Design and dynamic analysis of a novel scroll compressor-expander unit for the CO₂ air conditioning system in electric vehicles

Transcritical CO₂ refrigeration cycle systems hold significant promise for improving the energy efficiency of air conditioning system in vehicles, diminishing reliance on traditional energy sources, and reducing environmental impact. Utilizing a scroll compressor-expander unit (SCEU) to recover energy during the expansion process enables the effective conversion of expansion work into useful work, thereby enhancing the efficiency of the entire refrigeration cycle. This paper provides a detailed description of the geometric structure of the SCEU, and based on this, conducts an exhaustive mechanical analysis of its orbiting scrolls and main shaft, thus establishing dynamic models. Computational results indicate that in transcritical CO₂ refrigeration systems, the SCEU aids in recovering expansion work, increasing the coefficient of performance (COP) by 8.2% under standard operating condition. Additionally, this paper pioneers in studying the dynamic characteristics of SCEU under variable conditions. It is found that although the COP of the systems decreases with the rise of working pressure, compared to traditional systems, its rate of improvement progressively increases. Under conditions of negligible leakage and an isentropic efficiency of 60%, the SCEU can potentially increase the COP of the system by up to 9.8%.