Thermophysical properties of industrial fluids at high pressures from sound speed and density measurements

• Main Author: Lin, Chih-wei
• Other Authors: Trusler, Martin; Maitland, Geoffrey
• Published: Imperial College London 2013
• Subjects: 660
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.650610

The objective of this project was to provide reliable thermophysical property data, mainly density and sound speed, for industrial and academic use. This thesis investigates in detail the speed of sound and density of several industrial fluids at pressure up to 400 MPa and temperature from 248 K to 473 K. The experimental technique used was based on an ultrasonic cell implementing a double-path pulse-echo method with an ultrasound transducer placed between two unequally-spaced reflectors. The cell was calibrated in water at T = 298.15 K and p = 1 MPa against the speed of sound given by the 1995 equation-of-state formulation of the International Association for the Properties of Water and Steam (IAPWS-95) which, for that state point, has an uncertainty of ± 0.005 %. In this thesis, the ultrasonic cell was validated by water measurement over a wide range of temperature and pressure and was shown to have an uncertainty of ± 0.03 %. The uncertainty of the sound speed measurement for other fluids in general is less than 0.1 %. In addition, a densimeter was also used. The measured sound speed and density combined with the heat capacity can be used to develop advanced analytical equations of state and derive all of the thermodynamic properties for key mixtures by numerical-integration algorithms. All the thermophysical properties measured in this thesis were correlated into equations as a function of temperature and pressure. The correlated parameters were calculated by regression analysis in Microsoft Excel. The regression function is used to minimize the sum of squares of error of all the data which needs to be fitted into an equation. In our regression analysis from Excel, the objective was to fit the data to within the target uncertainty using the number of parameters required. Several working fluids were studied: pure water, hexafluoropropene (HFP), trifluoro-3-(trifluoromethyl)oxirane (common name hexafluoropropylene oxide, HFPO), carbon dioxide, and carbon dioxide + propane mixtures. The results extend our understanding of the thermophysical properties of these key industrial fluids and may lead to the development of improved thermodynamic models for application in air conditioning, refrigeration system and carbon capture and storage applications.