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Internal Pressure and Internal Energy of Saturated and Compressed Phases



Joe W. Magee, Ilmutdin Abdulagatov, Nikolai Polikhronidi, Rabiyat Batyrova


Following a critical review of the field, a comprehensive analysis is provided of the internal pressure of fluids and fluid mixtures and its determination in a wide range of temperatures and pressures. Further, the physical meaning is discussed of the internal pressure along with its microscopic interpretation by means of calorimetric experiments. A new relation is explored between the internal pressure and the isochoric heat capacity jump along the coexistence curve near the critical point. Various methods (direct and indirect) of internal pressure determination are discussed. Relationships are studied between the internal pressure and key thermodynamic properties, namely expansion coefficient, isothermal compressibility, speed of sound, enthalpy increments, and viscosity. Loci of isothermal, isobaric, and isochoric internal pressure maxima and minima were examined in addition to the locus of zero internal pressure. Details were discussed of the new method of direct internal pressure determination by a calorimetric experiment that involves simultaneous measurement of the thermal pressure coefficient , i.e. internal pressure and heat capacity . The chapter provides a detailed discussion of the internal pressure evaluated with equations of state (EOS) including van der Waals, cubic, virial, scaling and other theoretically-based EOS. The dependence of internal pressure on external pressure, temperature and density for pure fluids, and on concentration for binary mixtures is considered on the basis of reference (NIST REFPROP) and crossover EOS. The asymptotic scaling behavior of the internal pressure near the critical point was studied using a scaling type EOS.
Enthalpy and Internal Energy: Liquids, Solutions and Vapours
Publisher Info
Royal Society of Chemistry, Cambridge, -1


Coexistence curve, Critical point, Equation of state, Internal pressure, Internal energy, Isochoric heat capacity, Thermal pressure coefficient, Vapor pressure


Magee, J. , Abdulagatov, I. , Polikhronidi, N. and Batyrova, R. (2017), Internal Pressure and Internal Energy of Saturated and Compressed Phases, Enthalpy and Internal Energy: Liquids, Solutions and Vapours, Royal Society of Chemistry, Cambridge, -1, [online], (Accessed April 15, 2024)
Created September 12, 2017, Updated June 2, 2021