Para-ortho Hydrogen Conversion Research Articles

Research on matching supply of power and cold energy of liquid hydrogen cold chain logistics vehicles

Liquid hydrogen cold-chain logistics vehicle (LHCCLV) is a special vehicle using liquid hydrogen (LH2) as the source of both power and cold energy. A significant weakness of LH2 is its high energy consumption during the hydrogen liquefaction process, thus the utilization of cold energy in LHCCLV can improve the economic performance and competitiveness of LH2. Because of the high energy storage density of LH2 and the relatively high efficiency of fuel cells, we find that cold energy can not meet the demand of LHCCLV. Therefore, we consider enlarging the cold energy by efforts including the para-ortho hydrogen conversion (POC), whose reverse reaction consumes an energy level exceeding 20% during the hydrogen liquefaction process. In this paper, numerical models of discharging hydrogen from the LH2 and subcooling hydrogen tank are established, and the influence of POC and other efforts on the supply of cold energy is analyzed. The changes in instantaneous and total cold energy supply under different working conditions are analyzed, and the important influence of POC and other efforts is confirmed. The beneficial effect of POC is quantified in the paper, especially for the cold energy supply. This paper provides an essential reference for the research and development of LHCCLV. Also, it guides the comprehensive utilization of cold energy in other situations to promote the improvement of the economy of hydrogen energy utilization routes in the form of LH2.

Thermodynamic analysis of power generation thermal management system for heat and cold exergy utilization from liquid hydrogen-fueled turbojet engine

Hydrogen propulsion is generally treated as the ultimate net zero-emission option for aviation, therein liquid hydrogen storage appears to provide the only feasible solution for aircraft with the constraints imposed by aircraft weight and volume. Hydrogen liquefaction consumes a great amount of energy, which significantly boosts the cost of hydrogen as an aviation fuel. Besides the H2 chemical exergy for combustion to provide thrust, the H2 physical exergy in the form of cold energy is also a kind of high-quality clean energy to produce power output, which offers great opportunities to achieve cost-effective use of hydrogen fuel. Thus, this paper presents a Rankine cycle and H2 direct expansion cycle (RC-DEC) combined power generation thermal management system for the simultaneous utilization of exhaust gas heat exergy and hydrogen fuel cold exergy from the liquid hydrogen-fueled turbojet engine. In the Rankine cycle, the transcritical mode is applied on the hot side while the liquid separation condensation concept is adopted on the cold side to achieve better thermal matchings with heat and cold sources. The hydrocarbon/inert gas binary mixture is proposed as the working fluid of the Rankine cycle. The effects of key thermodynamic parameters and the influence of Para-Ortho hydrogen conversion on system performance are discussed, then a comparison of the mixture working fluid is conducted. Results show that there exists an optimal separation temperature ratio and condensation pressure of RC to obtain maximum total net power output. As the DEC expander inlet pressure increases, the total net power output first increases and then levels off. The introduction of the Para-Ortho hydrogen conversion has a negligible impact on net power output but leads to a significant reduction in the exergy efficiency, which is attributed to the cold energy release nature of Para-Ortho hydrogen conversion. The results of the working fluid comparison indicate that the optimal inert gas retardant for CH4 is Kr, while those for C2H6 and C3H8 are Xe to achieve the maximum net power output and exergy efficiency of the proposed power generation system. Among them, C2H6/Xe(0.6/0.4) obtains the maximum net power output of 2717.9 kW and maximum exergy efficiency of 33.1%, which suggests an opportunity to provide megawatts of electrical power for the aircraft in place of the APU.

Performance comparison of multilayer insulation coupled with vapor cooled shield and different para-ortho hydrogen conversion types

Application of para-ortho hydrogen conversion to a vapor cooled shield (VCS) in a multilayer insulation system can utilize more cooling capacity of cryogenic hydrogen vapor and achieve better thermal protection for liquid hydrogen storage. Based on energy conservation and layer-by-layer model, a thermodynamic model was developed to study a variable density multilayer insulation (VDMLI) structure coupled with one VCS and para-ortho hydrogen conversion. The effects of introducing the VCS and different para-ortho hydrogen conversion types were investigated. The maximum heat leakage reduction was 56.44 % after the VCS was installed at the middle of the 43-layer VDMLI with an optimal configuration. The ratio of the distance between the optimal VCS position and the cold boundary to the VDMLI thickness changed from 50 % to 40.41 % in the existence of a continuous para-ortho hydrogen conversion. The heat leakage of the VDMLI with one VCS could be further reduced by 12.99 %, 12.99 % and 10.09 % with a continuous conversion, single-stage isothermal conversion and single-stage adiabatic conversion, respectively. Notably, the adiabatic conversion could be implemented for its relative installation convenience. The heat leakage of the VDMLI could be reduced by 60.44 % after one VCS with an adiabatic conversion is adopted.

Determination of Hydrogen’s Thermophysical Properties Using a Statistical Thermodynamic Method

Accurate determination of the thermophysical properties of hydrogen is a crucial issue in hydrogen system design. By developing computational programs, a statistical thermodynamic model based on fundamental equations of state was implemented to determine hydrogen’s thermophysical properties, including the ortho-hydrogen fraction in equilibrium hydrogen, para-ortho hydrogen conversion heat, isobaric heat capacities and enthalpies. The deviations of calculated para-hydrogen enthalpies from REFPROP data were within 2.22%, ranging from 20 K to 300K at 0.1 MPa, and within 2.32% between 100 K and 1500 K at pressures from 0.1 MPa to 20 MPa. To quantitatively assess the convenience of the statistical thermodynamic method, the running speeds of programs with different methods for determining hydrogen’s thermophysical properties were compared. The time required for statistical thermodynamic calculation was 7.95% that required for treading REFPROP data when the performance of the variable density multilayer insulation combined with a one vapor-cooled shield and para-ortho hydrogen conversion was calculated. The programs developed based on the statistical thermodynamic method can be used to determine the thermophysical properties of hydrogen or other fluids.

Modeling of Liquid Hydrogen Tank Cooled with Para-Orthohydrogen Conversion

With the accelerating development of liquid-hydrogen storage facilities, the problem of boil-off hydrogen losses becomes very important. A promising method to reduce these losses is to utilize the endothermic para-orthohydrogen conversion of vented hydrogen, which can effectively decrease heat loads on a hydrogen tank. To model such a process, a hybrid computational model has been developed, based on the application of computational fluid dynamics for an ullage space, where knowledge of thermal stratification is important, and reduced-order models for other system elements. The simulation results for a spheroidal tank in selected conditions indicated a 10–25% reduction of boil-off losses due to cooling produced by vented hydrogen undergoing para-ortho-conversion.

Cooling effect analysis on para-ortho hydrogen conversion coupled in vapor-cooled shield

The conversion process from parahydrogen to orthohydrogen accompanies an endothermic effect. Embedment of a para-ortho hydrogen converter into the thermal insulation could enhance the thermal protection of a liquid hydrogen storage tank. A physical model was proposed to simulate the heat transfer behavior of the insulation structure that integrates a polyurethane foam, a blanket of multilayer insulation, a vapor-cooled shield, and a para-ortho hydrogen converter. The effect of the para-ortho conversion process was considered. The model was validated by experimental data and then used to investigate how the para-ortho hydrogen conversion influences the temperature distribution inside the composite insulation. It was found that a single converter improves the cooling performance most effectively if it is placed at the middle length of the venting pipe mounted on the vapor-cooled shield. Either incorporating more converters or extending the length of the vapor-cooled shield pipes brings limited further improvement. The optimum position of the vapor-cooled shield inside the multilayer insulation moves towards the cold boundary in the presence of para-ortho conversion, compared to conventional vapor-cooled shield and multilayer insulation structures. A net heat flux reduction of over 10% could be achieved when the para-ortho conversion is located at the optimal position inside the vapor-cooled shield.

Performance analysis of vapor-cooled shield insulation integrated with para-ortho hydrogen conversion for liquid hydrogen tanks

A composite thermal insulation system consisting of variable-density multi-layer insulation (VDMLI) and vapor-cooled shields (VCS) integrated with para-ortho hydrogen (P-O) conversion is proposed for long-term storage of liquid hydrogen. High-performance thermal insulation is realized by minimizing the thermal losses via the VDMLI design and fully recovering the cold energy released from the sensible heat and P-O conversion of the vented gas. Effects of different design considerations on the thermal insulation performance are studied. The results show that the maximum reduction of the heat leak with multiple VCSs can reach 79.9% compared to that without VCS. The heat leak with one VCS is reduced by 61.1%, and further reduced by 11.6% after adding catalysts. It is found that the deterioration of the insulation performance has an almost linear relationship with catalytic efficiency. A unified criterion with relative optimization efficiency is finally proposed to evaluate the improvement of the VCS number.

Analytical and numerical performance models of a Heisenberg Vortex Tube

Analytical and numerical investigations of a Heisenberg Vortex Tube (HVT) are performed to estimate the cooling potential with cryogenic hydrogen. The Ranque-Hilsch Vortex Tube (RHVT) is a device that tangentially injects a compressed fluid stream into a cylindrical geometry to promote enthalpy streaming and temperature separation between inner and outer flows. The HVT is the result of lining the inside of a RHVT with a hydrogen catalyst. This is the first concept to utilize the endothermic heat of para-orthohydrogen conversion to aid primary cooling. A review of 1st order vortex tube models available in the literature is presented and adapted to accommodate cryogenic hydrogen properties. These first order model predictions are compared with 2-D axisymmetric Computational Fluid Dynamics (CFD) simulations.

A study of spin isomer conversion kinetics in supercritical fluid hydrogen for cryogenic fuel storage technologies

A detailed kinetic study of para-ortho hydrogen conversion under supercritical conditions using rotational Raman scattering is presented. Isochoric measurements of initially low ortho concentrations over temperatures 32 < T < 280 K and densities 0.014 < ρ < 0.060 g/cm3 were used to derive kinetic rate constants k(ρ, T) by solving an autocatalytic kinetic rate equation. At low ortho concentrations and T < 100 K, k is found to be ∼2× higher than previous results based on thermal conductivity measurements, decreasing weakly with temperature, similar to Wigner’s original paramagnetic theory. Accurate modeling of k(ρ, T) is critical in predicting cryogenic hydrogen fuel tank dormancy performance for hydrogen-power vehicles.

A gas chromatographic-mass spectrometric technique for studying simultaneous hydrogen-deuteron exchange and para-orthohydrogen conversion in hydrogenases of Desulfovibrio vulgaris Hildenborough

An original gas chromatographic-mass spectrometric technique is described for studying simultaneous dihydrogen-deuteron exchange and para-ortho H 2 conversion catalyzed by different Desulfovibrio hydrogenases. Para and orthohydrogens are separated on an alumina column at the temperature of liquid nitrogen, but if both HD and ortho H 2 are present, their retention times are too close to each other for total separation and only one peak is observed with a thermal conductivity detector. In order to resolve the peaks from one another, a fraction of the gas released from the gas chromatograph column is admitted to the ion source of a mass spectrometer, where the gases are separated according to their respective masses. Because of a peak-jumping system, the different components involved in the exchange and in the conversion reactions can be scanned so that the spectra corresponding to mass m e 2 (para and ortho H 2), m e 3 (HD), and m e 4 (D 2) can be obtained simultaneously. This technique has been employed to resolve a controversial problem concerning the occurrence or lack of any para-orthohydrogen conversion in heavy water. Actually both exchange and conversion were demonstrated to occur with a (NiFe) hydrogenase, whereas with a (NiFeSe) hydrogenase, which had an exchange activity equivalent to that of the former, practically no para-ortho conversion could be observed in D 2O. These findings are related to the constitutional and catalytic properties of the hydrogenases belonging to the different classes.

Catalytic Activity and Reactivity of Aromatic Nitrile and Alkali Metal Ion Radical Salt. II. Hydrogen Exchange on Benzonitrile Ion Salt as a Function of Alkali Metals

Abstract The para-orthohydrogen conversion (rate constant keH and the deuterium exchange reaction (rate constant keD) over the benzonitrile-alkali metal ion radical salt were investigated as functions of the donor component–alkali metal. The sort of alkali metals in the ion radical salts greatly affected the catalytic activity and the reactivity. The activation energies obtained from the temperature dependence of keH and keD, EH and ED, and the value of α(depending on the ratio of keH to keD monotonously decreased as Na→K→Rb, but those values showed an irregular trend for the Cs-complex. The results suggest that the catalytic activity cannot be understood only in terms of the nature of the components; must also be considered the structural nature of the solid phase of the ion radical salt.

Catalytic behavior of organic semiconductors: Hydrogen exchange on barium-naphthacene ion salts

The hydrogen exchange reaction on alkali metal- and alkali earth metal-naphthacene ion salts was observed by means of para-ortho hydrogen conversion. In the case of mononegative ion salt (naphthacene) −M +, the para-ortho hydrogen conversion proceeded by the physical mechanism. On the contrary, in the case of the naphthacene dinegative ion salts with alkali metal (naphthacene) 2−2M +, the chemisorptive mechanism was predominant. Further, the hydrogen exchange over the (naphthacene) 2−Ba 2+ salt occurred by way of exchange reaction between gaseous hydrogen and the hydrogen atom of the hydrocarbon. A proposal to explain the surface reaction is submitted.

KINETIC STUDIES AND EFFECTIVE DIFFUSIVITIES IN PARA TO ORTHO HYDROGEN CONVERSION REACTION

Rate studies were carried out for the para-ortho hydrogen conversion at 4O°C and I atmosphere with NiO on kieselguhr and CuO•Cr2O3 catalysts, separately. Data were obtained for different pellet sizes of catalysts, from which the effective diffusivities were determined. The catalyst pellets were tested for diffusion experiments and it was found that the effective diffusivity values under the nonreactive diffusion condition were considerably greater than the ones determined from the hydrogen conversion reaction. The effective diffusivities in the reacting system were evaluated from a parallel pore model and compared with the experimentally determined data.

Comparison of Surface States of Quartz, Cristobalite, and Silicic Acid

The surface states of silica in the forms quartz, cristobalite, and silicic acid were studied by investigating the kinetics of para-ortho hydrogen conversion and of hydrogen-deuterium equilibration from 93° to 773°K. The products of conversion were analyzed by microthermal conductivity, and those of equilibration by mass spectrometry. The results are discussed in terms of the reaction mechanisms. The active sites for low-temperature conversion are thought to be stable free radicals produced by the thermal removal of hydroxyl groups from the surfaces. Reactivity at high temperatures depends on thermal activation procedure and time. The order of reactivity for equilibration at all temperatures is: quartz > cristobalite > silicic acid. For conversion at low temperatures the order is: quartz > cristobalite > silicic acid; at high temperatures, cristobalite > quartz > silicic acid.

The parahydrogen conversion on palladium-silver alloy films

The para-ortho hydrogen conversion has been studied on a series of evaporated silver-palladium alloy films, of composition 50% Ag-50% Pd, 70% Ag-30% Pd, 80% Ag-20% Pd, and 100% Ag, in the temperature range 273 ° to 413 °K. Details are given for the preparation and characterization of homogeneous palladium-silver alloy films (~2000-Å thickness), which were formed by controlled evaporation from palladium-silver alloy wires. X-Ray diffraction and X-ray fluorescence techniques were used to analyze the films throughout the reaction vessel. The compositions were constant to within 3% over geometric film areas of 120 cm 2. The activation energy for the conversion increased with silver content of the alloy, with a sharp rise between the 50% Ag and 70% Ag alloy. A linear compensation effect between the activation energy and frequency factor for the conversion on the alloy series was observed. Heats of adsorption of hydrogen on the alloy films were calculated from the pressure dependency of the reaction at constant temperature. By comparing the experimentally determined entropy changes upon adsorption with calculated values it is concluded that the adsorbed hydrogen film, on the silver-rich alloys, is mobile.

Conversion of parahydrogen to orthohydrogen using nickel/alumina catalysts

The para-ortho hydrogen conversion was studied with both powdered and pelleted nickel/alumina catalysts in a continuous-flow system in the range 25–65 °C and 0.15–0.95 atm. Results were compared with kinetic models developed by the steady state method using several postulated mechanisms. The observed reaction kinetics were consistent with a number of mechanisms, and the overall kinetics with the pellets were consistent with a simple pore-diffusion model. Activation energies for five powder catalysts fell in the unusually wide range of 1.6 to 10.4 kcal/mole and showed a compensation effect.

Equilibrium Coverage of Copper by Chemisorbed Hydrogen

SEVERAL instances have been given in the literature1–3 in which copper will catalyse the para-ortho hydrogen conversion. This process requires the chemisorption of hydrogen, regardless of the reaction mechanism which may be prevailing.

Kinetics of the para-ortho hydrogen conversion on charcoal

Kinetics of the para-ortho hydrogen conversion on charcoal

The Para-Ortho Hydrogen Conversion by the Hydrogen Iodide Reaction and by Iodine Atoms

The rate of conversion of para to ortho hydrogen was determined in the presence of equilibrium concentrations of hydrogen iodide and iodine. From these data, velocity constants and collision efficiencies for the conversion by iodine atoms were calculated. The results are in agreement with a theoretical equation derived by Wigner.

Activated Adsorption and Para-Ortho Hydrogen Conversion on Charcoal

THE para-ortho hydrogen conversion was used by us among other reactions, at the suggestion of Prof. A. Frumkin, in order to investigate the chemical properties of hydrogen adsorbed on charcoal at high temperatures.