Vol.:(0123456789) 1 3 Journal of Thermal Analysis and Calorimetry https://doi.org/10.1007/s10973-020-09657-0 Modifed thermal balance method for estimating minimum inerting concentraion of fammable refrigerant mixtures Nagarjuna Kumma 1  · Adhil Moideen 1  · P. Kaushik 1  · S. S. Harish Kruthiventi 1 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 fammability. The fammability of any fammable 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 fammability 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 modifed 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 efect 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 Chlorofuorocarbon CIC Critical inerting concentration C st Stoichiometric concentration of refrigerant (%) C in Inerting concentration of nonfammable refriger‑ ant (%) C O The oxygen coefcient in a reaction (dimensionless) CAFT Critical adiabatic fame temperature (K) GWP Global warming potential GCM Group contribution method HCs Hydrocarbons HFCs Hydrofuorocarbons HQR Heating/quenching ratio HFOs Hydrofuoroolefns HCFC Hydrochlorfuorocarbon H o Heating potential of oxygen based on air H F Heating potential of refrigerant LFL Lower fammability limit (%) MIC Minimum inerting concentration (%) MSDS Material safety data sheet ODP Ozone depletion potential PAG Polyalkylene glycol Q d Quenching potential of dilutants Q F Quenching potential of refrigerant T a Ambient temperature (°C) TBM Thermal balance method UFL Upper fammability limit V O Flame propagation velocity of fammable refrig‑ erants (cm/s) V U Flame propagation velocity of mixture in (m/s) X D Dilutant concentration (%) X L Lower fammability limit (volume ratio) (% or dimensionless) X st Stoichiometric refrigerant/air volume concentra‑ tion (% or dimensionless) X u Upper fammability limit (volume ratio) (% or dimensionless) Φ Inhibition coefcient * S. S. Harish Kruthiventi harish@nitt.edu 1 Refrigeration and Air‑Conditioning Laboratory, Department of Mechanical Engineering, National Institute of Technology Tiruchirappalli, Tiruchirappalli 620015, India