Hazard evaluation of difluoromethane cloud explosion

Abstract

Traditional refrigerants (such as R22) contribute greatly to the greenhouse gas emissions and ozone layer depletion. The R32 (difluoromethane, CH2F2) is an environmental substitute for R22 and R410a.This study is aimed at evaluating the hazard of difluoromethane cloud explosion by varying the oxygen content and equivalence ratio. In the experiment, the flame morphologies are recorded using the soap bubble method and the far-field pressure is measured using microphone pressure transducer. In the numerical simulation, the adiabatic flame temperature, thermal diffusivity and sensitivity analysis are obtained to reveal the factors affecting laminar burning velocity. The results demonstrate that the instability appears at high-oxygen content conditions and the diffusional-thermal instability is the leading factor of the lean flame, while the hydrodynamic instability is the leading factor of the rich flame. With the increase of the oxygen content, the laminar burning velocity, maximum explosion pressure, maximum pressure rise rate, positive pressure impulse increase while the negative pressure impulse decreases. With the increase of the equivalence ratio, the laminar burning velocity, maximum explosion pressure, maximum pressure rise rate, positive pressure impulse increases first and then decreases while the negative pressure impulse decreases first and then increases. The adiabatic flame temperature play a more important role comparing to the thermal diffusivity as the factor affecting the laminar burning velocity. Sensitivity analysis is conducted to anaylze the chemical influence on the laminar burning velocity. Chemical reactions H + O2 < = > O + OH, CHF2 + O2 = > CF2:O + O + H, CHF2 + H = CHF + HF and CF2:O + H = CF:O + HF show significant effects on the laminar burning velocity.