Thermal decomposition and interaction mechanism of HFC-134a/HFC-32 mixture in Organic Rankine Cycle

Organic Rankine Cycle (ORC) is an effective technology for the recovery of industrial waste heat and the utilization of renewable energy to produce electricity. Hydrofluorocarbon mixtures are more attractive used in ORC systems than pure working fluids due to the advantages of higher work outputs, higher cycle efficiencies, and lower exergy losses. For the supercritical ORC system, thermal stability is one of the main factors to screen the working fluids. In the present work, ReaxFF reactive molecular dynamic simulations and density functional theory calculations are performed to investigate the thermal decomposition and interaction mechanism of HFC-134a/HFC-32 mixture. The thermal decomposition process, the effects of temperature, and HFC-134a to HFC-32 ratio on the thermal decomposition of HFC-134a/HFC-32 mixture, and the interaction between HFC-134a and HFC-32 are investigated. The results showed that the hydrogen bond formed between HFC-134a and HFC-32 in HFC-134a/HFC-32 mixture, which inhibits the decomposition of HFC-134a. The HFC-134a/HFC-32 mixture used in ORC system has a better thermal stability than pure HFC-134a. The results of this study are beneficial to the screening of ORC working fluid and the safe operation of the ORC system. •The interaction mechanism of HFC mixture pyrolysis is first investigated.•H2 can be used as an indicator for the HFC-134a/HFC-32 mixture pyrolysis.•Hydrogen bond formed between HFC-134a and HFC-32 in mixture.•Thermal stability of HFC-134a is improved by hydrogen bond.•Thermal stability of HFC-134a/HFC-32 mixture is better than pure HFC-134a.