A novel application of Recursive Equation Method for determining thermodynamic properties of single phase fluids from density and speed-of-sound measurements

The determination of thermal quantities from mechanical properties is still a challenge in the thermodynamic field.In this work, the authors suggest a preliminary numerical calculation which allows to determine the constant pressure specific heat capacity, starting from density and speed-of-sound experimental values, as input data.This method is a variant of the well characterized Recursive Equation Method (REM) [1] and permits to develop empirical equations of state for single phase fluids. In particular, the isobaric specific heat capacity has been obtained, in a wide range of temperatures and pressures, for pure water, n-nonane, n-undecane, and rapeseed oil methyl ester. The results have been compared with those available in the literature, when it was possible. Moreover, the typical uncertainty of heat capacity has been estimated to be in the order of 1.5%; however it has been shown that it can be improved when proper distributions of the experimental points are available.

► A novel method for calculating the isobaric specific heat capacity is presented.
► Heat capacity (CpCp) was determined only by speed-of-sound and density measurements.
► (CpCp) temperature dependence has been related to speed-of-sound by a new expression.
► Heat capacity for water, nonane, undecane, and rapeseed oil methyl ester are obtained.