In this study, the evaporation heat transfer characteristics of an intermediate temperature of R744 in a smooth horizontal tube, when operating as an indirect refrigeration system (IRS) among hybrid cascade refrigeration systems (HCRSs), are evaluated. Studies on the characteristics of intermediate-temperature evaporation heat transfer under the operating conditions of evaporators used in actual refrigeration systems, such as IRS, cascade refrigeration systems, and HCRS, used in supermarkets are lacking. Thus, this study provides basic data on the characteristics of evaporation heat transfer of R744 in the evaporators of refrigerators used in supermarkets. The tube employed to the evaporation experiment in this study was a horizontal smooth copper tube with a length of 8000 mm and an inner diameter of 11.46 mm. The experimental variables were measured over a wide range of mass flux of 200–500 kg/(m2·s), heat flux of 10–40 kW/m2, and saturation temperature of −40–0 °C. The main results are summarized as follows: (1) The application of Kandlikar’s correlation formula at an evaporation temperature of −20 °C in an IRS helps in a good prediction of the R744 evaporation heat transfer coefficient. (2) The pressure drop according to the heat and mass flux showed the same heat transfer coefficient trend, but the pressure drop at saturation temperature was different from the trend of heat transfer coefficient.

This study evaluates the performance of an R744/R404A cascade refrigeration system (CRS) with internal heat exchangers (IHE) in supermarkets. R744 is used as the refrigerant in a low-temperature cycle, and R404A is used as the refrigerant in a high-temperature cycle. In previous studies, there are many studies including theoretical performance analysis of the CRS. However, experimental studies on the CRS are lacking, and experimental research on the R744/R404A system with an IHE is scarce. Therefore, this study provides basic data for optimal refrigeration system design by experimentally evaluating the results of modifying various parameters. The operating parameters considered in this study include subcooling and superheating, condensing and evaporating temperature, cascade evaporation temperature, and IHE efficiency in the R744 low- and R404A high-temperature cycle. The main results are summarized as follows: (1) By applying the results of this study, energy efficiency is achieved by optimizing the overall coefficient of performance (COP) of the CRS, and the refrigerant charge of the R404A cycle is minimized and economic efficiency is also obtained, enabling operation and maintenance as an environment-friendly system. (2) When designing the CRS, finding the cascade evaporation temperature that has the optimum and maximum COP according to the refrigerant combination should be considered with the highest priority.

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.

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This paper presents the comparison of heat transfer and pressure drop of various secondary refrigerants (single-phase and two-phase) in the indirect refrigeration system. The main results were summarized as follows: In case of heat transfer, it is useful to use secondary refrigerants in low evaporating temperature region and the heat transfer coefficient of single-phase is larger than two-phase secondary refrigerants. In case of pressure drop, it is useful to use secondary refrigerants in high evaporating temperature region and the pressure drop of two-phase is smaller than single-phase secondary refrigerant. Also, CO2 is the best useful because pressure drop of CO2 among the secondary refrigerants is the smallest.