(Pressure, density, temperature) measurements in the critical region of methane

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

“…Hence, the new values presented in this work describe the densities on the saturated-liquid line with an accuracy greater than ten times that of the previous measurements. Figure 8 presents the comparison between experimental saturated-vapour densities and values calculated from the saturated-vapour density equation (4). The r0 measurments of Zozulya and Blagoi (11) for T e 120 K deviate mostly by more than the claimed uncertainty of E6·10 −4 ·r'= at T 1 120 K and E=2.5·10 −3 ·r'= at T 1 126 K, respectively.…”

“…A summary of the selected sets of measurements together with their uncertainties given by the authors is listed in table 3; a comprehensive compilation of experimental ( p, r, T ) values published prior to 1986 is given by Jacobsen et al (22) Figures 6 to 8 show the deviations between the measured values and values calculated from the new correlation equations for the vapour pressure, equation (2), the saturated-liquid density, equation (3), and the saturated-vapour density, equation (4). In the case of very comprehensive sets of mesurements, not all values have been plotted for clarity.…”

“…As well as the saturation densities of methane, (3,4) carbon dioxide, (5) argon, (6) and ethylene, (7) the saturated-vapour densities of nitrogen along the largest part of the coexistence curve were determined in the following way. In the lid of the measuring cell (see the schematic drawing in reference 3), an especially designed small reference cell was included which was filled with nitrogen in such a way that the fluid was in the phase equilibrium (vapour + liquid).…”

“…Figure 5 shows an enlarged section of figure 4 for the temperature range (T c − 3.7 K) E T E T c . Taking into account the reproducibilities of the measured saturation densities, the probable course of r d in the critical region is plotted; the course of r d turns down significantly for temperatures above 125.7 K. Taking into account our experiences based on the investigations of the critical region of methane, (4) carbon dioxide, (5) argon, (6) and ethylene, (7) the illustrated course of r d is the probable one. But it should be noted that either a straight course or a stronger curvature of r d might also be possible.…”

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

“…This densimeter was developed in order to obtain accurate (p, r, T ) measurements of pure fluids in the homogeneous gas and liquid phase including the critical region and, in particular, the entire (vapour + liquid) coexistence curve. Up to now, comprehensive measurements on methane, (3)(4)(5)(6) carbon dioxide, (7)(8)(9) argon, (10,11) and ethylene (12,13) have been carried out successfully; nitrogen, (14) sulphur hexafluoride, (15) and the refrigerants R12 and R22 (16) have been measured in parts of the fluid region. The design of the densimeter was described in detail in previous papers; (3,6) therefore only the measuring principle is briefly explained here.…”