An experimental and numerical investigation of the hetero-/homogeneous combustion of fuel-rich hydrogen/air mixtures over platinum

The hetero-/homogeneous combustion of hydrogen/air mixtures over platinum was investigated experimentally and numerically in a channel-flow configuration at fuel-rich equivalence ratios ranging from 2 to 7, pressures up to 5 bar and wall temperatures 760–1200 K. Experiments involved in situ one-dimensional Raman measurements of major gas-phase species concentrations over the catalyst boundary layer and planar laser induced fluorescence (LIF) of the OH radical, while simulations included an elliptic 2-D model with detailed heterogeneous and homogeneous reaction mechanisms. The employed reaction schemes reproduced the measured catalytic reactant consumption, the onset of homogeneous ignition, and the post-ignition flame shapes at all examined conditions. Although below a critical pressure, which depended on temperature, the intrinsic gas-phase kinetics of hydrogen dictated lower reactivity for the fuel-rich stoichiometries when compared to fuel-lean ones, homogeneous ignition was still more favorable for the rich stoichiometries due to the lower molecular transport of the deficient oxygen reactant that resulted in modest catalytic reactant consumption over the gaseous induction zone. Above the critical pressure, the intrinsic gaseous hydrogen kinetics yielded higher reactivity for the rich stoichiometries, which resulted in vigorous gaseous combustion at pressures up to 5 bar, in contrast to lean stoichiometry studies whereby homogeneous combustion was altogether suppressed above 3 bar. Computations at fuel-rich stoichiometries in practical channel geometries indicated that homogeneous combustion was not of concern for reactor thermal management, since the larger than unity Lewis number of the deficient oxygen reactant confined the flames to the core of the channel, away from the solid walls.     

Two-dimensional numerical simulation on galloping detonation in a narrow channel

The numerical simulations of the two-dimensional galloping detonation performed by using two-dimensional full Navier–Stokes simulations with a detailed chemistry model are presented. The detonation in a narrow channel with d = 5 mm, which is approximately twice the half-reaction length of hydrogen, shows a feature of galloping detonation with two initiations during its propagation under the laminar flow assumption. The distance between these two initiations is approximately 1300 mm, which causes the induction time behind the leading shock wave. As the channel width increases, the galloping feature diminishes. The detonation propagates approximately 4% lower than D_CJ for d = 10 and 15 mm. By increasing the channel width, the strength of the detonation increases, as shown in the maximum pressure histories. The effects of turbulence behind the detonation show that the galloping feature disappears, although its propagation velocity becomes 0.9 D_CJ. The strength of the detonation becomes significantly weak compared with the detonation propagating in the wide channel widths, and this feature is similar to the laminar assumption. The trend of the velocity deficits in the NS simulations agrees fairly well with the trend of the modified ZND calculations with η = 0.25.     

Critical conditions of hydrogen-air detonation in partially confined geometry

This work presents the results of the large scale experiments with detonation propagating in hydrogen–air mixtures in partially confined geometries. The main aim of the work was to find the critical conditions for detonation propagation in semi-confined geometries with uniform and non-uniform hydrogen–air mixtures. The experimental facility consisted of rectangular 9 × 3 × 0.6 m channel open from the bottom, acceleration section and test section, safety vessel, gas injection and data acquisition system. Sooted plates technique was used as a witness of the detonation. The rectangular channel was placed in a 100 m³ safety vessel. For uniform hydrogen–air mixtures experiments with four different channel heights h were performed: 8, 5, 3 and 2 cm. The critical hydrogen–air mixture height h* for which the detonation may propagate in a layer is close to the 3 cm which corresponds to approximately three detonation cell sizes. For non-uniform hydrogen–air mixture with hydrogen concentration slope equal approximately ?1.1%H₂/cm the critical hydrogen concentration at the top of the layer is approximately equal 26% and the mean detonation layer height is close to the 8.5 cm corresponding to the hydrogen concentration at the bottom of the layer approximately equal 16–17%.     

Numerical simulation of laminar forced convection of water-CuO nanofluid inside a triangular duct

In this article, distilled water and CuO particles with volume fraction of 1%, 2% and 4% are numerically studied. The steady state flow regime is considered laminar with Reynolds number of 100, and nano-particles diameters are assumed 20 nm and 80 nm. The hydraulic diameter and the length of equilateral triangular channel are 8 mm and 1000 mm, respectively. The problem is solved for two different boundary conditions; firstly, constant heat flux for all sides as a validation approach; and secondly, constant heat flux for two sides and constant temperature for one side (hot plate). Convective heat transfer coefficient, Nusselt number, pressure loss through the channel, velocity distribution in cross section and temperature distribution on walls are investigated in detail. The fluid flow is supposed to be one-phase flow. It can be observed that nano-fluid leads to a remarkable enhancement on heat transfer coefficient. Furthermore, CuO particles increase pressure loss through the channel and velocity distribution in fully developed cross section of channel, as well. The computations reveal that the size of nano-particles has no significant influence on heat transfer properties. Besides, the study shows a good agreement between provided outcomes and experimental data available in the literature.     

High resolution simultaneous imaging of intracranial and extracranial arterial wall with improved cerebrospinal fluid suppression

PurposeTo develop a technique for three dimensional (3D) high resolution joint imaging of intracranial and extracranial arterial walls with improved cerebrospinal fluid (CSF) suppression and good blood suppression based on T1 weighted sampling perfection with application optimized contrast using different angle evolutions (T1w-SPACE) and to compare this technique (hereafter, iSPACE) with alternating with nutation for tailored excitation (DANTE) prepared SPACE sequence (DANTE-SPACE) for their CSF suppression performance around the mid cerebral arteries (MCA) and blood suppression at carotid arteries.Materials and methodsEight volunteers and twelve patients were prospectively recruited in this institutional review board approved study. A custom designed 32-channel coil set covering the intracranial and extracranial arteries was used for signal reception. Imaging was performed in each subject using DANTE-SPACE and iSPACE. Signal-to-noise ratios (SNR) of the vessel walls at the MCA and carotid arteries, and contrast-to-noise ratios (CNR) between vessel wall and CSF at the MCA and between vessel wall and lumen at carotid arteries from the two sequences were compared.ResultsIn volunteers, contrast between CSF and white matter (surrogate for vessel wall signal) at the M2 segments in iSPACE was 67.9% higher than in DANTE-SPACE. At the carotid region, the SNR of vessel wall in iSPACE was 11.6% higher than DANTE-SPACE while the CNR in iSPACE was 13% higher than DANTE-SPACE. In patients, images with 0.6 mm isotropic resolution were obtained in 7.5 min. iSPACE showed 70.9% improvement in CNR between plaque and CSF at the M2 segments compared to DANTE-SPACE.ConclusionSimultaneous extracranial and intracranial arterial wall imaging using iSPACE improved CSF suppression significantly at the M2 segment of MCA while blood suppression was comparable to DANTE-SPACE. The technique achieved 3D images with 0.6 mm isotropic spatial resolution and took 7.5 min using a custom made coil set. Using this technique, intracranial plaque visualization was improved with no observable image SNR degradation.     

Electrical effect of soot depositions in a co-axial wire pipe flow

An investigation was performed to study the electrical effects on the soot deposition in a co-axial wire cylinder with cooled walls. Experiments were performed for applied voltages from 0 to ?5 kV or +5 kV and a diesel exhaust mass flow rate of 20 kg/h or Reynolds number of approximately 9000. The outer wall was cooled using water with a temperature of approximately 40 °C, and the experiments were performed for exposure times of 2 h. The soot deposition layer thickness was measured using a non-destructive neutron radiography technique at the end of each experiment. The results show that the electric field had a significant effect on the soot deposition and increases it by a factor of approximately 4 at the applied voltage of 5 kV before spark on-set. The soot thickness was similar for the positive and negative polarities and the results show that there was significant deposition on the wire as well as the outer wall for both polarities. Since soot deposition even occurs on both corona wire and grounded pipe below corona on-set voltages of the clean system, there may be a significant pre-charging of the diesel soot with both polarities in the diesel exhaust gas as has been observed by the recent measurements of Marieq [On the electrical charge of motor vehicle exhaust particles, Journal of Aerosol Science 37 (7) (2006) 858–874].     

N2 emission-channel change in NO reduction over stepped Pd(211) by angle-resolved desorption

A sharp change in the N₂ emission channel from N₂O(a) → N₂(g) + O(a) to N(a) + N(a) → N₂(g) has been found at around 500 K in a steady-state NO + D₂ reaction over stepped Pd(211) = [(S)3(111) × (100)] by means of angle-resolved desorption. The desorbing N₂ is highly collimated at around 30° off normal toward the step-down direction below about 500 K due to the intermediate N₂O decomposition, whereas, above 500 K, the near normally directed desorption due to the recombination of N(a) is relatively enhanced. The N₂O decomposition channel is promoted when the reaction is carried out with hydrogen (deuterium) and the channel change is accelerated by quick changes of the amounts of surface hydrogen and oxygen (or NO(a)) into the opposite directions, and enhanced nitrogen removal as ammonia on the resultant hydrogen-rich surface. In the steady-state NO + CO reaction, the N₂ emission channel gradually changes above 500 K toward recombination. A model for the off-normal N₂ emission is briefly described.     

A deconvolution enhancement of the Navier–Stokes-αβ model

A deconvolution enhancement of the Navier–Stokes-αβ model for turbulent flow is introduced. The energy and energy-dissipation rate for the enhanced model are derived. It is also shown that the consistency error, relative to the Navier–Stokes equations, and the microscale of the enhanced model are less than those of the Navier–Stokes-αβ model. The proposed model is used to simulate the Taylor–Green vortex problem and results show a qualitatively improved representation of the mean-square vorticity when compared to the Navier–Stokes-αβ model. Numerical studies of the energy spectrum and the alignment between the vorticity and the eigenvectors of the stretching tensor for three-dimensional turbulent flows with Re = 200 are used to explore the utility of the model. A benchmark problem of a two-dimensional channel flow over a step for Re = 600 also indicates that this model can be applied to more general flows than those involving periodic boundary conditions.     

The thermodynamic and kinetic properties of hydrogen dimers on graphene

The thermodynamic and kinetic properties of hydrogen adatoms on graphene are important to the materials and devices based on hydrogenated graphene. Hydrogen dimers on graphene with coverages varying from 0.040 to 0.111 ML (1.0 ML = 3.8 × 10¹⁵cm^? 2) were considered in this report. The thermodynamic and kinetic properties of H, D and T dimers were studied by ab initio simulations. The vibrational zero-point energy corrections were found to be not negligible in kinetics, varying from 0.038 (0.028, 0.017) to 0.257 (0.187, 0.157) eV for H (D, T) dimers. The isotope effect exhibits as that the kinetic mobility of a hydrogen dimer decreases with increasing the hydrogen mass. The simulated thermal desorption spectra with the heating rate α = 1.0 K/s were quite close to experimental measurements. The effect of the interaction between hydrogen dimers on their thermodynamic and kinetic properties was analyzed in detail.     

In vitro infrared thermography assessment of temperature peaks during the intra-oral welding of titanium abutments

Control of heat dissipation and transmission to the peri-implant area during intra-oral welding is very important to limit potential damage to the surrounding tissue. The aim of this in vitro study was to assess, by means of thermal infrared imaging, the tissue temperature peaks associated with the thermal propagation pathway through the implants, the abutments and the walls of the slot of the scaffold, generated during the welding process, in three different implant systems. An in vitro polyurethane mandible model was prepared with a 7.0 mm v-shape slot. Effects on the maximum temperature by a single welding procedure were studied using different power supplies and abutments. A total of 36 welding procedures were tested on three different implant systems. The lowest peak temperature along the walls of the 7.0 mm v-shaped groove (31.6 ± 2 °C) was assessed in the specimens irrigated with sterile saline solution. The highest peak temperature (42.8 ± 2 °C) was assessed in the samples with a contemporaneous power overflow and premature pincers removal. The results of our study suggest that the procedures used until now appear to be effective to avoid thermal bone injuries. The peak tissue temperature of the in vitro model did not surpass the threshold limits above which tissue injury could occur.     

Flat and compact switchable dual wavelength output at 1060 nm from ytterbium doped fiber laser with an AWG as a wavelength selector

A dual-wavelength ytterbium doped fiber laser with a narrowest spacing of 0.53 nm and widest spacing of 12.2 nm at 1064 nm is presented in this paper. An arrayed waveguide grating (AWG) together with an optical channel selector (OCS) have also been incorporated in the proposed setup that works as a switchable mechanism giving 23 different wavelength tunings. Producing an average output power of ?8 dB m and side mode suppression ratio (SMSR) of 59.65 dB, this dual-wavelength fiber laser is quite stable with an output power variance as low as 0.47 dB giving it an advantage due to its switching ability and stable dual-wavelength output powers.     

Langevin simulations of rod-shaped object alignment by surface flow

Nano or micro-scale rod shaped objects suspended in a liquid flowing on a flat solid surface might be aligned or orientated by the nature of the liquid, type of flow and planar channel geometry containing the flow. Orientation might enhance or inhibit certain chemical reactions between the objects, the underlying surface, other chemicals or with the walls of the vessels holding the flowing suspension. The probability density function describing the orientations of the objects satisfies a Fokker–Planck equation whose solution is obtained with Langevin simulation for different surface flow parameters. The methods developed in the present work enable us to evaluate the orientation probability density function for a range of the Peclet number α covering several orders of magnitude, 10^? 4 ≤ α ≤ 10⁸. The experimental detection of orientation control is obtained optically from the measurement of dichroism and birefringence of the suspension. We describe different methods providing experimental proof of the onset of alignment control.     

Wide-band fanned-out supercontinuum source covering O-, E-, S-, C-, L- and U-bands

A wide-band supercontinuum source generated by mode-locked pulses injected into a Highly Non-Linear Fiber (HNLF) is proposed and demonstrated. A 49 cm long Bismuth–Erbium Doped Fiber (Bi–EDF) pumped by two 1480 nm laser diodes acts as the active gain medium for a ring fiber laser, from which mode-locked pulses are obtained using the Non-Polarization Rotation (NPR) technique. The mode-locked pulses are then injected into a 100 m long HLNF with a dispersion of 0.15 ps/nm km at 1550 nm to generate a supercontinuum spectrum spanning from 1340 nm to more than 1680 nm with a pulse width of 0.08 ps and an average power of ?17 dBm. The supercontinuum spectrum is sliced using a 24 channel Arrayed Waveguide Grating (AWG) with a channel spacing of 100 GHz to obtain a fanned-out laser output covering the O-, E-, S-, C-, L- and U-bands. The lasing wavelengths obtained have an average pulse width of 9 ps with only minor fluctuations and a mode-locked repetition rate of 40 MHz, and is sufficiently stable to be used in a variety of sensing and communication applications, most notably as cost-effective sources for Fiber-to-the-Home (FTTH) networks.     

High resolution measurement and modelling of magnetic domain structures in epitaxial FePd (0 0 1) L10 films with perpendicular magnetisation

Magnetic domain structures in two 50 nm thick chemically-ordered FePd (0 0 1) epitaxial films with different perpendicular anisotropies have been studied using Lorentz microscopy. Domain and domain wall structures vary significantly according to the magnitude of the anisotropy. For lower anisotropy films, a stripe domain structure with a period of ≈100 nm is formed in which there is a near-continuous variation in orientation of the magnetisation vector. By contrast, in the film with higher anisotropy, a maze-like domain structure is supported. The magnetisation within domains is perpendicular to the film plane and adjacent domains are separated by narrow walls, less than 20 nm wide. Micromagnetic modelling is generally in good quantitative agreement with experimental observations and provides additional information on the domain wall structure.     

Extinguishment of propane/air co-flowing diffusion flames by fine water droplets

In the present study, extinguishment of propane/air co-flowing diffusion flame by fine water droplets was investigated experimentally. Water droplets are generated by piezoelectric atomizers with the maximum droplets flow rate of 1500 ml/h. When the fuel injection velocity U_f is low, an attached laminar diffusion flame with a premixed flame at the base is stabilized. At some distance from the burner rim, a transition from laminar to turbulent diffusion flame occurs, and a turbulent diffusion flame is formed in the downstream region. When the fuel injector rim is thin (δ = 0.5 mm), the flame stability deteriorates with increase of the co-flowing air stream velocity U_a and the water droplets flow rate Q_m. The stability mechanism can be explained by the balance of the gas velocity and the burning velocity of premixed flame formed at the base. However, when the injector rim is thick (δ = 5 mm), a recirculation zone is produced downstream of the injector rim. The dependence of the quenching distance H_q on U_f and Q_m is relatively weak, and the stability diagram shows curious features. It was shown that U_a is crucially important since it determines flow residence time; if U_a < 0.4 m/s, water droplets can evaporate when they go by the recirculation zone, and the water vapor can diffuse into the recirculation zone. However, if U_a > 0.4 m/s, the water droplets should pass by the recirculation zone without sufficiently evaporated and are not so effective to extinguish the flame. The supply velocity of droplet-laden air should be low enough so that water droplets can evaporate and water vapor can diffuse into the premixed region at the base to obtain sufficient effectiveness of water droplets for fire suppression.     

Influence of stiffeners on plate vibration and radiated noise excited by turbulent boundary layers

The influence of stiffeners on plate vibration and noise radiation induced by turbulent boundary layers is investigated by wind tunnel measurements. Plates with and without stiffeners are tested under the flow speed of 60 m/s, 71 m/s and 86 m/s, respectively. The stiffeners are set either perpendicular or parallel to the direction of the free stream. Measured vibration and noise levels are compared with theoretical calculations, where wall pressure cross-spectra are described by the Corcos model. For the plates tested, it is evident that stiffeners perpendicular to the direction of the free stream could increase noise radiation, but have almost no influence on vibration level of plates.     

Catalytic activity of copper (II) oxide prepared via ultrasound assisted Fenton-like reaction

Copper (II) oxide nanoparticles were synthesized in an ultrasound assisted Fenton-like aqueous reaction between copper (II) cations and hydrogen peroxide. The reactions were initiated with the degradation of hydrogen peroxide by ultrasound induced cavitations at 0 °C or 5 °C and subsequent generation of the OH radical. The radical was converted into hydroxide anion in Fenton-like reactions and copper hydroxides were readily converted to oxides without the need of post annealing or aging of the samples. The products were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and Brunauer–Emmett–Teller (BET) surface area analysis. Catalytic activity of the nanoparticles for the hydrogen peroxide assisted degradation of polycyclic aromatic hydrocarbons in the dark was tested by UV–visible spectroscopy with methylene blue as the model compound. The rate of the reaction was first order, however the rate constants changed after the initial hour. Initial rate constants as high as 0.030 min⁻¹ were associated with the high values of surface area, i.e. 70 m²/g. Annealing of the products at 150 °C under vacuum resulted in the decrease of the catalytic activity, underlying the significance of the cavitation induced surface defects in the catalytic process.     

Intensification of depolymerization of polyacrylic acid solution using different approaches based on ultrasound and solar irradiation with intensification studies

Depolymerization of polyacrylic acid (PAA) as sodium salt has been investigated using ultrasonic and solar irradiations with process intensification studies based on combination with hydrogen peroxide (H₂O₂) and ozone (O₃). Effect of solar intensity, ozone flow and ultrasonic power dissipation on the extent of viscosity reduction has been investigated for individual treatment approaches. The combined approaches such as US + solar, solar + O₃, solar + H₂O₂, US + H₂O₂ and US + O₃ have been subsequently investigated under optimum conditions and established to be more efficient as compared to individual approaches. Approach based on US (60 W) + solar + H₂O₂ (0.01%) resulted in the maximum extent of viscosity reduction as 98.97% in 35 min whereas operation of solar + H₂O₂ (0.01%), US (60 W), H₂O₂ (0.3%) and solar irradiation resulted in about 98.08%, 90.13%, 8.91% and 90.77% intrinsic viscosity reduction in 60 min respectively. Approach of US (60 W) + solar + ozone (400 mg/h flow rate) resulted in extent of viscosity reduction as 99.47% in 35 min whereas only ozone (400 mg/h flow rate), ozone (400 mg/h flow rate) + US (60 W) and ozone (400 mg/h flow rate) + solar resulted in 69.04%, 98.97% and 98.51% reduction in 60 min, 55 min and 55 min respectively. The chemical identity of the treated polymer using combined approaches was also characterized using FTIR (Fourier transform infrared) spectra and it was established that no significant structural changes were obtained during the treatment. Overall, it can be said that the combination technique based on US and solar irradiations in the presence of hydrogen peroxide is the best approach for the depolymerization of PAA solution.     

Catalytic effect of 3d transition metals on hydrogen storage properties in mechanically milled graphite

In this paper, we examined the catalytic effect of 3d transition metals on hydrogen storage properties in nanostructural graphite prepared by ball milling under hydrogen atmosphere. The Fe-doped nanostructured graphite shows the most marked hydrogen storage properties among the Fe-, Co-, Ni- and Cu-catalyzed graphite systems. The absorbed hydrogen concentration reaches up to ∼4 wt% by mechanically milling for 32 h (∼7 wt% for 80 h), and two peaks of hydrogen (mass number=2) around 730 and 1050 K were observed in the thermal desorption mass spectra (TDS). The starting temperature for hydrogen desorption was ∼600 K. On the other hand, the Co-doped graphite indicates that absorbed hydrogen concentrations reaches up to ∼2 wt% by mechanically milling for 32 h. The TDS spectrum showed only a broad peak around 1100 K, but the starting point for hydrogen desorption lowered down to ∼500 K. The Ni- and Cu-doped graphites did not show any significant improvement for hydrogen storage. These results suggest that the catalytic effect on hydrogen storage properties strongly depends on the affinity of graphite and doped metals.     

Effect of training level and blood flow restriction on thermal parameters: Preliminary study

Training with blood flow restriction could lead to an effect on skin temperature. Additionally, this effect could be higher in people with lower physical fitness level due to their lower capacity of heat loss. The aim of this preliminary study was therefore to evaluate the effects of training experience on the acute and chronic thermal skin responses after performing exercise with and without blood flow restriction. The study included ten men, of these, five were trained. All subjects performed tests and re-tests for maximum strength (1 repetition maximum) through unilateral leg extensions (right thigh at 45 ± 6.7 kg and left thigh at 45.5 ± 8.1 kg, p > 0.05). The protocol consisted of four sets to concentric failure, with one-minute rest intervals between sets at an intensity corresponding to 40% of 1 RM. There were 7-day intervals between experimental sessions (150 mmHg versus unrestricted flow restriction). The thermal images were made before the protocol (pre), immediately after the end of the series (post), and 24 h afterward (post 24 h). When comparing temperature variation (Δ exercise and Δ 24 h) between groups, it was observed that the trained participants showed a greater drop in temperature 24 h after exercise with 150 mmHg restriction (confidence interval: 95% of Δ 24 h [−0.2 to −0.9 °C]) compared to untrained subjects (p = 0.006 and ES > 1.5, confidence interval: 95% Δ 24 h [−0.1 to 0.6 °C].) In conclusion, this preliminary study showed that training experience interferes with the chronic cutaneous thermal temperature of the anterior thigh when strength training associated with blood flow restriction 150 mmHg was performed.