The design of the injection mold cooling system is important. The cooling time consumes 70-80% of the injection molding cycle, so a well-designed cooling system can shorten the molding time and improve productivity significantly. Recently, many studies have been conducted for rapid cooling of a hot-spot area using CO₂ in injection molding. In this study, a cooling module based on CO₂ was designed and manufactured for uniform and rapid cooling of an injection mold with a large cavity, and cooling characteristics were investigated through experiments. As the CO₂ supply pressure increased, the cooling effect increased significantly, while the cooling uniformity decreased relatively. In the case of using the heat exchanger, the cooling effect increased by 10oC on average compared to the case without the heat exchanger, whereas the effect on the cooling uniformity was insignificant. When the CO₂ was injected from both sides, the cooling effect increased by approximately 8oC on average compared to the case of injection from one side, and the cooling uniformity was approximately 10% higher. By using a heat exchanger and applying CO₂ bidirectional supply, a cooling rate of up to 5.78℃/s and an average of 4.9℃/s could be achieved.

Since sCO₂ (Supercritical Carbon Dioxide) turbomachinery are generally small and operate at high rotational speed, the bearings remain a significant challenge to the design of the turbomachinery for the sCO₂ power cycles. However, a fluid induced instability similar to the oil whirl may occur even with the magnetic bearing under high pressure and high speed conditions of the sCO₂ turbomachinery. This paper presents experimental investigation on the instability of a sCO₂ compressor supported by the magnetic bearing. First, we introduce the sCO₂ compressor supported by the magnetic bearing. The procedure to guarantee the rotordynamic performance of the sCO₂ compressor supported by the magnetic bearing is provided. Then, the effects of the working condition such as the pressure and rotating speed on the fluid induced instability are investigated experimentally. Finally, a strategy to resolve the fluid-induced instability with conventional PID control is proposed and experimentally verified.