Heat transfer mechanism and influence factors in supercritical CO2 jet impingement cooling under unconventional physical property changes

The unconventional physical property variations of supercritical carbon dioxide (S-CO2) near the pseudocritical point present challenges in understanding the heat transfer mechanisms and heat transfer influencing factors when applying S-CO2 to jet impingement cooling. Therefore, a numerical model of CO2 jet impingement cooling in different phase states is established, considering the non-equilibrium phase change of CO2 and actual thermophysical properties while accounting for fluid-solid coupling heat transfer. This study examines the influence of high heat flux and various jet inlet conditions on the cooling performance of S-CO2 jets. In addition, the cooling effectiveness of sub-critical CO2 jet impingement is compared with that of S-CO2 jet impingement. This study found that S-CO2 exhibits significantly superior cooling performance compared to sub-critical CO2, with an increase in the average heat transfer coefficient of approximately 45%–50%. When the jet inlet temperature of S-CO2 is below the pseudo-critical temperature, the heat transfer coefficient is approximately 15%–20% higher than when it exceeds the pseudo-critical temperature. This enhancement is attributed to increased heat transfer capacity due to the large specific heat layer at the chip surface. Furthermore, S-CO2 jet cooling does not experience a critical heat flux (CHF) phenomenon, providing an advantage in high heat flux density cooling surfaces. In addition, it is found that once the jet inlet pressure increases to supercritical levels, the effect of further pressure increases on heat transfer becomes minimal. The results can provide references for the design of cooling systems in high-power electronic devices using S-CO2.