Density Of H2 Research Articles

Techno-Economic Optimisation of Green and Clean Hydrogen Production

AbstractEnergy is typically generated from fossil fuels, leading to significant greenhouse gas (GHG) emissions. Therefore, cleaner energy needs to be used to reduce GHG emissions in the energy sector. Hydrogen (H2) is identified as a potential resource suitable for replacing fossil fuels as H2 burns with oxygen to produce water (H2O) and generates no emissions as a result of this. However, H2 is normally produced through steam reforming of natural gas, which is a fossil fuel. Clean H2 can be produced if its derived from renewable pathways, such as solar powered water electrolysis, gasification of biomass, etc. However, determining a feasible renewable pathway is challenging. In addition, storage of H2 is another challenge as the energy density of H2 is considerably low. To increase the energy density, H2 must stored at high pressure and low temperature. This causes high storing costs for H2 before being transported to the end-users and high energy consumption requirements. H2 production from renewable sources is also lower in efficiency when compared with conventional production technology. Thus, it is critical to develop a systematic optimisation tool to analyse and optimise the production of clean H2 to overcome the abovementioned challenges. This work presents an optimisation model to optimise the production of clean H2 based on total annualised cost, yield, efficiency, storage and energy consumption of each technology. To illustate the proposed model, a case study with several scenarios, such as an economically feasible and clean H2 process and optimal H2 production and storage technologies in terms of energy consumption, is solved.

2D Raman imaging for vibrational and rotational temperature mapping in H2

We showcase a Raman scattering diagnostic for 2D imaging of the rotational and vibrational temperatures of H2. Applications include environments with vibrational-rotational non-equilibrium such as H2-containing supersonic jets and plasma reactors. We image segments of the laser scattering spectrum, containing one or more Raman features, using an ICCD camera that is equipped with one of several bandpass filters. Knowing their transmission spectrum allows the construction of calibration curves that relate the relative intensities of the multi-spectral image to the rotational and vibrational temperatures. Additionally, the absolute intensity indicates the density of H2. We illustrate the capability to independently measure rotational (300–3000 K, ±150 K) and vibrational temperatures (1000–3000 K, ±50 K). The technique is demonstrated on two different H2 microwave plasmas and validated against conventional fitting of 0D and 1D Raman spectra.

Temperature stratification in a molecular shock: Analysis of the emission of H2 pure rotational lines in IC443G

Context. Supernovae remnants (SNRs) represent a major source of feedback from stars on the interstellar medium of galaxies. During the latest stage of supernova explosions (which lasts 10–100 kyr), shock waves produced by the initial blast modify the chemistry of gas and dust, inject kinetic energy in the surroundings, and may alter star formation characteristics. Simultaneously, γ-ray emission is generated by the interaction between the ambient medium and cosmic rays, in particular those locally accelerated in the early stages of the explosion. Aims. We aim to estimate the total molecular mass, local density, and total column density of H2 and the temperature structure in a shocked clump interacting with the supernova remnant IC443 located in a region where cosmic rays interact with the interstellar medium. Measuring the mass of the dense and neutral component of the medium is a prerequisite to understanding the chemistry, energetics, and GeV to TeV γ-ray emission. Methods. Assuming that the emission of H2 pure rotational lines is produced by a collection of gas layers with variable temperature, we compared Spitzer/IRS emission maps for the ν = 0–0 S(0) to S(7) lines with a thermal admixture model. Our description is based on a power-law distribution of thermalized components with temperatures varying between Tmin = 25 K and Tmax = 1500 K. Results. Our thermal admixture model allows the level populations of H2 to be described by a power-law distribution dN = ΛT−ΓdT, with Γ ~ 2.2−4.7. We measured a total mass MH2 = 220−80+110 M⊙ across the Spitzer/IRS field of observations. Conclusions. Our analysis shows that an estimate of the cold molecular gas temperature is paramount to accurately constraining the H2 mass, although the mass remains affected by significant uncertainties due to the assumptions on the gas temperature distribution.

Thermodynamic trends for evaluating hydrogen storage density and energy flow on Maxsorb-III, HKUST-1 and UiO-66 (Zr) MOFs

For CO2-free power generation in power plants or vehicles, hydrogen should be implemented as H2 possesses not only the highest energy density (120 MJ/kg) but also can be generated from the environment and reactions. However, H2 is difficult to store due to its low density at ambient conditions. To understand the efficacy of hydrogen interactions in porous materials including the randomness of hydrogen adsorption in terms of storage density, energy flow and dissipation, a thermodynamic study is required. This paper at first focuses on the study of H2 adsorption on various porous adsorbents such as activated carbons (AC types Maxsorb-III) and metal–organic frameworks (types UiO-66 (Zr) and HKUST-1 MOFs) and the results are presented in temperature-density co-ordinate system. Employing experimentally confirmed isotherms data of AC/MOFs + H2 systems, the density of H2 adsorbed phase, entropy flow and generation are evaluated. These results indicate the feasibility of hydrogen adsorption on functional adsorbents at various temperature and pressure. The simulation results show that the adsorbed phase densities of H2 on Maxsorb-III and HKUST-1 increase up to 18 kg/m3 and 20 kg/m3 at 5 bar and 77 K. The temperature-entropy diagram shows a close loop for the charging and discharging of hydrogen and ensures the storage of internal energy with less entropy dissipation under cryo-adsorption conditions.

First Constraints on Dense Molecular Gas at z = 7.5149 from the Quasar Pōniuā‘ena

We report the detection of CO(6–5) and CO(7–6) and their underlying continua from the host galaxy of quasar J100758.264+211529.207 (Pōniuā‘ena) at z = 7.5149, obtained with the NOrthern Extended Millimeter Array. Pōniuā‘ena belongs to the HYPerluminous quasars at the Epoch of ReionizatION sample of 18 z > 6 quasars selected to be powered by supermassive black holes, which experienced the fastest mass growth in the first cosmic gigayear. The one reported here is the highest-redshift measurement of the cold and dense molecular gas to date. The host galaxy is unresolved, and the line luminosity implies a molecular reservoir of M(H2) = (2.2 ± 0.2) × 1010 M ⊙, assuming a CO spectral line energy distribution typical of high-redshift quasars and a conversion factor α = 0.8 . We model the cold dust spectral energy distribution to derive a dust mass of M dust = (1.7 ± 0.6) × 108 M ⊙ and thus, a gas-to-dust ratio ∼130. Both the gas and dust mass are remarkably similar to the reservoirs found for luminous quasars at z ∼ 6–7. We use the CO detection to derive an estimate of the cosmic mass density of H2, . This value is in line with the general trend suggested by literature estimates at z < 7 and agrees fairly well with the latest theoretical expectations of nonequilibrium molecular-chemistry cosmological simulations of cold gas at early times.

A Complete HCN Survey of the Perseus Molecular Cloud

We present a survey of the Perseus molecular cloud in the J = 1 → 0 transition of HCN, a widely used tracer of dense molecular gas. The survey was conducted with the CfA 1.2 m telescope, which at 89 GHz has a beamwidth of 11′ and a spectral resolution of 0.85 km s−1. A total of 8.1 deg2 was surveyed on a uniform 10′ grid to a sensitivity of 14 mK per channel. We compared the survey with similar surveys of CO and dust in order to study and calibrate the HCN line as a dense-gas tracer. We find the HCN emission to extend over a considerable fraction of the cloud. We show that the HCN intensity remains linear with H2 column density well into the regime where the CO line saturates. We use radiative-transfer modeling to show that this likely results from subthermal excitation of HCN in a cloud where the column and volume densities of H2 are positively correlated. To match our HCN observations the model requires an exponential decrease in HCN abundance with increasing extinction, consistent with HCN depletion onto grains. The modeling also reveals that the mean volume density of H2 in the HCN-emitting regions is ∼104 cm−3, well below the HCN critical density. For the first time, we obtain a direct measurement of the ratio of dense-gas mass to HCN luminosity for an entire nearby molecular cloud: α(HCN) = 92 M ⊙/(K km s−1 pc2).

The study of ignition and emission characteristics of hydrogen-additive hydro-processed renewable diesel

This study was conducted to understand the effects of hydrogen (H2) addition on the combustion and emission characteristics of hydro-processed renewable diesel. Experiments were performed in a constant volume combustion chamber (CVCC) at varying H2 concentrations (0%, 5%, and 10% (by vol.)) relative to air (100%, 95%, and 90% (by vol.)), initial temperatures (Tini) of 600, 650 and 700 K, equivalence ratios (φ) of 0.5, 1.0, and 1.5 and a fixed initial pressure (Pini) of 10 bar. Overall, HRD has lower ignition delay (ID) and total ID. However, H2 addition to HRD delayed the fuel's auto-ignition due to excess H2 oxidation (H2+OHH2O + H) reaction taking place, which turns the chain reactions from branching to propagation, resulting from increasing in ID. Moreover, increasing of H2 concentrations enhanced the maximum pressure rise (Pmax) and heat release rate (HRR), whereas carbon dioxide (CO2) and unburned hydrocarbon (HC) were decreased due to the higher magnitude of the lower heating value of H2 than that of pure HRD. Since H2 itself is a carbon-free molecule, the carbon content of the fuel is reduced. H2 has the characteristics of fast combustion, resulting in a more flammable and complete mixture, which also makes HC emissions to become lower. However, the higher energy density of H2 significantly raises the combustion temperature, and subsequent nitrogen oxides (NOx) were increased. The kinetic modeling predictions revealed that the IDs for HRD-H2 were elongated due to the increased hydroperoxyl (HO2) and hydrogen peroxide (H2O2) mole fractions which led to improved stability.

Graphene-Based Derivatives Heterostructured Catalytic Systems for Sustainable Hydrogen Energy via Overall Water Splitting

The global climate crisis has cultivated the demand for sustainable energy resources as fossil derivative fuels are functional in catalyzing the rate of environmental breakdown. Sustainable energy solutions generate various renewable energy prospects capable of delivering efficient energy operations. Among these prospects, green H2 energy generated via overall water splitting is an effective approach towards sustainability ascribed to the higher gravimetric density and efficiency of H2 fuel. In this review, we sought to discuss the applicability and challenges of graphene-based derivatives in H2 evolution operations through photochemical, electrochemical and photoelectrochemical water-splitting pathways. The unique layered structure of graphene-based derivatives alongside marvelous optoelectronic and physicochemical properties ease out the thermodynamic uphill of water splitting better than their non-layered counterparts. In addition, the heterojunction formation in the graphene derivatives with visible light catalysts propels the kinetics of HER. Functionalized GO and rGO derivatives of graphene are riveting catalysts that have received extensive interest from researchers attributed to their accelerated chemical and mechanical stability, tunable band structure and larger surface area, providing more exposed active sites for HER. The surface organic functional groups of GO/rGO assist in establishing synergetic interfacial contact with other catalysts. Thus, these groups provide structural and chemical versatility to GO/rGO-based heterostructured catalysts, which effectively improve their physicochemical parameters that drive their catalytic performance towards HER. In order to develop a cost-effective and highly efficient catalytic system, graphene-based derivatives are promising heterostructured catalysts that exhibit a good relationship between catalytic efficiency and robustness.

Molecular fraction in the Galactic Centre: The Central Molecular and H i Zones

ABSTRACT By mapping the molecular fraction of the Galactic Centre (GC), we quantitatively address the question of how much molecular and central the CMZ (central molecular zone) is. For this purpose, we analyse the CO and H i-line archival data, and determine the column- (surface-) and volume-molecular fractions, $f_{\rm mol}^\Sigma$ and $f_{\rm mol}^\rho$, which are the ratio of column-mass density of H2 projected on the sky to that of total gas (H2 + H i) from the line intensities, and the ratio of volume-mass densities of H2 to total gas from the brightness temperature, respectively. It is shown that $f_{\rm mol}^\Sigma$ is as high as ∼0.9–0.95 in the CMZ, and $f_{\rm mol}^\rho$ is 0.93–0.98 in the GC Arms I and II attaining the highest value of ∼0.98 toward Sgr B2. The expanding molecular ring (EMR, or the parallelogram) has a slightly smaller $f_{\rm mol}^\rho$ as ∼0.9–0.93. We define the CMZ as the region with $f_{\rm mol}^\Sigma \ge 0.8\rm {-\!\!-}0.9$ between the shoulders of plateau-like distribution of H2 column density from l = −1${_{.}^{\circ}}$1 to +1${_{.}^{\circ}}$8 having Gaussian vertical distribution with a half thickness of ±0${_{.}^{\circ}}$2. The CMZ is embedded in the Central H i Zone (CHZ), which is defined as an H i disc between l ∼ −2° and +2${_{.}^{\circ}}$5, b = −0${_{.}^{\circ}}$5 and +0${_{.}^{\circ}}$5. Based on the analysis, we discuss the origin of CMZ and interstellar physics such as the volume filling factors of molecular and H i gases inferred from the difference between $f_{\rm mol}^\Sigma$ and $f_{\rm mol}^\rho$.

Hydrogen storage in nanoporous media: Molecular dynamics simulations of the confinement effects

Hydrogen has attracted considerable interest as a clean substitute for fossil fuels. Especially, substantial efforts have been dedicated into the development of nanoporous materials for mobile H2 storage. However, the potential of this approach is significantly limited by the generally low H2 loading capacity. Moreover, the fundamental understanding of the H2 behavior in confined spaces is still lacking. In this study, the enhancement of the fluid-wall interaction with decreasing pore sizes was first investigated using a simple numerical model. Subsequently, molecular dynamics simulations were conducted to discern the influencing factors on confined H2 density. The results confirmed the importance of pore size and fluid-wall interaction in determining the H2 storage capacity. Specifically, the confined density of H2 increased with shrinking pore sizes only when the nanoporous material met the energy requirement. The reverse trend of the optimal pore size below and above the threshold H2-wall interaction energy was attributed, respectively, to the absence and presence of the adsorbed H2 layers. It was also found that the benefit of confinement decays with increasing pressure due to the disproportional density change in the adsorption layers. The findings in this study shed light on the defining factors influencing the H2 storage in nanoporous media and provide guidance on the selection and synthesis of the H2 hosting materials.

Ammonia as a hydrogen energy carrier

The gravimetric H2 densities and the heats of combustion of tanks stored ammonia (ammonia storage tanks) were similar to those of the liquid H2 tanks at the weight of 20–30ton, although the gravimetric H2 density of liquid H2 is 100 wt%. The volumetric H2 densities and the heats of combustion of ammonia storage tanks were about 2 times higher than those of liquid H2 tanks at 1–4 × 104 m3. Gray ammonia is synthesized from hydrogen through process known as steam methane reforming, nitrogen separated from air and Haber-Bosch process. Blue ammonia is the same as gray ammonia, but with CO2 emissions captured and stored. Green ammonia is produced by reacting hydrogen produced by electrolysis of water and nitrogen separated from air with Haber-Bosch process using renewable energies. The energy efficiencies of gray, blue and green ammonia were better than those of liquid hydrogen and methylcyclohexane (MCH) with high H2 density and similar to the efficiency of H2 gas. The energy efficiencies of ammonia decreased in the order, gray ammonia > blue ammonia > green ammonia. The production costs of green hydrogen energy carried increased in the order, ammonia < liquid H2<MCH. The amounts of energy consumption by N2 production and Haber-Bosch process were below 10% compared with the value of H2 production from water electrolysis.

Determination of H2 Densities Over a Wide Range of Temperatures and Pressures Based on the Spectroscopic Characterization of Raman Vibrational Bands.

Raman spectroscopy is a powerful method for determining the densities of gas species in fluid inclusions, especially for H2-bearing inclusions in which the microthermometry approach is difficult to apply. The relationships between Raman peak position and H2 density have been recorded in several previous studies. However, systematic discrepancies exist among these studies. In this study, the Raman spectral parameters (peak position, width, and intensity) of the vibrational bands of H2 (Q1(0), Q1(1), Q1(2), and Q1(3)) were systematically measured at temperatures from 25 to 400°C and pressures up to 150MPa using a high-pressure optical cell. The variation in each parameter as a function of H2 density was discussed. Several calibration polynomials derived from the measured peak positions and peak widths of these vibrational bands and the peak intensity ratios of Q1(1) to Q1(n = 0, 2, 3) were established to determine H2 densities up to 0.062g/cm3 at 25°C. For natural fluid inclusions, the peak position of the Q1(1) band is the best choice for density determination mainly because (i) Raman spectra derived from fluid inclusions are not always of applicable qualities and the strongest intensity Q1(1) band could be obtained easier than others, and (ii) the peak position is insensitive to instrumental factors. The relationship between the peak position of Q1(1) band and density can be represented by ΔQ1(1) = 90,246.070 × ρ4 - 5471.203 × ρ3 + 770.944 × ρ2- 41.038 × ρ (r2 = 0.999), where ρ is the density of H2 in g/cm3; ΔQ1(1) (cm-1) is the difference between the obtained peak position of Q1(1) band of H2 and the known peak position of Q1(1) band of H2 at near-zero density. This polynomial is independent of instrumental factors and can be applied in any laboratory, as long as the peak position of H2 with a near-zero density is known. The effects of temperature on the relationship between these spectral parameters and H2 density were also examined.

TISSUE-EQUIVALENCE OF H2 GAS FOR MICRODOSIMETRY IN NEUTRON FIELDS: A GEANT4 MONTE CARLO STUDY.

Hydrogen (H2) as filling gas in Tissue-equivalent proportional counter (TEPC) for measurements of microdosimetric distributions in neutron fields is investigated using the Monte Carlo-based Geant4 toolkit. The neutron fields considered are monoenergetic neutrons (1keV-14MeV) and ISO reference neutron sources 241Am-Be, 241Am-B, 252Cf and 252Cf+D2O. Based on the energy deposited in the gas cavities (tissue-equivalent (TE) propane and H2) of the TEPC, density scaling correction, ${f}_{\rho }$, to be applied on H2 gas to achieve tissue-equivalence is calculated for the above sources at 1μm site size. The calculated value of ${f}_{\rho }$ for the ISO-neutron sources is 0.40, which suggests that energy deposition in the gas cavities is predominantly due to crossers. In the case of monoenergetic neutrons, depending upon the energy, ${f}_{\rho }$ is in the range of 0.11-0.45. The study shows that the TE propane and H2-based microdosimetric distributions are comparable when the density of H2 is scaled appropriately. Mean quality factor $\overline{Q}$ calculated based on microdosimetric distribution increases initially with neutron energy up to 100keV and thereafter decreases with energy. Depending upon the neutron energy, TE propane and H2-based $\overline{Q}$ values are comparable to within 3-15%, and for the ISO sources, the comparison is within 5-8%. For the ISO neutron sources, $\overline{Q}$ values are in the range of ~10-15.

Precise Measurements of CH Maser Emission and Its Abundance in Translucent Clouds

Abstract We present high-sensitivity CH 9 cm ON/OFF observations toward 18 extragalactic continuum sources that have been detected with OH 18 cm absorption in the Millennium survey with the Arecibo telescope. CH emission was detected toward 6 of the 18 sources. The excitation temperature of CH has been derived directly through analyzing all detected ON and OFF velocity components. The excitation temperature of CH 3335 MHz transition ranges from −54.5 to −0.4 K and roughly follows a log-normal distribution peaking within [−5, 0] K, which implies overestimation by 20% to more than 10 times during calculating CH column density by assuming the conventional value of −60 or −10 K. Furthermore, the column density of CH would be underestimated by a factor of 1.32 ± 0.03 when adopting local thermal equilibrium assumption instead of using the CH three hyperfine transitions. We found a correlation between the column density of CH and OH following log N(CH) = (1.80 ± 0.49) log N(OH) −11.59 ± 6.87. The linear correlation between the column density of CH and H2 is consistent with that derived from visible wavelengths studies, confirming that CH is one of the best tracers of H2 components in diffuse molecular gas.

Bayesian inference of three-dimensional gas maps

Carbon monoxide (CO) is the best tracer of Galactic molecular hydrogen (H2). Its lowest rotational emission lines are in the radio regime, and thanks to Galactic rotation, emission at different distances is Doppler shifted. For a given gas flow model, the observed spectra can thus be deprojected along the line of sight to infer the gas distribution. We used the CO-line survey of Dame et al. (2001, ApJ, 547, 792) to reconstruct the three-dimensional density of H2. We considered the deprojection as a Bayesian variational inference problem. The posterior distribution of the gas densities allowed us to estimate the mean and uncertainty of the reconstructed density. Unlike most of the previous attempts, we took the correlations of gas on a variety of scales into account, which allowed us to correct for some of the well-known pathologies, such as finger-of-god effects. The two gas flow models that we adopted incorporate a Galactic bar that induces radial motions in the inner few kiloparsecs and thus offers spectral resolution towards the Galactic centre. We compared our gas maps with those of earlier studies and characterise their statistical properties, for instance the radial profile of the average surface mass density.

(Invited) Mass Transport Considerations for High Performance CO2 Electrolysers

Electrocatalytic CO2 reduction has the dual-promise of neutralizing carbon emissions in the near future, while providing a long-term pathway to create energy-dense chemicals and fuels from atmospheric and waste CO2. The field has advanced immensely in recent years, taking significant strides towards commercial realization. Gas diffusion electrodes (GDEs), composed of solid electrocatalysts on porous supports positioned near the interface of a conducting electrolyte and CO2 gas, have been able to demonstrate the substantial current densities needed for future commercialization. These higher reaction rates have often been ascribed to the presence of a three-phase interface, where solid, liquid, and gas provide electrons, water, and CO2, respectively. Conversely, mechanistic work on electrochemical reactions implicate a fully two-phase reaction interface, where gas molecules reach the electrocatalyst’s surface by dissolution and diffusion through the electrolyte. Here, we first outline the macro, micro and atomistic phenomena occurring within a gas-diffusion electrode to provide a focused introduction to the architecture of the often-discussed three-phase region for CO2 electrolysis.In addition, we use a 2-D model to examine the concentration gradients in the gas and electrolyte flow channels across a GDE, which provides longitudinal information along the length of a flow cell. In doing so, we quantify the extent of concentration overpotentials and ohmic drops throughout the catalyst layer across a range of applied potentials and flow rates. Various process parameters were modified to explore the effects on the CO2 mass transfer-limited current density, conversion, and outlet concentrations of CO2, CO and H2. Our model suggests that ohmic losses largely determine the current density distributions at low conversion rates where small gradients in concentration exist. However, as the concentration profiles become less uniform (e.g. high conversion rates), the non-electrochemical consumption of CO2 starts to overtake electrochemical conversion, and leads to non-uniform performance across the electrode. In addition, while higher flow rates allow the ability to substantially increase current density, this comes at the expense of ohmic drops and losses in selectivity, which become more prominent at high conversion rates. The ability to understand the interplay between process conditions and local environment will be necessary to further develop the science and technology of electrochemical CO2 reduction.

Strain and defect engineering of graphene for hydrogen storage via atomistic modelling

The adsorption of hydrogen molecules on monolayer graphene is investigated using molecular dynamics simulations (MDS). Interatomic interactions of the graphene layer are described using the well-known AIREBO potential, while the interactions between graphene and hydrogen molecule are described using Lennard-Jones potential. In particular, the effect of strain and different point defects on the hydrogen storage capability of graphene is studied. The strained graphene layer is found to be more active for hydrogen and show 6.28 wt% of H2 storage at 0.1 strain at 77 K temperature and 10 bar pressure. We also studied the effect of temperature and pressure on the adsorption energy and gravimetric density of H2 on graphene. We considered different point defects in the graphene layer like monovacancy (MV), Stone Wales (SW), 5-8-5 double vacancy (DV), 555–777 DV, and 5555-6-7777 DV which usually occur during the synthesis of graphene. At 100 bar pressure, graphene with 1% concentration of MV defects leads to 9.3 wt% and 2.208 wt% of H2 storage at 77 K and 300 K, respectively, which is about 42% higher than the adsorption capacity of pristine graphene. Impact of defects on the critical stress and strain of defected graphene layers is also studied.

Ionizing feedback from an O star formed in a filament

ABSTRACT We explore a simple semi-analytic model for what happens when an O star (or cluster of O stars) forms in an isolated filamentary cloud. The model is characterized by three configuration parameters: the radius of the filament, $R_{_{\rm FIL}}$, the mean density of H2 in the filament, $n_{_{\rm FIL}}$, and the rate at which the O star emits ionizing photons, $\dot{\cal N}_{_{\rm LyC}}$. We show that for a wide range of these configuration parameters, ionizing radiation from the O star rapidly erodes the filament, and the ionized gas from the filament disperses into the surroundings. Under these circumstances the distance, L, from the O star to the ionization front (IF) is given approximately by $L(t) \sim 5.2 {\rm pc} [R_{_{\rm FIL}}/0.2 {\rm pc}]^{-1/6} [n_{_{\rm FIL}}/10^4 {\rm cm^{-3}}]^{-1/3} [\dot{\cal N}_{_{\rm LyC}}/10^{49} {\rm s}^{-1}]^{1/6} [t/{\rm Myr}]^{2/3}$, and we derive similar simple power-law expressions for other quantities, for example the rate at which ionized gas boils off the filament, $\dot{M}_{_{\rm IF}}(t)$, and the mass, $M_{_{\rm SCL}}(t)$, of the shock-compressed layer that is swept up behind the IF. We show that a very small fraction of the ionizing radiation is expended locally, and a rather small amount of molecular gas is ionized and dispersed. We discuss some features of more realistic models, and the extent to which they might modify or invalidate the predictions of this idealized model. In particular we show that, for very large $R_{_{\rm FIL}}$ and/or large $n_{_{\rm FIL}}$ and/or low $\dot{\cal N}_{_{\rm LyC}}$, continuing accretion on to the filament might trap the ionizing radiation from the O star, slowing erosion of the filament even further.

Changes in Operating Characteristics of Transformer Oil under the Action of Ionizing Radiation

The changes in physicochemical parameters such as specific resistance, viscosity, density, and formation of gaseous products H2, CH4, C2H4, C2H6, C3H8, C4H10, C5H12, and C6H14 with respect to the adsorbed dose in the interval of 29.7–237.6 kGy are studied. It is established that the chemical composition of transformer oil changes under the action of γ irradiation, which is accompanied by the changes in specific resistance, viscosity, and density of oil. The degree of conversion depends on the adsorbed dose and grows when it increases. The IR spectra show =C–H stretching vibrations, –C=C in-plane deformation vibrations, and –CH out-of-plane deformation vibrations of aromatic compounds. In addition, there are –C–H stretching vibrations and antisymmetric and symmetric –C–CH3 deformation vibrations in alkanes. The IR absorption spectra are observed in the range of Δλ1 = 2800–3300 cm–1, Δλ2 = 2000 cm–1, Δλ3 = 1350–1450 cm–1, and Δλ4 = 600–1200 cm–1. The absorption band of Δλ4 = 600–1200 cm–1 is a smeared part of the spectrum with a number of weak absorption bands.

A priori DNS study of applicability of flamelet concept to predicting mean concentrations of species in turbulent premixed flames at various Karlovitz numbers

Complex-chemistry direct numerical simulation (DNS) data obtained earlier from lean hydrogen-air flames associated with corrugated flame (case A), thin reaction zone (case B), and broken reaction zone (case C) regimes of turbulent burning are analysed to directly assess capabilities of the flamelet approach to predict mean concentrations of species in a premixed turbulent flame. The approach consists in averaging dependencies of mole fractions, reaction rates, temperature, and density on a single combustion progress variable c, which are all obtained from the unperturbed laminar flame. For this purpose, four alternative definitions of c are probed and two probability density functions (PDFs) are adopted, i.e. either an actual PDF extracted directly from the DNS data or a presumed β-function PDF obtained using the DNS data on the first two moments of the c(x, t)-field. Results show that the mean density and mean mole fractions of H2, O2, and H2O are well predicted using both PDFs for each c, although the predictive capabilities are little worse in case C. In cases A and B, the use of the actual PDF and the fuel-based c also offers an opportunity to well predict mean mole fractions of O and H, whereas the mean mole fraction of OH is slightly underestimated. In the highly turbulent case C, the same approach performs worse, but still appears to be acceptable for evaluating the mean radical concentrations. The use of the β-function PDFs or another combustion progress variable yields substantially worse results for these radicals. When compared to the mean mole fractions, the mean rate of product creation, i.e. the source term in the transport equation for the mean combustion progress variable, is worse predicted even for a quantity (species concentration or temperature) adopted to define c and using the actual PDF. Consequently, turbulent burning velocity is not predicted either.