Heat Transfer of Supercritical CO₂ Near the Critical Condition Inside a Microchannel

Carbon dioxide (CO₂) is increasingly being used as a highly efficient, environmentally friendly and sustainable refrigerant/heat transfer fluid. Because of its high specific heat and cooling capacity, supercritical CO₂ has the potential to be widely used in a range of applications, such as power generation and thermal management of data centers/electronics. Near the critical condition, the thermo-physical properties undergo drastic changes, which can affect the heat transfer performance. Thus, knowledge about the heat transfer process in the supercritical phase of CO₂ is necessary.

In this experimental study, the heat transfer characteristics of supercritical CO₂ near the critical condition in a microchannel were studied. An experimental setup, microfluidic devices with embedded resistance temperature detectors (RTDs), and a LabVIEW data acquisition system (DAQ), were used to obtain a range of variables, such as temperature, pressure, heat flux, and mass flux. Heat transfer coefficients (HTC) were calculated for different flow conditions (i.e., mass fluxes and pressures). In addition, the effect of the downstream position was discussed. The independent variables included mass fluxes ranging from 1825 kg/m².s to 8080 kg/m².s, reduced pressure (p/p_R) ranging from 1.02 to 1.143, and heat fluxes up to 98 W/cm².