Shifting to a low GWP refrigerant is required for refrigeration and air-conditioning industries for the purpose of prevention of global warming. Since possible low GWP refrigerant candidates, including R1234yf, R1234ze(E) and R32, are mildly combustible, it is essential to collect fundamental information about the combustion characteristics of mildly combustible refrigerants and establish a reasonable risk assessment method for the wide dissemination of low GWP refrigerants. This paper provides a state-of-the-art review of the trend of HFC refrigerant regulation for the prevention of global warming both in Japan and overseas, as well as the fundamental researches on the combustion and anti-inflammatory characteristics of refrigerants, together with the ignition risk assessment when refrigerant leakage happens.

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Risk assessment of mini-split air conditioners (household air-conditioners), which started in 2011, has been completed for all applicable products. This report describes the procedure of risk assessment. FTA was conducted by integration time integral of flammable volume of leakage with computational fluid dynamics (CFD), the property of open flame and human error. The FTA results for wall-mounted air conditioners and one-to-one connection floor-mounted housing air conditioner are become below the allowance level by some countermeasures.

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The risk assessments were performed for VRF system with mildly flammable refrigerants. The probabilities of fire were estimated in the most severe installation cases at each life stage, indoor and outdoor operations, storage, installation, repairing and removal. Refrigerant leak velocity were calculated from the results of investigation of the diameter of leak hole at each parts recovered from real market. And the probability of rapid leak were estimated from the number of reporting from customers and service persons. If the probability of fire at the installation case without measure exceeded the given allowable level, we proposed the safety measures that can reduce the probability lower than the allowable level, once every 100 years. With these safety measures, it is clarified that the fire risk was able to be lower than the allowable level. It is necessary in the next step that we summarize these safety requests and establish them as the technical industry standard.

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The use of Low-GWP refrigerants, R1234ze(E), R1234yf, and R32 are very important measures to reduce the impact of the global warming problem. But the refrigerants have mild flammability characteristics. Since the refrigerants are adopted for water chillers installed in machine rooms and heat pumps on tops, a risk assessment has been executed at the view of mild flammability. As the result, probability of occurrence of fire accident is 3.89x10^-12 cases/unit/year by using reasonable mechanical ventilation systems as safety measure. The value is calculated by using actual accident record of refrigerant leakage and probability of occurrence of ignition sources.

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The positions where shock waves happen inside ejectors vary based on working conditions and dimension of ejectors, and the influence from shock waves occur would finally affect the overall performance of ejectors. In this research Schlieren photography method is adapted to visualize the characteristics of shock waves inside the ejector. Comparison of driving flow characteristics between converging nozzle and de Laval nozzle are conducted in the free-jet condition, and the converging nozzle is applied into the ejector to investigate driving flow expansion inside mixing section. By combining visualization experiment and numerical simulation results, the characteristics of shock waves occur in the driving flow are concluded, and the relationship between driving flow expansion and ejector`s performance is also discussed in this research.

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To characterize post-mortem muscle softening phenomenon, the meat qualities before and after frozen storage were compared between spotted mackerel Scomber australasicus and Pacific mackerel S. japonicus. In unfrozen fresh fish, the breaking strength of muscle specimen of spotted mackerel was lower than that of Pacific mackerel during ice storage, indicating that spotted mackerel meat was softer than that of Pacific mackerel meat. Histological observation showed that connective tissue area in the unfrozen meat of spotted mackerel was smaller than that of Pacific mackerel. The ice crystal size in the meat of spotted mackerel was bigger than that of Pacific mackerel. In the frozen-thawed meat, the breaking strength of the spotted mackerel meat was also lower than that of the Pacific mackerel meat. These findings suggest that muscle structure of fish meat before freezing may influence on the ice crystals formation and the reduction of meat toughness after thawing.

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Measurements of the vapor-liquid coexistence curve near the critical point for five compositions of the binary R 245fa + R 134a mixture were made by the direct observation of meniscus． With respect to 90.00 mass%, 70.00 mass%, 50.00 mass%, 30.00 mass%, and 20.00 mass% R 245fa mixtures, 16, 14, 14, 11, and 13 saturated density data were obtained，respectively. The critical parameters for five compositions were determined by the disappearing meniscus level as well as the intensity of critical opalescence. In addition, the correlation of the critical locus for the R 245fa + R 134a mixture was proposed.

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Measurements of PρTx properties for five compositions of the binary R 245fa + R 134a mixture were made by the isochoric method． With respect to 90.00 mass%, 70.00 mass%, 50.00 mass%, 30.00 mass%, and 20.00 mass% R 245fa mixtures, 134, 125, 119, 122, and 43 PρTx data were obtained in the temperature range from 310 K to 430 K, and pressure up to 6.94 MPa, respectively. The vapor-liquid equilibrium data were determined with an aid of the break point along the isochores. The critical pressure for five compositions were measured and the correlation of the critical locus for the R 245fa + R 134a mixture was also formulated.

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