Rabiyat G. Batyrova

Saturated and compressed liquid heat capacity at constant volume for 1-hexyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide)

One-phase liquid and two-phase liquid + vapour equilibrium, isochoric heat capacities () and densities () were measured for ionic liquid (IL) 1-hexyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([C6mim][NTf2]). Measurements were concentrated near the liquid-gas phase transition curve in order to closely observe the changes. The measurements have been made over the temperature range from (330 to 480) K and pressures up to 20 MPa using a high-temperature, high-pressure, nearly constant volume adiabatic calorimeter. The values of temperature at the liquid-gas phase transition curve for each measured isochore (phase transition parameters, ) were obtained by analysis of the quasistatic thermograms (readings of PRT, T− plot) and barograms (readings of the pressure transducer, P− plot). The combined expanded uncertainty of the density, , and isochoric heat capacity, , measurements at the 95% confidence level with a coverage factor of k = 2 is estimated to be 0.06% and 2.0%, respectively.

Chapter 15. Yang–Yang Critical Anomaly

Following a critical review of related research, a method is described to evaluate the Yang–Yang critical anomaly strength function, Rμ(T), from experimental measurements of two-phase liquid and vapor isochoric heat capacities and liquid (V′) and vapor (V″) specific volumes. Direct measurements of internal energy ΔU(V,T) increments and its temperature derivative cV(T,V)=(∂U/∂T)V are made possible with a highly specialized adiabatic calorimeter. The proposed method has been applied to molecular liquids (hydrocarbons, alcohols, water, carbon dioxide, nitrogen tetroxide, etc. to accurately determine the values of the Yang–Yang anomaly strength parameter, Rμ(T=TC)=Rμ0. The calorimeter provides two-phase (liquid and vapor) isochoric heat capacities and liquid and vapor specific volumes (V″, V′) data at saturation near the critical point. These measurements have been used to evaluate the Yang–Yang anomaly strength function, Rμ(T). The values of Rμ(T)=Rμ(TC) (Yang–Yang anomaly strength parameter) derived from the calorimetric measurements for a series of fluids vary from −8 to 0.46, which is consistent with the theoretical prediction of Cerdeirina et al. (C. A. Cerdeirina and G. Orkoulas, M. E. Fisher, Phys. Rev. Lett., 2016, 116, 040601–040605) Near the critical point, the (T,V) variation of Rμ0 characterizes thermodynamic behavior in this region. For the first time, experimental determinations of Rμ0 have validated theoretical predictions by Cerdeirina et al. (C. A. Cerdeirina and G. Orkoulas, M. E. Fisher, Phys. Rev. Lett., 2016, 116, 040601–040605) that were based on the Compressible Cell Gas (CCG) model which obeys the Complete Scaling model with pressure mixing. With a valid Complete Scaling model for the physical nature and details of the temperature and the specific volume dependences of the cV2, we may now separate the measured total two-phase heat capacity into individual contributions of chemical potential cVμ and vapor pressure cVP and further, to illustrate their relative importance as a function of temperature.

Chapter 16:Internal Pressure and Internal Energy of Saturated and Compressed Phases

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 are discussed of a new method of direct internal pressure determination by a calorimetric experiment that involves simultaneous measurement of the thermal pressure coefficient (∂P/∂T)V, i.e. internal pressure Pint=(∂U/∂V)T and heat capacity cV=(∂U/∂T)V. 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.