Modified thermal balance method for estimating minimum inerting concentraion of flammable refrigerant mixtures

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%.