Key words: adiabatic calorimeter, aqueous solution, coexistence curve, critical amplitude, critical point, ethanol, equation of state, isochoric heat capacity, partial molar volume, supercritical water, water
Isochoric heat capacity of binary mixture (0.1446) H2O + (0.8554) C2H5OH have been
measured in the sub- and supercritical conditions with a high-temperature adiabatic
and nearly constant-volume calorimeter. Measurements of CV were performed as a
function of temperature along various near-critical isochores in the range from 234.8
to 391.1 kg·m-3 at temperatures between 439.3 and 521.5 K. In total 16 isochores — 4 vapor and 12 liquid, have been studied. The coverage includes the one- and twophase
regions near the liquid.gas coexistence curve at the sub- and the supercritical parameters of state. The uncertainty of isochoric heat capacity, density, and temperature
measurements was estimated to be less than 2÷3 %, 0.05 %, and 15 mK, respectively. The
values of temperature at coexistence curve, TS(ρ), for each measured densities (isochores)
were determined in calorimetric experiment using a quasi-static thermogram
technique supplemented by the sensor of adiabatic control. Using the measured values
of heat capacity (CVS), temperature (TS) and density
(ρS) on the coexistence curve
near the critical point (CP) the values of the critical parameters (TC,
ρC) for the
mixture (0.1446 m.f.) H2O + (0.8554 m.f) C2H5OH were determined. The measured
values of CV and TS, ρS for the saturated liquid and vapor have been analyzed and
interpreted in terms of extended scaling theory to accurately calculate the values of
the asymptotical critical amplitude (A0± and B0) of the power laws and in theory of
isomorphism of the critical phenomena in binary mixtures. The values of the
characteristic parameters (K1, K2, τ1, τ2, &Delta&rho1, &Delta&rho2)
of the mixture were estimated by using
the critical-curve data for H2O + C2H5OH mixture. It was shown that the heat capacity
of the mixture (o = 0.8554 m.f. C2H5OH or 96% by volume) near the CP behave just
like of CV for pure fluid. The same behavior of CV for this mixture was also predicted
from the analysis of the critical line behavior.