Speed of sound measurements in supercooled water at temperatures between (254.65 and 273.15) K and at pressures up to 190 MPa

Experimental speed of sound measurements in supercooled ordinary water (freshly double-distilled) at temperatures between (254.65 and 273.15) K and for pressures up to 190 MPa were performed and reported. During the measurements cycles, some pre-freezing processes and phase transitions in the water were observed and reported as a contribution to further investigations for understanding of the process at a molecular level. Our 35 speed of sound results for the liquid state metastable with respect to Ice Ih are the first such results measured with the double pulse-echo technique. The estimated relative expanded uncertainty ( k = 2 ) is better than 0.02% for pressures up to 10 MPa and better than 0.05% in the higher pressure range. The obtained speed of sound data have been compared, in stable states, with values predicted by the reference equation for pure water (IAPWS-95 formulation) of Wagner and Pruß and, in metastable state, with those calculated from the Equation of state (EoS) for supercooled water by Holten et al. All relative deviations are within the uncertainties stated for the equations. The comparison of the obtained results with the most recent speed of sound data by Lin and Trusler and by El Hawary and Meier shows that all the results are consistent and the agreement is within the declared uncertainties. • High pressure speed of sound (SoS) experimental measurements in supercooled water. • For the first time, metastable SoS values obtained up to 190 MPa and down to 254 K. • Some pre-freezing processes and phase transitions in water have been observed.