Relationship between the speed of sound and temperature for binary mixtures of hydrofluorocarbons (R-125, R-152a, or R-227ea) with hydrofluoroolefins (R-1234yf or R-1234ze(E)) along several pseudo-isochores. The systems and molar compositions are (a) R-125/1234yf (0.33351/0.66649), (b) R-125/1234yf (0.66643/0.33357), (c) R-1234yf/152a (0.33342/0.66658), (d) R-1234yf/152a (0.66526/0.33474), (e) R-1234ze(E)/227ea (0.33265/0.66735), and (f) R-1234ze(E)/227ea (0.66803/0.33197). Symbols represent experimental data points while lines represent predictions with REFPROP [6] along the nominal density; for clarity, only every other isochore is shown