Speed of sound in pure water at temperatures between 274 and 394 K and at pressures up to 90 MPa

A newly designed experimental apparatus has been used to measure the speed of sound u in high-purity water on nine isotherms between 274 and 394 K and at pressures up to 90 MPa. The measurement technique is based on a traditional double-reflector pulse-echo method with a single piezoceramic transducer placed at unequal distances from two stainless steel reflectors. The transit times of an acoustic pulse are measured at a high sampling rate by a digital oscilloscope. The distances between the transducer and the reflectors were obtained at ambient temperature and pressure by direct measurements with a coordinate measuring machine. The speeds of sound are subject to an overall estimated uncertainty of 0.05 %. The acoustic data were combined with available values of density rho and isobaric heat capacity c(p) along one isobar at atmospheric pressure to calculate the same quantities over the whole temperature and pressure range by means of a numerical integration technique. These results were compared with those calculated from the IAPWS-95 formulation with corresponding relative deviations which are within 0.1%.