Hydrogen Mass Fraction Research Articles

A Computational Study of the Mass Transport Behavior of Hydrogen in In-Service Carbon Steel Pipeline Fillet Welds During Deposition and Desorption

Numerical calculations were used to study the diffusion and thermotransport of hydrogen during deposition and diffusion of hydrogen during desorption of in-service carbon steel pipeline fillet welds prone to hydrogen cracking. During deposition, only a small amount of hydrogen migrates into the HAZ and little migrates into the pipe. Thermotransport decreases the hydrogen concentration in the HAZ and regions of the weld closer to the HAZ, and increases the concentration toward the outer edge of the weld. This effect increases the rate of desorption of hydrogen from the weld, which increases with weld size/pipe wall thickness. The activation energy for desorption varies with the fraction of hydrogen removed and appears to be a function of the activation energy for diffusion and mass fraction of hydrogen in the weld, HAZ, and pipe. The differences in the desorption rate due to thermotransport appear to be due to differences in the activation energy for desorption and hydrogen concentration gradients. Maintaining a 121 °C preheat/interpass temperature during welding significantly reduces post-weld heating times necessary to reach hydrogen levels considered to be safe from hydrogen cracking. Calculated results and experimental results from another study show good agreement for desorption at 132 °C for up to 30 minutes.

Nonlinear thermoacoustic instability investigation on ammonia-hydrogen combustion in a longitudinal combustor with double-ring inlets

The greenhouse effect induced by the combustion of hydrocarbon fuel is an urgent environmental problem. Ammonia gas, as a renewable energy with a high proportion of hydrogen content, can achieve zero CO2 emission. In order to ignite ammonia and obtain continual flame, a partial premix entry condition of NH3/H2/O2 with double-ring inlets is adopted. The RNG k-ε model and EDC model are used to analyse the self-excited oscillation and the total heat release. After the numerical results and experimental data are validated, the following aspects are investigated: (1) total mass flow rate; (2) mass fraction of hydrogen; (3) mass flow ratio of inlets; and (4) the temperature of the heat exchanger. The results are compared with the traditional single-ring structure under the same condition. It is found that the exothermic heat of double-ring structure increases by 98.7% on average. The frequency of intermittent oscillation increases with the decrease in HN3 proportion. When pure hydrogen is passed through the outer ring, the combustion limit can be greatly expanded even if the inlet mass fraction of hydrogen is very small. This study contributes to provide an alternative method to enhance ammonia combustion and improve its flammability limit.

R Coronae Borealis Star Evolution: Simulating 3D Merger Events to 1D Stellar Evolution Including Large-scale Nucleosynthesis

Abstract R Coronae Borealis (RCB) stars are rare hydrogen-deficient carbon-rich variable supergiants thought to be the result of dynamically unstable white dwarf mergers. We attempt to model RCB stars through all the relevant timescales by simulating a merger event in Octo-tiger, a 3D adaptive mesh refinement (AMR) hydrodynamics code, and mapping the post-merger object into MESA, a 1D stellar evolution code. We then post-process the nucleosynthesis on a much larger nuclear reaction network to study the enhancement of s-process elements. We present models that match observations or previous studies in most surface abundances, isotopic ratios, early evolution, and lifetimes. We also observe similar mixing behavior to previous modeling attempts that result in the partial He-burning products visible on the surface in observations. However, we do note that our subsolar models lack any enhancement in s-process elements, which we attribute to a lack of hydrogen in the envelope. We also find that the 16O/18O isotopic ratio is very sensitive to initial hydrogen abundance and increases outside of the acceptable range with a hydrogen mass fraction greater than 10−4.

An effective approach of dropping the backfire possibilities of a hydrogen‐fuelled opposed rotary piston engine

AbstractBackfire of hydrogen‐fuelled internal combustion engines limits the hydrogen fuel applications and drops the power output. Opposed rotary piston (ORP) engines are characterized by high power density, smooth operations, and few moving parts. However, the intake structures of ORP engines tend to deliver high possibility of backfire under hydrogen utilization conditions due to more residual exhaust. This paper proposed an effective approach of eliminating backfire for a hydrogen fuelled ORP engine, and it did not generate any penalty of power output theoretically. The effectiveness of this method was demonstrated using a 3D numerical simulation method. The results indicated that the average in‐cylinder temperature started to increase at the start of the intake process if without any backfire control strategies; however, it decreased continuously if backfire control was applied. The mass flow rates of the intake fluid were at a low level without backfire control, but it increased sharply if backfire control was adopted. Backfire in this investigation was caused by the pre‐ignition of mixture in cylinders. The temperature in intake pipes reached up to 1000 K over backfire scenarios, and heat of reaction was higher than 3 W. Hydrogen mass fractions at the bottom of intake pipes were low at the start of intake process due to the backfire; meantime, slight backflow also happened in the intake process due to the pre‐ignition of cylinders mixture. The fluid velocity was higher than 100 m/s at the beginning of intake process if backfire was controlled.

Multiphysics Design of Pet-Coke Burner and Hydrogen Production by Applying Methane Steam Reforming System

Pet-coke (petroleum coke) is identified as a carbon-rich and black-colored solid. Despite the environmental risks posed by the exploitation of pet-coke, it is mostly applied as a boiling and combusting fuel in power generation, and cement production plants. It is considered as a promising replacement for coal power plants because of its higher heating value, carbon content, and low ash. A computational fluid dynamics (CFD) computational model of methane steam reforming was developed in this research. The hydrogen production system is composed from a pet-coke burner and a catalyst bed reactor. The heat released, produced by the pet-coke combustion, was utilized for convective and radiative heating of the catalyst bed for maintaining the steam reforming reaction of methane into hydrogen and carbon monoxide. This computational algorithm is composed of three steps—simulation of pet-coke combustion by using fire dynamics simulator (FDS) software coupled with thermal structural analysis of the burner lining and a multiphysics computation of the methane steam reforming (MSR) process taking place inside the catalyst bed. The structural analysis of the burner lining was carried out by coupling the solutions of heat conduction equation, Darcy porous media steam flow equation, and structural mechanics equation. In order to validate the gaseous temperature and carbon monoxide mole fraction obtained by FDS calculation, a comparison was carried out with the literature results. The maximal temperature obtained from the combustion simulation was about 1440 °C. The calculated temperature is similar to the temperature reported, which is also close to 1400 °C. The maximal carbon dioxide mole fraction reading was 15.0%. COMSOL multi-physics software solves simultaneously the catalyst media fluid flow, heat, and mass with chemical reaction kinetics transport equations of the methane steam reforming catalyst bed reactor. The methane conversion is about 27%. The steam and the methane decay along the catalyst bed reactor at the same slope. Similar values have been reported in the literature for MSR temperature of 510 °C. The hydrogen mass fraction was increased by 98.4%.

Optimization of Fuel Cell Performance Using Computational Fluid Dynamics.

A low cost bipolar plate materials with a high fuel cell performance is important for the establishment of Proton Exchange Membrane (PEM ) fuel cells into the competitive world market. In this research, the effect of different bipolar plates material such as Aluminum (Al), Copper (Cu), and Stainless Steel (SS) of a single stack of proton exchange membrane (PEM) fuel cells was investigated both numerically and experimentally. Firstly, a three dimensional (3D) PEM fuel cell model was developed, and simulations were conducted using commercial computational fluid dynamics (CFD) ANSYS FLUENT to examine the effect of each bipolar plate materials on cell performance. Along with cell performance, significant parameters distributions like temperature, pressure, a mass fraction of hydrogen, oxygen, and water is presented. Then, an experimental study of a single cell of Al, Cu, and SS bipolar plate material was used in the verification of the numerical investigation. Finally, polarization curves of numerical and experimental results was compared for validation, and the result shows that Al serpentine bipolar plate material performed better than Cu and SS materials. The outcome of the investigation was in tandem to the fact that due to adsorption on metal surfaces, hydrogen molecules is more stable on Al surface than Cu and SS surfaces.

Dynamic analysis of internal reactants and water content distribution during anode purge in a proton‐exchange membrane fuel cell

For proton-exchange membrane fuel cell, anode purge is a commonly used method to increase utilization rate of hydrogen and proton-exchange membrane fuel cell durability. Limited by experiment condition, it is hard to analyze reactants and water content distribution in fuel cell during purge. This article uses transient simulation to dynamic analyze distribution of reactants and water content in a full flow field fuel cell (active area 82.14 cm2) with serpentine flow field during purge. From simulation result, it is found that corresponding structures relationship of anode and cathode flow channel causes reactants fluctuating greatly. The direction of water transport across membrane is not fixed. The transmission direction is also affected by local water content of anode and cathode. Dynamic analysis of purge is divided into three stages: purge interval, purging and after purge. During purge interval, water content increases with time. During purging, water content decreases with time in inlet and outlet sections, but in serpentine section water content still increases with time. During after purge, water content increases with time, except inlet section. After multiple purge, purge has little influence on hydrogen distribution in anode flow channel, but value of hydrogen mass fraction increases and increase magnitude gradually decreases, finally reach dynamic equilibrium.

Coupling gamma ray spectrometry and tomography in a Bayesian frame

To investigate the possibility to characterize radioactive wastes using available information and measurements in a coherent frame, a Bayesian formalism is built to couple gamma-ray spectrometry and tomographic scans. The gamma ray spectrometry is performed with four High Purity Germanium (HPGe) detectors placed around the waste and scanning 2 cm thick slices of a radioactive waste drum in a Gamma Scanning mode. The tomography provides the density of the drum matrix and identifies heterogeneities. The unknown chemical composition of the matrix and heterogeneities is handled with two parameters that represent the mass fractions of carbon and hydrogen of a fictive {C; Sn; H} material that would show a gamma ray attenuation behavior similar to that of the true material. The approach is tested by simulating the measurement of 239Pu gamma rays produced by a PuO2 sphere placed in a drum slice in which two distinctive zones have been identified by tomography, in presence of 137Cs background. With the studied simulated examples, depending on the sphere position, the use of the density prior information allows decreasing the plutonium mass uncertainty by up to a factor 3 compared to the case when the density prior is not used. In addition, the use of the density prior information provides a posterior plutonium mass distribution having a significant number of event related to the true plutonium mass, which is not the case when the density prior information is not used.

Effect of wind condition on unintended hydrogen release in a hydrogen refueling station

Ambient condition, especially the wind condition, is an important factor to determine the behavior of hydrogen diffusion during hydrogen release. However, only few studies aim at the quantitative study of the hydrogen diffusion in a wind-exist condition. And very little researches aiming at the variable wind condition have been done. In this paper, the hydrogen diffusion in different wind condition which including the constant wind velocity and the variable wind velocity is investigated numerically. When considering the variable wind velocity, the UDF (user defined function) is compiled. Characteristics of the FGC (flammable gas cloud) and the HMF (hydrogen mass fraction) are analyzed in different wind condition and comparisons are made with the no-wind condition. Results indicate that the constant wind velocity and the variable wind velocity have totally different effect for the determination of hydrogen diffusion. Comparisons between the constant wind velocity and the variable wind velocity indicate that the variable wind velocity may cause a more dangerous situation since there has a larger FGC volume. More importantly, the wind condition has a non-negligible effect when considering the HMF along the radial direction. As the wind velocity increases, the distribution of the HMF along the radial direction is not Gaussian anymore when the distance between the release hole and the observation line exceeds to a critical value. This work can be a supplement of the research on the hydrogen release and diffusion and a valuable reference for the researchers.

Large Eddy Simulation of low Reynolds number turbulent hydrogen jets - Modelling considerations and comparison with detailed experiments

The main objective of this work is to apply Large Eddy Simulation (LES) on hydrogen subsonic round jets in order to evaluate modelling strategies and to provide guidelines for similar applications. The ADREA-HF code and the experiments conducted by Sandia National Laboratories are used for that purpose. These experiments are very suitable for LES studies because turbulent fluctuations have been measured which is something rare in hydrogen experiments. Hydrogen is released vertically from a small orifice of 1.91 mm diameter into stagnant environment. Three experimental cases are simulated with different Reynolds number at the release area, namely 885, 1360 and 2384. Hydrogen mass fraction and velocity mean values and fluctuations are compared against the experimental data. Several grid resolutions are used to assess the effect on the results, using mainly the Smagorinsky subgrid scale model. In the lowest Reynolds number case, an Implicit LES code, used independently from a different scientific group, is also tested. In this case, the performance of the RNG-LES subgrid scale model of the ADREA-HF code is also examined. Additionally, the effect of Smagorinsky constant and of the Van Driest correction is evaluated. The amount of the resolved turbulence and of the velocity spectra are presented. Finally, the effect of the release modelling is discussed. The analysis shows that even a coarse discretization of the release area can give acceptable results for hydrogen safety engineering applications. However, dense grids are required for the more accurate prediction of the turbulent characteristics. The two LES codes gave similar results and the overall agreement with the experiment was satisfactory.

Characterisation of La0.9Ce0.1Ni5 alloy for the development of single‐stage thermally driven sorption hydrogen compressor

SummaryIn this study, La0.9Ce0.1Ni5 alloy is characterised to investigate the performance of a single‐stage thermally driven sorption hydrogen compressor (TDSHC). The pressure‐concentration isotherm (PCI) properties of La0.9Ce0.1Ni5 alloy are measured through Sievert's Apparatus, and the thermodynamic properties are estimated by constructing van't Hoff plots at different temperature ranges between 20°C and 140°C. The effects of an increase in operating temperature on hydrogen storage capacity as well as on thermodynamic properties and the corresponding effects on TDSHC performance are studied. It is observed that the hydrogen storage capacity decreased, whereas reaction enthalpy increased, with an increase in operating temperature. It is also observed that the equilibrium pressure increased dramatically with an operating temperature; therefore, this alloy is employed, in this study, for the development of TDSHC. The proposed TDSHC operates at the supply temperature and pressure of 20°C and 15 bar, respectively, in which the compressed hydrogen is delivered at 40°C, 60°C, 80°C, 100°C, 120°C and 140°C with a maximum pressure output of 270 bar. The measured PCI and thermodynamic data are employed to investigate the thermodynamic performance of TDSHC which results in the maximum compressor work of 10.13 W and the maximum cycle efficiency of 27.57% with an average heat input of 35 ± 3 W. The increase in discharge temperature on system performance are observed to increase in compressor work and efficiency due to the increase in discharge pressure, whereas the effect on heat input is not significant due to the reduction in hydrogen discharge amount. Also, the behaviour of metal hydride (MH) bed is predicted through the finite volume method in terms of variations in MH bed temperature and hydrogen transmission. The numerical investigation is carried out by solving the required energy equations and are validated with experimental data. The numerical investigation results into minimum cycle time of 2700 seconds for the operation of TDSHC. It is also observed that the increase in discharge temperature increases the reaction kinetics and hydrogen mass fraction.

Evaluation of tomato introgression lines diversified for peel color as a source of functional biocompounds and biomass for energy recovery

Aim of the work was to characterize the peels of novel tomato lines (with red, orange, pink, black-red, and dark-red fruit) for the content of bioactive substances and for some parameters linked to no-food use. Chlorophyll, polyphenols, and carotenoid content, energy value, theoretical biochemical methane potential (TBMP) through stochiometric method were evaluated. The peel color mirrored a different content of the bioactive substances: the dark-red fruits showed a significant increase of the carotenoid content, while the peel of the black-red fruits had the highest values of polyphenols. The preferential accumulation of functional compounds influenced the values of the other parameters. The colored lines compared to the red-fruited control (C) contained less carbon and hydrogen mass fractions and, subsequently, a lower LHV. This, in turn, led to a substantial difference in the estimation of the TBMP. Interestingly, this production was higher in the highly pigmented line, which contained a gene present in some high-lycopene commercial varieties. A circular production model for exhaustive use of peel is proposed.

Effect of hydrogen enrichment of laminar ethylene diffusion flames on thermal structure and soot yields at pressures up to 10 bar

A series of high-pressure experiments were conducted to assess the influence of hydrogen enrichment of laminar diffusion flames of nitrogen-diluted ethylene on the thermal flame structure and soot yields at pressures above atmospheric. In parallel experiments, added hydrogen is replaced by helium, either in equal mole fractions or in mass fractions, to evaluate the thermal, dilution, and direct chemical interaction effects of hydrogen in soot formation. Experiments covered pressures from atmospheric to 10 bar. In the first set of experiments, conducted at 3, 6, and 10 bar pressure, base fuel was an ethylene-nitrogen mixture with 33.3% ethylene and 66.7% nitrogen (by mole as well as by mass). This base fuel was doped with either hydrogen or helium such that hydrogen and helium mass fractions and mole fractions in the fuel stream are matched in two cases. In the second set of experiments, which were conducted at 1.2 bar pressure with ethylene as the base fuel, hydrogen or helium is added such that additive mole fraction in the fuel stream was 44%. Temperature measurements in the first set of experiments indicate that, when hydrogen is added to nitrogen-diluted ethylene, the changes in the temperature field of the co-flow diffusion flames are negligible, except at lower in the flame where hydrogen added flames display slightly higher temperatures. When helium is added instead of hydrogen, however, the temperatures were measurably lower than those of the base fuel. Results show that, once the dilution effects are accounted for, the hydrogen addition to ethylene does not suppress soot formation by direct chemical interaction at elevated pressures. These findings, which are not in agreement with the previous experimental results obtained at atmospheric pressure, are discussed in terms of the higher molecular diffusivity of hydrogen and shorter residence times of high-pressure flames.

Large eddy simulation of non-reacting flow and mixing fields in a rotating detonation engine

Large Eddy Simulations (LES) of the non-reacting flow and mixing fields in a Rotating Detonation Engine (RDE) from Air Force Research Laboratory (AFRL) are performed. Effects of the total number of fuel injection orifices and air flow rates on the mixing in the AFRL RDE are studied using a periodic burner sector with five injection orifices. The instantaneous vortex structures and shock wave in the non-reactive AFRL RDE are identified, and the structures are found to be similar to those in jet in crossflow. Also, the compositional non-uniformity in the height and azimuthal directions of the burner is observed. The mixing efficiency, root-mean-square value of the hydrogen mass fraction and mixing area ratios are introduced to quantify the mixing process. The observations from LES qualitatively justify the behaviors of detonation fronts observed in the experiments. Finally, results based on full scale AFRL RDE are briefly discussed.

Evaluation of mean species mass fractions in premixed turbulent flames: A DNS study

Direct Numerical Simulation (DNS) data obtained by Dave and Chaudhuri (2020) from a lean, complex-chemistry, hydrogen-air flame associated with the thin-reaction-zone regime of premixed turbulent burning are analyzed (by adapting five alternative definitions of combustion progress variable c) in order to examine three different models that (i) are based on the flamelet paradigm and (ii) aim at evaluating mean concentrations of various species in applied CFD research into turbulent combustion. Mean mole fractions of all considered species and mean density are predicted if the laminar-flame profiles of species mole fractions and density, respectively, are directly averaged using a Probability Density Function (PDF) P(c). The best predictions are obtained by extracting P(c) from the DNS data and defining c based on hydrogen mass fraction. These predictions suggest that mean mole fractions of various species in a premixed turbulent flame can be evaluated at a post-processing stage of a CFD study by adopting P(c), obtained at the major stage of the simulations, to average a flamelet library. When applied in such a way, the flamelet paradigm is useful even for lean hydrogen-air flames and even at Karlovitz number as large as 13. If the same PDF is applied to average reaction rates from the same flamelet library, the mean rates of production/consumption of species n are poorly predicted, e.g. for radicals H, O, OH, HO2, and H2O2 if c is defined using hydrogen mass fraction. A hypothesis that conditioned rates 〈Wn|c〉 can be predicted using conditioned mole fractions 〈Xn|c〉, temperature 〈T|c〉, and density 〈ρ|c〉 is not supported either, e.g. for radicals O and OH. These differences between predictive capabilities of the first approach (directly averaging concentration profiles) and two other approaches (averaging reaction rates) are attributed to weakly (highly) non-linear dependencies of the concentrations (rates, respectively) on c.

NOx emission reduction reaction of ammonia-hydrogen with self-sustained pulsating oscillations

Unlike hydrocarbon fuel, ammonia (NH3) is an alternative but promising carbon-free renewable fuel. The utilization of NH3 as an energy resource can effectively reduce greenhouse gas CO2 emission. Here we explore interdisciplinary physics of ammonia-hydrogen-fueled combustion-sustained pulsating oscillations and its impact on NOx emission via numerical simulations. A longitudinal combustor with both ends acoustically open is modeled. The premixed flame and constant-temperature heat exchangers are implemented upstream and downstream respectively. With the model validated, it is applied to gain insights on the effects of 1) the mass flow rate ṁ of the fuel mixture, 2) the hydrogen mass fraction wH2 relative to the fuel mixture, and 3) the temperature TH of the heat exchangers. It is found that nonlinear pulsating oscillations could be generated, depending on ṁ Furthermore, the oscillation amplitude and dominant mode frequency are shown to strongly depend on ṁ andwH2. In addition, as wH2 is reduced from 45% to 15%, intermittent oscillations with a period of 100 s are observed to superimpose on the acoustic resonance nature of the combustor with a time scale of 10−2 s. Finally, varying temperatures of the heat exchanger are found to affect NOx generation and decrease the amplitude of the pulsating oscillations somehow.

Quantitative imaging performance of MARS spectral photon-counting CT for radiotherapy.

To evaluate the quantitative imaging performance of a spectral photon-counting computed tomography (SPCCT) scanner for radiotherapy applications. An experimental comparison of the quantitative performance of a Siemens dual-energy CT (DECT) and a MARS SPCCT scanner is performed to estimate physical properties relevant to radiotherapy of human substitute materials and contrast agent solutions. In human substitute materials, the accuracy of quantities relevant to photon therapy, proton therapy, and Monte-Carlo simulations, such as the electron density, proton stopping power, and elemental composition is evaluated. For contrast agent solutions, the accuracy of the contrast agent concentrations and the virtual non-contrast (VNC) electron density is evaluated. Human tissue substitute phantoms (Gammex 467 and 472) as well as diluted solutions of contrast agents (iodine and gadolinium based) are scanned with two commercial systems: a Siemens dual-source CT (SOMATOM Definition Flash, Siemens Healthineers, Forchheim, Germany) and a MARS spectral photon-counting micro-CT (MARS V5.2, MARS Bioimaging Ltd., Christchurch, New Zealand). Material decomposition is performed in a maximum a posteriori framework with an optimized material basis tailored to characterize either human substitute materials or contrast agents in the context of experimental multi-energy CT data. The root-mean-square error (RMSE) of the electron density calculated over all Gammex inserts is reduced from 1.09 to 0.89% when going from DECT to SPCCT. For the proton stopping power, the RMSE is reduced from 1.92 to 0.89%. Elemental mass fractions of hydrogen, carbon, nitrogen, oxygen, and calcium are more accurately estimated with the MARS scanner. The RMSE on the iodine-based contrast agents concentration is reduced from 0.27 to 0.12mg/mL with SPCCT, and the VNC electron density from 0.40 to 0.22%. In the present phantom study, a MARS photon-counting scanner provides superior accuracy compared to a Siemens SOMATOM Definition Flash DECT scanner to quantify physical parameters relevant to radiotherapy. This work experimentally demonstrates the benefits of using more energies to characterize human tissue equivalent materials. This highlights the potential of SPCCT for particle therapy, where more accurate tissue characterization is needed, as well as for Monte-Carlo based planning, which requires accurate elemental mass fractions.

One-dimensional simulation of hydrogen production kinetic models by water vapor plasmolysis in a DBD plate reactor

The results of one-dimensional time-dependent simulation modeling of hydrogen production from water vapor dissociation using non-thermal discharge plasma in a plate-type reactor were developed. Three different water vapor dissociation reaction mechanisms pathway models were simulated at a water vapor temperature of 573 K and same boundary conditions. The electron collision cross sections of electron water vapor were utilized based on the reaction mechanisms. The electron attachment and detachment processes were described in detail; additionally, the surface charge accumulation, recombination of charged species, positive and negative ions production and losses are considered. The electron density, electric field, electric potential, electron temperature and the hydrogen mass fraction are presented across the plasma discharge gap and over time. The first model was described as direct water vapor decomposition into their constituent’s elements hydrogen and oxygen molecules. It was revealed that the formed hydrogen molecules increased across the plasma discharge gap over time. In model II, the simulation reaction mechanisms pathway included products of H2O+, OH+, and O+ ions. It was found a significant change in the electric potential and electric field across the discharge gap due to the charged species inside the plasma gap. In model III, it was introduced H− radicals which controlled H atoms production by the electron detachment reaction. The most interesting results of these simulation models were the growing of hydrogen molecules across the plasma gap over time. Further, it was observed that the produced hydrogen mass fraction from model III was higher than model II and model I.

An ultra-massive white dwarf with a mixed hydrogen–carbon atmosphere as a likely merger remnant

White dwarfs are dense, cooling stellar embers consisting mostly of carbon and oxygen, or oxygen and neon (with a few percent carbon) at higher initial stellar masses. These stellar cores are enveloped by a shell of helium which in turn is usually surrounded by a layer of hydrogen, generally prohibiting direct observation of the interior composition. However, carbon is observed at the surface of a sizeable fraction of white dwarfs, sometimes with traces of oxygen, and it is thought to be dredged-up from the core by a deep helium convection zone. In these objects only traces of hydrogen are found as large masses of hydrogen are predicted to inhibit hydrogen/helium convective mixing within the envelope. We report the identification of WDJ055134.612+413531.09, an ultra-massive (1.14 $M_\odot$) white dwarf with a unique hydrogen/carbon mixed atmosphere (C/H=0.15 in number ratio). Our analysis of the envelope and interior indicates that the total hydrogen and helium mass fractions must be several orders of magnitude lower than predictions of single star evolution: less than $10^{-9.5}$ and $10^{-7.0}$, respectively. Due to the fast kinematics ($129\pm5$ km/s relative to the local standard of rest), large mass, and peculiar envelope composition, we argue that WDJ0551+4135 is consistent with formation from the merger of two white dwarfs in a tight binary system.

Investigation of Hydrogen Production from Bio-Oil Substances Using Aspen Plus

In this study, a base-case process diagram was established and simulated in Aspen Plus to explore effect of temperature on hydrogen production. The evaluated compounds were acetic acid, ethylene glycol, acetone, ethyl acetate and m-xylene, which are representative of the main bio-oil derived components. UNIQUAC was used as property model to simulate the process in Aspen Plus. Bio-oil components conversions, mass and molar fractions, and the molar flow rates of hydrogen were studied over a range of temperature starting from 30 °C to 1100 °C. The results obtained from the simulation suggest that all of the five components reach approximately 100% conversion with acetic acid to be the first to reach 100% conversion. The reactor temperature for 100% conversion of the components increases in the following orders: acetic acid > ethylene glycol > ethyl acetate > acetone > m-xylene. It was found that at high temperatures m-xylene was able to produce highest mass fraction of hydrogen and the order was the following: m-xylene> ethyl acetate > acetone > ethylene glycol > acetic acid. Such simulation approaches can be exploited for robust design and optimization of hydrogen production reducing operating cost and taking this process one step closer to industrialization.