Density Measurements of an Air-Like Binary Mixture over the Temperature Range from 100 K to 298.15 K at Pressures up to 8.0 MPa

AbstractDensities 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

Accurate density measurements on gaseous and liquefied pure fluids and mixtures at cryogenic temperatures

Dem Klimawandel entgegenzuwirken und gleichzeitig den wachsenden, globalen Energiebedarf zu decken, ist eine der größten Hürden der heutige Gesellschaft. Diese Herausforderung kann nur durch den grundlegenden Wandel und die Dekarbonisierung der Haushalts-, Industrie- und Verkehrssektoren erreicht werden. Die Entwicklung und Optimierung der relevanten technischen Prozesse erfordert dabei genaue Kenntnis der thermodynamischen Eigenschaften, wie z.B. der Dichte, der verwendeten Fluide. Diese Arbeit adressiert die genaue Dichtemessung bei tiefen Temperaturen und hohen Drücken. Mit einer präzisen Ein-Senkkörper Dichtemessanlage wurden Studien für verschiedene Fluidsysteme bei flüssigen, überkritischen und gasförmigen Zuständen durchgeführt. Zudem wurde ein kommerzieller Biegeschwinger im Rahmen einer Machbarkeitsstudie bei tiefen Temperaturen in Betrieb genommen. Die erreichbaren experimentellen Unsicherheiten wurden auf Basis umfangreicher Kalibrierungs- und Validierungsmessungen ermittelt.Counteracting the progression of climate change while meeting the growing global energy demand is one of the biggest challenges facing society nowadays. Accomplishing these challenges simultaneously can only be achieved by substantial transformation and decarbonization of the domestic, industrial, and transport sectors. Developing and optimizing related technical processes requires accurate knowledge of the thermodynamic properties, such as the density, of employed fluids. This work addresses the measurement of fluid densities at low temperatures and high pressures. Various measurements were carried out utilizing an accurate single-sinker densimeter. These studies cover investigations at liquid, supercritical, and gaseous states for different fluid systems. Moreover, a commercial vibrating tube densimeter was commissioned within a low-temperature feasibility study. Here, achievable experimental uncertainties were evaluated based on comprehensive calibration and validation measurements