Determination of the thermodynamic properties of liquid n-hexadecane from the measurements of the velocity of sound

Abstract

The density, the isobaric expansion coefficient, the specific heats at constant pressure and constant volume, and the isothermal compressibility coefficient of liquid n-hexadecane have been calculated in the range of temperatures 298-433 K and pressures 0.1-140 MPa from the data on the velocity of sound. The coefficients of the Tate equation in the above parametric range have been determined. The table of the thermodynamic properties of n-hexadecane has been presented. Introduction. Normal hexadecane (C 16 ) has been the subject of numerous investigations of thermodynamic properties for years. A considerable volume of experimental data on the thermodynamic properties of n-hexadecane at atmospheric pressure is accumulated at present; also, the results of measurements of the density (1-10) and the veloc- ity of sound (11-15) in the high-pressure range are available. However, there are no experimental data on the density at pressures and temperatures higher than 3.5 MPa and 393 K. It is only in (11) that the velocity of sound has been measured at pressures higher than 70 MPa. In the only experimental investigation (8), the specific heat at constant pressure has been determined at elevated pressures up to 10 MPa and temperatures of 318 to 373 K. The other ther- modynamic properties at elevated pressure have virtually not been studied experimentally. At the same time, such properties as density, heat capacity, and compressibility can be determined by calculation from the experimental de- pendences of the density, specific heat at constant atmospheric pressure, and velocity of sound on temperature and pressure. The accuracy of calculation is comparable with the accuracy of direct measurements of the above quantities. The present work seeks to calculate the thermodynamic properties of liquid n-hexadecane at temperatures of 298 to 433 K and pressures up to 140 MPa. Initial Data. We have used, as the initial data on the velocity of sound, our measurements (4, 15) performed at temperatures of 298 to 433 K and pressures up to 100 MPa with an error of 0.1%, the results of experiments (11) at T = 293-473 K and p = 0.1-140.1 MPa having an accuracy of 0.1%, the data of (12) at T = 303-393 K and p = 0.1-70 MPa with an accuracy of 0.2%, and the results of (16-20) at atmospheric pressure, having an error of less than 0.1%. An analysis of the mentioned works has shown that their results are consistent with a deviation no higher than 0.1-0.2%.