A Risk Assessment for Leakages of Flammable Refrigerants into a Closed Space

This study proposes a procedure for a risk analysis for leakages of flammable refrigerants into a poorly ventilated three-dimensional space. It also presents several test cases of risk analyses on flammability and ignitions to a leaked refrigerant. Concentration of a leaked flammable refrigerant at a leakage window, Cin, is determined by mass balance, providing information on the capacity of an air-refrigerant mixture, and the leakage rate. Five flammable refrigerants, 2,3,3,3-tetrafluoropropene (R-1234yf), difluoromethane (R-32), 1,1-difluoroethane (R-152a), propane (R-290), and ammonia (R-717) have been used to analyze risk of ignitions and flammability. A computational fluid mechanics (CFD) technique has been applied to the present risk analyses, and temporal development of velocity, concentration, and temperature profiles of an air-refrigerant mixture in a three-dimensional space are computed. The obtained concentration profiles are compared with the lower flammability limits to analyze detailed risk of ignitions and flammability. The results of this study demonstrate that risk of ignitions can be investigated successfully based on the current CFD technique. This study furthermore shows that risk of ignitions and flammability is different depending on the flammability characteristics of each refrigerant. This study proposes an indicator, the Safety Index, to evaluate risk of ignitions in individual cases easily as screening of flammability without performing threedimensional calculations based on a CFD technique.