Simultaneous Viscosity−Density Measurements on Ethane and Propane over a Wide Range of Temperature and Pressure Including the Near-Critical Region

Abstract

An apparatus combining a vibrating-wire viscometer and a single-sinker densimeter was used to provide accurate ηρpT data for four isotherms on ethane at (293.15, 307.15 [ethane 3.5 and 5.0], and 423.15) K and five isotherms on propane at (273.15, 298.15, 366.15, 373.15, and 423.15) K. The maximum pressure was chosen to be about 95 % of the saturated vapor pressure for the subcritical isotherms and 30 MPa at maximum for the supercritical isotherms. The relative uncertainty in the density is estimated to be less than ± 0.1 %, except for the low-density range. Near the critical region, allocation errors for temperature and pressure have a significant impact on the uncertainty of the experimental densities. The density data agree within ± 0.1 %, when comparing them with values calculated from the equations of state by Bücker and Wagner (2006) for ethane and by Lemmon et al. (2009) for propane, excluding the low-density and the near-critical regions. The near-critical isotherms at 307.15 K for ethane and at 373.15 K for propane reveal differences of +2.1 % and +1.2 %, respectively, in accordance with the estimated maximum total uncertainties of the experimental pρT data for these isotherms. The viscosity measurements are characterized by a relative uncertainty of ± (0.25 to 0.3) %, only increased by 0.04 % in the near-critical region due to the allocation errors arising from the temperature and density measurements. The new viscosity data and additionally re-evaluated earlier data of our group are compared with the viscosity surface correlations by Hendl et al. (1994) for ethane and by Scalabrin et al. (2006) for propane as well as with selected experimental data for the low-density region. For ethane, the maximum deviations of the new data exceed the stated uncertainty of ± 2.5 % for the viscosity surface correlation. For propane, the deviations do not exceed ± 0.7 %, except for the near-critical isotherm at 373.15 K. The effect of the critical enhancement became evident for the near-critical isotherms, about 2 % for ethane at 307.15 K and about 1 % for propane at 373.15 K. The new viscosity data should be used to improve the viscosity surface correlations available in the literature.

Intermolecular potential energy surface and thermophysical properties of propane

“…5, the viscosity values obtained using the adjusted potential function, η adj , are compared with those obtained using the unadjusted one, η unadj , with the experimental data reported by Seibt et al, 60 sets are the most accurate to date for propane in the dilute gas phase with an uncertainty of only 0.3%. They are mutually consistent and extend over the whole range of temperatures at which experimental data for the gas phase are available (273 K to 625 K).…”

Viscosity and density of isobutane measured in wide ranges of temperature and pressure including the near‐critical region

“…In principle, the impact of the uncertainties of Δ T and Δ p is minor in wide thermodynamic regions due to its small values, as proven by Seibt et al for the measurements on helium and nitrogen, for which the total uncertainty of the density determination was for . But near the critical region, a significant influence on the uncertainty of the density follows from the distinctly increased values for the partial derivatives ( ∂ρ∕∂T ) p and ( ∂ρ∕∂p ) T , as illustrated by Seibt et al for ethane and propane.…”

“…Seibt et al demonstrated the performance of the combined viscometer‐densimeter on the basis of measurements on helium and nitrogen. In addition, they carried out a profound error analysis, which was extended to the somewhat more challenging situation of measurements on fluids like ethane and propane, particularly with regard to the near‐critical region …”

“…Recently, Seibt et al published the results of density and viscosity measurements on ethane and propane. In addition, Herrmann et al are preparing a report with new data of the density and viscosity for normal butane determined with the measuring apparatus under discussion, too.…”

Update: Reference Correlation for the Viscosity of Ethane [J. Phys. Chem. Ref. Data 44, 043101 (2015)]

“…and of Seibt et al24 are situated, an expanded uncertainty of 1.5% is assumed. In the near-critical region 1.001 < T /T c < 1.010 and 0.8 < ρ/ρ c < 1.2, the expanded uncertainty is estimated to be 3.0%, increasing with decreasing temperature.…”