Effects of temperature and humidity on the flammability limits of several 2L refrigerants

Flammability limits were measured in air for several compounds classified as 2L refrigerants by American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). The compounds treated are ammonia, CH2F2 (HFC-32), CH3CF3 (HFC-143a), CH2CFCF3 (HFO-1234yf), and CHFCHCF3 (HFO-1234ze). The measurements of flammability limits were made in a 12L spherical glass flask following ASHRAE method. The temperature range examined was from 5 to 100 °C, and the humidity was ranged from 0 to 90% corrected for 23 °C. The temperature dependences of flammability limits of ammonia, HFC-32, and HFC-143a were found basically explainable by Whiteʹs rule. On the other hand, the temperature dependences of flammability limits of HFO-1234yf and HFO-1234ze are considerably larger than the predictions by Whiteʹs rule. For ammonia, HFC-32, and HFC-143a, the flammability limits are not much affected by the humidity of air used. On the other hand, the flammable ranges of HFO-1234yf and HFO-1234ze whose molecules contain more F-atoms than H-atoms markedly depend on the humidity of air. In particular, HFO-1234ze is non-flammable if the humidity of air is equal to or less than 10% corrected for 23 °C.