Preliminary Study of Supercritical CO₂ Mixed With Gases for Power Cycle in Warm Environments

The supercritical carbon dioxide (S-CO₂) Brayton power cycle has been receiving worldwide attention due to the high thermal efficiency and compact system configuration. Because of the incompressible liquid like characteristic (e.g. high density, low compressibility) of the CO₂ near the critical point (30.98 °C, 7.38MPa), an S-CO₂ Brayton cycle can achieve high efficiency by reducing compression work. In order to utilize the S-CO₂ power conversion technology in various applications, such as distributed power generation and marine propulsion, air-cooled waste heat removal system is necessary. However, the critical temperature of CO₂ (30.98 °C) is an intrinsic limitation on the system minimum temperature. Because of the small difference with atmospheric temperature, a large amount of cooling air flow or a very large heat exchanger is required to reach the target minimum temperature. In this paper, to improve the system efficiency and ease the problem of air-cooled waste heat removal system, the mixture of supercritical CO₂ with other fluids has been studied. Also, the preliminary performance test results of CO₂ mixture with pre-existing experimental facility are evaluated.