The trends in the performance index suggest operating conditions are of utmost importance to obtain the optimal performance of the CO2-cooled heat sink. In general, increasing the CO2 mass flux improves the overall performance of the heat sink with convergent minichannels. At the same time, it worsens the overall performance of the heat sink with divergent and hybrid minichannels. The simultaneous convergence of the minichannels in two directions reduces the base temperature of the heat sink by 27.2%, leading to a maximum performance index of 1.56 at the operating pressure of 10 MPa and the mass flux of 750 kg m−2 s−1.