Dynamic Viscosity of Graphene- and Ferrous Oxide-Based Nanofluids: Modeling and Experiment

This study focused on measuring the viscosity and analyzing the behavior of two types of nanofluids: ferrous oxide-deionized (DI) water nanofluids and graphene-DI water nanofluids at different temperatures and volume fractions. Zeta potential measurement, which was performed to check the stability of the nanofluids, showed stable suspensions. All viscosity measurements were conducted using a capillary viscometer at temperatures ranging between 25 and 65°C. Both types of nanofluids showed increasing viscosity with increasing nanoparticle loading and decreasing viscosity with increasing temperature. Furthermore, experiments on different-sized ferrous oxide-based nanofluids revealed inverse relation between the size of nanoparticles and viscosity. An accurate model was developed based on the Buckingham Pi theorem to fit all factors affecting viscosity in a dimensionless form. These factors are the viscosity of the base fluid, nanoparticles’ volume fraction, nanoparticles’ size, the temperature of the system, some molecular properties, and zeta potential

Period Increase and Amplitude Distribution of Kink Oscillation of Coronal Loop

Coronal loops exist ubiquitously in the solar atmosphere. These loops puzzle astronomers over half a century. Solar magneto-seismology (SMS) provides a unique way to constrain the physical parameters of coronal loops. Here, we study the evolution of oscillations of a coronal loop observed by the Atmospheric Imaging Assembly (AIA). We measure geometric and physical parameters of the loop oscillations. In particular, we find that the mean period of the oscillations increased from 1048 to 1264 s during three oscillatory cycles. We employ the differential emission measure method and apply the tools of SMS. The evolution of densities inside and outside the loop is analyzed. We found that an increase of density inside the loop and decrease of the magnetic field strength along the loop are the main reasons for the increase in the period during the oscillations. Besides, we also found that the amplitude profile of the loop is different from a profile would it be a homogeneous loop. It is proposed that the distribution of magnetic strength along the loop rather than density stratification is responsible for this deviation. The variation in period and distribution of amplitude provide, in terms of SMS, a new and unprecedented insight into coronal loop diagnostics

Measurements of helium adsorption on natural clinoptilolite at temperatures from (123.15 to 423.15) K and pressures up to 35 MPa

Helium (He) is an increasingly valuable gas that is relatively difficult to recover: most of the global helium supply is produced through the application of deep cryogenic separation processes to the overheads from a nitrogen rejection unit in an LNG plant. Pressure swing adsorption (PSA) offers an alternative low-cost process for recovering He from natural gas, particularly if a helium selective adsorbent with sufficient capacity could be identified. However, the accurate measurement of the helium equilibrium capacity on narrow pore adsorbents is particularly challenging. Here, the uptake of helium on a natural clinoptilolite-rich Escott zeolite was measured with a volumetric adsorption apparatus at temperatures from 123.15 to 423.15 K and pressures up to 5 MPa, and with a gravimetric adsorption apparatus at temperatures in the range 243.15–423.15 K and pressures up to 35 MPa. We used these two experimental data sets to determine the specific inaccessible solid volume (vs) and true void volume of the Escott zeolite by eliminating the common assumption of zero helium uptake. Instead, the data analysis workflow established by Sircar (2001) and by Gumma and Talu (2003) was applied to the adsorption isotherms measured using the gravimetric apparatus. This led to a specific inaccessible solid volume for the Escott zeolite of 0.462 cm3·g−1, with a maximum helium adsorption capacity of 0.9 mmol·g−1 measured at 253.15 K and 35 MPa. The isosteric heat of adsorption for helium on the Escott zeolite was estimated to be 3.05 kJ·mol−1. The uptake of N2 on the Escott zeolite was also measured; these data were used together with the helium measurements to estimate conditions at which an equilibrium selectivity of 3 for He over N2 might be achieved in an equimolar He + N2 mixture

Isobaric heat capacity measurements on ternary mixtures of natural gas components methane, propane and n-heptane by differential scanning calorimetry at temperatures from 197 K to 422 K and pressures up to 32 MPa

Heat capacities for single-phase mixtures of the natural gas components methane (1), propane (2) and n-heptane (3) have been determined at temperatures (197 to 421) K and pressures up to 32 MPa using two differential scanning calorimeters with a combined standard uncertainty of (2.0 to 2.6) % (k = 1). In addition, measurements were performed at pressures (0.01 to 4.40) MPa higher than saturation conditions to estimate the heat capacities of the mixtures at their bubble points. The ternary mixture data were compared with three models: the Groupe Européen de Recherches Gazières (GERG) 2008 multi-parameter equation of state (EOS), the Peng-Robinson (PR) EOS, and the Statistical Associating Fluid Theory (SAFT)-γ Mie EOS incorporating group contributions. The relative deviations of the measured heat capacities from the values calculated by the three models show similar, systematic dependences on density, with larger deviations at cryogenic temperatures. The root mean square deviations from the measurements (with ideal gas heat capacity corrected) were 8.2%, 7.0% and 5.9% for the GERG-2008, PR and SAFT-γ Mie EOS, respectively. The presence of n-heptane increased the deviation up to 20% at the lowest temperature. The addition of methane to the binary mixture [0.500 C3H8 + 0.500 C7H16] was found to always increase the heat capacity. This work shows that the SAFT-γ Mie EOS can describe the single-phase measurements at above-ambient temperatures, while none of the models provides reliable predictions for cryogenic single-phase and near-bubble-point measurements

Isobaric heat capacities of a methane (1) + propane (2) mixture by differential scanning calorimetry at near-critical and supercritical conditions

Isobaric heat capacity data are needed to test and improve thermodynamic models of natural gas over wide ranges of temperature and pressure. Measurements are reported here at temperatures between (184 and 421) K and pressures between (5 and 32) MPa for supercritical mixtures of methane (1) + propane (2) at x1 = 0.950 (±0.005). Estimated relative uncertainties in the measured heat capacities range from (1.8 to 4.5) %. In addition, measurements at temperatures of (184, 190, 197, 203 and 209) K were performed at pressures (1.67 to 2.39) MPa higher than saturation conditions to estimate the heat capacity of the mixture at the bubble point. The binary mixture data were compared with the predictions of three models: the Groupe Européen de Recherches Gazières (GERG) 2008 multi-parameter equation of state (EOS), the Peng-Robinson (PR) EOS used widely by chemical engineers, and the Statistical Associating Fluid Theory (SAFT)-γ Mie EOS incorporating group contributions. Among the three models, the PR EOS was found to describe the heat capacity values best. A brief investigation indicated that the Joback and Reid method that the SAFT-γ Mie EOS is based on fails to accurately predict the ideal gas heat capacity of methane at cryogenic temperatures, while the inaccuracy of the GERG-2008 EOS stems from the residual part of the methane (1) + propane (2) mixing functions

Isobaric heat capacity measurements of natural gas model mixtures (methane + n-heptane) and (propane + n-heptane) by differential scanning calorimetry at temperatures from 313 K to 422 K and pressures up to 31 MPa

Heat capacities of pure methane (1), propane (2) and n-heptane (3), and binary mixtures of (methane or propane + n-heptane) at n-heptane mole fractions of (0.070 to 0.750), were measured at temperatures (313 to 42) K and pressures (6.00 to 31.10) MPa using a Tian-Calvet-type differential scanning calorimeter with a combined standard uncertainty of (2.20 to 2.68) % (k = 1). The results for pure methane, propane and n-heptane agreed within 2% of the values calculated from reference equations of state (EOS). In contrast, for the two sets of mixtures measured above their cricondenbars, averaged absolute deviations of 4.6%, 3.7% and 1.2% were observed between the measured cp values and those predicted by the GERG-2008, Peng-Robinson (PR) and SAFT-γ Mie EOS, respectively. The divergences of cp from model calculations for the binary mixtures near the critical region were also investigated. The root mean square (r.m.s.) deviations of the measured heat capacities from those calculated using the GERG-2008, PR, and SAFT-γ Mie exhibited relatively large but similar values of 7.1%, 7.4% and 7.2% for [0.850 CH4 + 0.150 n-C7H16] and 9.1%, 6.9% and 8.0% for [0.930 C3H8 + 0.070 n-C7H16]. This work reveals that the SAFT-γ Mie EOS can adequately describe most heat capacity data above the cricondenbar, while none of the models provide reliable predictions near the critical region

Hydrogen liquefaction: a review of the fundamental physics, engineering practice and future opportunities

Hydrogen is emerging as one of the most promising energy carriers for a decarbonised global energy system. Transportation and storage of hydrogen are critical to its large-scale adoption and to these ends liquid hydrogen is being widely considered. The liquefaction and storage processes must, however, be both safe and efficient for liquid hydrogen to be viable as an energy carrier. Identifying the most promising liquefaction processes and associated transport and storage technologies is therefore crucial; these need to be considered in terms of a range of interconnected parameters ranging from energy consumption and appropriate materials usage to considerations of unique liquid-hydrogen physics (in the form of ortho–para hydrogen conversion) and boil-off gas handling. This study presents the current state of liquid hydrogen technology across the entire value chain whilst detailing both the relevant underpinning science (e.g. the quantum behaviour of hydrogen at cryogenic temperatures) and current liquefaction process routes including relevant unit operation design and efficiency. Cognisant of the challenges associated with a projected hydrogen liquefaction plant capacity scale-up from the current 32 tonnes per day to greater than 100 tonnes per day to meet projected hydrogen demand, this study also reflects on the next-generation of liquid-hydrogen technologies and the scientific research and development priorities needed to enable them