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

Abstract

Measurement and correlation of the (p, r, 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 P. Nowak, R. Kleinrahm, and W. Wagner

Apparatus for accurate density measurements of fluids based on a magnetic suspension balance

“…Our data agree well with the literature data, and they exhibit considerably less scatter than the data of Ben et al [11] and Ejaz S. [12]. Ben et al [11]; +, Duschek et al [8]; ×,Nowak et al [9]; ,Ejaz S. [12].…”

“…FIGURE 4 shows the comparison of the present experimental results with the literature data which overlap our temperature and pressure range. The data from Duschek et al [8] and Nowak et al [9] were measured by a two-sinker densimeter, and were used to fit the equation of Span et al [7]. The literature data [12] were measured by a single-sinker densimeter.…”

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

“…These pressure differences, ranging from about 2.5 kPa to 0.2 kPa, were achieved by setting different filling levels above the sinkers. Then, the saturated-liquid density was determined by extrapolating these isothermal liquid densities to ( p − p s ) = 0, again by non-linearly fitting equation (1) to the ( p, r, T ) values.…”

“…In the critical region, however, the measurements were carried out in a way similar to FIGURE 1. Schematic illustration of the new procedure to determine the saturated-vapour densities very close (in this case at T = 126.170 K) to the critical temperature Tc = 126.192 K. A: filling of the measuring cell; B: Phase equilibrium (vapour + liquid) in the measuring cell; q, (p, r, T) measurements in the homogeneous gas region close to the phase boundary (vapour + liquid); w, (p, r, T) measurements in the homogeneous gas region extremely close to the phase boundary (vapour + liquid); these values were measured in a quasi-equilibrium state while the fluid in the measuring cell was slowly condensing; = w, ( p, r, T ) value measured after phase equilibrium (vapour + liquid) had been achieved in the measuring cell; (, saturated-vapour density r0 determined by extrapolating all measured ( p, r, T ) values in the gas-phase to ( p − ps ) = 0 by means of equation (1). Also, Dphyd corresponds to the hydrostatic pressure of the gas column between the phase boundary (vapour + liquid) a few mm above the bottom of the measuring cell and the reference height of the two sinkers (see figure 1 in reference 3); this distance only amounts to a few cm and is very well known.…”

“…The first part, (1) where the reasons for these new comprehensive measurements are given, describes the experimental results 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. This second paper presents the measurements of the saturated-liquid and the saturated-vapour densities and the vapour pressure of nitrogen along the entire coexistence curve from T = 64 K (triple-point temperature T t = 63.151 K) up to slightly below the critical temperature T c = 126.192 K. The aim of this work was to provide a comprehensive and reliable set of measurements, which accurately describes the coexistence curve and allows the establishment of new correlation equations for the thermal saturation properties.…”