
N.G. Polikhronidi, R.G. Batyrova, I.M. Abdulagatov
Critical and Supercritical Phenomena in Benzene
Single (\(C_{V_1}\)) and twophase (\(C_{V_2}\)) 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 liquid—gas 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 hightemperature,
highpressure, nearly constantvolume 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 twophase (\(C_{V_2}\))
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 twophase \(C_{V_2}\) data were used to estimate the values of asymmetric parameters
a_{3} («complete» scaling parameter) and b_{2} of the coexistence curve singular diameter.
The experimentally determined asymptotical critical amplitudes \(A^+_0\) and \(B_0\) (fluidspecific
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 vaporpressure \(\frac{d^2P_S}{dT^2}\)
and chemical potential \(\frac{d^2\mu}{dT^2}\)
and to estimate the value of Yang—Yang anomaly strength parameter \(R_\mu\) for benzene. The
contributions of the vaporpressure,
\(C_{VP} = V_CT\frac{d^2P_S}{dT^2}\), and chemical potential,
\(C_{V_\mu} = T\frac{d^2\mu}{dT^2}\), to the measured total
twophase \(C_{V_2}\) were estimated.
Key words: adiabatic calorimeter, asymmetryparameter, benzene, critical amplitude, critical point, isochoric heat capacity, Yang—Yang anomaly parameter
RIS
