Measurement and correlation of the (p,ρ,T) relation of nitrogen. II. Saturated-liquid and saturated-vapour densities and vapour pressures along the entire coexistence curve

Abstract

Comprehensive and accurate measurements of the saturated-liquid and saturated-vapour densities together with the vapour pressure of pure nitrogen were carried out from the temperature T = 64 K (triple-point temperature Tt = 63.151 K) to 0.022 K below the critical temperature. The typical values of the total uncertainties of the measurements are: Q=2·10 −4 ·ps = for the vapour pressures, Q=1.2·10 −4 ·r'= for the saturated-liquid densities, and Q=3·10 −4 ·r0= for the saturated-vapour densities. The critical constants (Tc = 126.192 K, rc = 313.3 kg·m −3 , pc = 3.3958 MPa) and the isothermal compressibilities in the critical region close to the phase boundary have also been determined from these measurements. Comparisons with experimental results of previous workers are presented. Based on the new values of this work, new correlation equations for the vapour pressure, the saturated-liquid density, and the saturated-vapour density have been established. 7

Measurement and correlation of the (p,ρ,T) relation of nitrogen. I. The homogeneous gas and liquid regions in the temperature range from 66 K to 340 K at pressures up to 12 MPa

“…(1) In this region, small deviations in pressure correspond to relatively large deviations in density. Therefore, the total uncertainty in pressure is more suitable for comparisons than the uncertainty in density.…”

“…Thus, the total relative uncertainty in density of the (p, r, T ) measurements was estimated to be Q(=1.0·10 (1) at densities between 150 kg·m −3 and 450 kg·m −3 (critical density r c = 313.3 kg·m −3 ). (1) In this region, small deviations in pressure correspond to relatively large deviations in density.…”

“…With this new, comprehensive, and consistent set of (p, r, T ) values, covering the most essential parts of the fluid region, the previous data situation has been considerably improved up to a very high level of accuracy. Based on these new (p, r, T ) measurements, including the new measurements on the entire (vapour + liquid) coexistence curve, (1) a new equation of state is being developed by Span et al (2) This equation will describe the entire fluid region of nitrogen in reference quality. (26) , Friedman; (25) w, Straty and Diller; (23) , Zozulya and Blagoi; (24) …”

“…This first paper presents comprehensive (p, r, T ) measurements on pure nitrogen in the homogeneous gas and liquid region, including the largest part of the critical region in the temperature range from 66 K to 340 K at pressures up to 12 MPa. The second paper (1) reports the measurement and correlation of saturated-liquid and saturated-vapour densities, together with the vapour pressure along the entire coexistence curve of nitrogen.…”

The vapour pressure of cyclohexane over the whole fluid range determined using comparative ebulliometry

“…Xiang's (14) form of the equation provided the best fit with (3 + 1) terms but the deviations were strongly systematic with σ {ln( p)} = 9.5 · 10 −7 and deviations as great as 0.05 per cent. The "standard" form of the Wagner equation, (19) which has (4 + 1) adjustable parameters with terms in τ , τ 1.5 , τ 2.5 , and τ 5 fitted the results with σ {ln( p)} = 9.5·10 −7 ; but a significantly better fit, with σ {ln( p)} = 6.2·10 −7 was obtained using an equivalent equation that had terms in τ , τ 1.5 , τ 2 , and τ 4. (6) which was fitted to results at temperatures between 317 K and 378 K.…”