Thermodynamic and transport properties of fluids and solids in a Cu–Cl solar hydrogen cycle

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Sustainable methods of clean fuel production are needed in the face of depleting oil reserves and to reduce carbon dioxide emissions. The technology of fuel cells for electricity production or the transport sector is already developed. However, a key missing element is a large-scale economical method of hydrogen production. The Cu–Cl thermochemical cycle is a promising thermochemical cycle to produce hydrogen. This paper focuses on a copper–chlorine (Cu–Cl) cycle and solar hydrogen production technology and describes the models how to calculate thermodynamic and transport properties. This paper discusses the mathematical model for computing the thermodynamic properties for pure substances and their mixtures such as CuCl in the solid phase with an aid of statistical thermodynamics and kinetic theory. The developed mathematical model takes into account vibrations of atoms in molecules and intermolecular forces. This mathematical model can be used for the calculation of thermodynamic properties of polyatomic crystals on the basis of the Einstein and Debye equations. We developed the model in the low-temperature and high-temperature region. All analytical data are compared with experimental results, and these show good agreement. For the transport properties, we have used kinetic theory. For fluid phase, we have calculated viscosity and thermal conductivity on the basis of the Chung–Lee–Starling kinetic model; for the solid phase, we have developed a model for calculations of thermal conductivity on the basis of electron and phonon contributions.