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2019, N2, pp. 73-104

N.G. Polikhronidi, R.G. Batyrova, I.M. Abdulagatov

Critical and Supercritical Phenomena in Benzene

Single- (\(C_{V_1}\)) and two-phase (\(C_{V_2}\)) isochoric heat capacities, densities (\(\rho_S\)), and phasetransition temperatures (\(T_S\)) of benzene were measured in the critical and supercritical regions. Measurements were made in the immediate vicinity of the liquidgas phase transition and the critical point in order to accurately determine the phase transition properties (\(T_S\), \(\rho_S\), \(C_{V_1}\) and \(C_{V_2}\)). The measurements have been made over the temperature range from 347 to 616 K for 6 liquid and 5 vapor isochores between 265 and 653 kg · m-3 at pressures up to 7,5 MPa. The measurements were performed using a high-temperature, high-pressure, nearly constant-volume adiabatic calorimeter. The combined expanded uncertainty of the measurements of density, temperature, and isochoric heat capacity, \(C_{V}\), at the 95 % confidence level with a coverage factor of k = 2 is estimated to be 0,15%, 15 mK, and 3,0 %, respectively. The measured single- (\(C_{V_1}\)) and two-phase (\(C_{V_2}\)) isochoric heat capacities along the critical isochore and the saturated liquid (\(\rho'_S\)) and vapor (\(\rho''_S\)) densities near the critical point were used to accurately estimate the theoretically meaningful asymptotic critical amplitudes (\(A^+_0\) and \(B_0\)) and related amplitudes for other properties (\(\Gamma^+_0\), \(D_0\), \(\xi_0\)) as well as their universal relations, \(A^+_0/A^-_0\), \(A^+_0\Gamma^+_0B^2_0\), \(\alpha A^+_0\Gamma^+_0B^{-2}_0\), \(\xi_0\left(\frac{\alpha A^+_0}{\nu_C}\right)^{1/3}\). Saturated liquid and vapor densities together with measured two-phase \(C_{V_2}\) data were used to estimate the values of asymmetric parameters a3 (complete scaling parameter) and b2 of the coexistence curve singular diameter. The experimentally determined asymptotical critical amplitudes \(A^+_0\) and \(B_0\) (fluid-specific parameters) were used to check and confirm the predictive capability of the universal correlation in terms of their dependence on the acentric factor ω, based on \(C_{V_2}\) as a function of the specific volume Valong various isotherms were used to calculate second temperature derivatives of the vapor-pressure \(\frac{d^2P_S}{dT^2}\) and chemical potential \(\frac{d^2\mu}{dT^2}\) and to estimate the value of YangYang anomaly strength parameter \(R_\mu\) for benzene. The contributions of the vapor-pressure, \(C_{VP} = V_CT\frac{d^2P_S}{dT^2}\), and chemical potential, \(C_{V_\mu} = -T\frac{d^2\mu}{dT^2}\), to the measured total two-phase \(C_{V_2}\) were estimated.

Key words: adiabatic calorimeter, asymmetryparameter, benzene, critical amplitude, critical point, isochoric heat capacity, YangYang anomaly parameter

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