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Chemical Physics Letters, 2012
Using adiabatic scanning calorimetry, we have found the first experimental evidence of the Yang-Yang anomaly in liquid-liquid criticality from high-resolution two-phase isobaric heat capacity measurements for the binary mixture 3-pentanol + nitromethane. The results suggest a rather strong effect. The critical amplitude of the partial molar heat capacity is higher for the component with larger molecular volume, in accordance with the predictions of complete scaling as obtained from the customary observed asymmetric behavior of the coexistence-curve diameter. This consolidates complete scaling as the true formulation of fluid-fluid criticality. The quantitative analysis indicates that molecular size is not the only microscopic factor at play in asymmetric liquid-liquid criticality.
A new relation between the internal pressure and isochoric heat capacity jump of liquids along the coexistence curve near the critical point was found. Our previously reported one-and two-phase isochoric heat capacities and specific volumes at saturation were used to calculate internal pressure of molecular liquids (water, carbon dioxide, alcohols, n-alkanes, DEE, etc.).The internal pressure derived from the calorimetric measurements was compared with the values calculated from the reference (NIST, REFPROP) and crossover equations of state. Locus of the isothermal and isochoric internal pressure maxima and minima was studied using calorimetric data and the reference and crossover equations of state near the critical point. The maximum of the internal pressure of light and heavy water around the temperature of 460 K along the liquid saturation curve was found. We also found very simple relation between the internal pressure, ΔP int sat , and isochoric heat capacity, ΔC V , jumps near the critical point.
New technique of the YangeYang critical anomaly strength function, R m (T), determination from direct two-phase liquid (C 0 V2) and vapor (C 00 V2) isochoric heat capacity and liquid (V 0) and vapor (V 00) specific volumes measurements at the saturation have been developed. Our measured two-phase (liquid and vapor) isochoric heat capacities (C 00 V2 ; C 0 V2) and liquid and vapor specific volumes (V 00 ,V 0) data at saturation near the critical point have been used to accurately determine the YangeYang anomaly strength parameter, R m (T ¼ T c) ¼ R m0 , for various molecular liquids. The derived values of the YangeYang critical anomaly strength function show trend to negative infinity near the critical point as predicted by the theory (Cerdeiri~ na et al., 2015) based on compressible cell gas (CCG) model that obey complete scaling with pressure mixing. The physical nature and details of the temperature and the specific volume dependences of the C V2 and correct estimations of the contributions of various terms (chemical potential C Vm and vapor-pressure C VP) to the measured total two-phase heat capacity were discussed in terms of the YangeYang anomaly parameter.
Isochoric Heat Capacity Measurements for Light and Heavy Water Near the Critical Point
International Journal of Thermophysics
The isochoric heat capacity of equimolar 0.5H2O + 0.5D2O mixture was measured in the temperature range from 391 to 655 K, at near-critical liquid and vapor densities between 274.05 and 385.36 kg·m -3 using a high-temperature and high-pressure nearly constant volume adiabatic calorimeter. The measurements were performed in the one-and two-phase regions including coexistence curve. Uncertainties of the measurements are estimated to be within 2 %. The liquid and vapor one-and two-phase isochoric heat capacities, temperatures, and densities at saturation were extracted from experimental data for each measured isochore. The critical temperature and the critical density for equimolar 0.5H2O + 0.5D2O mixture are derived from isochoric heat capacity measurements using method of quasi-static thermograms. The results of measurements were compared with crossover equation of state for H2O + D2O mixture. The near-critical isochoric heat capacity behavior for 0.5H2O + 0.5D2O mixture is studied using the principle of isomorphism of the critical phenomena. The experimental isochoric heat capacity of 0.5H2O + 0.5D2O mixture exhibit a weak singularity like for the pure components. To confirm reliability of the measured pure light water isochoric heat capacity was measured for the critical isochore 321.99 kg·m -3 in the two-and one phase regions. The result for phase transition temperature (the critical temperature, TC=647.1040.003 K) show excelent agreements with IAPWS-95 excepted values (TC=647.096 K) of the critical temperature. KEY WORDS: adiabatic calorimeter; coexistence curve; critical point; crossover equation of state; heavy water; isochoric heat capacity; light water.
International Journal of Thermophysics, 2007
Isochoric heat-capacity measurements for pure methanol are presented as a function of temperature at fixed densities between 136 and 750 kg·m −3 . The measurements cover a range of temperatures from 300 to 556 K. The coverage includes the one-and two-phase regions, the coexistence curve, the near-critical, and the supercritical regions. A high-temperature, high-pressure, adiabatic, and nearly constant-volume calorimeter was used for the measurements. Uncertainties of the heat-capacity measurements are estimated to be 2-3% depending on the experimental density and temperature. Temperatures at saturation, T S (ρ), for each measured density (isochore) were measured using a quasi-static thermogram technique. The uncertainty of the phase-transition temperature measurements is 0.02 K. The critical temperature and the critical density for pure methanol were extracted from the saturated data (T S , ρ S ) near the critical point. For one near-critical isochore (398.92 kg·m −3 ), the measurements were performed in both cooling and heating regimes to estimate the effect of thermal decomposition (chemical reaction) on the heat capacity and phase-transition properties of methanol. The measured values of C V and saturated densities (T S , ρ S ) for methanol were compared with values calculated from various multiparametric equations of state (EOS) (IUPAC, Bender-type, polynomial-type, and nonanalytical-type), scaling-type (crossover) EOS, and various correlations. The measured C V data have been analyzed and interpreted in terms of extended scaling equations for 163 0195-928X/07/0200-0163/0 © 2007 Springer Science+Business Media, LLC 164 Polikhronidi et al.
The Journal of …, 2007
The predictions from a recently reported (J. Chem. Phys. 2004, 120, 6648) two-state association model (TSAM) have been tested against experimental data. The temperature, T, and pressure, p, dependence of the isobaric heat capacity, C p , for three pure alcohols and the temperature dependence at atmospheric pressure of the excess heat capacity, C p E , for four alcohol + ester mixtures have been measured. The branched alcohols were 3-pentanol, 3-methyl-3-pentanol, and 3-ethyl-3-pentanol, and the mixtures were 1-butanol and 3-methyl-3pentanol mixed with propyl acetate and with butyl formate. These data, together with literature data for alcohol + n-alkane and alcohol + toluene mixtures, have been analyzed using the TSAM. The model, originally formulated for the C p of pure liquids, has been extended here to account for the C p E of mixtures. To evaluate its performance, quantum mechanical ab initio calculations for the H-bond energy, which is one of the model parameters, were performed. The effect of pressure on C p for pure liquids was elucidated, and the variety of C p E (T) behaviors was rationalized. Furthermore, from the C p data at various pressures, the behavior of the volume temperature derivative, (∂V/∂T) p , was inferred, with the existence of a (∂V/∂T) p versus T maximum for pure associated liquids such as the branched alcohols being predicted. It is concluded that the TSAM captures the essential elements determining the behavior of the heat capacity for pure liquids and mixtures, providing insight into the macroscopic manifestation of the association phenomena occurring at the molecular level. * Corresponding authors. Phone: (34) (988) 387217 (C.A.C.); (52) (55) 56223520 (M.C.). Fax: (34) (988) 387001 (C.A.C.); (52) (55) 56223521 (M.C.).
Thermodynamic consistency near the liquid-liquid critical point
The Journal of chemical …, 2009
The thermodynamic consistency of the isobaric heat capacity per unit volume at constant composition C p,x and the density near the liquid-liquid critical point is studied in detail. To this end, C p,x ͑T͒, ͑T͒, and the slope of the critical line ͑dT / dp͒ c for five binary mixtures composed by 1-nitropropane and an alkane were analyzed. Both C p,x ͑T͒ and ͑T͒ data were measured along various quasicritical isopleths with a view to evaluate the effect of the uncertainty in the critical composition value on the corresponding critical amplitudes. By adopting the traditionally employed strategies for data treatment, consistency within 0.01 K MPa −1 ͑or 8%͒ is attained, thereby largely improving the majority of previous results. From temperature range shrinking fits and fits in which higher-order terms in the theoretical expressions for C p,x ͑T͒ and ͑T͒ are included, we conclude that discrepancies come mainly from inherent difficulties in determining the critical anomaly of accurately: specifically, to get full consistency, higher-order terms in ͑T͒ are needed; however, the various contributions at play cannot be separated unambiguously. As a consequence, the use of C p,x ͑T͒ and ͑dT / dp͒ c for predicting the behavior of ͑T͒ at near criticality appears to be the best choice at the actual experimental resolution levels. Furthermore, the reasonably good thermodynamic consistency being encountered confirms that previous arguments appealing to the inadequacy of the theoretical expression relating C p,x and for describing data in the experimentally accessible region must be fairly rejected.
Heat and Mass Transfer, 1997
Flow and convective heat transfer are conventionally described by nondimensional numbers to reduce the amount of variables and to identify physically similar conditions. The description by nondimensional numbers based on representative values of fluid properties may fail or be difficult to handle, if properties vary strongly in the physical domain considered, if flow and heat transfer depend on many fluid-properties, e.g. for heat transfer with phase transition, or if fluid properties are not known. For such cases the concept of extended thermodynamic similarity (ETS) is suggested to predict flow and heat transfer phenomena in arbitrary fluids from measurements or numerical simulations for representative fluids. (ETS) applies the principle of corresponding states to other fluid properties than properties of state and to physical quantities depending on fluid properties, but takes into account for nonsimilar, fluid-specific features characterized by nondimensional fluid-specific parameters. For ETS-considerations physical quantities are scaled by critical data or by fluid-specific scaling units being power products of critical data, universal constants and molar mass. Scaled quantities are correlated with reduced properties of state and fluid-specific parameters. In the present study the ETS concept is used to correlate data of boiling critical heat flux obtained from the Zuberand-Kutadeladze equation with fluid-specific parameters for various fluids. A correlation of only one fluid specific parameter, the vapor-pressure parameter , is sufficient to predict critical heat flux values for the reference state p 3 0 0:1 with a standard deviation of only 4.2%. The correlation is expected to be valid for other fluids, of which the fluid are poorly known. The same correlation modified by introducing a function of reduced pressure represents experimental data with a standard deviation of only 24%. Erweiterte thermodynamische Ähnlichkeit zur Voraussage des Wärmeüberganges in wenig bekannten Fluiden, angewendet auf die kritische Wärmestromdichte beim Sieden
The Journal of Chemical Thermodynamics, 2008
A new method for determining isobaric thermal expansivity of liquids as a function of temperature and pressure through calorimetric measurements against pressure is described. It is based on a previously reported measurement technique, but due to the different kind of calorimeter and experimental set up, a new calibration procedure was developed. Two isobaric thermal expansivity standards are needed; in this work, with a view on the quality of the available literature data, hexane and water are chosen. The measurements were carried out in the temperature and pressure intervals (278.15 to 348.15) K and (0.5 to 55) MPa for a set of liquids, and experimental values are compared with the available literature data in order to evaluate the precision of the experimental procedure. The analysis of the results reveals that the proposed methodology is highly accurate for isobaric thermal expansivity determination, and it allows obtaining a precise characterisation of the temperature and pressure dependence of this thermodynamic coefficient.