A thermodynamic property formulation for cyclohexane

Abstract

A Ibrmt, lation for the thermodynanlic properties of cyclohexane is presented. The equation is valid for single-phase and saturation states from the melting line to 700 K at pressures up to 80 MPa. It includes aft, ndamental equation explicit in reduced Hel,nholtz energy with independent variables of reduced density and temperature. The functional form and coefficients of the ancillary equations were determined by weighted linear regression analyses of evahmted experimental data. An adaptive regression algorithm was t, sed to determine the final eqt,atinn. To ensure correct thermodynanlic behavior of the Helmholtz energy surface, the coefficients of the fundamental equation were determined with multiproperty fitting. Pressure-density-temperature I P-p-T} and isobaric heat capacity [C~, P-TI data were used to develop the fundamental equation. Saturation P-p-T valt, es, calculated from the estimating functions, were used to enst, re thermodynamic consistency at the wlpor-liquid phase boundary. Separate fnnctions were used for the vapor pressure, satt, rated liquid density, satt, rated vapor density, ideal-gas heat capacity, and pressure on the melting curve. Comp~,risons between experimental dat~, and values calculated using the fundamental equation are given to verify the accuracy of the formulation. The formulation given here may be used to calculate densities within +0.1 °~,b, heat capacities to within +2"/0. and speed of sound to within + I%, except near the critical point.

Measurement and correlation of the (p,ρ,T) relation of liquid cyclohexane, toluene, and ethanol in the temperature range from 233.15 K to 473.15 K at pressures up to 30 MPa for use as density reference liquids

“…This densimeter was developed by Brachthäuser et al [7] in the early 1990s and several improvements were performed by Klimeck et al [8], Claus et al [9], and Schilling et al [4] in subsequent years; the apparatus was briefly described by Wagner et al [10,11] and Wagner and Kleinrahm [12]. The densimeter covers a technically and scientifically important region of the (p, q, T) surface of fluids, namely, a temperature range from 233 K to 523 K, a pressure range from 0.1 MPa to 30 MPa, and a density range from 2 kg Á m À3 to 2000 kg Á m À3 . Since putting this densimeter into operation, comprehensive measurements on argon [8], nitrogen [8], methane [13], carbon dioxide [13], ethylene [9], ethane [9], sulphur hexafluoride [9], n-heptane [4], n-nonane [4], 2,4-dichchlorotoluene [4], and bromobenzene [4] have been performed.…”

“…For comparison, values calculated from the equations of state of Span and Wagner [18] and of Penoncello et al [30] are also plotted in the diagrams. The uncertainty of the equation of Penoncello et al was given to be 0.1%.…”

“…Therefore, it was the aim of a previous project to provide comprehensive and accurate sets of (p, q, T) data, covering a technically important temperature range from 233.15 K to 473.15 K at pressures up to 30 MPa, for four selected density reference liquids. The selected liquids, with densities below and above the density of water, were n-heptane, n-nonane, 2,4-dichlorotoluene, and bromobenzene; their densities at T = 293.…”

“…+, this work; d, Kerimov and Apaev[27]; , Toscani et al[28]; s, Sun et al[29]; 4, Rastorguev et al[25]; -ÁÁ -ÁÁ -, phase boundary (vapour + liquid); ---, values calculated from the equation of state of Span and Wagner[18], and -Á -Á -, values calculated from the equation of state of Penoncello et al[30] are plotted for comparison. The uncertainty of the density measurements of this work was estimated to be 0.015% (k = 2), see Section 3.2.…”

Reference Correlation of the Viscosity of Cyclohexane from the Triple Point to 700 K and up to 110 MPa

“…1 There is thus a need to establish reference values of thermophysical properties of cyclohexane that are both accurate and thermodynamically consistent. For some time, the thermodynamic properties have been described by the existing equation of state (EOS), 2 and their representation is being improved by the development of a new EOS (Ref. 3) that is both more accurate and is valid over a wider range of thermodynamic conditions.…”