Vicinity Of Critical Pressure Research Articles

Optical characterization of ethane droplets in the vicinity of critical pressure

The characterization of the properties of fuel droplets around the critical pressure is an experimental challenge. The aim of this study is to measure the size and the refractive index of droplets in high pressure conditions, close to the ones of the critical point. For this purpose, an experimental facility of injection of quasi-monodispersed droplets at high pressure has been developed. Rainbow refractometry has been used to probe droplets in the pressure range 1–50 bar. For water and ethanol droplets, evolutions of their index of refraction with pressure were obtained. For measurements with a liquid fluid near its critical point, ethane was selected because its critical point is 48.7 bar and 32.2 °C. Refractive index measurements on ethane droplets were carried out in the range of pressure and temperature 40–46 bar and 18–25 °C respectively. These unique results show that the rainbow refractometry diagnosis offers undeniable potentials for studying fuel injection under transcritical thermodynamic conditions.

Density characteristics of CO2–CH4 binary mixtures at temperatures from (300 to 308.15) K and pressures from (2 to 18) MPa

The accurate densities of CO2–CH4 binary mixtures with CO2 mole fraction of 0.0998, 0.2017, 0.3997, 0.6015, 0.7985 and 0.8988 at temperatures from (300 to 308.15)K and pressures from (2 to 18)MPa were measured using a high-precision magnetic suspension balance. The combined standard uncertainties of temperature and pressure were estimated as 0.02K and 0.001MPa, respectively. The density measurement uncertainty of MSB was estimated as 0.029kg·m−3. Taking the effect of composition uncertainty and sorption into account, the combined standard uncertainties in the density measurement of CO2–CH4 mixtures were around 0.30% with CO2 mole fraction lower than 0.60 while they increased up to 0.96% with CO2 mole fraction higher than 0.80 at pressure of 9.0–11.0MPa. The measured densities were compared with the calculation from GERG-2008 EOS. It showed relatively good agreements between the GERG-2008 EOS and the measured densities with CO2 mole fraction lower than 0.60 at 300K as the relative deviations were generally within 2.0%. When CO2 mole fraction was higher than 0.80 at 300K, the relative deviations firstly increased to the maximum 3.73% in the vicinity of critical pressure and then decreased close to zero with the increasing pressure. The experimental data at other temperatures have the similar variation trends. Thus it’s difficult to apply GERG-2008 EOS to predict the density characteristics of CO2–CH4 binary mixtures with high CO2 mole fraction in the vicinity of the critical point accurately.

Study of the Anomalous Sorption Behavior of CO2 into Poly(methyl methacrylate) Films in the Vicinity of the Critical Pressure and Temperature Using a Quartz Crystal Microbalance (QCM)

The anomalous solubility maximum of CO2 in polymer thin films in the vicinity of the critical temperature and pressure has not yet been clearly understood when the quartz crystal microbalance (QCM) technique has been used to determine the micromass change. In this study, the adsorption of CO2 on the surface of bare polished and unpolished crystals at different pressures and temperatures was investigated using the QCM technique to illustrate why a plot of the true frequency shift as a function of temperature and pressure can intuitively exhibit the adsorption behavior of CO2 on bare crystals. The sorption of CO2 into a PMMA film at different temperatures, pressures, and PMMA film thicknesses was also investigated. An accurate solubility for CO2 in the PMMA film could be obtained by an improved data correction method from the linear relation between the true frequency shift and the polymer film mass, and the anomalous solubility maximum could be corrected by this method. The mechanism of nonabsorbed CO2 transitorily staying in the interspace between the PMMA film and the crystal surface can be explained by the morphology change of the PMMA film. The assumption of "passerby CO2" was satisfactorily confirmed to explain the anomalous sorption behavior of CO2 into PMMA films in the vicinity of the CO2 critical temperature and pressure, and this assumption could be valid for other CO2-polymer thin film systems.

Modelling the swelling of crosslinked elastomers by supercritical fluids

Despite the general knowledge that near-critical and supercritical CO 2 will swell elastomers extensively, there has been little work done to date on modelling the phenomenon. We have used the mean-field-lattice-gas model of Kleintjens et al. for the free energy of mixing with an additional elastic term due to Flory, in order to model the swelling of crosslinked silicones by supercritical CO 2. Whereas the model reproduces the pressure trends in both volume change and weight fraction fluid absorbed well for the poly(dimethylsiloxane)—CO 2 system, the absolute predictions of weight fraction CO 2 absorbed are too high in the vicinity of critical pressure.

A model of instability of liquid propellant engine with radial injection

A chamber model is achieved to study Ariane Viking engine combustion instabilities. This three-dimensional unsteady state model is linearized about a one-dimensional mean flow, but tries to take into account the radial injection salient feature of the Viking with the help of a first rough two-dimensional mean flow description which introduces amplification factors. Analytical solutions are searched by the use of a concentrated combustion approach; a separate routine supplies the needed time lags and indices estimated data. Intended to provide the chamber transfer functions, the model already permits, by intrinsic stability analysis, to corroborate and explain the main tendencies observed during SEP firing tests. For further improvements, attention must be paid to mean flow description and combustion process in the vicinity of critical pressure.