Single-sinker Magnetic Suspension Densimeter Research Articles

Density Measurements of an Air-Like Binary Mixture over the\xa0Temperature Range from 100\xa0K to 298.15\xa0K at Pressures up to 8.0\xa0MPa

Densities of an air-like binary mixture (0.2094 oxygen + 0.7906 nitrogen, mole fractions) were measured along six isotherms over the temperature range from 100 K to 298.15 K at pressures up to 8.0 MPa, using a low-temperature single-sinker magnetic suspension densimeter. The measurements were carried out at T = (100, 115, and 130) K in the homogeneous gas and liquid region, and at T = (145, 220, and 298.15) K in the supercritical region (critical temperature TC = 132.35 K); in total, we present results for 52 (T, p) state points. The relative expanded combined uncertainty (k = 2) of the experimental densities was estimated to be between 0.03 % and 0.13 %, except for four values near the critical point. The largest error is caused by the magnetic suspension coupling in combination with the mixture component oxygen, which is strongly paramagnetic; the resulting force transmission error is up to 1.1 %. However, this error can be corrected with a proven correction model to an uncertainty contribution in density of less than 0.044 %. Due to a supercritical liquefaction procedure and the integration of a special VLE-cell, it was possible to measure densities in the homogeneous liquid phase without changing the composition of the liquefied mixture. Moreover, saturated liquid and saturated vapor densities were determined at T = (100, 115, and 130) K by extrapolation of the experimental single-phase densities to the saturation pressure. The new experimental results were compared with the mixture model of Lemmon et al. for the system (nitrogen + argon + oxygen) and the GERG-2008 equation of state.

Density Measurements of (0.99 Methane\u2009+\u20090.01 Butane) and (0.98 Methane\u2009+\u20090.02 Isopentane) over the Temperature Range from (100 to 160) K at Pressures up to 10.8\xa0MPa

Densities of two methane-rich binary mixtures were measured in the homogeneous liquid and the supercritical region at temperatures between (100 and 160) K using a low-temperature single-sinker magnetic-suspension densimeter. For each mixture, four isotherms were studied over the pressure range from (0.3 to 10.8) MPa. Molar compositions of the gravimetrically prepared methane-rich binary mixtures were approximately 0.01 butane and 0.02 isopentane, respectively, with the balance being methane. The relative expanded combined uncertainty (k = 2) of the experimental densities was estimated to be in the range of (0.02 to 0.06) %. Due to a supercritical liquefaction procedure and the integration of a special VLE-cell, it was possible to measure densities in the homogeneous liquid phase without changing the composition of the liquefied mixture. Based on the supercritical liquefaction procedure, a new time-saving measurement procedure was developed and applied. Moreover, saturated-liquid densities were determined by extrapolation of the experimental single-phase liquid densities to the vapor pressure calculated with an equation of state (EOS); here, the relative expanded combined uncertainty (k = 2) is less than 0.05 % in most cases. The new experimental results were compared with the GERG-2008 equation of state, the EOS-LNG and the enhanced revised Klosek and McKinley (ERKM) method.

Determination of the force transmission error in a single-sinker magnetic suspension densimeter due to the fluid-specific effect and its correction for use with gas mixtures containing oxygen

Density measurements from single-sinker magnetic suspension densimeters need to be corrected to compensate for the magnetic effects of the measuring cell materials and the fluid on the coupling transmission system. While the magnetic effect of the densimeter materials can be easily determined, the fluid effect requires the calculation of an apparatus-specific constant, ερ. In this work, the apparatus-specific constant of the single-sinker magnetic suspension densimeter at the University of Valladolid has been determined by using two alternative methods. The first method, which uses density data for the same fluid and conditions and different sinkers, yielded a value of ερ = 4.6·10−5. The second method, obtained from measurements with pure oxygen, yielded a value of ερ = 8.822·10−5. The second value is considered as more reliable, as the first method presents inherent limitations in this case.

Gaseous PvTx measurements of HFO-1234yf + HFC-32 binary mixture by single-sinker magnetic suspension densimeter

The measurements of PvTx properties of HFO-1234yf/HFC-32 binary mixture in the vapor phase were carried out by single-sinker magnetic suspension densimeter in the range of temperatures from 279.8 to 347.9 K, pressures from 0.10 to 2.66 MPa, densities from 2.30 to 66.02 kg m−3, and mole fractions of HFO-1234yf from 0.062 to 0.610. The experimental expanded uncertainty (k = 2) in temperature, pressure, and mole fraction are estimated to be 12 mK, 1.4 kPa, and 0.0002, respectively. The relative expanded uncertainty (k = 2) in density is 0.029–0.104%. On the basis of the experimental PvTx properties data, a truncated virial equation of state was developed for the binary HFO-1234yf/HFC-32 system. It reproduces the experimental values with average absolute deviations of 0.10% and 0.11% for pressure and density, respectively.

Density measurements of liquefied natural gas (LNG) over the temperature range from (105 to 135) K at pressures up to 8.9 MPa

The (p, ρ, T, x) behaviour of five different synthetic liquefied natural gas (LNG) mixtures was investigated over the temperature range from (105 to 135)K at pressures up to 8.9MPa utilizing a single-sinker magnetic suspension densimeter for cryogenic liquid mixtures. Due to the supercritical liquefaction procedure and the integration of a special VLE-cell, it was possible to measure densities in the homogeneous liquid phase of LNG without changing the composition. The mixtures were prepared gravimetrically and then analysed by gas chromatography according to highest metrological standards. The relative combined expanded uncertainty (k=2) in density considering all effects, including the uncertainty in composition, was approximately 0.044% for all measurements. Comparisons of the new experimental data to the GERG-2008 equation of state for natural gas mixtures revealed clear and systematic deviations up to 0.22%. The reported uncertainty for the GERG-2008 equation is (0.1 to 0.5)% for the conditions considered, thus, all measured densities are represented well within this uncertainty range. Comparisons to density calculation methods often used in LNG industry, such as the revised Klosek and McKinley method as well as the COSTALD correlation, revealed that the quality of the calculations clearly depends on the pressure range and on the composition of the LNG mixture.

Accurate Density Measurements on Ternary Mixtures (Carbon Dioxide + Nitrogen + Argon) at Temperatures from (323.15 to 423.15) K with Pressures from (3 to 31) MPa using a Single-Sinker Densimeter

The densities of two ternary mixtures (0.900 carbon dioxide + 0.050 nitrogen + 0.050 argon and 0.950 carbon dioxide + 0.040 nitrogen + 0.010 argon in mole fraction) were measured at temperatures from (323.15 to 423.15) K with pressures from (3 to 31) MPa using a single-sinker magnetic suspension densimeter. The expanded measurement uncertainties (k = 2) were 35 mK for temperature, 3.4 kPa for pressure, and 0.033 % for density. Mixture samples were prepared gravimetrically with the expanded uncertainty (k = 2) in composition 0.001 mole fraction. With all of the measurement and composition effects considered, the expanded combined uncertainty (k = 2) in the density determination was generally within 0.2 % except at thermal states at the vicinity of the critical point near the Widom line. Relative deviations of the experimental data from the GERG-2008 equation of state (EOS), a Helmholtz energy model for natural gas mixtures, and from the EOS-CG, another new Helmholtz energy model for humid gases and fluid m...

Accurate density measurements on a binary mixture (carbon dioxide + methane) at the vicinity of the critical point in the supercritical state by a single-sinker densimeter

Pressure, density, and temperature measurements on a binary mixture (carbon dioxide + methane) with the composition 0.950 mol fraction carbon dioxide were carried out at the vicinity of the critical point in the supercritical state using a single-sinker magnetic suspension densimeter. The expanded measurement uncertainties (k = 2) were 35 mK for temperature, 3.4 kPa for pressure, and 0.033% for density. The mixture sample was prepared gravimetrically with the expanded uncertainty in the composition less than 0.001 mol fraction. Relative deviations of the experimental densities at temperature 301.15 K with pressures from (2.0–12.0) MPa from the values calculated by the GERG-2008 equation of state were generally within approximately 1.0%, and these experimental data agreed well with the experimental results from other groups. The relative deviations from the results calculated by the GERG-2008 equation of state for the experimental data measured at temperatures from (300.15–313.15) K with pressures from (8.0–10.0) MPa were within 5.0%. The absolute values of the relative deviations first increased and then decreased with increasing pressure for each isotherm, and the pressure of the peaking point was close to the pressure of the maximum value of (∂ρ/∂T)p, calculated using the experimental data, on the same isotherm.

Thermodynamic characterization of deepwater natural gas mixtures with heavy hydrocarbon content at high pressures

This paper includes high-accuracy density measurements and phase envelopes for deepwater natural gas mixtures. Mixtures primarily consist of (0.88 and 0.94) mole fraction methane and both mixtures includes heavy components (C6+) more than 0.002 mole fraction. Experimental density and phase envelope data for deep and ultra-deep reservoir mixtures are scarce in literature and high accuracy measurements for such parameters for such natural gas-like mixtures are essential to validate the benchmark equations for custody transfer such as AGA8-DC92 and GERG-2008 equation of states (EOS). Thus, in this paper we report density and phase envelope experimental data via compact single-sinker magnetic suspension densimeter and isochoric apparatuses. Such data help gas industry to avoid retrograde condensation in natural gas pipelines.

Measurement of the (pressure, density, temperature) relation of a (methane + nitrogen) gaseous mixture using an accurate single-sinker densimeter

A single-sinker magnetic suspension densimeter based on Archimedes’ buoyancy principle is described. Density measurements on high-purity nitrogen demonstrate the performance of the densimeter. Comprehensive (p,ρ,T) measurements at low densities on a gaseous mixture with mole fraction of (0.8977CH4+0.1023N2) were carried out on this densimeter at six temperatures from (170.586 to 270.054)K and at pressures ranging from (0.1333 to 1.5945)MPa. The overall uncertainty in density is estimated to be 0.1%. The uncertainty in temperature is estimated to be 5mK and that in pressure is 250Pa for (0 to 1.5)MPa and 390Pa for (1.5 to 3)MPa, respectively. The experimental results of the (methane+nitrogen) mixture were compared with REFPROP 9.0, which used GERG-2008 and AGA8 equations of state to predict thermophysical properties of natural gas. The absolute relative deviations of density measurements are all within 0.1%. Meanwhile the experimental results were correlated using the virial equation of state (Virial EOS) with three different mixing rules. The calculated results using the virial EOS combined with VDW mixing rule show good agreement with the experimental data.

P–ρ–T Behavior of Three Lean Synthetic Natural Gas Mixtures Using a Magnetic Suspension Densimeter and Isochoric Apparatus from (250 to 450) K with Pressures up to 150 MPa: Part II

Work reported in this paper is the continuation of a previous work (Atilhan et al. J. Chem. Eng. Data2011, 56, 212–221) and reports measurements of density and phase envelope characteristics of three synthetic natural gas-like mixtures. These mixtures consist of primarily 0.9000 methane in mole fraction and variable amounts of ethane, propane, 2-methylpropane, butane, 2-methylbutane, and pentane as well as the presence or absence of nitrogen and carbon dioxide. A high-pressure single-sinker magnetic suspension densimeter was used to measure the density of the mixtures along three isotherms at (250, 350, and 450) K with pressures up to 150 MPa. Density measurements are compared to the GERG04 and AGA-8 equations of state, which are the two leading models used for natural gas density predictions. Predictions from both equations have a similar agreement with the data, yet it is observed that GERG04 model shows better performance in predictions with deviations less than around 0.2 % at different temperatures (T = 350 K and T = 450 K) and pressures (p > 20 MPa). An isochoric apparatus was used for phase envelope experiments, and the data are compared to several cubic biparametric, cubic triparametric, and molecular-based equation of states. Equation-of-state predictions for the mixtures and comparison with the experimental data are shown. Equation-of-state predictions show substantial deviations around the entire phase envelope for the third mixture, in which the nitrogen and carbon dioxide have not been included.

Accurate P−ρ−T Data and Phase Boundary Determination for a Synthetic Residual Natural Gas Mixture

This paper reports P−ρ−T data (P is pressure, ρ is mass density, T is temperature) for a ternary mixture that resembles a residual natural gas. The measurements utilized a high-pressure, single-sinker magnetic-suspension densimeter (MSD) from (200 to 450) K up to 170 MPa and an automated isochoric apparatus to determine densities and phase boundary data up to 20 MPa. The MSD technique yielded accurate data, with better than a 0.05 % estimated error at two standard deviations up to 200 MPa. The relative uncertainties for phase-boundary temperatures and pressures were 0.45 % and 0.04 %, respectively. The isochoric densities had essentially the same estimated error as the MSD data. The GERG-2004 and AGA8-DC92 equations of state compared well to the density data. A new method provided saturation densities from isochoric data with a relative uncertainty of 0.12 %, compensating the isochoric densities for cell and transfer-line volume changes and for mass interchange between the cell and the combination of the transfer line and pressure transducer.

New P−ρ−T Data for Nitrogen at Temperatures from (265 to 400) K at Pressures up to 150 MPa

This paper reports P−ρ−T data for pure nitrogen measured with a high-pressure, single-sinker magnetic suspension densimeter (MSD) at (265, 293, 298.15, 350, and 400) K. The MSD yields data with less than 0.03 % estimated error over the pressure range of (10 to 200) MPa. A comparison of the experimental data to the equation of state (EoS) developed by Span et al. indicates they are consistent at pressures below 30 MPa. The EoS has a relative uncertainty with respect to density of 0.02 % over this range. At higher pressures, the density predictions of this model agree with the experimental data reported in this paper within a 0.05 % deviation band.

P-ρ-T Data for Carbon Dioxide from (310 to 450) K up to 160 MPa

This paper presents P-ρ-T data for pure carbon dioxide measured with a high-pressure single-sinker magnetic suspension densimeter (MSD). The data cover four isotherms (310, 350, 400, 450) K. The MSD technique yields data with less than 0.03 % relative uncertainty over the pressure range of (10 to 200) MPa. A comparison of the experimental data to the equation of state developed by Span and Wagner indicates that the equation and the data are consistent within the low range of pressure. The reference equation has a relative uncertainty of ± 0.03 % to ± 0.05 % below 30 MPa. At higher pressures, the density predictions of this model agree with the experimental data with a maximum relative deviation of 0.1 %.

Force Transmission Error Analysis for a High-Pressure Single-Sinker Magnetic Suspension Densimeter

The magnetic suspension densimeter (MSD) is a sophisticated, state-of-the-art device that provides extremely accurate results for density measurements. The MSD uses a magnetic technique to couple a mass inside a measurement cell with an external mass balance for mass measurement. This article presents a force transmission error (FTE) analysis for a high-pressure, single-sinker MSD. Due to the magnetic working principle of the apparatus, magnetic properties of the high-pressure cell and external magnetic fields affect the measurements slightly. For the analysis, McLinden et al. suggest making measurements using two different sinkers, a titanium sinker and a copper sinker, having the same mass. The measurements cover densities for methane, ethane, carbon dioxide and nitrogen over the temperature range from 265 K to 450 K (±5 mK stability) up to 180 MPa (uncertainty of 0.01 % full scale: 200 MPa). Comparing and manipulating the measurements permit determination of apparatus and fluid specific effects that contribute to the FTE. For this MSD, the apparatus effect is about 200 ppm, which effectively masks any fluid specific effect. A comprehensive analysis of the FTE produces a uniform deviation for density values of about 0.05 % at 2σ across the full range of pressure.

Accurate density measurements for a 91% methane natural gas-like mixture

Accurate density data are necessary to validate equations of state (EOS) used in custody transfer of natural gas. The American Gas Association (AGA) AGA8-DC92 EOS, currently the industry standard, has been validated against a databank of gas mixtures composed mostly of binary data. Accurate density data for multicomponent mixtures are necessary to check the ability of AGA8-DC92 to cover the entire range of pressure, temperature, and compositions encountered in custody transfer. This paper uses a magnetic suspension densimeter to measure the densities of mixtures containing nine components with n-pentane being the heaviest. We have used a high pressure, high temperature, compact single-sinker magnetic suspension densimeter to measure densities of a simulated natural gas mixture having 91% methane composition after validating its operation by measuring densities of pure argon, nitrogen, and methane in the range (270 to 340) K and (3.447 to 34.474) MPa. The agreement with the reference EOS for the pure components is about 0.03%. The estimated 2 σ uncertainty of the densities after compensating for apparatus and fluid effects is 0.12% with 93% of that value coming from the composition uncertainty. The measured data indicate the advisability of performing an extensive study of the AGA8-DC92 EOS for natural gas mixtures.