Mixed refrigerant (MR) Cascade Refrigeration Systems are widely employed in industries requiring both extremely low temperatures and large cooling capacity, such as semiconductors and displays. The composition of the MR has a significant impact on the performance of the cascade refrigeration systems, so optimizing the MR composition is essential. The current studies mainly focus on optimization that changes only the composition ratio with a limited number of refrigerants. Therefore, there may be a configuration and composition ratio that can improve the performance of the system more than existing methods. This study presents the need to find the optimal combination and number of MRs before determining the performance of MRs according to changes in composition. The proposed method selects five types of refrigerants that meet the conditions, then classifies cases according to the number of refrigerants in MR and analyzes the performance of each MR at various HTC evaporation temperatures based on energy and exergy through cycle simulation for each case. The proposed method showed COP up to 14.85 % higher than the conventional method, so it is expected to contribute to improving system performance by finding the optimal refrigerant combination and number before optimizing the composition of the MR.

In this study, to investigate the performance characteristics of a seawater ice-making device, using a scraped surface double tube evaporator, experiments were conducted under various operating conditions, including inlet temperature and flow rate of seawater, evaporating temperature, and scraper rotation speed. The main results are summarized as follows: (1) The section where stable ice making is possible, is determined by the inlet temperature and the flow rate range of seawater. By controlling the flow rate of seawater, the ice packing factor (IPF) of the device can be adjusted from 0.3 to 14.7%. (2) The IPF increases in cases where the evaporating temperature decreases linearly, until −13 °C. As the temperature of refrigerant that flows into the evaporator changes, the IPF is changed. Consideration is required for these connections. (3) The IPF increases when speeding up the scraper. The minimum rotating speed of the scraper was 350 rpm in these experiments. Optimum operating conditions for the seawater ice slurry maker are established through experiments. These results will be considered as important data for designing a slurry type seawater ice-making device.

This study investigated the evaporative heat transfer coefficient and pressure drop characteristics of R-1234yf in a horizontal tube with an inner diameter of 6.95 mm under various experimental conditions. The heat transfer coefficient increased with an increase in quality but showed a sharp decrease in the high-quality area. In addition, the heat transfer coefficient increased as the mass flux, heat flux, and saturation temperature increased. Although R-1234yf and R-134a presented similar heat transfer coefficients, that of R-134a was higher. The pressure drop increased with an increase in the quality and mass flux but decreased with an increase in the saturation temperature. The pressure drop of R-134a was larger than that of R-1234yf. In light of the flow pattern diagram by Taitel and Dukler, most of the experiments were included in the annular flow region, and some regions showed intermittent and stratified corrugated flow regions. Kandlikar’s heat transfer coefficient correlation provided the best prediction for the experimental database, with approximately 84% of the predicted data within ±30%. Moreno Quibén and Thome’s equation for pressure drop predicted approximately 88.71% of the data within ±30%.