Modified thermal balance method for estimating minimum inerting concentraion of flammable refrigerant mixtures
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Modified thermal balance method for estimating minimum inerting concentraion of flammable refrigerant mixtures Nagarjuna Kumma1 · Adhil Moideen1 · P. Kaushik1 · S. S. Harish Kruthiventi1 Received: 24 October 2019 / Accepted: 30 March 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract R1234yf is considered as a better alternative for R134a (the conventional refrigerant) due to its low global warming potential value, while its usage is limited because of its flammability. The flammability of any flammable refrigerant can be reduced by adding dilutants that are inert. Two methods (group contribution method and thermal balance method) were used to estimate the minimum inerting concentration (which decides the flammability zone) of the binary mixtures (refrigerant + dilutant). It was observed that the group contribution method and the thermal balance method predicted minimum inerting concentration of the refrigerant mixture (refrigerant + dilutant) with an absolute error of more than 50% and 8%, respectively. Therefore, a modified thermal balance method is proposed in this study to estimate the minimum inerting concentration and found that the proposed method predicts the values with reasonable accuracy when compared with the available experimental data. Further, the minimum inerting concentration for the dilutants R125 and R245fa (that are not experimentally known) with R1234yf is estimated. The results indicated that R227ea has better inert effect with R1234yf when compared to other dilutants (R125, R134a and R245fa) considered in this study. It was also found that the critical inerting concentration for R1234yf is 36.5%. Keywords Thermal balance method · Group contribution method · Minimum inerting concentration · R1234yf List of symbols A & B Constants depends upon refrigerant and dilutant respectively CFC Chlorofluorocarbon CIC Critical inerting concentration Cst Stoichiometric concentration of refrigerant (%) Cin Inerting concentration of nonflammable refriger‑ ant (%) CO The oxygen coefficient in a reaction (dimensionless) CAFT Critical adiabatic flame temperature (K) GWP Global warming potential GCM Group contribution method HCs Hydrocarbons HFCs Hydrofluorocarbons HQR Heating/quenching ratio HFOs Hydrofluoroolefins HCFC Hydrochlorfluorocarbon * S. S. Harish Kruthiventi [email protected] 1
Refrigeration and Air‑Conditioning Laboratory, Department of Mechanical Engineering, National Institute of Technology Tiruchirappalli, Tiruchirappalli 620015, India
Ho Heating potential of oxygen based on air HF Heating potential of refrigerant LFL Lower flammability limit (%) MIC Minimum inerting concentration (%) MSDS Material safety data sheet ODP Ozone depletion potential PAG Polyalkylene glycol Qd Quenching potential of dilutants QF Quenching potential of refrigerant Ta Ambient temperature (°C) TBM Thermal balance method UFL Upper flammability limit VO Flame propagation velocity of flammable refrig‑ erants (cm/s) VU Flame propagation velocity of mixture in (m/s) XD Dilutant concentra
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