Parahydrogen Gas Research Articles

The role of the dynamic pressure in stationary heat conduction of a rarefied polyatomic gas

Abstract The effect of the dynamic pressure (non-equilibrium pressure) on stationary heat conduction in a rarefied polyatomic gas at rest is elucidated by the theory of extended thermodynamics. It is shown that this effect is observable in a non-polytropic gas. Numerical studies are presented for a para-hydrogen gas as a typical example.

Heterogeneous solution NMR signal amplification by reversible exchange.

A novel variant of an iridium-based organometallic catalyst was synthesized and used to enhance the NMR signals of pyridine in a heterogeneous phase by immobilization on polymer microbead solid supports. Upon administration of parahydrogen (pH2) gas to a methanol mixture containing the HET-SABRE catalyst particles and the pyridine, up to fivefold enhancements were observed in the (1)H NMR spectra after sample transfer to high field (9.4 T). Importantly, enhancements were not due to any residual catalyst molecules in solution, thus supporting the true heterogeneity of the SABRE process. Further significant improvements may be expected by systematic optimization of experimental parameters. Moreover, the heterogeneous catalyst is easy to separate and recycle, thus opening a door to future potential applications varying from spectroscopic studies of catalysis, to imaging metabolites in the body without concern of contamination from expensive and potentially toxic metal catalysts or accompanying organic molecules.

Heterogeneous Solution NMR Signal Amplification by Reversible Exchange

AbstractA novel variant of an iridium‐based organometallic catalyst was synthesized and used to enhance the NMR signals of pyridine in a heterogeneous phase by immobilization on polymer microbead solid supports. Upon administration of parahydrogen (pH2) gas to a methanol mixture containing the HET‐SABRE catalyst particles and the pyridine, up to fivefold enhancements were observed in the 1H NMR spectra after sample transfer to high field (9.4 T). Importantly, enhancements were not due to any residual catalyst molecules in solution, thus supporting the true heterogeneity of the SABRE process. Further significant improvements may be expected by systematic optimization of experimental parameters. Moreover, the heterogeneous catalyst is easy to separate and recycle, thus opening a door to future potential applications varying from spectroscopic studies of catalysis, to imaging metabolites in the body without concern of contamination from expensive and potentially toxic metal catalysts or accompanying organic molecules.

Optimal operation of a large-scale liquid hydrogen plant utilizing mixed fluid refrigeration system

This work proposes a new modified liquid hydrogen plant that uses a multi-component refrigerant (MR) refrigeration system. A plant capable of producing 100 tons of liquid hydrogen per day is simulated and optimized. Based on a previously published work, this paper represents an improvement for more realistic large-scale plant cycles. Importantly, this work contains a preliminary study of the variables and constraints together with methods for adjustment to achieve optimal steady-state operation. The optimization problem contains 23 variables and 26 constraints. Similar to the MR system, this system can be used to cool the normal feed hydrogen gas from 25 °C to the equilibrium temperature of −193 °C, and a simplified five-component mixture of refrigerant suggested for the plant is described. However, the novelty of this work relative to the previous work lies in the transition of the equilibrium ortho–para hydrogen gas from −193 °C to −253 °C via a new proposed configuration, which recommends a four H2 Joule–Brayton cycle refrigeration system with optimization. Additionally, the plant optimization was conducted using two additional pinch temperatures (1 °C and 3 °C). The overall power savings is increased with a pinch temperature of 1 °C compared with that of 3 °C. The simulated overall power consumption of the proposed plant is 5.91kWh/kgLH2, which represents a 50% reduction compared with the current plant in Ingolstadt with an energy consumption of 13.58kWh/kgLH2. Pressure drops are also employed in the heat exchangers in the study simulation, but the results show that they do not have a significant impact on the overall plant total power consumption.

ウラン濃縮用パラ水素ラマンレーザーにおけるパラ‐オルソ水素転換の観測とパラ水素の再生

In the 16μm Raman laser for molecular laser isotope separation of uranium, pure parahydrogen gas is the Raman medium, and then natural conversion from pure para-hydrogen to para-ortho mixture causes always serious reduction of Raman conversion efficiency. The authors have measured temporal decay of para-hydrogen concentration in a Raman cell and obtained a decay time constant of 102 days. Using the Raman cell combined with a parahydrogen regenerator designed with the above value, they have demonstrated that the concentration of para-hydrogen was maintained to be high enough for the Raman conversion.

Depolarized light scattering of parahydrogen gas at low temperatures.

The low-density, collision-induced, depolarized, translational Raman spectrum of gaseous parahydrogen has been measured at 36 K and compared to quantum line-shape calculations. The calculations were made in the isotropic potential approximation using a modified dipole\char21{}induced-dipole model of interaction.

Observations on the use of a thermal conductivity cell to measure the para hydrogen concentration in a mixture of para and ortho hydrogen gas

This paper describes the use of a thermal conductivity cell to measure the para hydrogen concentration in a mixture of para and ortho hydrogen gas. The device was calibrated over its entire range and the output compared with the theoretically expected form. The output of this device had been previously assumed to be linear, this assumption can lead to systematic errors of up to 5.6% in the determination of the para hydrogen concentration. A simple calibration procedure is described.

A 16-µm radiation source utilizing four-wave mixing in cooled parahydrogen gas

Improvements in a 16-μm radiation source based upon the combined effects of stimulated rotational Raman scattering and resonantly enhanced four-wave mixing in parahydrogen gas are described. For this source, the input waves of which are provided by temporally and spatially coincident pulsed beams from a ruby and CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> TEA laser, it was found that cooling the parahydrogen gas from 300 K to <100 K, at constant molecular density, increased the output at 16 μm by roughly a factor 4. The maximum output was measured to be <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sim 40 \mu</tex> J/pulse, which is near the theoretical limit for the 2.5 MW CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> laser intensities that were applied.

Translational Hydrodynamics and Light Scattering from Molecular Fluids

The density fluctuations in a molecular fluid are studied by treating the fluid as a multicomponent reacting mixture. The ordinary hydrodynamic equations for a reacting mixture form the starting point of the present derivation. The description is then contracted to that appropriate for the one-component molecular fluid. The resulting translational hydrodynamics theory contains memory effects due to the internal relaxation process. The results are compared with a recent kinetic model and with two previous theories of Mountain. The dynamic structure factor $S(k, \ensuremath{\omega})$ and the roots of the dispersion relation are computed for parahydrogen gas and studied as a function of density. The results indicate that the treatment of the thermal-diffusivity mode in the theories by Mountain breaks down in the low-density region. It is suggested that Rayleigh-Brillouin scattering experiments on dilute parahydrogen gas at room temperature and densities between 5 and 30 amagats can quantitatively verify the predictions of translational hydrodynamics.

Pressure-volume isotherms of hydrogen gas between 19 and 23°K

Pressure-volume isotherms of para-hydrogen gas have been determined at temperatures from 19 to 23°K and at pressures almost up to the saturated vapour pressure. From these measurements the second virial coefficient has been determined while the third virial coefficient could be estimated. The results for B and C are in good agreement with data given by Goodwin, Diller, Roder and Weber. The thermodynamic temperatures determined from the isotherms at 23.3°K and 22.7°K have been compared with the hydrogen vapour pressure-temperature scale.

Slow Neutron Scattering by Molecular Hydrogen and Deuterium

The cross sections for neutrons scattering from ${\mathrm{H}}_{2}$ and ${\mathrm{D}}_{2}$ have been calculated taking into account the spin correlations, rotations, and vibrations of the molecules exactly, to the extent that the vibrations are harmonic and do not interact with the rotations. Free translations of the molecules are assumed, but this assumption is expected to be valid in the liquid, as well as the gas, for neutron energies above 0.007 eV, the Debye temperature for hydrogen. Numerical results are given for the total cross section for both orthohydrogen and parahydrogen gas at 20.4\ifmmode^\circ\else\textdegree\fi{}K which agree reasonably well with the limited experimental results available. Also, curves of the double differential cross section are shown for selected incident neutron energies and scattering angles. These latter curves show very clearly the various rotational and vibrational transitions. The formulas given here are applicable at all temperatures below the thermal excitation of the first vibrational level.

Quantum symmetry effects in hydrogen gas

The nuclear magnetic resonance technique was used to measure diffusion at 20.35 deg K in normal hydrogen gas and in a mixture of 37.5% ortho-hydrogen- 62.5% parahydrogen gas. Results showed that ortho-molecules in different spin quantum states must actually be treated as distinguishable particles in calculating the measured diffusion cross sections. (C.E.S.)

Rotational Transition of Hydrogen Molecule by Collision

The previous calculation of rotational transition probability for para-hydrogen gas is improved by adding an attractive term to the intermolecular potential. Using the result of recent calculations by Evett and Margenau of intermolecular force, good agreement is obtained between the calculated and experimental values of transition probability. The transition probability is also calculated for H2-H collisions, because of its importance for the cooling of interstellar matter. According to our present knowledge of the intermolecular forces the H2-H potential shows much more appreciable anisotropy than does the H2-H2 potential, so that H2-H collisions are much more effective than H2-H2 collisions for the rotational transition, nearly 10 times for 100-1000°K.