Vapor-liquid equilibrium, excess properties, and absorption refrigeration performance of R1234yf-[Cₙmim,PF₆](n=4,6,8) working pairs using an improved SRK-WS-NRTL Model

To address the drawbacks of traditional absorption refrigeration working pairs, such as corrosion, crystallization tendency and the requirement for additional rectification equipment, this work considers R1234yf– [C n mim,PF 6 ] (n = 4, 6 and 8) hydrofluoroolefin ionic liquid working pairs. Their phase equilibrium behavior is correlated using the SRK equation of state, the Wong Sandler mixing rule and the NRTL activity-coefficient model. A Margules-type binary interaction parameter k ij is introduced as a correction to the excess Gibbs energy, and the NRTL interaction parameters are regressed using a two-step strategy. Excess Gibbs energy (G E ), excess enthalpy (H E ) and excess entropy (S E ) are then evaluated along the calculated vapor liquid equilibrium paths as functions of temperature and liquid-phase composition. The modified model gives pressure ARDs of 1.61%, 1.18% and 1.42% for the three systems, respectively. The k ij correction is negligible for the n = 4 and 6 systems but substantially improves the correlation of the n = 8 system. G E , H E and S E are positive over the investigated domain, whereas G E decreases with increasing cation alkyl chain length, consistent with the enhanced solubility of R1234yf. A single effect absorption refrigeration cycle calculation further shows that the coefficient of performance increases with alkyl-chain length. These results support the screening of HFO-IL working pairs and the optimization of absorption refrigeration processes.