Thermal conductivity measurements of refrigerant mixtures containing hydrofluorocarbons (HFC-32, HFC-125, HFC-134a), hydrofluoroolefins (HFO-1234yf), and carbon dioxide (CO2)

Abstract

Thermal conductivity measurements of eight binary refrigerant mixtures were conducted in the homogeneous liquid and vapour phases with the transient hot-wire technique. The temperature range of the measurements spanned from (224.3 to 386.6) K with pressures ranging between (1.0 and 6.5) MPa. The binary mixtures were equimolar (R125 + R32), (R32 + R134a), (R32 + CO2), (R125 + R134a), (R125 + CO2), (R134a + R1234yf), (R134a + CO2) and (R1234yf + CO2). Additionally, two multi-component mixtures, (R32 + R1234yf + CO2) and (R32 + R1234yf + R134a + R125 + CO2), were investigated. The transient hot-wire apparatus was validated with measurements of pure CO2 in the liquid and vapour regions. The relative combined expanded uncertainty (k = 2) in the experimental thermal conductivity was on the order of 2.0%. The relative deviations of the measured thermal conductivities in the vapour phase from those calculated using the extended corresponding states (ECS) model with default binary interaction parameters (BIPs), as implemented in the software REFPROP 10, were between (−12 and +8) %, while those in the liquid phase were between (−15 and +4) %. The new experimental data were used to tune the BIPs in the ECS model. Significant improvements were observed especially in the liquid phase of the five-component mixture, with the root-mean-square of the relative difference between the experimental data and the model estimation reduced by a factor of nearly three.