Experimental and numerical analysis of high-pressure CO2 injection flow inside a homogeneous porous microchip model

Supercritical carbon dioxide (sCO2) possesses unique physical properties in the critical region—characterized by high density, low viscosity, and strong solvation capacity—exhibiting critical flow and heat transfer behaviors in porous media that are crucial for applications such as carbon sequestration, soil remediation, and oil/gas recovery. This study systematically investigates the phase transition behavior, flow characteristics, and heat transfer mechanisms of CO2 during trans-critical processes in porous media through an integrated approach employing a visualization experimental platform, optical imaging techniques, and numerical simulations. Key findings reveal that during the trans-critical process: (1) an increase in inlet temperature suppresses the enhancing effect of back pressure on flow pressure drop, while elevated back pressure amplifies the impact of volumetric flow rate on flow pressure drop; (2) turbulent phenomena persist for 47.26 % of the entire trans-critical duration during the transition from liquid CO2 to supercritical state, accompanied by significant density gradient fluctuations at phase interfaces; (3) transient simulations of the trans-critical process demonstrate three heat transfer mechanisms: deteriorated heat transfer by phase chaos, enhanced heat transfer in transitional state, and drastically enhanced heat transfer in supercritical state. Furthermore, alterations in boundary conditions induce substantial numerical discrepancies in local heat transfer coefficients during periods of drastic fluctuation.