Thermal properties of compressed liquids: Experimental determination via an indirect acoustic technique and modeling using the volume fluctuations approach

During this research, we present an acoustic method used for determination of the thermal properties, such as the thermal expansivities and heat capacities from 293.15 K to 313.15 K of compressed liquid α,ω-dibromo-alkanes. A designed in our lab experimental apparatus has been used to measure the speed of sound in liquid dibromo-alkanes on five isotherms between 293 and 313 K and at pressures up to 100 MPa. The measurement technique is based on a traditional single-reflector pulse-echo method with a single piezo-ceramic transducer. The speed of sound data were combined with values of density and isobaric heat capacity along one isobar at atmospheric pressure to calculate the density, thermal expansivity and heat capacity over the whole temperature and pressure range by means of the acoustic numerical method. To explore the possibility of analytical description of the data, we propose the method based on the continuation of inverse reduced volume fluctuations into a single-phase region. The resulting expression contains two parameters characterizing the inverse volume fluctuations in the liquid and the isobaric heat capacity along the referent line and allows to predict the density and the isobaric heat capacity for the whole studied region with the accuracy, which does not exceed 0.1% and 1% correspondingly. (authors)