• Initial tank pressure defines supply logic: pressurize first or supply first; • Supercritical-pressure supply: stable but with a higher mass penalty; • Subcritical-pressure supply: lighter but supply instability risk due to flashing. Stable carbon dioxide (CO 2 ) supply is essential for effective cooling in hypersonic vehicles. In system design, higher supply pressures increase system mass, raising the question: does lower supply pressure always offer an advantage? In particular, when the pressure drops below the critical pressure, could the potential phase change affect supply stability? To address this question, this study presents a comparative experimental investigation of CO 2 supply behavior under supercritical pressure (∼8 MPa) and subcritical pressure (∼3.5 MPa). The results reveal that the initial tank pressure relative to the preset supply pressure governs the system’s start-up sequence, defining two operational modes: “pressurization-before-supply” for low initial pressure and “supply-before-pressurization” for high initial pressure. Compared with the subcritical pressure condition, the supercritical pressure supply provides more stable operation but requires approximately 142% more total pressurant gas mass. This additional mass stems primarily from the higher gas density required at elevated pressure, with dissolution loss playing a secondary role. In contrast, subcritical pressure operation reduces system mass yet suffers from flow instability due to CO 2 flashing. Therefore, stable subcritical operation demands more effective thermal insulation of the CO 2 tank. These findings reveal the inherent trade-off between system mass and operational stability, providing a scientific and engineering basis for designing lightweight CO 2 -based cooling systems under variable environmental conditions.
Xiong et al. (Fri,) studied this question.